Physics Design of the National Spherical Torus Experiment

The mission of the National Spherical Torus Experiment (NSTX) is to prove the principles of spherical torus physics by producing high-_t plasmas that are noninductively sustained and whose current profiles are in steady state. The NSTX will be one of the first ultralow-aspect-ratio tori (R/a 1.3) to operate at high power (P_input up to 11 MW) to produce high-_t (25 to 40%), low-collisionality, high-bootstrap-fraction (70%) discharges. Both radio-frequency and neutral beam heating and current drive will be employed. Built into the NSTX is sufficient configurational flexibility to study a range of operating space and the resulting dependences of the confinement, micro- and magnetohydrodynamic stability, and particle- and power-handling properties. NSTX research will be carried out by a nationally based science team.