DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 221: Investigate Impact of ECH on Alfvenic Activity | ||
| Name: | Michael Van Zeeland ( |
Affiliation: | General Atomics |
| Research Area: | Energetic Particles | Presentation time: | Requested | Co-Author(s): | W. Heidbrink, R. Nazikian, W. Solomon |
| Description: | The primary goal of this experiment is to further our understanding of the ECH suppression of RSAEs observed during the last run campaign. | ||
| Experimental Approach/Plan: | Begin with discharge 128560 as a reference in which RSAEs were stabilized by ECH deposition near qmin. All discharges thus far have begun with ECH and NBI starting simultaneously at t=300 ms. ECH injection will be delayed to successively later times in a series of discharges and the impact on the RSAE as well as TAE suppression documented. The time of initial ECH injection may alter the stabilization if the actual mechanism relies on some type of feedback process that can only be triggered early in the discharge when the relative change in Te possible with limited gyrotron power is largest. Also, delaying the ECH to much later in the discharge will test whether or not ECH stabilization of RSAE or TAE is possible in H-mode plasmas as opposed to the L-mode, current ramp phase studied so far. To investigate the dependence of ECH deposition radial width relative to RSAE mode width, the gyrotron deposition will then be spread out about qmin in a series of discharges. Next, to build on modulation experiments carried out in 2007, ECH modulation will be carried out at several different rates and deposition locations. The impact of modulation on RSAE suppression is convoluted by the fact that RSAEs have transient chirping frequencies. To make clear the impact on RSAEs, 50% duty cycle modulation will be carried out with two nominally similar discharges and the ECH modulation180 degrees out of phase on each. This results in essentially two spectra with ECH off and two with ECH on for comparison. Also, the impact of ECH on weakly driven AEs will be studied by lowering the injected NB power. | ||
| Background: | Alfven eigenmodes cause fast ion transport and as a result, their presence can range from detrimental to advantageous depending on the circumstances. A tool for targeting and altering the amplitude of specific AEs would thus be extremely beneficial.
Experimental results obtained in the 2007 run period showed ECH suppression of RSAEs and the concomitant reduction of fast ion transport. Currently, the mechanism for ECH induced RSAE suppression is not understood and further experiments aimed at understanding this interaction should be carried out to identify the underlying physics. In the process, these experiments will help to elucidate the roles electron temperature and finite plasma pressure play in AE physics, as well as the possibility for extending this method to impact other types of AEs. | ||
| Resource Requirements: | Machine Time: 1 day
4 gyrotrons, 2 neutral beam sources | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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