Equilibrium and stability investigations in the belt pinch

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Abstract
The paper summarizes experimental results obtained in the Garching Belt Pinch I. Here, toroidal high- β- plasmas are produced by shock heating, the plasma cross-section being highly elongated in the direction of the major torus axis. The plasma can be confined for about 100 μs until the toroidal plasma current is Ohmically damped out. With various diagnostic techniques, it is shown that the plasma reaches a quasi-stationary equilibrium in shape, temperature and density after about 25 μs. This equilibrium is investigated and compared with theoretical predictions. In the experiment, the plasma displays macroscopically stable behaviour for low plasma currents. If the plasma current is increased gradually, the first instability that occurs is an m = 1, n = 1 kink mode. This mode is excited artificially by a suitable current pulse in an external coil in order to determine the stability limit. For a plasma with highly elongated cross-section area (axis ratio ε = 5 − 6), the stability limit qcrit = 2.4 is found.