Study of Critical beta Non-Circular Tokamak Equilibria Sustained in Steady State by Beam Driven Currents

摘要

A MHD-equilibrium/current-drive analysis code was developed to analyze the high beta tokamak equilibria consistent with the beam drive current profiles. In this code, the critical beta equilibrium, which is stable against the ballooning, kink, and Mercier mode, is determined first using MHD equilibrium and stability analysis codes (EQLAUS/ERATO). Then, the current drive and plasma parameters, required to sustain this critical beta equilibrium, are determined by iterative calculations. The beam driven current profiles are evaluated by the Fokker-Planck calculations on individual flux surfaces, where the toroidal effects on the beam ion and plasma electron trajectories are considered. The pressure calculation takes into account the beam ion and fast alpha components. A peculiarity of the method is that the obtained solution is not only consistent with the MHD equilibrium but also consistent with the critical beta limit conditions, in the current profile and the pressure profile. Using the beta is approximately 21 percent bean and beta is approximately D-type critical beta equilibria were scanned for various parameters. It was found that the achievable Q value for the bean type was always about 30 percent larger than for the D-type cases, where Q = fusion power/beam power. With strong beanness, Q is approximately 6 for DEMO type tokamaks (approximately 500 MWth) and Q is approximately 20 for power reactor size (4.5 GWth) are achievable. On the other hand, the Q value would not exceed sixteen for the D-type machines.