Session KP01 - Poster Session III.
POSTER session, Tuesday afternoon, March 23
Exhibit Hall, GWCC
This work investigates the key stability issue of beta limiting bootstrap current-driven external kink modes as well as pressure-driven ballooning modes in quasi-axisymmetric stellarators (QAS)(G.Y. Fu et al., the 1998 IAEA Fusion Energy Conference). The 3D MHD code TERPSICHORE(W.A. Cooper, Phys. Plasmas 3), 275(1996) is used to calculate the stability of low-n external kink modes. The results show that the external kink modes can be stabilized at high beta (\sim 5%) without conducting wall by combination of edge magnetic shear and 3D plasma boundary shaping. In contrast, the equivalent tokamaks with high bootstrap fraction have much lower beta limits. The physics mechanism for the kink stability is being studied by examining the contributions of individual terms in \delta W of the energy principle. Initial results show that the plasma current is the main driving force while the pressure gradient also plays a significant role. Methods have been successfully developed that enable us to simultaneously maximize the kink stability, ballooning stability and quasi-axisymmetry. High beta, MHD stable plasmas configurations have been obtained by the optimal choice of boundary shape as well as plasma pressure and current profiles. Details of parameter dependence of kink and ballooning stability and robustness of the stability limits will be reported.