SHAFRANOV PARAMETER LIMITS OF OHMIC AND RF HEATED PLASMAS IN TCA
The maximum parameters achieved in the TCA tokamak using Alfv'en Wave Heating have been studied over a wide range of excitation modes and plasma currents. When a large data set of stationary ohmic conditions is examined, we find that the parameter Lambda"ast"=(beta+li/2-0.7)times l-"p"/l-"p(q=3)" best describes the variation of (beta+li/2) as a function of density. When the RF pulse is applied, Lambda"ast" reacts very quickly, exceeding the ohmic value for the instantaneous density but Lambda"ast" never exceeds the maximum ohmic value. This limit can be achieved with less delivered RF power when the excitation structure is unfavourable, in the sense that the resonant surfaces are near the plasma edge. As the value of Lambda"ast" approaches its limit, there is a reproducible increase in m=2 MHD activity which does not depend on the excitation mode and which resembles the increase associated with the density limit in ohmically heated discharges. This suggests that the phenomena related to the density limit may be related in the ohmic case to the same parameter Lambda"ast". Previously, we had reported that the disruptions occurred at thresholds in the Alfv'en wave spectrum. This remains true, since the value of Lambda"ast" nearly always reaches its maximum just before such a threshold. It is considered that the link between the increase in (beta+li/2), the resonant surface positions and the enhanced MHD activity may be the current profile evolution.
Bibliographic Reference: 15TH EUROPEAN CONFERENCE ON CONTROLLED FUSION AND PLASMA HEATING, DUBROVNIK (YUGOSLAVIA), MAY, 16-20, 1988, AVAILABILITY: CEC-LUXEMBOURG, DG-XIII-C-3, POB 1907, MENTIONING PAPER EN 34068 ORA
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Record Number: 1989126118500 / Last updated on: 1989-06-01
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