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The sustainment of Ultra-low-q (ULQ) and Reversed Field Pinch (RFP) discharges longer than the vertical field penetration time constant of the shell in the HBTX1C device reveals new unstable modes arising from resistive shell instabilities. Their suppression in ULQ discharges has been achieved by controlling the value of the edge safety factor, q(a). The q(a) boundary or current limitation often seen in low-q Tokamak and ULQ plasma is found to be related to a resonant mode with a growth rate that is fast compared to the vertical field time constant of the shell. The interaction of these two types of unstable mode results in stepwise plasma current behaviour in ULQ discharges. Resistivity anomaly in ULQ discharges is larger than that in RFP discharges and can be interpreted in terms of the low density and rapid particle recycling. Different plasma relaxation phenomena are observed in these regimes.

Additional information

Authors: TSUI H Y W, UKAEA/Euratom Fusion Association, Culham Laboratory, Abingdon, Oxon. (GB);LA HAYE R J, General Atomic, San Diego, CA (US);CUNNANE J A, University College, Cork (IE)
Bibliographic Reference: Report: CLM-P865 EN (1990)
Availability: Available from the Librarian, UKAEA, Culham Laboratory, Abingdon, Oxon. OX 14 3DB (GB)
Record Number: 199010629 / Last updated on: 1994-12-01
Original language: en
Available languages: en
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