Toroidal effects on a helical pinch configuration with pitch reversal

Abstract

Toroidal effects on the outer magnetic surfaces of a configuration having a large toroidal plasma current that is stabilized by a pitch reversal produced by an external helical coil (OHTE) are investigated by both field-line tracing and an analytic expansion of the magnetic surfaces. Results of the two methods are compared. It is shown that both plasma position control and the helical coil winding law can be used to compensate undesired toroidal effects at both low and high beta.

MHD equilibria of current-carrying plasma in a toroidal-helical configuration

“…The present mode expansion method has been applied for the evaluation of vacuum magnetic fields in a toroidal-helical configuration, where the toroidal curvature effect is stronger than in the central plasma region. Numerical results have been found to be in good agreement with the results of the field-line tracing, and thus they have proved useful [2].…”

“…( 44) for the OHTE configuration in which the pitch of the external helical field is chosen opposite to the pitch of the paramagnetic field in the central region in order to aid the pitch reversal near the plasma edge [ 1 ]. In the OHTE configuration, the resonant magnetic surface is that at which the pitch of unperturbed magnetic field in the plasma coincides with that of external helical winding, so ag = 0 is expected to be outside of the plasma [1,2].…”

“…The purpose of this paper is to present a method for studying the MHD equilibrium of a high-current toroidal-helical configuration, OHTE [1,2]. OHTE is a toroidal Z-pinch with field reversal aided by an externally imposed helical magnetic field.…”

Electron thermal conductivity in an ergodic magnetic limiter

“…In the EML, the multiple resonances and primary island on each resonant surface in the limiter region are made by externally applied helical perturbations. In a toroidal system, when a helical perturbation 5B r with mode numbers (m, n) is applied, toroidal mode coupling will create sideband perturbations with (m±l,n) [8], which make additional resonant surfaces and may lead to ergodization of the field lines. Above a certain stochastic threshold of 5B r , which is approximately determined from the overlapping condition of the primary islands on neighbouring resonant surfaces, many modes will be generated in addition to the original perturbations.…”

“…Equations ( 4) through (8) can then be written as follows, when K\\ and /q are treated as constants:…”