Fusion power - Wikipedia

核融合発電は、核融合反応を利用して発電用の熱を生成することによってエネルギーを生成する、理論的な発電形態です。核融合過程では、2つの軽い原子核が結合してより重い核を形成し、同時にエネルギーを放出します。これは私達の太陽のように星を動かすのと同じプロセスです。このエネルギーを利用するように設計された装置は核融合炉として知られています。

核融合プロセスでは、核融合が起こりうるプラズマを生成するために、燃料と高温高圧の高度に閉じ込められた環境が必要です。星では、最も一般的な燃料は水素です、そして重力は核融合に必要な高温と閉じ込めを作り出します。核融合炉は一般的に重水素や三重水素のような水素同位体を使いますが、それらは反応しやすく、慣性法（レーザー）や磁気法（トカマクなど）を使って数百万度のプラズマを作り出​​します。核融合力を実現する上での主な課題は、長期間の反応が起こるのに十分な高温と密度でプラズマを十分長く閉じ込めることができ、反応中に放出される中性子を管理できるシステムを設計することです。時間が経つと、反応室内で使用される多くの一般的な材料が劣化する可能性があります。

動力源として、核融合は核分裂よりもいくつかの理論的な利点を持つと期待されている。これには、運転中の放射能の減少と核廃棄物の減少、十分な燃料供給、そして安全性の向上が含まれます。しかしながら、制御された融合は、実用的かつ経済的な方法で製造することが極めて困難であることが証明されている。核融合炉の研究は1940年代に始まったが、今日まで、電力入力よりも多くの核融合電力出力を生み出す設計はなかった。したがって、既存の設計はすべて負の電力収支を示しています。 ^[1]

長年にわたり、核融合研究者はさまざまな閉じ込めの概念を調査してきました。初期の重点は3つの主なシステムに集中していました：Zピンチ、ステラレータと磁気ミラー。現在主流となっている設計は、レーザーによるトカマクと慣性閉じ込め（ICF）です。どちらの設計も非常に大規模で、特にフランスのITERトカマク、そしてアメリカのNational Ignition Facilityレーザーで構築されています。研究者たちはまた、より安価なアプローチを提供するかもしれない他のデザインも研究しています。これらの選択肢の中で、磁化ターゲット融合および慣性静電閉じ込めに対する関心が高まっている。
背景 [ edit ]

太陽は、他の星と同様に、恒星の核合成がより軽い元素をより重い元素にエネルギーを放出しながら変換する自然の核融合炉です。異なる原子核に対する結合エネルギーIron-56が最も高く、最も安定しています。左側の核は融合する可能性があります。

メカニズム [ edit ]

核反応が起こるのに十分なほど長い間、2つ以上の原子核が接近すると核融合反応が起こります。静電気力がそれらを引き離し、より重い核に融合させます。鉄-56より軽い原子核の場合、反応は発熱性で、エネルギーを放出します。鉄56より重い原子核の場合、反応は吸熱性であり、外部エネルギー源を必要とする^[2] したがって、鉄56より重い原子核は融合する可能性が高く、鉄56より重い原子核はばらばらになる可能性が高い。

強い力は短い距離でのみ作用します。反発静電気力は長距離にわたって作用します。核融合を起こすためには、強い力が作用するのに十分なほど近くに互いに接近するのに十分なエネルギーを燃料原子に与える必要があります。燃料原子を十分に近づけるのに必要な運動エネルギーの量は「クーロン障壁」として知られている。このエネルギーを提供する方法には、粒子加速器内の原子を加速すること、またはそれらを高温に加熱することが含まれる。

原子がそのイオン化エネルギーを超えて加熱されると、その電子は取り除かれ（イオン化され）、裸の核（イオン）だけが残ります。結果はイオンの熱い雲と以前それらに付着していた電子です。この雲はプラズマとして知られています。電荷が分離されているので、プラズマは導電性で磁気的に制御可能です。多くの融合装置は、粒子が加熱されるときにこれを利用して粒子を制御する。

断面 編集]

核融合反応速度は、最大になるまで急速に上昇し、その後徐々に低下します。重水素 - トリチウム核融合速度は、低温（約70 keV、または8億ケルビン）で、核融合エネルギーで一般的に考えられている他の反応よりも高い値でピークに達します。核融合反応が起こる確率。これは2つの核の相対速度に依存します。より高い相対速度は一般に確率を増加させるが、確率は非常に高いエネルギーで再び減少し始める。多くの核融合反応の断面積は、粒子線を使用して測定されました（主に1970年代）。 ^[3]

プラズマでは、粒子速度は確率分布を使用して特徴付けることができます。プラズマが熱化されると、分布はベル曲線またはマクスウェル分布のようになります。この場合、速度分布全体の平均粒子断面を使用すると便利です。これは、体積融合率に入力される。

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フュージョン




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ここで、

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  は、時間と体積ごとのフュージョンによって生成されるエネルギーです


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  Lawson Criterion edit ]
  

  Lawson Criterionは、エネルギー出力が温度、密度、衝突速度、および燃料によってどのように変化するかを示しています。この方程式は、John Lawsonによる熱プラズマを用いた核融合の解析の中心でした。ローソンは以下に示すようにエネルギー収支を仮定した^[4]
  

  
  

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    {19} [19] [19] [19] [19] [19] [19]]年[19659021年]放射線
    
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    { displaystyle P _ { text {out}} P _ {{ text {out}}} "/>、核融合からの正味電力
  
  
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    核融合によって生成されたエネルギーの割合である
    
    
    
    
    
    
    
    
    
    
  
  

  プラズマ雲は、伝導や放射線によってエネルギーを失います^[4] イオン、電子または中性物質が他の物質、通常はデバイスの表面に衝突し、それらの運動エネルギーの一部を他の原子に伝達すると、伝導が起こります。放射線は、可視スペクトル、UVスペクトル、IRスペクトル、またはX線スペクトルの光として雲を離れるエネルギーです。放射線は温度とともに増加します。核融合発電技術はこれらの損失を克服しなければなりません。
  

  
  

  トリプル積：密度、温度、時間 ]

  
  

  
  

  ローソンの基準では、熱損失のある準中性プラズマを保持する機械は、放射損失を克服するための基本基準を満たす必要があります。 ^[4][5] これは「トリプル積」として知られるようになりました：プラズマ密度、温度、閉じ込め時間。^[6] トリプル積を増やそうとする試みは、より大きな植物をターゲットにすることにつながりました。大規模プラントでは構造材料をプラズマの中心からさらに遠ざけます。これにより、より多くの放射が内部で反射されるため、伝導損失と放射損失が減少します。 $$
  
  
  
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  プラズマの挙動 [編集]

  
  

  プラズマは電気を通すイオン化ガスです。 19659124バルクでは、流体を支配するNavier-Stokesの式と磁場と電場の振る舞いを支配するMaxwellの式の組み合わせである磁気流体力学を使ってモデル化されています。
  

  
  
  • 自己組織化プラズマは電場と磁場を伝導します。 ^[9]
  
  
  • 反磁性プラズマはそれ自身の内部磁場を発生させることができます。 ^[10]
  
  
  • 磁気ミラーがプラズマを低磁場から高密度磁場に移動させるとプラズマを反射させることができます
    
    
    • edit ]エネルギー回収のために複数のアプローチが提案されてきた。最も簡単な方法は流体を加熱することです。ほとんどの設計はD-T反応に集中しています。D-T反応は中性子でそのエネルギーの多くを放出します。電気的に中性で、中性子は閉じ込めから逃げます。そのような設計のほとんどにおいて、それは最終的に原子炉の炉心を囲むリチウムの厚い「ブランケット」に捕獲される。高エネルギー中性子が衝突すると、リチウムはトリチウムを生成し、それが原子炉にフィードバックされます。この反応のエネルギーもブランケットを加熱し、次にブランケットは作動流体で積極的に冷却され、次にその流体が従来のターボ機械の駆動に使用されます。
      

      核分裂 - 核融合ハイブリッドとして知られている概念である、核廃棄物の覆いの中で追加の核分裂燃料を生成するために中性子を使用することも提案されています。これらのシステムでは、電力出力は核分裂事象によって強化され、電力は従来の核分裂炉のシステムのようなシステムを使用して取り出されます ^[12] 。
      

      他の燃料、特にp-B反応を使用する設計では、はるかに多くのエネルギーを荷電粒子の形で放出します。これらの場合、これらの電荷の移動に基づく代替の電力抽出システムが可能である。核融合反応生成物を用いて電圧を維持する方法として、直接エネルギー変換が１９８０年代にＬＬＮＬで開発された。 ^[13]
      

      
      

      Methods

      
      

      磁気閉じ込め [ edit ]

      
      
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        • ^{]核融合エネルギーに対する最もよく開発され、資金が供給されているアプローチ。この方法は、内部電流で、磁気的に閉じ込められたトーラスの中で熱いプラズマの周りを走ります。完成すると、ITERは世界最大のトカマクになります。 2012年4月現在、推定215の実験用トカマクが計画されているか、廃止されているか、または現在稼働している（35）} 球状トーラス ]。球形のトカマクの変形
        
        
        • Stellarator：高温プラズマのねじれた輪。ステラレータは外部磁石を使って自然なねじれプラズマ経路を作り出そうとしますが、トカマクは内部電流を使ってそれらの磁場を作り出します。ステラレータは1950年にLyman Spitzerによって開発され、4つのデザインがあります。Torsatron、Heliotron、Heliac、Heliasです。その一例が、2015年12月10日に最初のプラズマを生成したドイツの核融合装置Wendelstein 7-Xです。これは、このタイプの装置が発電所に適しているかどうかを調査するために設計された^[15] です。 [Levitated Dipole Experiment（LDX）] これらは固体超伝導トーラスを使用しています。これは反応室の内部で磁気的に浮揚している。超伝導体はプラズマを含む軸対称磁場を形成します。 LDXは、2000年以降、Jay KesnerとMichael E. MauelによってMITとColumbia Universityによって開発されました ^{[194590906] 磁気ミラー：}リチャードF.ポストとLLNLのチームによって開発されました。磁気ミラーは熱いプラズマを一列に前後に反射した。タンデムミラー、マグネットボトル、バイコニックカスプなどのバリエーションがあります^[18] 主にローレンスリバモア国立研究所で、1970年代から1980年代にかけて、米国政府によって、十分な資金を得た大型のミラーマシンが建造されました^{。 [19]}
        
