Beta Drive for Diamagnetic Plasma Confinement
Author: Pierre-A Gourdain
Submitted: 2005-12-20 17:43:04
1040 Veteran Ave.
Los Angeles, CA 90024
One paramount requirement for economical fusion reactors is a high beta regime, where the ratio of kinetic pressure to magnetic pressure is relatively elevated. One major characteristic of stable high beta plasmas is their strong diamagnetism, where poloidal currents reduce the confining toroidal field in the core of the plasma, creating a magnetic well. Unfortunately reaching such regimes is hardly possible. Plasmas instabilities rising with beta tend to disrupt the operations of modern fusion machines. A novel approach is to enforce plasma diamagnetism before increasing the effective beta. Once a magnetic well has been dug, pressure can be increased and â€œnaturalâ€? diamagnetism sustained. We propose here to generate an edge poloidal electric field to run diamagnetic currents into the plasma. Theoretical results show the feasibility of this â€œbeta driveâ€?. The time evolution of the diamagnetic currents using a 1-D simple transport code (STC) will be presented. A high beta MHD code (CUBE) and a stability code (DCON) were coupled to the transport code to verify the existence of 2-D stable equilibriums. A simple first step to create experimentally strongly diamagnetic plasmas is to generate an AC poloidal electric field. By running an AC current in addition to the usual DC current in the toroidal field coils of a tokamak configuration, strongly diamagnetic plasmas can be obtained in one part of the AC cycle. To demonstrate this innovative concept of improved confinement, a small machine has been designed. A non-conductive vacuum vessel and a low inductance toroidal field magnet are key items to produce an efficient AC beta drive. Edge heating using skin currents is also possible and code results will also be presented.