Numerical study for design of the passive stabilizer and its impact on MHDstability in the proposed KSTAR plasma

The effect of the passive plate stabilizer on the ideal magnetohydrodynamic (MHD) stability is numerically studied in order to guide its design in the proposed Korea Superconducting Tokamak Advanced Research (KSTAR). The para metric study is systematically performed by taking into account the two maj or variables: the plate's distance from the plasma surface, and the poloida l (toroidally continuous) vacuum gap required for the access of neutral bea m ports and other diagnostics near the outboard mid-plane. Extensive calcul ations are carried out on the plasma beta limits for low-n (Iz being toroid al mode number) MHD modes in several major operating regimes. The results l ead to a practical and optimistic design point: plasma-wall separation appr oximate to 10 cm, and the outboard gap having a vertical separation of abou t 80 cm between the upper and lower plates. This is one of the choices that will make it feasible to achieve the advanced operation with bootstrap cur rent fraction of over 80% at beta(n) = 5 in the reversed shear mode in KSTA R. (C) 1999 Elsevier Science S.A. All rights reserved.