Test of a Steady State Tokamak Concept in ET
Author: Robert J. Taylor
Submitted: 2005-12-21 17:16:09
Co-authors: J.-L.Gauvreau, P.-A.Gourdain, L.W. Schmitz
University of California at Los Angeles (UCLA)
1040 Veteran Ave
Los Angeles, CA 90024
The studies on ET have shown that in the presence of low fluctuational transport, the radial electric field determines the direction of radial mass transport [Nucl. Fusion 45 (2005) 1634-1641]. This is inward when self-consistent effects are at play. The explanation is as follows: The inward pinch is driven by energetic ion banana loss due to classical collisions. This results in a negative central plasma potential and poloidal rotation. This pinch is larger than the Ware pinch even in pulsed machines. The nearly axi-symmetric ion transport carries the 3D electrons with them in or out. The 3D electron mobility is based on the local flux tube charge neutrality to the extent that the â€œsimplerâ€? 2D ambipolarity is violated. We will argue that in a steady state tokamak, the radial potential has to be positive for mass replacement or else a reactor has to run in a cyclical state, where the radial potential is periodically reversed. Research shows that this static and cyclic steady states can be carried out only in large experiments. Two possibilities are worth noting; (1) implement a 3D ion and electron transport on the proper scale (Stellarator?) or achieve omnigenous high beta tokamak (Jensen, static ET) or alternatively (2) use induced instabilities to periodically remove mass. This is not an attractive scheme. An instability-based cyclic operation will not be proposed at this time. Rather, a centrally fueled tokamak experiment will be proposed to generate positive potentials in the absence of alpha particles. The presence of energetic alpha particle will decrease the potential. The effect of the alpha particle rotation drive would be avoided in a high beta omnigenous reactor.