        
        • でこぼこトーラス：トロイダルリングの中にいくつかの磁気ミラーが端から端まで配置されています。一方から漏れる燃料イオンは隣接するミラーに閉じ込められ、プラズマ圧力を損失なしに任意に高く上昇させることができる。実験施設であるELMO B T orusまたは EBT は、1970年代にオークリッジ国立研究所で建設され、試験された。反転構成：この装置は、自己組織化準安定構造でプラズマを捕捉します。粒子の運動が内部磁場を作り、それが次にそれ自身を閉じ込める ^[20]
        
        
        • スフェロマック：プラズマを使って作られた半安定プラズマ構造。自己発生磁界。スフェロマックにはトロイダル磁場とポロイダル磁場の両方がありますが、Field Reversed Configurationにはトロイダル磁場しかありません ^[21]
        
        
        • 逆磁場ピンチ：ここでプラズマはリングの内側を動きます。それは内部磁場を持っています。このリングの中心から外に出ると、磁場は方向を逆にします
        
        

        慣性閉込め 編集

        
        
        • ダイレクトドライブ：この技術では、レーザーで直接ペレットをブラストします。燃料の。目標は、融合連鎖反応を起こすことです。着火は1972年にJohn Nuckollsによって最初に示唆されました。^[22] 注目に値するダイレクトドライブ実験がレーザーエネルギー研究所、レーザーメガジュールおよびGEKKO XII施設で行われました。良好な爆縮は、高密度プラズマを生成する対称内向き衝撃波を生成するために、完全な形状に近い燃料ペレットを必要とする
        
        
        • 高速点火：この方法は、2つのレーザーブラストを使用する。最初の爆発は核融合燃料を圧縮し、2番目の高エネルギーパルスはそれを点火します。実験は、OmegaおよびOmega EPシステムを使用してレーザーエネルギー研究所で、および大阪のレーザー工学研究所でGEKKO XIIレーザーで行われている。
        
        
        • 間接駆動：この技術では、レーザーは構造を爆破する。燃料のペレットの周り。この構造はホールラウムとして知られています。それが崩壊するにつれて、ペレットはより均一なＸ線光に浸され、より良い圧縮を生み出す。この方法を使った最大のシステムは、National Ignition Facilityです。
        
        
        • 磁気慣性核融合または磁気ライナー慣性核融合：これはレーザーパルスと磁気ピンチを組み合わせたものです。ピンチコミュニティはそれを磁化ライナー慣性核融合と呼び、ICFコミュニティはそれを磁気慣性核融合と呼びます
        
        
        
        
        • 重イオンビーム慣性閉じ込めを行う提案もあります。レーザービームではなくイオンビームとの核融合^[24] 主な違いは、ビームは質量による運動量を持っているのに対し、レーザーはそうではないことです edit 19659162] Zピンチ：この方法は、プラズマを通して（z方向に）強い電流を送ります。電流は、プラズマを核融合状態に絞る磁界を発生させる。ピンチが人工の制御された融合のための最初の方法でした。^[25][26] いくつかの例には、Sandia National Laboratoriesの高密度プラズマフォーカス（DPF）およびZ機が含まれます。 DPFでは、焦点は、銅またはベリリウムから作られ、低圧の可溶ガスを含む真空チャンバーに収容された2つの同軸の円筒形電極で構成されています。電気パルスが電極間に印加され、ガスを加熱してプラズマにする。この電流は機械の軸に沿って微小渦に形成され、次にそれは関連する磁場と共に電流のケージにねじれます。電流と磁場閉じ込めプラズマのケージはプラズモイドと呼ばれます。磁力線を中心とした電子の加速により、プラズモイド内の核が核融合温度まで加熱される
        
        
        • シータ - ピンチ：この方法は、プラズマの内側にシータ方向に電流を流す。 ^[27]
        
        

        edit ]

        
        
        
        • この方法では、熱を加えるために電場を使用しています。融合条件へのイオン。機械は典型的には２つの球形ケージ、アノードの内側のカソード、真空の内側のカソードを使用する。これらの機械は、伝導損失と放射損失が大きいため、正味電力への実行可能なアプローチとは見なされません^[28] 。 ^[29]
        
        
        • ポリウェル：この設計は、磁場の閉じ込めと静電場を組み合わせて、伝導による損失を回避しようとしています。 ^[30]
        
        

        その他編集]

        
        
        • 磁化標的核融合：この方法では、磁場を使って高温プラズマを閉じ込め、慣性力を使って絞ります。例としては、LANL FRX-L機、General Fusionおよびプラズマライナー実験がある ^[32]
        
        
        • クラスター衝撃核融合重水の微小液滴が高速でターゲットに加速される。またはお互いに。 Brookhavenの研究者らは、後の実験で反論された肯定的な結果を報告しています。
        
        
        • 制御不能：融合は、いわゆる水素爆弾を発火させるために制御されていない核分裂爆発を利用して、人間によって開始されました。核融合力に関する初期の提案には、反応を開始するための爆弾の使用が含まれていた。
        
        
        • ビーム核融合：高エネルギー粒子のビームを別のビームまたはターゲットで発射すると融合が起こる。これは1970年代から1980年代にかけて高エネルギー核融合反応の断面積を研究するために使用された ^[3]
        
        
        • バブル核融合：これは異常に大きな内部で起こると考えられていた。音響液体キャビテーション中に発生する気泡の崩壊^[33] このアプローチは信頼できない
        
        
        • 常温核融合：これは室温またはそれに近い温度で発生する仮想的なタイプの核反応である。 ^[34] [edit]
        
        
        • ミューオン触媒核融合はプラズマ中の電子をミューオンに置き換えます。 - 同じ電荷を持つはるかに重い粒子。それらのより大きな質量は、核がはるかに接近しそしてより容易に衝突することを可能にするので、それは核融合を開始するのに必要とされる運動エネルギー（熱と圧力）を大いに減少させる。問題は、ミューオン触媒核融合から得られるよりもミューオンが生成するのにより多くのエネルギーを必要とし、このアプローチは発電には実用的ではないということである
        
        
        • 。そして、大規模な核融合力を達成するための扱いやすい方法は、カルノーサイクルではなく光子を介してエネルギーを捕らえる非常に大きな宇宙プラットフォームを構築することです。このような手段による発電の理論的限界は、Dyson Sphereを使った2型文明である
        
        

        edit

        
        

        暖房 [ edit ]

        
        

        ガスを加熱して核融合反応を開始させるのに十分な高温のプラズマを形成します。数多くの加熱方式が検討されています。
        高周波加熱電波がプラズマに照射され、プラズマが振動します。これは電子レンジと基本的に同じ概念です。これは電子サイクロトロン共鳴加熱または誘電加熱としても知られている。 ^{[引用が必要]}
        

        静電加熱電場は荷電イオンまたは電子に作用し、それらを加熱することができます ^[37]
        

        中性ビーム注入外部の水素源が電場によってイオン化され加速され、中性水素ガスの源を通してそれ自体がイオン化されプラズマ中に含まれる荷電ビームを形成する。磁場による反応器。中間の水素ガスのいくらかは中性のまま荷電ビームとの衝突によってプラズマに向かって加速される。この中性のビームは磁場の影響を受けないのでそれを通ってプラズマの中に輝く。一旦プラズマの内側に入ると、中性ビームは衝突によってエネルギーをプラズマに伝達し、その結果として中性ビームはイオン化されて磁場に閉じ込められ、それによって一回の操作で反応器を加熱および燃料補給する。荷電ビームの残りの部分は、磁場によって冷却ビームダンプに向けられます。 ^[38]
        

        反陽子消滅理論的には、ある量の核融合燃料に注入された反陽子の量が熱核反応を引き起こす可能性があります。反物質触媒核パルス推進として知られている宇宙船推進の方法としてのこの可能性は、提案されたAIMStarプロジェクトに関連してペンシルバニア州立大学で調査された。
        磁気振動^[39]
        

        
        

        測定 編集

        
        

        トムソン散乱プラズマから光が散乱します。この光を検出してプラズマの振る舞いを再構築するために使用することができます。この手法は、密度と温度を求めるために使用できます。それは慣性閉込め核融合、^[40] 、トカマク^[41] 、および融合子では一般的です。 ＩＣＦシステムでは、これは、第２のビームをターゲットに隣接する金箔内に発射することによって行うことができる。これにより、プラズマを散乱または横断するX線が発生します。トカマクでは、これは鏡と検出器を使用して平面全体（2次元）または一列（1次元）に光を反射することで実現できます。
        

        ラングミュアプローブこれはプラズマ中に置かれた金属物体です。電位がそれに印加され、周囲のプラズマに対して正または負の電圧を与える。金属は荷電粒子を集め、電流を引き込みます。電圧が変化すると、電流も変化します。これはIVカーブを作ります。 IV曲線を使用して、局所プラズマ密度、電位、および温度を決定することができます ^[42]
        

        中性子検出器重水素または三重水素の核融合は中性子を生成します。中性子は、検出可能な方法で周囲の物質と相互作用します。核融合反応中に中性子が生成される速度を記録することができるいくつかのタイプの中性子検出器が存在する。彼らは成功を実証するための不可欠なツールです。
        

        磁束ループワイヤのループが磁場に挿入されます。電場がループを通過すると、電流が発生します。電流が測定され、そのループを通る総磁束が求められます。これは、National Compact Stellarator Experiment ^[43] 、polywell ^[44] 、およびLDXマシンで使用されています。
        

