A MEGA-AMPERE SPHERICAL TOKAMAK DESIGN FOR BETA-LIMIT AND CONFINEMENTSTUDIES

Recent favorable results on START have caused renewed interest in low aspect ratio tokamaks. To design an economical next-step spherical tok amak to study confinement scaling and high beta plasmas, we have devel oped a transport scaling and device optimization code. This code OPT, benchmarked against START, includes 10 empirical confinement scaling l aws and essential tokamak physics such as stability limits. Parameters are optimized separately for each scaling law and physics goal. Using OPT we find for R/a=1.2 to 2.0 one can achieve beta(N)=5 and [beta]ap proximate to 30% with just two neutral beams (P-NB<3.5 MW) for I-p gre ater than or equal to 0.75 MA, and R(o) greater than or equal to 0.6 m . In contrast, if one insists on using the nominal device parameters, I-p=1 MA and R(o)=0.8 m, with each scaling law, achieving beta(N)=5 re quires typically P-NB=7.5 MW.