Relaxation of spheromak configurations with open flux
- Centro Atomico Bariloche (CNEA) and Instituto Balseiro (UNCuyo-CNEA), Bariloche, Rio Negro 8400 (Argentina)
The relaxation of several kink unstable equilibria with open flux representative of spheromaks sustained by dc helicity injection is studied by means of three-dimensional, resistive magnetohydrodynamic simulations. No external driving is applied, but the initial conditions are chosen to reproduce the current profiles existing in a gun driven spheromak, which has a high current density in the open flux region and a low current density in the closed flux region. The growth and nonlinear saturation of various unstable modes, the dynamo action which converts toroidal flux into poloidal flux, and the evolution of the {lambda} profile ({lambda}={mu}{sub 0}J{center_dot}B/B{sup 2}) are studied. An initial condition is found which results in a dynamo that produces enough poloidal flux to compensate the resistive losses occurred during a characteristic time of the instability. The flux amplification factor around which this case oscillates is consistent with existing experimental data. During the relaxation, the central open flux tube develops a helical distortion and the closed flux surfaces are destroyed. After the relaxation event, close flux surfaces form again but the final profiles are not fully relaxed and the central open flux tube remains distorted. The effect of the Lundquist number on the evolution and its impact on the required level of fluctuations are evaluated. Finally, the dynamics of the system for different current levels in the open flux region is studied.
- OSTI ID:
- 21274260
- Journal Information:
- Physics of Plasmas, Vol. 16, Issue 11; Other Information: DOI: 10.1063/1.3264077; (c) 2009 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Three-dimensional numerical simulations of the relaxation process in spheromak plasmas
The Spheromak path to fusion energy