DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 294: Search for Structures Predicted in RMP ELM control modeing | ||
| Name: | Richard A. Moyer ( |
Affiliation: | University of California, San Diego |
| Research Area: | ELM Control & Pedestal Physics | Presentation time: | Requested | Co-Author(s): | Evans, Joseph, Kruger, Izzo, Park, Menard, Boozer, Schmitz |
| Description: | An outstanding issue for understanding RMP ELM control is the plasma response to the applied n=3 RMP. The goal of this experiment is to test predictions of various models for the magnetic field in the plasma by searching for structures in 2D Thomson scattering data. We will run upper and lower single null, low collisionality, ITER-similar shape discharges, apply n = 3 RMP from the I-coil to suppress ELMs, and shift the plasma rigidly across the Thomson view chord to build 2D images of electron density and Te. Islands, convective cells, and/or significant displacement of the equilibrium flux surfaces should be visible on the Thomson scattering data. This proposal has significant overlap with Schimitz #100. | ||
| Experimental Approach/Plan: | 1) Establish good RMP ELM suppression with n = 3 RMP in LSN, ITER-similar shape discharges. 2) Move the plasma boundary across the Thomson view chord on a timescale slow compared to the laser spacings. 3) construct 2D images of the boundary of the discharges, looking for evidence for islands, ExB convective cells, or plasma equilibrium displacements near the crown of the discharge where they are predicted to occur and to be easiest to see due to flux expansion. 4) Scan I-coil current 5) vary momentum input with co/ctr beams 6) repeat with USN discharges time permitting to image the region near the Xpoint. | ||
| Background: | Understanding the plasma response to the applied n = 3 RMP is crucial to understanding how RMP ELM suppression works. We have several models which make predictions about structures that form in the flux expanded regions near the crown and Xpoints. TRIP3D provides a vacuum field model (no plasma response) which predicts remnant islands with maximum physical size near the crown and Xpoint. NIMROD and JORIK extended MHD codes predict formation of ExB convectice cells in this region of the plasma that drive enhanced particle transport without significantly increasing thermal transport (relative to e.g. ripping open closed field lines in a stochastic layer). Most recently, the IPEC code has begun to be used to predict the plasma response to the I-coil RMP, and predicts significant plasma displacements near the crown and xpoint regions.
We propose to use the Thomson scattering diagnostic to build 2D images of electron density and pressure by moving the plasma boundary across the Thomson view chord on a time scale slow compared to the laser spacing. This technique has been used successfully for example in ASDEX-Upgrade to image "blobs" in the SOL and "holes" in the pedestal, and should be useful here to image the predicted structures if they exist. Rick Moyer has written and IDL tool for constructing such 2D images from existing data in which the edge was "breathed" past the Thomson chords to improve the spatial resolution of the measured profiles. This tool is being developed to optimize the image construction but the discharges available have little Rmajor movement which limits the "field of view". | ||
| Resource Requirements: | 4-5 co sources; 2 counter sources
cryopumps n = 3 I-coil with 6.5 kA capability | ||
| Diagnostic Requirements: | CER and Thomson scattering
fluctuation diagnostics pedestal and boundary diagnostics | ||
| Analysis Requirements: | TRIP3D runs to: 1) test the vacuum field/island overlap model against imaged structure sizes and to provide RMP fields to other models, 2) validate IPEC predictions of flux surface displacements; 3) NIMROD and/or JORIK runs for validation of convective cell predictions. 4) EMC3/EIRENE runs for comparison with data. | ||
| Other Requirements: | -- | ||
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