ORNL's Compact Stellarator Program explores two promising approaches that combine the compactness of tokamaks with the disruption immunity of stellarators. They differ in the degree to which the plasma-generated bootstrap current is used to supplement currents in external windings in producing the confining poloidal magnetic field.

The National Compact Stellarator Experiment (NCSX) is proposed as a joint PPPL-ORNL experimental facility to test promising compact stellarator configurations. The goals are to demonstrate disruption-free operation at high beta and study beta limits, stability, transport, plasma control, and power and particle handling. The NCSX will be constructed by modifying the PBX-M tokamak facility at PPPL and installing new coils inside the vacuum vessel to provide the 3-D shaping fields. A Quasi-Axisymmetric (QA) stellarator configuration optimized for low transport and for stability at high beta will be tested first. Initial machine parameters are B = 1 T, R = 1.5 m, a = 0.4 m, P(NB) = 6 MW and t(pulse) = 0.3 s. Upgrade possibilities are to add 6 MW of ICRF heating power, increase t(pulse) to 3 s, increase B to 2 T, and reconfigure the coils to test a QO configuration.

A promising approach to improving transport in stellarators relies on Quasi-Omnigeneity (QO), that is the bounce-average particle drift surfaces lie approximately on flux surfaces. It has been found that such configurations can have good neoclassical confinement, high ballooning and kink stability beta limits, and good energetic orbit confinement, and this can be done at the low aspect ratio appropriate for compact stellarator reactors. The device parameters for the QOS Experiment are: R = 1 m, <a> = 0.28 m, B = 1 T, P(ECH) = 0.4 MW, P(ICRF) = 1 MW, and t(pulse) = 1 s. The experimental program addresses improvement of neoclassical and anomalous confinement and use of external coils rather than a plasma current to create most of the confining poloidal magnetic field.