        X線検出器すべてのプラズマは光を放出することによってエネルギーを失います。これは全スペクトルをカバーしています：可視、IR、UV、そしてX線。 ^[45] 理由が磁場による偏向である場合、放射は低速のサイクロトロン放射と高速のシンクロトロン放射です。その理由が他の粒子による偏向の場合、プラズマは制動放射として知られているX線を放射します。 X線は、そのエネルギーに基づいて、ハードとソフトの両方で呼ばれています。
        発電 [編集]
        

        蒸気タービンを使用して核融合チャンバーからの熱を電気に変換することが提案されている^[46] 。熱は作動流体に伝達され、それが蒸気に変わり、発電機を駆動します。
        

        中性子ブランケット重水素とトリチウムの融合により中性子が発生します。これはテクニックによって異なります（NIFは1秒間に3E14中性子を記録しています^[47] が、一般的な核融合炉は1秒間に1E5-1E9中性子を発生します）。これらの中性子を使用済み核分裂燃料を再生する方法として、あるいは液体リチウムからなる増殖ブランケットを使ってトリチウムを繁殖させる方法として、あるいはより最近の原子炉設計のようにからなるヘリウム冷却ペブルベッドとして使うことが提案されている。チタン酸リチウム、オルトケイ酸リチウム、またはこれらの相の混合物などの材料から製造されたリチウム含有セラミックペブル。 ^[49]
        

        直接変換これは、粒子の運動エネルギーを電圧に変換する方法です^[50] 磁気ミラーと組み合わせてRichard F. Postによって最初に提案されました。フィールド反転構成にも推奨されています。このプロセスはプラズマを取り、それを膨張させ、核融合生成物のランダムエネルギーの大部分を指向性運動に変換します。粒子は次に様々な大きな電位で電極上に集められる。 ^[51]
        

        
        

        Records [ edit ]

        
        

        フュージョンレコードは、多くの機器によって設定されています。ここにあるいくつかの：
        

        
        

        Q [ edit ]

        
        

        供給されたエネルギー量に対する抽出されたエネルギーの比率。この記録は1997年に装置が16MWの電力を引き出したときにJoint European Torus（JET）によって設定されたと考えられています。^[52] しかしながら、この比率は3つの異なる方法で見ることができます。
        

        
        
        • 0.69は「核融合電力」とプラズマ内の実際の入力電力（23 MW）との間の実際の時点比である
        
        
        • 0.069は「核融合」電力と23MW入力を生成するのに必要な電力との間の比パワー（基本的にNBシステムの効率を考慮に入れる）
        
        
        • 0.0069は、「フュージョン」パワーとJETパルスに必要な合計ピークパワーの比です。これは、グリッドからのすべての電力と2つの大型JETフライホイールジェネレータからの電力を考慮に入れたものです。
        
        

        ランタイム [ edit ]

        
        

        Field Reversed Configurationsにおいて、最長実行時間は2016年8月にPrinceton Field Reversed Configurationによって設定された300ミリ秒です。^[53] しかし、これは融合を含みませんでした。
        

        
        

        Beta edit

        
        

        プラズマの閉じ込めが4乗に上昇するにつれて、核融合の電力は増加傾向にあります。発電所。プラズマは非常に良好な導電率を有する。これはプラズマを磁場で閉じ込める可能性を開くものであり、これは一般に磁場閉じ込めとして知られている。磁場はプラズマに磁気圧力をかけ、それを保持します。核融合における磁気トラッピングの広く使われている尺度はベータ比です。
        

        $$
          
            
              
                β［１９４５９２３６］ ＝ ［１９６５９２３７］ ｐ ［１９６５９２３９］ ｍ ［１９６５９２４０］ ｇ ［１９６５９２４２］ ＝ ［１９６５９２４３］ ｎ ［１９６５９２４４］ ｋ ［１９６５９２４５］ ｐ ［１９６５９２４７］ ｐ ［１９６５９２３７］ ｐ ［１９６５９２３９］ ]（
        
        B
        
        2 /
        
        2
        
        μ
        
        0
        
        
        ）
        
        
        
        
        
        { displaystyle beta = { frac {p} {p} {mag}}} = { frac {nk_ {B} T} {（B ^ {2} / 2 mu _ {0}）}}}
        
        ^[55]
        

        これはプラズマの内圧に対する外部からの電場の比です。値1は理想的なトラッピングです。ベータ値の例は次のとおりです。
        

        
        
        1. STARTマシン：0.32
        
        
        2. 浮上双極子実験：^[56] 0.26
        
        
        3. スロマック：≒0.1、^[57] メルシエ限界に基づいて最大0.2 ^{[194590223] DIII-D機：0.126 ]}
        
        
        4. 磁気ミラー：5E-3秒間で0.6 ^{[59] [60]}
        
        
        5. ロスアラモス国立研究所での持続性スフェロマックプラズマ実験<0.05 [4E-6秒間]
           
        
        
        6. [編集]
           
           
           
           

           閉じ込めとは、必要なすべての条件を指します。プラズマを核融合を起こすのに十分長く高密度で高温に保つ。これがいくつかの一般原則です。
           

           
           
           • 平衡：プラズマに作用する力は封じ込めのために釣り合っていなければなりません。 One exception is inertial confinement, where the relevant physics must occur faster than the disassembly time.
           
           
           • Stability: The plasma must be so constructed so that disturbances will not lead to the plasma disassembling.
           
           
           • Transport or conduction: The loss of material must be sufficiently slow.^[4] The plasma carries off energy with it, so rapid loss of material will disrupt any machines power balance. Material can be lost by transport into different regions or conduction through a solid or liquid.
           
           

           To produce self-sustaining fusion, the energy released by the reaction (or at least a fraction of it) must be used to heat new reactant nuclei and keep them hot long enough that they also undergo fusion reactions.
           

           
           

           Unconfined[edit]

           
           

           The first human-made, large-scale fusion reaction was the test of the hydrogen bomb, Ivy Mike, in 1952. As part of the PACER project, it was once proposed to use hydrogen bombs as a source of power by detonating them in underground caverns and then generating electricity from the heat produced, but such a power station is unlikely ever to be constructed.
           

           
           

           Magnetic confinement[edit]

           
           

           Magnetic Mirror One example of magnetic confinement is with the magnetic mirror effect. If a particle follows the field line and enters a region of higher field strength, the particles can be reflected. There are several devices that try to use this effect. The most famous was the magnetic mirror machines, which was a series of large, expensive devices built at the Lawrence Livermore National Laboratory from the 1960s to mid 1980s.^[62] Some other examples include the magnetic bottles and Biconic cusp.^[63] Because the mirror machines were straight, they had some advantages over a ring shape. First, mirrors were easier to construct and maintain and second direct conversion energy capture, was easier to implement.^[13] As the confinement achieved in experiments was poor, this approach was abandoned.^{[citation needed]}
           

           Magnetic Loops Another example of magnetic confinement is to bend the field lines back on themselves, either in circles or more commonly in nested toroidal surfaces. The most highly developed system of this type is the tokamakwith the stellarator being next most advanced, followed by the Reversed field pinch. Compact toroids, especially the Field-Reversed Configuration and the spheromak, attempt to combine the advantages of toroidal magnetic surfaces with those of a simply connected (non-toroidal) machine, resulting in a mechanically simpler and smaller confinement area.
           

           
           

           Inertial confinement[edit]

           
           

           Inertial confinement is the use of rapidly imploding shell to heat and confine plasma. The shell is imploded using a direct laser blast (direct drive) or a secondary x-ray blast (indirect drive) or heavy ion beams. Theoretically, fusion using lasers would be done using tiny pellets of fuel that explode several times a second. To induce the explosion, the pellet must be compressed to about 30 times solid density with energetic beams. If direct drive is used—the beams are focused directly on the pellet—it can in principle be very efficient, but in practice is difficult to obtain the needed uniformity. The alternative approach, indirect drive, uses beams to heat a shell, and then the shell radiates x-rays, which then implode the pellet. The beams are commonly laser beams, but heavy and light ion beams and electron beams have all been investigated.
           

           
           

           Electrostatic confinement[edit]

           
           

           There are also electrostatic confinement fusion devices. These devices confine ions using electrostatic fields. The best known is the Fusor. This device has a cathode inside an anode wire cage. Positive ions fly towards the negative inner cage, and are heated by the electric field in the process. If they miss the inner cage they can collide and fuse. Ions typically hit the cathode, however, creating prohibitory high conduction losses. Also, fusion rates in fusors are very low because of competing physical effects, such as energy loss in the form of light radiation.^[66] Designs have been proposed to avoid the problems associated with the cage, by generating the field using a non-neutral cloud. These include a plasma oscillating device,^[67] a magnetically-shielded-grid, a penning trap, the polywell^[68] and the F1 cathode driver concept. The technology is relatively immature, however, and many scientific and engineering questions remain.
           

           
           

           History of research[edit]

           
           
           
           

           1920s[edit]

           
           

           Research into nuclear fusion started in the early part of the 20th century. In 1920 the British physicist Francis William Aston discovered that the total mass equivalent of four hydrogen atoms (two protons and two neutrons) are heavier than the total mass of one helium atom (He-4), which implied that net energy can be released by combining hydrogen atoms together to form helium, and provided the first hints of a mechanism by which stars could produce energy in the quantities being measured. Through the 1920s, Arthur Stanley Eddington became a major proponent of the proton–proton chain reaction (PP reaction) as the primary system running the Sun.
           

           
           

           1930s[edit]

           
           

           Neutrons from fusion was first detected by staff members of Ernest Rutherfords' at the University of Cambridge, in 1933. The experiment was developed by Mark Oliphant and involved the acceleration of protons towards a target at energies of up to 600,000 electron volts. In 1933, the Cavendish Laboratory received a gift from the American physical chemist Gilbert N. Lewis of a few drops of heavy water. The accelerator was used to fire heavy hydrogen nuclei deuterons at various targets. Working with Rutherford and others, Oliphant discovered the nuclei of Helium-3 (helions) and tritium (tritons).^[72][73][74]
           

           A theory was verified by Hans Bethe in 1939 showing that beta decay and quantum tunneling in the Sun's core might convert one of the protons into a neutron and thereby producing deuterium rather than a diproton. The deuterium would then fuse through other reactions to further increase the energy output. For this work, Bethe won the Nobel Prize in Physics.
           

