Studies on the formation process and the stability properties of the double-spheromak configuration in a cusp shaped magnetic field

Computer analyses and preliminary experiments are carried out to investigate the formation process and the stability problems of double-spheromak configurations in a cusp-shaped magnetic field. For the finite-beta and nondynamical plasmas, 3-D MHD simulation shows the existence of the tilt and shift motions whose growth rate depends on the beta value and curvature of the separatrix surface. Formations of the configuration by the zeta-theta-pinch method are simulated by 2-D axisymmetric MHD code. During the formation period, a fluid velocity of about 0.3 Alfven speed is generated. This formation scheme is experimentally investigated with the TODAI spheromak producing machine, TS-3. The life time of produced plasmas is about 30 μs. During this period, no global instabilities are observed; however, complete stabilization is yet to be investigated. (author)