J-ASTERISK OPTIMIZATION OF SMALL ASPECT RATIO STELLARATOR TOKAMAK HYBRID DEVICES/

A new class of low aspect ratio toroidal hybrid stellarators is found using a more general plasma confinement optimization criterion than qu asisymmetrization. The plasma current profile and shape of the outer m agnetic flux surface are used as control variables to achieve near con stancy of the longitudinal invariant J on internal flux surfaces (qua siomnigeneity), in addition to a number of other desirable physics tar get properties. A range of compact (small aspect ratio A), low plasma current devices have been found with significantly improved confinemen t, both for thermal as well as energetic (collisionless) particle comp onents. With reasonable increases in magnetic field and geometric size , such devices can also be scaled to confine 3.5 MeV alpha particle or bits.