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This paper discusses the power step-down approach to steady-state operation of deuterium plasmas in the hot-ion edge-localized mode (ELM)-free H-mode of the Joint European Torus (JET) tokamak. Being ELM-free, when full heating power is maintained, these plasmas are usually transient and terminate with a variety of magnetohydrodynamic (MHD) phenomena. With power step-down, instabilities are delayed or avoided and nearly constant plasma conditions are maintained. Global ELM-free H-mode confinement scaling is examined in this regime, without recourse to large transient corrections. The confinement times increase after the transition to quasi-steady conditions, and are between 10% and 25% above the scaling law predictions, with the same parametric dependence. Code simulations of the experimentally observed neutron rate and the lack of a major discontinuity in the rate before and after power step-down confirm that neutron production is predominantly from thermal fusion. Optimization experiments indicate that the stored energy and neutron production are maximized and the density rise minimized by preferentially retaining the JET high energy 140 keV beams. The power step-down method provides a significant advance towards the regime of steady-state high performance and will be utilised in future deuterium-tritium experiments.

Additional information

Authors: MARCUS F B ET AL, JET Joint Undertaking, Abingdon, Oxon (GB)
Bibliographic Reference: Report: JET-P(96)59 EN (1996) 20pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon, OX14 3EA (GB)
Record Number: 199710055 / Last updated on: 1997-02-26
Original language: en
Available languages: en