HINST: A two-dimensional code for high-n toroidicity induced Alfven eigenmodes stability

A high-n stability code, HINST, has been developed to study the stability of TAE (toroidicity induced Alfven eigenmodes) in large tokamaks such as the International Thermonuclear Experimental Reactor (ITER) [D. E. Post, Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 239] where the spectrum of unstable TAE modes is shifted toward medium to high-n modes. The code solves the two-dimensional (2-D) eigenmode problem by expanding the eigenfunction in terms of basis functions. Based on the Fourier-ballooning formalism the eigenmode problem is reduced to a system of coupled one-dimensional equations, which is solved numerically by using the finite element method. The numerical method allows one to include nonperturbatively nonideal effects such as: finite ion Larmor radius, trapped electron collisional damping, etc. The 2-D numerical results of TAE and resonance TAE (RTAE) modes are compared with those from local ballooning calculations and the global magnetohydrodynamic nonvariational code NOVA [C. Z. Cheng and M. S. Chance, J. Comput. Phys. 71, 124 (1987)]. The results show that for ITER-like plasma parameters, TAE and RTAE modes can be driven unstable by alpha particles for n = 10-20. The growth rate for the most unstable mode is within the range gamma/omega(A)similar or equal to 0.3%-1.5%. The most unstable modes are localized near r/a similar or equal to 0.5 and have a broad radial mode envelope width. (C) 1998 American Institute of Physics. [S1070-664X(98)04409-7]