DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 229: Beam Ion Excitation of Beta Induced Alfvenic Acoustic Eigenmodes | ||
| Name: | Nikolai Gorelenkov ( |
Affiliation: | Princeton Plasma Physics Laboratory |
| Research Area: | Energetic Particles | Presentation time: | Requested | Co-Author(s): | M. Van Zeeland |
| Description: | The core of the proposed experiment is to investigate recently discovered instabilities, called Beta-induced Alfvén-acoustic eigenmodes, which appear due to coupling of two fundamental MHD branches, Alfvénic and acoustic. | ||
| Experimental Approach/Plan: | The evolution of the current profile will be measured with MSE and complete equilibrium diagnostic data as well as FIDA measurements of confined fast ions will be collected. The experiment will target plasma conditions with a strong NB fast ion component and high electron temperature such as D3D #128926 in which the BAAE has been observed. The main study will be focused on BAAE mode structure and frequency measurements. Te variation and its effect on the BAAE frequency when the mode is inside the Alfvénic and acoustic gap will be also studied. | ||
| Background: | Global BAAE modes were discovered on NSTX, and on JET in different regimes but in both cases with rather high fast ion to plasma beta ratio. These modes have low frequency, typically below RSAE/TAE frequency range and are due to the coupling of the Alfvénic and acoustic branches mediated by the geodesic acoustic curvature and the plasma pressure. On NSTX these modes were successfully identified with the internal structure measured by the SXR and reflectometer diagnostics. The frequency was in excellent agreement with the theory based on the MSE q-profile in NSTX. The frequency of BAAEs often is observed as chirping in time from the plasma rotation frequency as q relaxes. Agreement of the BAAE frequency evolution inferred q_min and MSE q_min validates BAAE based spectroscopy. In JET BAAE frequency was reaching the saturation level predicted by the theory due to the mode entering the Alfvén-acoustic continuum gap. The major problem in the comparison was that the having quantitative and qualitative agreement with the theory predicted BAAE frequency for the saturated values was well above the measured one in JET, by at least 70%. Part of the uncertainty comes from the undiagnosed safety factor profile and ICRH minority ion pressure in JET. A DIIID experiment would help to resolve this issue and investigate the correlation of the BAAE instabilities and possible fast ion transport with its powerfull fast ion diagnostics. One puzzle of the theory of BAAEs is that they are observed despite of the strong expected damping of acoustic component and strong expected Landau damping. | ||
| Resource Requirements: | Run-Time: 1 day
4 gyrotrons 2 NB sources | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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