DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 185: Completion of MP 2007-01-02: test RMP effect on ELM stability and increase neped with pellets | ||
| Name: | Richard A. Moyer ( |
Affiliation: | University of California, San Diego |
| Research Area: | ELM Control & Pedestal Physics | Presentation time: | Requested | Co-Author(s): | Evans, Fenstermacher, Baylor, Jernigan |
| Description: | On June 24th, 2007, we began an experiment (MP 2007-01-02 to investigate the mechanisms for density pumpout in RMP ELM suppressed discharges. As part of this experiment, we used rapid (10 Hz) HFS pellets to investigate 1) evidence for a direct effect of the applied RMP on the Peeling-Ballooning stability independent of the pedestal density, and 2) to attempt to raise the pedestal density during ELM suppression to widen the operating space and recover a portion of the lost pedestal pressure. Unfortunately, we ran out of liquid helium (and hence pellets) before we were able to inject successfully into the discharges. This proposal is to conclude this part of the MP. | ||
| Experimental Approach/Plan: | 1. Investigate the direct effect of the RMP on ELM stability, independent of the density pumpout: use repetitive pellets with inter-pellet spacing < density pumpout timescale (typically a few tens of ms in the pedestal; a few hundreds of ms in the core) in RMP ELM suppressed discharges to vary the pedestal conditions on a time scale too fast for transport to respond, but relatively slowly in terms of MHD stability. 2) Attempt to broaden the RMP ELM-suppressed operating window and recover some portion of the lost pedestal pressure by using core fueling with rapid HFS launch pellets. | ||
| Background: | At low collisionality and high triangularity, we stabilize ELMs by reducing the pedestal density. The operating window has consequently been rather narrow in neped when using gas puff fueling. Attempts to increase the neped level lead to onset of small ELM-like events (grassy or type II ELMs perhaps) coincident with the reduction in pedestal toroidal rotation below a critical value and increase in pedestal density above a critical value. Concomittent with these changes, the Er well broadens and flattens (Er shear decreases in the pedestal). Linear peeling-ballooning stability analysis indicates that these small ELMs onset when the pedestal becomes again unstable. Core fueling with pellets might avoid increased rotation damping/increased viscosity in the edge from gas puffing and enable the core and pedestal density to be raised while maintaining ELM suppression.
by selecting an inter-pellet spacing that is long compared to MHD timescales but short compared to the pedestal transport change timescales (50 ms in the pedestal for density pumpout), we will also be able to test whether or not the applied RMP directly effects the ELM stability without reducing the pedestal density. | ||
| Resource Requirements: | 5 co and 2 counter NB sources
cryopumping HFS repetitive pellets n = 3 I coil operation up to 6.5 kA | ||
| Diagnostic Requirements: | standard RMP ELM control diagnostics :
profiles: core, tangential, and divertor Thomson; CER, profile reflectometry fast and slow magnetics poloidal and toroidal SXR filterscopes fluctuation diagnostics fast framing camera IRTVs in the divertor | ||
| Analysis Requirements: | Requires extensive analysis: kinetic EFIT equilibrium reconstructions, fast stored energy loss from fast magnetics, profile and Er analysis, ELITE stability analysis. May provide good dataset for further NIMROD and/or IPEC modeling of RMP penetration. | ||
| Other Requirements: | -- | ||
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