Abstract
The idea of controlling the radial electric field (Er) by means of a radial current resulting from ion orbit loss caused by counter neutral beam injection has been theoretically and experimentally investigated. A large fraction (≃ 38%) of the 75 keV deuterium ions counter-injected into a IOW-Ip plasma (≃ 0.4 MA) suffers prompt orbit loss, which forces an inward ion current to maintain charge neutrality. Monte Carlo guiding-centre orbit calculations predict a radial current of 80 A at the last closed flux surface. In these discharges, Er is negative everywhere, owing to the counter-going toroidal rotation, and exhibits a double-bump shape, in contrast to the usual positive parabolic shape for the co-injection case. The measured carbon impurity ion toroidal rotation profile shows a pedestal over the outer region where fast ions are lost, possibly due to the effect of Jrorbit x B torque. The momentum diffusion process tends to slow down and to spatially spread the Jrorbit x B torque effect. The L-H transition did not occur more quickly in these discharges than in similar co-injected discharges.
Original language | English |
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Pages (from-to) | 1479-1485 |
Number of pages | 7 |
Journal | Plasma Physics and Controlled Fusion |
Volume | 38 |
Issue number | 8 |
DOIs | |
State | Published - 1996 |
Externally published | Yes |