DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 176: Investigation of fast wave damping at 2nd and 3rd harmonics on injected hydrogen beams | ||
| Name: | Robert I. Pinsker ( |
Affiliation: | General Atomics |
| Research Area: | Hydrogen Discharges | Presentation time: | Not requested | Co-Author(s): | W.W. Heidbrink, M. Porkolab, J.C. Hosea, F.W. Baity, E. Fredd, T. Scoville |
| Description: | DIII-D experiments have shown that 60 MHz fast waves can be damped on injected 80 keV deuterium beams at the 4th harmonic (2 T) quite strongly, to the point where the accelerated deuterons can partially stabilize sawteeth ('monsters'). Furthermore, 60 MHz fast waves have been shown to be damped strongly on thermal hydrogen at the 2nd harmonic if the hydrogen fraction exceeds around 25%. We therefore expected that 90 MHz fast waves could be strongly damped on injected hydrogen beams at 2 T and thereby produce a similar effect on sawteeth as the 4th harmonic at 60 MHz on deuterium beams had. However in a short (~1/3 of a day) experiment in FY07, no evidence was found of strong damping of 90 MHz fast waves on injected H beams. Instead, direct electron damping appeared to dominate. The FIHA diagnostic saw only a very weak H signal, suggesting the possibility that the two sources run in H were producing a significantly lower power full-energy component than expected.
We propose to revisit this experiment after careful tuning of the operation of the beams in hydrogen is carried out, and to add 60 MHz power (2nd harmonic) for comparison with the 90 MHz, 3rd harmonic case. (The latter had not been possible in the FY07 experiment due to poor 60 MHz antenna performance, which we hope to have remedied in the autumn 2007 vent.) | ||
| Experimental Approach/Plan: | Reproduce the L-mode discharges with hydrogen beam injection, perhaps operating a second beamline in H to allow greater H beam power, and emphasizing careful measurement of the injected H-beam power (modulation studies, etc.) Quantitative understanding of the FIHA signals in the absence of FW power as a function of injected H beam power is a prerequisite to understanding the effect of the FW power to the proton distribution function. Compare the effect of 60 MHz power and 90 MHz power in otherwise identical discharges with H beam injection. | ||
| Background: | This experiment should dovetail well with plans for a hydrogen campaign, in that presumably full H beam operation is needed for such experiments. Understanding the FIHA signals with H beams is also needed for such experiments, since we lose all of the neutron diagnostics and are thereby weak on other probes of the beam distribution functions in such discharges. | ||
| Resource Requirements: | At least one beamline (two sources) operated in H with sufficient time beforehand to have optimized the source operation in hydrogen. Prefer two beamlines (four sources) in hydrogen. The plasma can be either deuterium or hydrogen, though a purely hydrogen plasma is preferred for simplicity. All three FW sources, two at ~90 MHz and one at 60 MHz, at greater than 1 MW each, are needed. One full day experiment. | ||
| Diagnostic Requirements: | FIHA diagnostic is crucial. | ||
| Analysis Requirements: | Analysis of absorbed power from the H beams, via modulation analysis. FIHA data must be quantitatively analyzed. | ||
| Other Requirements: | -- | ||
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