Physics design of the National Spherical Torus Experiment

The mission of the National Spherical Torus Experiment (NSTX) is to prove t he principles of spherical torus physics by producing high-beta(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 le ss than or equal to 1.3) to operate at high power (P-input up to 11 MW) to produce high-beta(t) (25 to 40%), low-collisionality, high-bootstrap-fracti on (less than or equal to 70%) dis charges. Both radio-frequency and neutra l beam heating and current drive will be employed Built into the NSTX is su fficient configurational flexibility to study a range of operating space an d the resulting dependences of the confinement, micro- and magnetohydrodyna mic stability, and particle- and power-handing properties. NSTX research wi ll be carried out by a nationally based science team.