           
           

           1940s[edit]

           
           

           The first patent related to a fusion reactor was registered in 1946^[75] by the United Kingdom Atomic Energy Authority. The inventors were Sir George Paget Thomson and Moses Blackman. This was the first detailed examination of the Z-pinch concept. Starting in 1947, two UK teams carried out small experiments based on this concept and began building a series of ever-larger experiments.
           

           
           

           1950s[edit]

           
           
           

           The first man-made device to achieve ignition was the detonation of this fusion device, codenamed Ivy Mike.
           
           
           

           Early photo of plasma inside a pinch machine (Imperial College 1950/1951)
           
           

           The first successful man-made fusion device was the boosted fission weapon tested in 1951 in the Greenhouse Item test. This was followed by true fusion weapons in 1952's Ivy Mike, and the first practical examples in 1954's Castle Bravo. This was uncontrolled fusion. In these devices, the energy released by the fission explosion is used to compress and heat fusion fuel, starting a fusion reaction. Fusion releases neutrons. These neutrons hit the surrounding fission fuel, causing the atoms to split apart much faster than normal fission processes—almost instantly by comparison. This increases the effectiveness of bombs: normal fission weapons blow themselves apart before all their fuel is used; fusion/fission weapons do not have this practical upper limit.
           

           In 1949 an expatriate German, Ronald Richter, proposed the Huemul Project in Argentina, announcing positive results in 1951. These turned out to be fake, but it prompted considerable interest in the concept as a whole. In particular, it prompted Lyman Spitzer to begin considering ways to solve some of the more obvious problems involved in confining a hot plasma, and, unaware of the z-pinch efforts, he developed a new solution to the problem known as the stellarator. Spitzer applied to the US Atomic Energy Commission for funding to build a test device. During this period, James L. Tuck who had worked with the UK teams on z-pinch had been introducing the concept to his new coworkers at the Los Alamos National Laboratory (LANL). When he heard of Spitzer's pitch for funding, he applied to build a machine of his own, the Perhapsatron.
           

           Spitzer's idea won funding and he began work on the stellarator under the code name Project Matterhorn. His work led to the creation of the Princeton Plasma Physics Laboratory. Tuck returned to LANL and arranged local funding to build his machine. By this time, however, it was clear that all of the pinch machines were suffering from the same issues involving instability, and progress stalled. In 1953, Tuck and others suggested a number of solutions to the stability problems. This led to the design of a second series of pinch machines, led by the UK ZETA and Sceptre devices.
           

           Spitzer had planned an aggressive development project of four machines, A, B, C, and D. A and B were small research devices, C would be the prototype of a power-producing machine, and D would be the prototype of a commercial device. A worked without issue, but even by the time B was being used it was clear the stellarator was also suffering from instabilities and plasma leakage. Progress on C slowed as attempts were made to correct for these problems.
           

           In 1954, Lewis Strauss, then chairman of the United States Atomic Energy Commission (U.S. AEC, forerunner of the U.S. Nuclear Regulatory Commission and the United States Department of Energy) spoke of electricity in the future being "too cheap to meter".^[76] Strauss was very likely referring to hydrogen fusion^[77] —which was secretly being developed as part of Project Sherwood at the time—but Strauss's statement was interpreted as a promise of very cheap energy from nuclear fission. The U.S. AEC itself had issued far more realistic testimony regarding nuclear fission to the U.S. Congress only months before, projecting that "costs can be brought down... [to]... about the same as the cost of electricity from conventional sources..."^[78]
           

           By the mid-1950s it was clear that the simple theoretical tools being used to calculate the performance of all fusion machines were simply not predicting their actual behavior. Machines invariably leaked their plasma from their confinement area at rates far higher than predicted. In 1954, Edward Teller held a gathering of fusion researchers at the Princeton Gun Club, near the Project Matterhorn (now known as Project Sherwood) grounds. Teller started by pointing out the problems that everyone was having, and suggested that any system where the plasma was confined within concave fields was doomed to fail. Attendees remember him saying something to the effect that the fields were like rubber bands, and they would attempt to snap back to a straight configuration whenever the power was increased, ejecting the plasma. He went on to say that it appeared the only way to confine the plasma in a stable configuration would be to use convex fields, a "cusp" configuration.^[79]
           

           When the meeting concluded, most of the researchers quickly turned out papers saying why Teller's concerns did not apply to their particular device. The pinch machines did not use magnetic fields in this way at all, while the mirror and stellarator seemed to have various ways out. This was soon followed by a paper by Martin David Kruskal and Martin Schwarzschild discussing pinch machines, however, which demonstrated instabilities in those devices were inherent to the design.
           

           The largest "classic" pinch device was the ZETA, including all of these suggested upgrades, starting operations in the UK in 1957. In early 1958, John Cockcroft announced that fusion had been achieved in the ZETA, an announcement that made headlines around the world. When physicists in the US expressed concerns about the claims they were initially dismissed. US experiments soon demonstrated the same neutrons, although temperature measurements suggested these could not be from fusion reactions. The neutrons seen in the UK were later demonstrated to be from different versions of the same instability processes that plagued earlier machines. Cockcroft was forced to retract the fusion claims, and the entire field was tainted for years. ZETA ended its experiments in 1968.
           

           The first experiment to achieve controlled thermonuclear fusion was accomplished using Scylla I at the Los Alamos National Laboratory in 1958.^[80] Scylla I was a θ-pinch machine, with a cylinder full of deuterium. Electric current shot down the sides of the cylinder. The current made magnetic fields that pinched the plasma, raising temperatures to 15 million degrees Celsius, for long enough that atoms fused and produce neutrons.^[25][26] The sherwood program sponsored a series of Scylla machines at Los Alamos. The program began with 5 researchers and 100,000 in US funding in January 1952.^[81] By 1965, a total of 21 million had been spent on the program and staffing never reached above 65.
           

           In 1950–1951 I.E. Tamm and A.D. Sakharov in the Soviet Union, first discussed a tokamak-like approach. Experimental research on those designs began in 1956 at the Kurchatov Institute in Moscow by a group of Soviet scientists led by Lev Artsimovich. The tokamak essentially combined a low-power pinch device with a low-power simple stellarator. The key was to combine the fields in such a way that the particles orbited within the reactor a particular number of times, today known as the "safety factor". The combination of these fields dramatically improved confinement times and densities, resulting in huge improvements over existing devices.
           

           
           

           1960s[edit]

           
           

           A key plasma physics text was published by Lyman Spitzer at Princeton in 1963.^[82] Spitzer took the ideal gas laws and adapted them to an ionized plasma, developing many of the fundamental equations used to model a plasma.
           

           Laser fusion was suggested in 1962 by scientists at Lawrence Livermore National Laboratory, shortly after the invention of the laser itself in 1960. At the time, Lasers were low power machines, but low-level research began as early as 1965. Laser fusion, formally known as inertial confinement fusion, involves imploding a target by using laser beams. There are two ways to do this: indirect drive and direct drive. In direct drive, the laser blasts a pellet of fuel. In indirect drive, the lasers blast a structure around the fuel. This makes x-rays that squeeze the fuel. Both methods compress the fuel so that fusion can take place.
           

           At the 1964 World's Fair, the public was given its first demonstration of nuclear fusion.^[83] The device was a θ-pinch from General Electric. This was similar to the Scylla machine developed earlier at Los Alamos.
           

           The magnetic mirror was first published in 1967 by Richard F. Post and many others at the Lawrence Livermore National Laboratory.^[17] The mirror consisted of two large magnets arranged so they had strong fields within them, and a weaker, but connected, field between them. Plasma introduced in the area between the two magnets would "bounce back" from the stronger fields in the middle.
           

           The A.D. Sakharov group constructed the first tokamaks, the most successful being the T-3 and its larger version T-4. T-4 was tested in 1968 in Novosibirsk, producing the world's first quasistationary fusion reaction.^[84] When this was first announced, the international community was highly skeptical. A British team was invited to see T-3, however, and after measuring it in depth they released their results that confirmed the Soviet claims. A burst of activity followed as many planned devices were abandoned and new tokamaks were introduced in their place — the C model stellarator, then under construction after many redesigns, was quickly converted to the Symmetrical Tokamak.
           

           In his work with vacuum tubes, Philo Farnsworth observed that electric charge would accumulate in regions of the tube. Today, this effect is known as the Multipactor effect.^[85] Farnsworth reasoned that if ions were concentrated high enough they could collide and fuse. In 1962, he filed a patent on a design using a positive inner cage to concentrate plasma, in order to achieve nuclear fusion.^[86] During this time, Robert L. Hirsch joined the Farnsworth Television labs and began work on what became the fusor. Hirsch patented the design in 1966^[87] and published the design in 1967.^[88]
           

           
           

           1970s[edit]

           
           
           

           Shiva laser, 1977, the largest ICF laser system built in the seventies

           

           The Tandem Mirror Experiment (TMX) in 1979

           
           

           In 1972, John Nuckolls outlined the idea of ignition.^[22] This is a fusion chain reaction. Hot helium made during fusion reheats the fuel and starts more reactions. John argued that ignition would require lasers of about 1 kJ. This turned out to be wrong. Nuckolls's paper started a major development effort. Several laser systems were built at LLNL. These included the argus, the Cyclops, the Janus, the long path, the Shiva laser and the Nova in 1984. This prompted the UK to build the Central Laser Facility in 1976.^[89]
           

           During this time, great strides in understanding the tokamak system were made. A number of improvements to the design are now part of the "advanced tokamak" concept, which includes non-circular plasma, internal diverters and limiters, often superconducting magnets, and operate in the so-called "H-mode" island of increased stability. Two other designs have also become fairly well studied; the compact tokamak is wired with the magnets on the inside of the vacuum chamber, while the spherical tokamak reduces its cross section as much as possible.
           

