Stability of a toroidal plasma by hot electron annulus in a bumpy torus

An analytical study of the ballooning instability is presented in a bumpy configuration using a relatively simple fluid model of an inhomogeneous slab plasma with gravitational field simulating the bad curvature effect and the grad-B effect due to hot electron annulus. Mathieu type equation is derived to investigate a linear analysis. Stability boundary giving the maximum stable βsub(p) (beta value of bulk plasma) as a function of βsub(h) and the threshold for βsub(h) (beta value of hot electron annulus) are studied for Nagoya Bumpy Torus (NBT) parameters. The relevance of our theoretical analysis is discussed in a comparison with the previous results. (author)