DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 230: Modulated ECCD for 2/1 NTM suppression | ||
| Name: | Anders Welander ( |
Affiliation: | General Atomics |
| Research Area: | NTM Stabilization | Presentation time: | Requested | Co-Author(s): | R.J. La Haye, F. Volpe |
| Description: | The purpose is to investigate the effectiveness of modulated electron cyclotron current drive (ECCD) for suppression of the m/n = 2/1 NTM and compare with continuous wave (cw) ECCD. The first goal is to suppress a 2/1 NTM using modulated ECCD with the best guess of phase for the modulation based. The phase detection of the island is done using Mirnov signals. The second goal is to obtain cw-ECCD data under the same target plasma conditions for comparison. Physics data on the dependence of suppression rate on modulation phase error will be collected by sweeping the phase of modulation. | ||
| Experimental Approach/Plan: | A combination of co- and counter beams will be used to trigger a 2/1 NTM and drop the frequency to a few kHz. Suppression of the 2/1 NTM will be attempted using modulation with best guess of correct phase difference between the deposition location and the outboard midplane where the island is detected using the Mirnov signals. After that a reference shot with cw-ECCD will be taken. After that the phase difference will be varied to study the suppression rate and to check whether the guess was correct. | ||
| Background: | Continuous wave ECCD has proven effective in completely suppressing NTMs. It can also prevent NTMs, when preemptively applied in the correct radial location. The cw-ECCD requires good alignment and a narrow deposition region with respect to the island width. In ITER the ECCD will have a relatively wide deposition region which will make cw-ECCD less effective since the destabilizing effect from current driven in the X-point will nearly cancel the stabilizing effect from the current driven in the O-point. This problem can be solved by switching the gyrotrons on when the O-point passes by their respective line-of-sight and off when the X-point passes by. Predictions made by F.W. Perkins suggest that a modulation scheme using a square pulse train with a 50% duty cycle will give close to maximum feasible suppression rate. Previous work on ASDEX-UG has demonstrated the efficacy of modulated ECCD. The present experiment seeks to study the suppression of the 2/1 NTM with modulated ECCD, and demonstrate the use of modulated ECCD with realtime frequency/phase detection along with sustained synchronization with the mode. The system to be demonstrated constitutes a general solution for mode frequency/phase detection that will be readily extendable to simultaneous suppression of multiple modes using launcher steering in future DIII-D upgrades. | ||
| Resource Requirements: | Lower pump (upper pumps desirable), He cooled.
All NB sources required including 30L and 330L for diagnostics (MSE, CER) and both 210 sources for counter injection and to control rotation. I coils in I240 configuration, powered by the SPAs. | ||
| Diagnostic Requirements: | Magnetic (fast and slow)
CER on 30L and 330L. MSE Thomson. CO2 interferometers. ECE radiometer | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | Real-time Mirnov acquisition.
Control of gyrotron modulation. | ||
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