7 research outputs found
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Synergy in two-frequency fast wave cyclotron harmonic absorption in DIII-D
Fast waves (FWs) at 60 MHz and at 90 MHz are coupled to DIII-D discharges for central heating and current drive at net FW power up to 3.5 MW. The primary absorption mechanism is intended to be direct electron damping in the plasma core. In discharges at B=2T with fast deuteron populations from neutral beam injection, 4th and 6th deuterium cyclotron harmonic absorption on the fast ions competes with direct electron damping. Previous experiments have shown that the 6ΩD absorption of the 90 MHz FWs is weaker than the 4ΩD absorption of 60 MHz FWs, in agreement with a model that includes unspecified edge losses. Recent experiments have shown that if the fast deuterons are accelerated by absorption of 60 MHz (4ΩD) FWs, adding 90 MHz power (6ΩD) can increase the fusion neutron rate by a larger increment than is obtained with 90 MHz power alone. Details of this synergy between 4ΩD and 6ΩD absorption are presented. © 2009 American Institute of Physics
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Experiments on ion cyclotron damping at the deuterium fourth harmonic in DIII-D
Absorption of fast Alfven waves by the energetic ions of an injected beam is evaluated in the DIII-D tokamak. Ion cyclotron resonance absorption at the fourth harmonic of the deuteron cyclotron frequency is observed with deuterium neutral beam injection (f = 60 MHz, B{sub T} = 1.9 T). Enhanced D-D neutron rates are evidence of absorption at the Doppler-shifted cyclotron resonance. Characteristics of global energy confinement provide further proof of substantial beam acceleration by the rf. In many cases, the accelerated deuterons cause temporary stabilization of the sawtooth (monster sawteeth), at relatively low rf power levels of {approximately}1 MW
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Absorption of fast waves at moderate to high ion cyclotron harmonics on DIII-D
The absorption of fast Alfvén waves (FW) by ion cyclotron harmonic damping in the range of harmonics from fourth to eighth is studied theoretically and with experiments in the DIII-D tokamak. A formula for linear ion cyclotron absorption on Maxwellian ion species is used to estimate the single-pass damping for various cases of experimental interest. It is found that damping on fast ions from neutral beam injection can be significant even at the eighth harmonic if the fast ion beta and the background plasma density are both high enough. The predictions are tested in several L-mode experiments in DIII-D with FW power at 60 MHz and at 116 MHz. It is found that 4th and 5th harmonic absorption of the 60 MHz power on the beam ions can be quite strong, but 8th harmonic absorption of the 116 MHz power appears to be weaker than expected. Possible explanations of the discrepancy are discussed. © 2005 American Institute of Physics
Recommended from our members
Absorption of fast waves at moderate to high ion cyclotron harmonics on DIII-D
The absorption of fast Alfvén waves (FW) by ion cyclotron harmonic damping in the range of harmonics from fourth to eighth is studied theoretically and with experiments in the DIII-D tokamak. A formula for linear ion cyclotron absorption on Maxwellian ion species is used to estimate the single-pass damping for various cases of experimental interest. It is found that damping on fast ions from neutral beam injection can be significant even at the eighth harmonic if the fast ion beta and the background plasma density are both high enough. The predictions are tested in several L-mode experiments in DIII-D with FW power at 60 MHz and at 116 MHz. It is found that 4th and 5th harmonic absorption of the 60 MHz power on the beam ions can be quite strong, but 8th harmonic absorption of the 116 MHz power appears to be weaker than expected. Possible explanations of the discrepancy are discussed. © 2005 American Institute of Physics