           In 1974 a study of the ZETA results demonstrated an interesting side-effect; after an experimental run ended, the plasma would enter a short period of stability. This led to the reversed field pinch concept, which has seen some level of development since. On May 1, 1974, the KMS fusion company (founded by Kip Siegel) achieves the world's first laser induced fusion in a deuterium-tritium pellet.^[90]
           

           In the mid-1970s, Project PACER, carried out at Los Alamos National Laboratory (LANL) explored the possibility of a fusion power system that would involve exploding small hydrogen bombs (fusion bombs) inside an underground cavity.^[91] As an energy source, the system is the only fusion power system that could be demonstrated to work using existing technology. It would also require a large, continuous supply of nuclear bombs, however, making the economics of such a system rather questionable.
           

           In 1976, the two beam Argus laser becomes operational at livermore.^{[citation needed]} In 1977, The 20 beam Shiva laser at Livermore is completed, capable of delivering 10.2 kilojoules of infrared energy on target. At a price of $25 million and a size approaching that of a football field, Shiva is the first of the megalasers.^{[citation needed]} That same year, the JET project is approved by the European Commission and a site is selected.
           

           
           

           1980s[edit]

           
           
           

           Magnetic mirrors suffered from end losses, requiring high power, complex magnetic designs, such as the baseball coil pictured here.

           
           
           

           The Novette target chamber (metal sphere with diagnostic devices protruding radially), which was reused from the Shiva project and two newly built laser chains visible in background.

           

           Inertial confinement fusion implosion on the Nova laser during the 1980s was a key driver of fusion development.
           
           

           As a result of advocacy, the cold war, and the 1970s energy crisis a massive magnetic mirror program was funded by the US federal government in the late 1970s and early 1980s. This program resulted in a series of large magnetic mirror devices including: 2X,^[92] Baseball I, Baseball II, the Tandem Mirror Experiment, the Tandem mirror experiment upgrade, the Mirror Fusion Test Facility and the MFTF-B. These machines were built and tested at Livermore from the late 1960s to the mid 1980s.^[93][94] A number of institutions collaborated on these machines, conducting experiments. These included the Institute for Advanced Study and the University of Wisconsin–Madison. The last machine, the Mirror Fusion Test Facility cost 372 million dollars and was, at that time, the most expensive project in Livermore history.^[95] It opened on February 21, 1986 and was promptly shut down. The reason given was to balance the United States federal budget. This program was supported from within the Carter and early Reagan administrations by Edwin E. Kintner, a US Navy captain, under Alvin Trivelpiece.^[96]
           

           In Laser fusion progressed: in 1983, the NOVETTE laser was completed. The following December 1984, the ten beam NOVA laser was finished. Five years later, NOVA would produce a maximum of 120 kilojoules of infrared light, during a nanosecond pulse.^{[citation needed]} Meanwhile, efforts focused on either fast delivery or beam smoothness. Both tried to deliver the energy uniformly to implode the target. One early problem was that the light in the infrared wavelength, lost lots of energy before hitting the fuel. Breakthroughs were made at the Laboratory for Laser Energetics at the University of Rochester. Rochester scientists used frequency-tripling crystals to transform the infrared laser beams into ultraviolet beams. In 1985, Donna Strickland^[97] and Gérard Mourou invented a method to amplify lasers pulses by "chirping". This method changes a single wavelength into a full spectrum. The system then amplifies the laser at each wavelength and then reconstitutes the beam into one color. Chirp pulsed amplification became instrumental in building the National Ignition Facility and the Omega EP system. Most research into ICF was towards weapons research, because the implosion is relevant to nuclear weapons.
           

           During this time Los Alamos National Laboratory constructed a series of laser facilities.^[98] This included Gemini (a two beam system), Helios (eight beams), Antares (24 beams) and Aurora (96 beams).^[99][100] The program ended in the early nineties with a cost on the order of one billion dollars.^[98]
           

           In 1987, Akira Hasegawa ^[101] noticed that in a dipolar magnetic field, fluctuations tended to compress the plasma without energy loss. This effect was noticed in data taken by Voyager 2, when it encountered Uranus. This observation would become the basis for a fusion approach known as the Levitated dipole.
           

           In Tokamaks, the Tore Supra was under construction over the middle of the eighties (1983 to 1988). This was a Tokamak built in Cadarache, France.^[102] In 1983, the JET was completed and first plasmas achieved. In 1985, the Japanese tokamak, JT-60 was completed. In 1988, the T-15 a Soviet tokamak was completed. It was the first industrial fusion reactor to use superconducting magnets to control the plasma. These were Helium cooled.
           

           In 1989, Pons and Fleischmann submitted papers to the Journal of Electroanalytical Chemistry claiming that they had observed fusion in a room temperature device and disclosing their work in a press release.^[103] Some scientists reported excess heat, neutrons, tritium, helium and other nuclear effects in so-called cold fusion systems, which for a time gained interest as showing promise. Hopes fell when replication failures were weighed in view of several reasons cold fusion is not likely to occur, the discovery of possible sources of experimental error, and finally the discovery that Fleischmann and Pons had not actually detected nuclear reaction byproducts.^[104] By late 1989, most scientists considered cold fusion claims dead,^[105] and cold fusion subsequently gained a reputation as pathological science.^[106] However, a small community of researchers continues to investigate cold fusion^{[105][107][108][109]} claiming to replicate Fleishmann and Pons' results including nuclear reaction byproducts.^[110][111] Claims related to cold fusion are largely disbelieved in the mainstream scientific community.^[112] In 1989, the majority of a review panel organized by the US Department of Energy (DOE) found that the evidence for the discovery of a new nuclear process was not persuasive. A second DOE review, convened in 2004 to look at new research, reached conclusions similar to the first.^[113]
           

           In 1984, Martin Peng of ORNL proposed^[114] an alternate arrangement of the magnet coils that would greatly reduce the aspect ratio while avoiding the erosion issues of the compact tokamak: a Spherical tokamak. Instead of wiring each magnet coil separately, he proposed using a single large conductor in the center, and wiring the magnets as half-rings off of this conductor. What was once a series of individual rings passing through the hole in the center of the reactor was reduced to a single post, allowing for aspect ratios as low as 1.2.^[115][116] The ST concept appeared to represent an enormous advance in tokamak design. However, it was being proposed during a period when US fusion research budgets were being dramatically scaled back. ORNL was provided with funds to develop a suitable central column built out of a high-strength copper alloy called "Glidcop". However, they were unable to secure funding to build a demonstration machine, "STX". Failing to build an ST at ORNL, Peng began a worldwide effort to interest other teams in the ST concept and get a test machine built. One way to do this quickly would be to convert a spheromak machine to the Spherical tokamak layout.^[116] Peng's advocacy also caught the interest of Derek Robinson, of the United Kingdom Atomic Energy Authority fusion center at Culham. Robinson was able to gather together a team and secure funding on the order of 100,000 pounds to build an experimental machine, the Small Tight Aspect Ratio Tokamak, or START. Several parts of the machine were recycled from earlier projects, while others were loaned from other labs, including a 40 keV neutral beam injector from ORNL. Construction of START began in 1990, it was assembled rapidly and started operation in January 1991.^[117]
           

           
           

           1990s[edit]

           
            
           
           
           

           In 1991 the Preliminary Tritium Experiment at the Joint European Torus in England achieved the world's first controlled release of fusion power.^[118]
           

           In 1992, a major article was published in Physics Today by Robert McCory at the Laboratory for laser energetics outlying the current state of ICF and advocating for a national ignition facility.^[119] This was followed up by a major review article, from John Lindl in 1995,^[120] advocating for NIF. During this time a number of ICF subsystems were developing, including target manufacturing, cryogenic handling systems, new laser designs (notably the NIKE laser at NRL) and improved diagnostics like time of flight analyzers and Thomson scattering. This work was done at the NOVA laser system, General Atomics, Laser Mégajoule and the GEKKO XII system in Japan. Through this work and lobbying by groups like the fusion power associates and John Sethian at NRL, a vote was made in congress, authorizing funding for the NIF project in the late nineties.
           

           In the early nineties, theory and experimental work regarding fusors and polywells was published.^[121][122] In response, Todd Rider at MIT developed general models of these devices.^[123] Rider argued that all plasma systems at thermodynamic equilibrium were fundamentally limited. In 1995, William Nevins published a criticism ^[124] arguing that the particles inside fusors and polywells would build up angular momentum, causing the dense core to degrade.
           

           In 1995, the University of Wisconsin–Madison built a large fusor, known as HOMER, which is still in operation.^[125] Meanwhile, Dr George H. Miley at Illinois, built a small fusor that has produced neutrons using deuterium gas ^[126] and discovered the "star mode" of fusor operation.^[127] The following year, the first "US-Japan Workshop on IEC Fusion", was conducted. At this time in Europe, an IEC device was developed as a commercial neutron source by Daimler-Chrysler and NSD Fusion.^[128][129]
           

           In 1996, the Z-machine was upgraded and opened to the public by the US Army in August 1998 in Scientific American.^[130][131] The key attributes of Sandia's Z machine^[132] are its 18 million amperes and a discharge time of less than 100 nanoseconds. This generates a magnetic pulse, inside a large oil tank, this strikes an array of tungsten wires called a liner.^[133] Firing the Z-machine has become a way to test very high energy, high temperature (2 billion degrees) conditions.^[134] In 1996, the Tore Supra creates a plasma for two minutes with a current of almost 1 million amperes driven non-inductively by 2.3 MW of lower hybrid frequency waves. This is 280 MJ of injected and extracted energy. This result was possible because of the actively cooled plasma-facing components^{[citation needed]}
           

           In 1997, JET produced a peak of 16.1MW of fusion power (65% of heat to plasma^[135]), with fusion power of over 10MW sustained for over 0.5 sec. Its successor, the International Thermonuclear Experimental Reactor (ITER), was officially announced as part of a seven-party consortium (six countries and the EU).^[136] ITER is designed to produce ten times more fusion power than the power put into the plasma. ITER is currently under construction in Cadarache, France.
           

