Abstract
Runaway electrons with energies >100 keV are observed with the appearance of an m=1 magnetic island in the core of otherwise stochastic Madison Symmetric Torus [Dexter, Fusion Technol. 19, 131 (1991)] reversed-field-pinch plasmas. The island is associated with the innermost resonant tearing mode, which is usually the largest in the m=1 spectrum. The island appears over a range of mode spectra, from those with a weakly dominant mode to those, referred to as quasi single helicity, with a strongly dominant mode. In a stochastic field, the rate of electron loss increases with electron parallel velocity. Hence, high-energy electrons imply a region of reduced stochasticity. The global energy confinement time is about the same as in plasmas without high-energy electrons or an island in the core. Hence, the region of reduced stochasticity must be localized. Within a numerical reconstruction of the magnetic field topology, high-energy electrons are substantially better confined inside the island, relative to the external region. Therefore, it is deduced that the island provides a region of reduced stochasticity and that the high-energy electrons are generated and well confined within this region.
Original language | English |
---|---|
Article number | 012505 |
Journal | Physics of Plasmas |
Volume | 17 |
Issue number | 1 |
DOIs | |
State | Published - 2010 |
Externally published | Yes |
Funding
The authors would like to thank the MST team for their support in this research and the RFX-mod team for their collaboration. This work was supported by the U.S. Department of Energy cooperative agreement DE-FC02-05ER54814.