Hard magnetohydrodynamic limit in 1/3 sawtooth like activity in LHD
- National Institute for Fusion Science, Oroshi-cho 322-6, Toki 509-5292 (Japan)
The optimization of LHD discharges in inward-shifted configurations with 1/3 sawtooth like activity is an open issue. These relaxation events limit the LHD performance driving a periodic plasma deconfinement. The aim of this study is to analyze the 1/3 sawtooth like activity in plasmas with different stability properties to foreseen the best operation conditions and minimize its undesired effects. We summarize the results of several MHD simulations for plasmas with Lundquist numbers between 10{sup 5} and 10{sup 6} in the slow reconnection regime, studying the equilibria properties during the onset of a chain of 1/3 sawtooth like events. The research conclusions point out that the hard MHD limit can be reached in the inner plasma region after the onset of a strong 1/3 resonant sawtooth like event and trigger a plasma collapse. The collapse can be avoided if the system remains in the soft MHD limit, namely, in a regime with a pressure gradient and a magnetic turbulence below the critical values to drive the soft-hard MHD transition. In the soft MHD limit the system relaxations are the non resonant 1/3 sawtooth like events or a weak version of the 1/3 resonant sawtooth like events. A system relaxation in the soft MHD regime drives a minor plasma deconfinement that does not limit the LHD performance if the event periodicity is not very high.
- OSTI ID:
- 22251987
- Journal Information:
- Physics of Plasmas, Vol. 21, Issue 3; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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