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 Quote by DT_tokamak Plasma stability is not a problem in modern tokamaks. The poloidal and toroidal coils keeps the plasma stable for the most part and the correction coils take care of the remainder of instabilities. Energy input is not a problem either... we've been firing up tokamaks for decades and achieving fusion reactions. TFTR hit 500 million C. No troubles there. The only thing we need is to get more energy out than we put in. And that's simply a matter of dollars which will create us larger reactors... that's not a question of science.
We're not there yet, hence the goal of ITER to hopefully demonstrate the feasibility.

 . . . . Following on from the PDX (Poloidal Diverter Experiment) and PLT (Princeton Large Torus) devices, it was hoped that TFTR would finally achieve fusion energy break-even. Unfortunately, the TFTR never achieved this goal. However it did produce major advances in confinement time and energy density, which ultimately contributed to the knowledge base necessary to build ITER. TFTR operated from 1982 to 1997.
http://en.wikipedia.org/wiki/TFTR

Achievements of TFTR - http://www.pppl.gov/projects/pages/t...ievements.html

TFTR did identify some instability issues, e.g. ballooning, but they also identified an enhanced reversed-shear mode during 1995, but TFTR was shutdown in 1997, so it's not clear that enhanced confinement methods are fully vetted.

 Quote by PPPL December 1993, for the first time in history, a reactor fuel mix of 50% deuterium and 50% tritium was used in a tokamak. Initial TFTR experiments yielded 6.0 million watts. By November, 1994, TFTR achieved 10.7 million watts of power, about 100 million times the power produced by tokamaks twenty years ago.
http://w3.pppl.gov/tftr/info/tftrparams.html - note Plasma Parameters for Shot 80539. While it achieved 10.7 MW of generated fusion power, the confinement time $\tau$ was 0.21 sec. One needs to achieve continuous operation on the order of 3.156 E7 sec, or a 90% CF to approach performance of current LWRs.

Hopefully ITER will demonstrate or perfect some of the processes developed with TFTR.

For reference - http://www.pppl.gov/projects/pages/tftr_docs.html