Attaining neoclassical transport in ignited tokamaks

The requirements to stabilize microinstabilities with velocity shear in tok amaks are examined for both aspect ratio A = 3 and A = 1.4. A comprehensive linear gyrokinetic code is used to compute growth rates in realistic numer ical equilibria. Growth rates for A = 3 and A = 1.4 are generally similar f or electron drift modes and ion temperature gradient modes. Velocity shear is stronger at low aspect ratio; how-ever, low A profiles have a stronger m icrotearing mode which is more difficult to shear stabilize. Nonetheless, l ow aspect ratio devices are predicted to have good confinement and may igni te at very small size. Profiles are presented which may allow high beta, MH D stable operation at A = 1.4 with high confinement. The possibility of usi ng a controlled application of non-turbulent loss processes to control prof iles to prevent turbulent transport and to maximize beta is suggested.