           In the late nineties, a team at Columbia University and MIT developed the Levitated dipole a fusion device which consisted of a superconducting electromagnet, floating in a saucer shaped vacuum chamber. Plasma swirled around this donut and fused along the center axis.
           

           
           

           2000s[edit]

           
           
           
           
           
           

           The Mega Ampere Spherical Tokamak became operational in the UK in 1999
           
           

           In the March 8, 2002 issue of the peer-reviewed journal ScienceRusi P. Taleyarkhan and colleagues at the Oak Ridge National Laboratory (ORNL) reported that acoustic cavitation experiments conducted with deuterated acetone (C₃D₆O) showed measurements of tritium and neutron output consistent with the occurrence of fusion.^[142] Taleyarkhan was later found guilty of misconduct,^[143] the Office of Naval Research debarred him for 28 months from receiving Federal Funding,^[144][145] and his name was listed in the 'Excluded Parties List'.^[144]
           

           "Fast ignition" was developed in the late nineties, and was part of a push by the Laboratory for Laser Energetics for building the Omega EP system. This system was finished in 2008. Fast ignition showed such dramatic power savings that ICF appears to be a useful technique for energy production. There are even proposals to build an experimental facility dedicated to the fast ignition approach, known as HiPER.
           

           In April 2005, a team from UCLA announced^[146] it had devised a way of producing fusion using a machine that "fits on a lab bench", using lithium tantalate to generate enough voltage to smash deuterium atoms together. The process, however, does not generate net power (see Pyroelectric fusion). Such a device would be useful in the same sort of roles as the fusor.
           

           In 2006, China's EAST test reactor is completed. This was the first tokamak to use superconducting magnets to generate both the toroidal and poloidal fields.
           

           In the early 2000s, Researchers at LANL reasoned that a plasma oscillating could be at local thermodynamic equilibrium. This prompted the POPS and Penning trap designs.^[147][148] At this time, researchers at MIT became interested in fusors for space propulsion^[149] and powering space vehicles.^[150] Specifically, researchers developed fusors with multiple inner cages. Greg Piefer graduated from Madison and founded Phoenix Nuclear Labs, a company that developed the fusor into a neutron source for the mass production of medical isotopes.^[151] Robert Bussard began speaking openly about the Polywell in 2006.^[152] He attempted to generate interest^[153] in the research, before his death. In 2008, Taylor Wilson achieved notoriety^[154][155] for achieving nuclear fusion at 14, with a homemade fusor.^{[156][157][158]}
           

           In March 2009, a high-energy laser system, the National Ignition Facility (NIF), located at the Lawrence Livermore National Laboratory, became operational.^[159]
           

           The early 2000s saw the founding of a number of privately backed fusion companies pursuing innovative approaches with the stated goal of developing commercially viable fusion power plants.^[160] Secretive startup Tri Alpha Energy, founded in 1998, began exploring a field-reversed configuration approach.^[161][162] In 2002, Canadian company General Fusion began proof-of-concept experiments based on a hybrid magneto-inertial approach called Magnetized Target Fusion.^[161][160] These companies are funded by private investors including Jeff Bezos (General Fusion) and Paul Allen (Tri Alpha Energy).^[161] Toward the end of the decade, UK-based fusion company Tokamak Energy started exploring spherical tokamak devices.^[163]
           

           
           

           2010s[edit]

           
           
           

           The preamplifiers of the National Ignition Facility. In 2012, the NIF achieved a 500-terawatt shot.
           
           
           

           The Wendelstein7X under construction
           
           
           

           Example of a stellarator design: A coil system (blue) surrounds plasma (yellow). A magnetic field line is highlighted in green on the yellow plasma surface.
           
           

           NIF, the French Laser Mégajoule and the planned European Union High Power laser Energy Research (HiPER) facility continued researching inertial (laser) confinement.
           

           In 2010, NIF researchers conducted a series of "tuning" shots to determine the optimal target design and laser parameters for high-energy ignition experiments with fusion fuel.^[164][165] Firing tests were performed on October 31, 2010 and November 2, 2010. In early 2012, NIF director Mike Dunne expected the laser system to generate fusion with net energy gain by the end of 2012.^[166] However, that did not happen until August 2013. The facility reported that their next step involved improving the system to prevent the hohlraum from either breaking up asymmetrically or too soon.^[167]
           

           A 2012 paper demonstrated that a dense plasma focus had achieved temperatures of 1.8 billion degrees Celsius, sufficient for boron fusion, and that fusion reactions were occurring primarily within the contained plasmoid, a necessary condition for net power.^[168]
           

           In April 2014, Lawrence Livermore National Laboratory ended the Laser Inertial Fusion Energy (LIFE) program and redirected their efforts towards NIF.^[169] In August 2014, Phoenix Nuclear Labs announced the sale of a high-yield neutron generator that could sustain 5×10¹¹ deuterium fusion reactions per second over a 24-hour period.^[170]
           

           In October 2014, Lockheed Martin's Skunk Works announced the development of a high beta fusion reactor, the Compact Fusion Reactor, intending on making a 100-megawatt prototype by 2017 and beginning regular operation by 2022.^{[171][172][173]} Although the original concept was to build a 20-ton, container-sized unit, the team later conceded that the minimum scale would be 2,000 tons.^[174]
           

           In January 2015, the polywell was presented at Microsoft Research.^[175]
           

           In August, 2015, MIT announced a tokamak it named ARC fusion reactor using rare-earth barium-copper oxide (REBCO) superconducting tapes to produce high-magnetic field coils that it claimed produce comparable magnetic field strength in a smaller configuration than other designs.^[176]
           

           In October 2015, researchers at the Max Planck Institute of Plasma Physics completed building the largest stellarator to date, named Wendelstein 7-X. On December 10, they successfully produced the first helium plasma, and on February 3, 2016 produced the device's first hydrogen plasma.^[177] With plasma discharges lasting up to 30 minutes, Wendelstein 7-X is attempting to demonstrate the essential stellarator attribute: continuous operation of a high-temperature hydrogen plasma.
           

           General Fusion developed its plasma injector technology and Tri Alpha Energy constructed and operated its C-2U device.^[178][179]
           

           In 2017 Helion Energy's fifth-generation plasma machine went into operation, seeking to achieve plasma density of 20 Tesla and fusion temperatures. In 2018 General Fusion was developing a 70% scale demo system to be completed around 2023.^[174]
           

           In 2018, Zap Energy became the only ARPA-E Alpha Programme fusion initiative to meet and exceed its milestones, producing neutrons using a sheer-flow Z-pinch configuration. Zap Energy is the most compact solution to fusion energy without complex and costly magnetic coils. In late 2018, Zap Energy was awarded $6.8 million ARPA-E OPEN funding. ^[180]
           

           In 2018, energy corporation Eni announced a $50 million investment in the newly founded Commonwealth Fusion Systems, to attempt to commercialize ARC technology using a test reactor (SPARC) in collaboration with MIT.^{[181][182][183][184]}
           

           
           
           

           By firing particle beams at targets, many fusion reactions have been tested, while the fuels considered for power have all been light elements like the isotopes of hydrogen—protium, deuterium, and tritium.^[3] The deuterium and helium-3 reaction requires helium-3, an isotope of helium so scarce on Earth that it would have to be mined extraterrestrially or produced by other nuclear reactions. Finally, researchers hope to perform the protium and boron-11 reaction, because it does not directly produce neutrons, though side reactions can.^[185]
           

           
           

           Deuterium, tritium[edit]

           
           
           

           Diagram of the D-T reaction
           
           

           The easiest nuclear reaction, at the lowest energy, is:
           

           
           

           ²
           ₁D
           + ³
           ₁T
           → ⁴
           ₂He
           (3.5 MeV) + ¹
           ₀n
           (14.1 MeV)

           
           

           This reaction is common in research, industrial and military applications, usually as a convenient source of neutrons. Deuterium is a naturally occurring isotope of hydrogen and is commonly available. The large mass ratio of the hydrogen isotopes makes their separation easy compared to the difficult uranium enrichment process. Tritium is a natural isotope of hydrogen, but because it has a short half-life of 12.32 years, it is hard to find, store, produce, and is expensive. Consequently, the deuterium-tritium fuel cycle requires the breeding of tritium from lithium using one of the following reactions:
           

           
           

           ¹
           ₀n
           + ⁶
           ₃Li
           → ³
           ₁T
           + ⁴
           ₂He
           

           
           

           ¹
           ₀n
           + ⁷
           ₃Li
           → ³
           ₁T
           + ⁴
           ₂He
           + ¹
           ₀n
           

           
           

           The reactant neutron is supplied by the D-T fusion reaction shown above, and the one that has the greatest yield of energy. The reaction with ⁶Li is exothermic, providing a small energy gain for the reactor. The reaction with ⁷Li is endothermic but does not consume the neutron. At least some neutron multiplication reactions are required to replace the neutrons lost to absorption by other elements. Leading candidate neutron multiplication materials are beryllium and lead however the ⁷Li reaction above also helps to keep the neutron population high. Natural lithium is mainly ⁷Li however this has a low tritium production cross section compared to ⁶Li so most reactor designs use breeder blankets with enriched ⁶Li.
           

