Thermal Instability and Control of Inhomogeneous Plasma in a D-T Fusion Reactor

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Abstract
When a D-T fusion reactor is operated in steady state, the core plasma deviates from equilibrium below a critical temperature. This instability has already been analyzed when the plasma is distributed uniformly. In nonuniform plasmas, however, the stability is not yet known. In this article the stability of a radially nonuniform plasma is discussed analytically, assuming cylindrical symmetry. As a result, it is made clear that the stability of a nonuniform plasma is essentially the same as that of a uniform plasma, and that the critical temperature is determined by the dependence of the diffusion rate and the thermal conduction on the plasma density and temperature. When the diffusion rate is independent of the density and temperature, the critical temperature is higher than that in Böhm diffusion, and lower than in classical diffusion. When a reactor is operated in an unstable region, feedback control is indispensable. The possibility of stabilization is discussed when the feedback is applied to the plasma density or temperature with different periods of delay after monitoring the peak temperature deviation from equilibrium. The instability and its control are also analyzed numerically. The analytical results are in a good agreement with computer calculations.

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