DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 122: ECCD stabilization of NTMs to improve the high beta phase of steady-state scenario discharges | ||
| Name: | John Ferron ( |
Affiliation: | General Atomics |
| Research Area: | Fully Noninductive High Beta Operation | Presentation time: | Not requested | Co-Author(s): | -- |
| Description: | NTMs commonly occur during the high-performance phase of discharges designed to achieve 100% noninductive current. This limits the maximum stable betaN (and thus the bootstrap current fraction) and, in the case of a 3/2 mode, reduces the confinement so that the limited total beam energy available is used up more quickly. The goal here is to test the use of ECCD for NTM stabilization and to develop a gyrotron aiming that will be effective for NTM stabilization and simultaneously provide sufficient off-axis current drive for maintenance of the current profile. With NTM stabilization, increase the betaN to the maximum achievable and determine the effect on the noninductive current fraction. | ||
| Experimental Approach/Plan: | 1) Dedicate the ECCD during the high-performance phase to NTM stabilization, preferably preemptive. While NTMs are stabilized, maximize the betaN. 2) If the previous step was successful, determine whether the gyrotron aiming for NTM stabilization is compatible with current drive to maintain the steady-state phase. If possible, broaden the deposition profile of the ECCD in order to satisfy both the NTM stabilization and the current profile maintenance requirements. Or, dedicate some gyrotrons to each task. | ||
| Background: | The phase of steady-state scenario discharges with high noninductive current fraction must be operated at high beta, above the no-wall stability limit, in order to achieve a large bootstrap current. In past experiments, NTMs are often observed. Prior to 2007 the number of discharges that ran for the full 2 second high-performance phase without a 2/1 mode occurring was small. During 2007, the 2/1 mode was not common during the high beta phase but a 3/2 mode was nearly always present. A 2/1 mode will eliminate the high-performance. A 3/2 reduces confinement requiring that higher beam power be injected in order to reach the programmed betaN value. This uses up the available beam pulse length and limits the duration available for the study of the high noninductive current fraction plasma. | ||
| Resource Requirements: | -- | ||
| Diagnostic Requirements: | -- | ||
| Analysis Requirements: | -- | ||
| Other Requirements: | -- | ||
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