           Several drawbacks are commonly attributed to D-T fusion power:
           

           
           
           1. It produces substantial amounts of neutrons that result in the neutron activation of the reactor materials.^[186]
           
           
           2. Only about 20% of the fusion energy yield appears in the form of charged particles with the remainder carried off by neutrons, which limits the extent to which direct energy conversion techniques might be applied.^[187]
           
           
           3. It requires the handling of the radioisotope tritium. Similar to hydrogen, tritium is difficult to contain and may leak from reactors in some quantity. Some estimates suggest that this would represent a fairly large environmental release of radioactivity.^[188]
           
           

           The neutron flux expected in a commercial D-T fusion reactor is about 100 times that of current fission power reactors, posing problems for material design. After a series of D-T tests at JET, the vacuum vessel was sufficiently radioactive that remote handling was required for the year following the tests.^[189]
           

           In a production setting, the neutrons would be used to react with lithium in the context of a breeder blanket comprising lithium ceramic pebbles or liquid lithium, in order to create more tritium. This also deposits the energy of the neutrons in the lithium, which would then be transferred to drive electrical production. The lithium neutron absorption reaction protects the outer portions of the reactor from the neutron flux. Newer designs, the advanced tokamak in particular, also use lithium inside the reactor core as a key element of the design. The plasma interacts directly with the lithium, preventing a problem known as "recycling". The advantage of this design was demonstrated in the Lithium Tokamak Experiment.
           

           
           

           Deuterium[edit]

           
           
           

           Deuterium fusion cross section (in square meters) at different ion collision energies.
           
           

           This is the second easiest fusion reaction, fusing two deuterium nuclei. The reaction has two branches that occur with nearly equal probability:
           

           
           

           
           
           
           
           
           
           
           
           

           D + D	→ T	+ 1H
           D + D	→ 3He	+ n

           
           

           This reaction is also common in research. The optimum energy to initiate this reaction is 15 keV, only slightly higher than the optimum for the D-T reaction. The first branch does not produce neutrons, but it does produce tritium, so that a D-D reactor will not be completely tritium-free, even though it does not require an input of tritium or lithium. Unless the tritons can be quickly removed, most of the tritium produced would be burned before leaving the reactor, which would reduce the handling of tritium, but would produce more neutrons, some of which are very energetic. The neutron from the second branch has an energy of only 2.45 MeV (0.393 pJ), whereas the neutron from the D-T reaction has an energy of 14.1 MeV (2.26 pJ), resulting in a wider range of isotope production and material damage. When the tritons are removed quickly while allowing the ³He to react, the fuel cycle is called "tritium suppressed fusion"^[190] The removed tritium decays to ³He with a 12.5 year half life. By recycling the ³He produced from the decay of tritium back into the fusion reactor, the fusion reactor does not require materials resistant to fast 14.1 MeV (2.26 pJ) neutrons.
           

           Assuming complete tritium burn-up, the reduction in the fraction of fusion energy carried by neutrons would be only about 18%, so that the primary advantage of the D-D fuel cycle is that tritium breeding would not be required. Other advantages are independence from scarce^{[dubious – discuss]} lithium resources and a somewhat softer neutron spectrum. The disadvantage of D-D compared to D-T is that the energy confinement time (at a given pressure) must be 30 times longer and the power produced (at a given pressure and volume) would be 68 times less.^{[citation needed]}
           

           Assuming complete removal of tritium and recycling of ³He, only 6% of the fusion energy is carried by neutrons. The tritium-suppressed D-D fusion requires an energy confinement that is 10 times longer compared to D-T and a plasma temperature that is twice as high.^[191]
           

           
           

           Deuterium, helium-3[edit]

           
           

           A second-generation approach to controlled fusion power involves combining helium-3 (³He) and deuterium (²H):
           

           
           
           
           

           This reaction produces a helium-4 nucleus (⁴He) and a high-energy proton. As with the p-¹¹B aneutronic fusion fuel cycle, most of the reaction energy is released as charged particles, reducing activation of the reactor housing and potentially allowing more efficient energy harvesting (via any of several speculative technologies).^{[citation needed]} In practice, D-D side reactions produce a significant number of neutrons, resulting in p-¹¹B being the preferred cycle for aneutronic fusion.^{[citation needed]}
           

           
           

           Protium, boron-11[edit]

           
           

           If aneutronic fusion is the goal, then the most promising candidate may be the hydrogen-1 (protium) and boron reaction, which releases alpha (helium) particles, but does not rely on neutron scattering for energy transfer.
           

           
           

           ¹H + ¹¹B → 3 ⁴He

           
           

           Under reasonable assumptions, side reactions will result in about 0.1% of the fusion power being carried by neutrons.^[192] At 123 keV, the optimum temperature for this reaction is nearly ten times higher than that for the pure hydrogen reactions, the energy confinement must be 500 times better than that required for the D-T reaction, and the power density will be 2500 times lower than for D-T.
           

           Because the confinement properties of conventional approaches to fusion such as the tokamak and laser pellet fusion are marginal, most proposals for aneutronic fusion are based on radically different confinement concepts, such as the Polywell and the Dense Plasma Focus. Results have been extremely promising:
           

           
           

           "In the October 2013 edition of Nature Communications,^[193] a research team led by Christine Labaune at École Polytechnique in Palaiseau, France, reported a new record fusion rate: an estimated 80 million fusion reactions during the 1.5 nanoseconds that the laser fired, which is at least 100 times more than any previous proton-boron experiment. " ^[194]

           
           

           Material selection[edit]

           
           
           

           Considerations[edit]

           
           

           Even on smaller plasma production scales, the material of the containment apparatus will be intensely blasted with matter and energy. Designs for plasma containment must consider:
           

           
           
           

           Depending on the approach, these effects may be higher or lower than typical fission reactors like the pressurized water reactor (PWR).^[195] One estimate put the radiation at 100 times that of a typical PWR.^{[citation needed]} Materials need to be selected or developed that can withstand these basic conditions.^[196][197] Depending on the approach, however, there may be other considerations such as electrical conductivity, magnetic permeability and mechanical strength. There is also a need for materials whose primary components and impurities do not result in long-lived radioactive wastes.
           

           
           

           Durability[edit]

           
           

           For long term use, each atom in the wall is expected to be hit by a neutron and displaced about a hundred times before the material is replaced. High-energy neutrons will produce hydrogen and helium by way of various nuclear reactions that tends to form bubbles at grain boundaries and result in swelling, blistering or embrittlement.^[195]
           

           
           

           Selection[edit]

           
           

           One can choose either a low-Z material, such as graphite or beryllium, or a high-Z material, usually tungsten with molybdenum as a second choice. Use of liquid metals (lithium, gallium, tin) has also been proposed, e.g., by injection of 1–5 mm thick streams flowing at 10 m/s on solid substrates.^{[citation needed]}
           

           If graphite is used, the gross erosion rates due to physical and chemical sputtering would be many meters per year, so one must rely on redeposition of the sputtered material. The location of the redeposition will not exactly coincide with the location of the sputtering, so one is still left with erosion rates that may be prohibitive. An even larger problem is the tritium co-deposited with the redeposited graphite. The tritium inventory in graphite layers and dust in a reactor could quickly build up to many kilograms, representing a waste of resources and a serious radiological hazard in case of an accident. The consensus of the fusion community seems to be that graphite, although a very attractive material for fusion experiments, cannot be the primary plasma-facing material (PFM) in a commercial reactor.
           

           The sputtering rate of tungsten by the plasma fuel ions is orders of magnitude smaller than that of carbon, and tritium is much less incorporated into redeposited tungsten, making this a more attractive choice. On the other hand, tungsten impurities in a plasma are much more damaging than carbon impurities, and self-sputtering of tungsten can be high, so it will be necessary to ensure that the plasma in contact with the tungsten is not too hot (a few tens of eV rather than hundreds of eV). Tungsten also has disadvantages in terms of eddy currents and melting in off-normal events, as well as some radiological issues.
           

           
           

           Safety and the environment[edit]

           
           

           Accident potential[edit]

           
           

           Unlike nuclear fission, fusion requires extremely precise and controlled temperature, pressure and magnetic field parameters for any net energy to be produced. If a reactor suffers damage or loses even a small degree of required control, fusion reactions and heat generation would rapidly cease.^[198] Additionally, fusion reactors contain only small amounts of fuel, enough to "burn" for minutes, or in some cases, microseconds. Unless they are actively refueled, the reactions will quickly end. Therefore, fusion reactors are considered immune from catastrophic meltdown.^[199]
           

           For similar reasons, runaway reactions cannot occur in a fusion reactor. The plasma is burnt at optimal conditions, and any significant change will simply quench the reactions. The reaction process is so delicate that this level of safety is inherent. Although the plasma in a fusion power station is expected to have a volume of 1,000 cubic metres (35,000 cu ft) or more, the plasma density is low and typically contains only a few grams of fuel in use.^[199] If the fuel supply is closed, the reaction stops within seconds. In comparison, a fission reactor is typically loaded with enough fuel for several months or years, and no additional fuel is necessary to continue the reaction. It is this large amount of fuel that gives rise to the possibility of a meltdown; nothing like this exists in a fusion reactor.^[200]
           

           In the magnetic approach, strong fields are developed in coils that are held in place mechanically by the reactor structure. Failure of this structure could release this tension and allow the magnet to "explode" outward. The severity of this event would be similar to any other industrial accident or an MRI machine quench/explosion, and could be effectively stopped with a containment building similar to those used in existing (fission) nuclear generators. The laser-driven inertial approach is generally lower-stress because of the increased size of the reaction chamber. Although failure of the reaction chamber is possible, simply stopping fuel delivery would prevent any sort of catastrophic failure.^{[citation needed]}
           

           Most reactor designs rely on liquid hydrogen as both a coolant and a method for converting stray neutrons from the reaction into tritium, which is fed back into the reactor as fuel. Hydrogen is highly flammable, and in the case of a fire it is possible that the hydrogen stored on-site could be burned up and escape. In this case, the tritium contents of the hydrogen would be released into the atmosphere, posing a radiation risk. Calculations suggest that at about 1 kilogram (2.2 lb), the total amount of tritium and other radioactive gases in a typical power station would be so small that they would have diluted to legally acceptable limits by the time they blew as far as the station's perimeter fence.^[201]
           

           The likelihood of small industrial accidents, including the local release of radioactivity and injury to staff, cannot be estimated yet. These would include accidental releases of lithium or tritium or mishandling of decommissioned radioactive components of the reactor itself.^{[citation needed]}
           

           
           

           Magnet quench[edit]

           
           

           A quench is an abnormal termination of magnet operation that occurs when part of the superconducting coil enters the normal (resistive) state. This can occur because the field inside the magnet is too large, the rate of change of field is too large (causing eddy currents and resultant heating in the copper support matrix), or a combination of the two.
           

