Advanced toroidal physics.

Presentations on frontiers in advanced toroidal physics were given by Drs. David Baldwin (General Atomics), Earl Marmar (MIT), Martin Peng (ORNL), and Hutch Neilson (PPPL).

Dr. Baldwin said "the advanced tokamak has come of age" and "advanced tokamak stability theory points to states with very broad pressure profiles and hollow current profiles and nearly 100% bootstrap current as perhaps the ultimate potential of the tokamak." Researchers at General Atomics, using DIII-D, have nearly doubled the usual limits on pressure by spinning the plasma. He said the "solution of the transport question is in sight," saying "plasma turbulence simulation codes use full toroidal geometry to calculate transport rates."

Dr. Marmar said the Alcator C-Mod facility at MIT had "unique aspects and strengths" to address key questions using "advanced diagnostics." The said the Alcator had a "broad physics program organized along two parallel complementary paths: (1) advanced tokamak quasi-steady-state configurations with high bootstrap fraction and RF current and flow profile control, and (2) high field, high pressure regimes providing the physics basis for compact, high field approach to ignition." He said "the vision of the tokamak reactor has improved dramatically in the last decade."

Dr. Peng said the "spherical torus (ST) is reaching important new frontiers in fusion energy science." He said the ST research goal is to "investigate and understand physics & potential of very low aspect ratio and high beta," both of which, he said, "engender new frontiers in fusion energy science." He said that ST had the potential to benefit fusion energy by "simplified magnets and device design; lowered magnet and device costs; smaller unit size and sustained burn; more efficient fusion and RF heating and current drive; and survivable plasma facing components." Success in the ST program "may also lead to a more affordable development path," he said. He noted that the National Spherical Torus Experiment (NSTX) at PPPL was the most advanced of several ST experiments around the world. He said the NSTX had already exceeded its plasma energy goal aimed for October 2002 by achieving a central beta of about 70%. He said that the energy confinement measured in NSTX "exceeds empirical scaling expectations."

Dr. Neilson said "toroidal plasmas have many configuration variables," citing things like aspect ratio, shape, magnetic symmetry, rotational transform, divertor configuration and startup/control strategy. He said the "challenge for tomorrow's designers is to find the most attractive configuration; what combination of variables is optimum?" He said that "stellarators advance the frontier in unique ways." He said there is a "strong connection between stellarators and other 3-dimensional plasma physics problems." He said "the world stellarator program is substantial," citing large stellarator facilities in Japan and Germany. He said that recent understandings have led to the design of compact stellarators that combine high beta, and low aspect ratio. He said a balanced program was being proposed that included two new US experiments that would complement facilities abroad. The ten-year goal, he said, is to "evaluate compact stellarator physics benefits and costs and assess attractiveness." He said that constructi on of the US devices was planned for 2003-2006. He noted that FESAC had endorsed one of the facilities (NCSX) as a proof of principle" experiment and affirmed support for the program in August 2001. He said that compact stellarators "combine the best characteristics of stellarators and tokamaks, possibly eliminate disruptions, and are intrinsically steady state."