Session 7E - Space and Basic.
ORAL session, Thursday morning, November 14
Majestic Ballroom, Adam's Mark
The stability of ballooning modes is studied in an application for the experiments developed at Budker Institute of Nuclear Physics, Novosibirsk, Russia. Specifically, two concepts are considered: a mirror-based neutron generator (NG)\footnote I.A.Kotel'nikov, V.V.Mirnov, V.P.Nagorniy, D.D.Ryutov, in Proc. of the 10th IAEA Conf., London, v.2, Vienna, (1985) and a multiple mirror trap (MMT)\footnote A.Lichtenberg, V.V.Mirnov, Reviews of Plasma Physics, v.19, Plenum Corp., New York, 1996. To enhance the neutron flux in NG, oblique injection of fast tritium atoms is used yielding P_\parallel \gg P_\perp, that drives "fire hose" instability if \beta = 8\pi P_\parallel/B^2 > 2. Besides the "fire hose" instability ballooning modes also exist. Their stability and connection with the "fire hose" modes are treated on the basis of the paraxial MHD energy principle. The ballooning limits on \beta are found to be not so severe such that "fire hose" criterion \beta \leq 2 can be used for a rough estimate of marginal stability. Axisymmetric MMT where the margin of stability is shown to be \beta \leq \pi ^2 /N^2I , I =(3l/r_max^4) \int_-l/2^l/2 dz r^2(z) \left (dr/dz \right )^2 is strongly different from the previous case. For an optimal "square root" profile of the cells r(z) and number of cells, N=10, a low ballooning margin, \beta \simeq 5%, is predicted in line-tying stabilized MMT.