           More rarely a defect in the magnet can cause a quench. When this happens, that particular spot is subject to rapid Joule heating from the enormous current, which raises the temperature of the surrounding regions. This pushes those regions into the normal state as well, which leads to more heating in a chain reaction. The entire magnet rapidly becomes normal (this can take several seconds, depending on the size of the superconducting coil). This is accompanied by a loud bang as the energy in the magnetic field is converted to heat, and rapid boil-off of the cryogenic fluid. The abrupt decrease of current can result in kilovolt inductive voltage spikes and arcing. Permanent damage to the magnet is rare, but components can be damaged by localized heating, high voltages, or large mechanical forces.
           

           In practice, magnets usually have safety devices to stop or limit the current when the beginning of a quench is detected. If a large magnet undergoes a quench, the inert vapor formed by the evaporating cryogenic fluid can present a significant asphyxiation hazard to operators by displacing breathable air.
           

           A large section of the superconducting magnets in CERN's Large Hadron Collider unexpectedly quenched during start-up operations in 2008, necessitating the replacement of a number of magnets.^[202] In order to mitigate against potentially destructive quenches, the superconducting magnets that form the LHC are equipped with fast-ramping heaters which are activated once a quench event is detected by the complex quench protection system. As the dipole bending magnets are connected in series, each power circuit includes 154 individual magnets, and should a quench event occur, the entire combined stored energy of these magnets must be dumped at once. This energy is transferred into dumps that are massive blocks of metal which heat up to several hundreds of degrees Celsius—because of resistive heating—in a matter of seconds. Although undesirable, a magnet quench is a "fairly routine event" during the operation of a particle accelerator.^[203]
           

           
           

           Effluents[edit]

           
           

           The natural product of the fusion reaction is a small amount of helium, which is completely harmless to life. Of more concern is tritium, which, like other isotopes of hydrogen, is difficult to retain completely. During normal operation, some amount of tritium will be continually released.^{[citation needed]}
           

           Although tritium is volatile and biologically active, the health risk posed by a release is much lower than that of most radioactive contaminants, because of tritium's short half-life (12.32 years) and very low decay energy (~14.95 keV), and because it does not bioaccumulate (instead being cycled out of the body as water, with a biological half-life of 7 to 14 days).^[204] Current ITER designs are investigating total containment facilities for any tritium.
           

           
           

           Waste management[edit]

           
           
           

           The large flux of high-energy neutrons in a reactor will make the structural materials radioactive. The radioactive inventory at shut-down may be comparable to that of a fission reactor, but there are important differences.
           

           The half-life of the radioisotopes produced by fusion tends to be less than those from fission, so that the inventory decreases more rapidly. Unlike fission reactors, whose waste remains radioactive for thousands of years, most of the radioactive material in a fusion reactor would be the reactor core itself, which would be dangerous for about 50 years, and low-level waste for another 100.^[205] Although this waste will be considerably more radioactive during those 50 years than fission waste, the very short half-life makes the process very attractive, as the waste management is fairly straightforward. By 500 years the material would have the same radiotoxicity as coal ash.^[201]
           

           Additionally, the choice of materials used in a fusion reactor is less constrained than in a fission design, where many materials are required for their specific neutron cross-sections. This allows a fusion reactor to be designed using materials that are selected specifically to be "low activation", materials that do not easily become radioactive. Vanadium, for example, would become much less radioactive than stainless steel. Carbon fiber materials are also low-activation, as well as being strong and light, and are a promising area of study for laser-inertial reactors where a magnetic field is not required.
           

           In general terms, fusion reactors would create far less radioactive material than a fission reactor, the material it would create is less damaging biologically, and the radioactivity "burns off" within a time period that is well within existing engineering capabilities for safe long-term waste storage.
           

           
           

           Nuclear proliferation[edit]

           
           
           

           Although fusion power uses nuclear technology, the overlap with nuclear weapons would be limited. A huge amount of tritium could be produced by a fusion power station; tritium is used in the trigger of hydrogen bombs and in a modern boosted fission weapon, but it can also be produced by nuclear fission. The energetic neutrons from a fusion reactor could be used to breed weapons-grade plutonium or uranium for an atomic bomb (for example by transmutation of U²³⁸ to Pu²³⁹or Th²³² to U²³³).
           

           A study conducted 2011 assessed the risk of three scenarios:^[206]
           

           
           
           • Use in small-scale fusion station: As a result of much higher power consumption, heat dissipation and a more recognizable design compared to enrichment gas centrifuges this choice would be much easier to detect and therefore implausible.^[206]
           
           
           • Modifications to produce weapon-usable material in a commercial facility: The production potential is significant. But no fertile or fissile substances necessary for the production of weapon-usable materials needs to be present at a civil fusion system at all. If not shielded, a detection of these materials can be done by their characteristic gamma radiation. The underlying redesign could be detected by regular design information verifications. In the (technically more feasible) case of solid breeder blanket modules, it would be necessary for incoming components to be inspected for the presence of fertile material,^[206] otherwise plutonium for several weapons could be produced each year.^[207]
           
           
           • Prioritizing a fast production of weapon-grade material regardless of secrecy: The fastest way to produce weapon usable material was seen in modifying a prior civil fusion power station. Unlike in some nuclear power stations, there is no weapon compatible material during civil use. Even without the need for covert action this modification would still take about 2 months to start the production and at least an additional week to generate a significant amount for weapon production. This was seen as enough time to detect a military use and to react with diplomatic or military means. To stop the production, a military destruction of inevitable parts of the facility leaving out the reactor itself would be sufficient. This, together with the intrinsic safety of fusion power would only bear a low risk of radioactive contamination.^[206]
           
           

           Another study concludes that "[..]large fusion reactors – even if not designed for fissile material breeding – could easily produce several hundred kg Pu per year with high weapon quality and very low source material requirements." It was emphasized that the implementation of features for intrinsic proliferation resistance might only be possible at this phase of research and development.^[207] The theoretical and computational tools needed for hydrogen bomb design are closely related to those needed for inertial confinement fusion, but have very little in common with the more scientifically developed magnetic confinement fusion.
           

           
           

           Energy source[edit]

           
           

           Large-scale reactors using neutronic fuels (e.g. ITER) and thermal power production (turbine based) are most comparable to fission power from an engineering and economics viewpoint. Both fission and fusion power stations involve a relatively compact heat source powering a conventional steam turbine-based power station, while producing enough neutron radiation to make activation of the station materials problematic. The main distinction is that fusion power produces no high-level radioactive waste (though activated station materials still need to be disposed of). There are some power station ideas that may significantly lower the cost or size of such stations; however, research in these areas is nowhere near as advanced as in tokamaks.^{[citation needed]}
           

           Fusion power commonly proposes the use of deuterium, an isotope of hydrogen, as fuel and in many current designs also use lithium. Assuming a fusion energy output equal to the 1995 global power output of about 100 EJ/yr (= 1 × 10²⁰ J/yr) and that this does not increase in the future, which is unlikely, then the known current lithium reserves would last 3000 years. Lithium from sea water would last 60 million years, however, and a more complicated fusion process using only deuterium would have fuel for 150 billion years.^[208] To put this in context, 150 billion years is close to 30 times the remaining lifespan of the sun,^[209] and more than 10 times the estimated age of the universe.
           

           
           

           Economics[edit]

           
           

           While fusion power is still in early stages of development, substantial sums have been and continue to be invested in research. In the EU almost €10 billion was spent on fusion research up to the end of the 1990s, and the new ITER reactor alone is budgeted at €6.6 billion total for the timeframe between 2008 and 2020.^[210]
           

           It is estimated that up to the point of possible implementation of electricity generation by nuclear fusion, R&D will need further promotion totalling around €60–80 billion over a period of 50 years or so (of which €20–30 billion within the EU) based on a report from 2002.^[211] Nuclear fusion research receives €750 million (excluding ITER funding) from the European Union, compared with €810 million for sustainable energy research,^[212] putting research into fusion power well ahead of that of any single rivaling technology. Indeed, the size of the investments and time frame of the expected results mean that fusion research is almost exclusively publicly funded, while research in other forms of energy can be done by the private sector. In spite of that, a number of start-up companies active in the field of fusion power have managed to attract private money.^[213]
           

           
           

           Advantages[edit]

           
           

           Fusion power would provide more energy for a given weight of fuel than any fuel-consuming energy source currently in use,^[214] and the fuel itself (primarily deuterium) exists abundantly in the Earth's ocean: about 1 in 6500 hydrogen atoms in seawater is deuterium.^[215] Although this may seem a low proportion (about 0.015%), because nuclear fusion reactions are so much more energetic than chemical combustion and seawater is easier to access and more plentiful than fossil fuels, fusion could potentially supply the world's energy needs for millions of years.^[216][217]
           

           A scenario has been presented of the effect of the commercialization of fusion power on the future of human civilization.^[218] ITER and later DEMO are envisioned to bring online the first commercial nuclear fusion energy reactor by 2050. Using this as the starting point and the history of the uptake of nuclear fission reactors as a guide, the scenario depicts a rapid take up of nuclear fusion energy starting after the middle of this century.^{[citation needed]}
           

           Fusion power could be used in interstellar space where solar energy is not available.^[219]
           

           
           

           See also[edit]

           
           
           
           
           
           

           References[edit]

           
           
           
           

           
           
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           External links[edit]