The suppression behaviour of magnetic island growth using electron cyclotron heating and lower hybrid current drive is analysed. A quasi-linear model is developed for island suppression, including the local peaking effect of the resistivity and the RF-driven current within the island. Pulsed launching of lower hybrid waves synchronized with the plasma diamagnetic rotation frequency can strongly suppress the magnetic island.
The empirical scaling of the electron thermal diffusivity, Xe, is investigated for more than 100 beam-heated discharges. These discharges include two major features: 1) high-temperature and highdensity plasma (T e (O)«Tj(O)« 2.5-3 keV at n ^ (5-7) X 10 13 cm" 3 , P NB i £ 4 MW), which will be the basis for the breakeven experiments in the next-generation tokamaks, 2) three types of discharges, i.e. good and poor confinement divertor discharges and limiter discharges. -All kinds of discharges (good heating and poor heating divertor discharges, limiter discharges) have fhe same functional form in x e within ~ 40% at 0.25 a < r <0.65 a, where Xe in the simplest expression scales as Xe a Vn e -The * on t n e r m a l diffusivity, Xi, is consistent with the assumption that the neoclassical Xi can be applicable to our three kinds of discharges. For discharges with different heating efficiency, there is no systematic difference, in the adjustable multiplier, to the neoclassical theory by Hinton-Hazeltine for an ion collisionality of v*= 0.02-0.5.
A tokamak reactor concept for steady-state operation has been studied. This reactor uses the compressional Alfvén wave to sustain the plasma current. Its structure is simplified by eliminating the poloidal coils in the torus centre. The start-up scenario is obtained by minimizing the wave and electric powers of the coils through solving the power balance and Grad-Shafranov equations. The steady-state operating point is obtained from the viewpoint of maximizing the Q-value (Q = fusion power/current drive power). The largest Q-value is obtained by using compressional Alfvén wave rather than other RF waves.
Divertor effects on the particle confinement time in a tokamak plasma are investigated by modelling of particle, momentum and energy transports in the divertor plasma and particle transport in the main plasma, with a simplified model for neutral-particle transport. The divertor plasma has three equilibrium states in a limited range of the ion flux entering the divertor. It is found that the existence of the three equilibrium states might lead to mode conversion of the particle confinement characteristics during additional heating.
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