Editing Tokamak (section)

=== Heating: US takes the lead ===
[[File:Princeton Large Torus 1975.jpg|thumb|upright=1.5|Overhead view of the Princeton Large Torus in 1975. PLT set numerous records and demonstrated that the temperatures needed for fusion were possible.]]

Experiments on the Symmetric Tokamak began in May 1970, and by early the next year they had confirmed the Soviet results and then surpassed them. The stellarator was abandoned, and PPPL turned its considerable expertise to the problem of heating the plasma. Two concepts seemed to hold promise. PPPL proposed using magnetic compression, a pinch-like technique to compress a warm plasma to raise its temperature, but providing that compression through magnets rather than current.{{sfn|Bromberg|1982|p=169}} Oak Ridge suggested [[neutral beam injection]], small particle accelerators that would shoot fuel atoms through the surrounding magnetic field where they would collide with the plasma and heat it.{{sfn|Bromberg|1982|p=171}}

PPPL's [[Adiabatic Toroidal Compressor]] (ATC) began operation in May 1972, followed shortly thereafter by a neutral-beam equipped Ormak. Both demonstrated significant problems, but PPPL leapt past Oak Ridge by fitting beam injectors to ATC and provided clear evidence of successful heating in 1973. This success "scooped" Oak Ridge, who fell from favour within the Washington Steering Committee.{{sfn|Bromberg|1982|p=212}}

By this time a much larger design based on beam heating was under construction, the [[Princeton Large Torus]], or PLT. PLT was designed specifically to "give a clear indication whether the tokamak concept plus auxiliary heating can form a basis for a future fusion reactor".<ref name=timeline>{{cite web |title=Timeline |website=PPPL |url=https://www.pppl.gov/about/history/timeline}}</ref> PLT was an enormous success, continually raising its internal temperature until it hit 60 million Celsius (8,000&nbsp;eV, eight times T-3's record) in 1978. This is a key point in the development of the tokamak; fusion reactions become self-sustaining at temperatures between 50 and 100 million Celsius, PLT demonstrated that this was technically achievable.<ref name=timeline/>

These experiments, especially PLT, put the US far in the lead in tokamak research. This is due largely to budget; a tokamak cost about $500,000 and the US annual fusion budget was around $25 million at that time.{{sfn|Bromberg|1982|p=151}} They could afford to explore all of the promising methods of heating, ultimately discovering neutral beams to be among the most effective.{{sfn|Bromberg|1982|p=173}}

During this period, [[Robert L. Hirsch|Robert Hirsch]] took over the Directorate of fusion development in the [[U.S. Atomic Energy Commission]]. Hirsch felt that the program could not be sustained at its current funding levels without demonstrating tangible results. He began to reformulate the entire program. What had once been a lab-led effort of mostly scientific exploration was now a Washington-led effort to build a working power-producing reactor.{{sfn|Bromberg|1982|p=173}} This was given a boost by the [[1973 oil crisis]], which led to greatly increased research into [[alternative energy]] systems.{{sfn|Bromberg|1982|p=175}}