DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN
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| Title | 143: Particle confinement regimes with RMP in n=3 | ||
| Name: | Oliver Schmitz ( |
Affiliation: | FZ Juelich |
| Research Area: | Transport | Presentation time: | Not requested | Co-Author(s): | tbd |
| Description: | At TEXTOR-DED two particle confinement regimes were obtained under application of RMP fields from the DED - an improved particle confinement and a controlled degradation, the particle pump out. These experiments were done in m/n=6/2 and m/n=3/1 base mode configuration (m -> poloidal mode number, n-> toroidal mode number). Recently a transition between both regimes just by increasing the perturtbation field strength was found. With this proposal we suggest to reproduce these results with n=3 I-coil (unique for D3D) in HFS limited L-mode configuration and see how this setting affects the limiter H-mode transition. Furthermore the role of plasma elongation (islands will be deformed) and the transition towards the poloidally diverted topology should be studied. | ||
| Experimental Approach/Plan: | Do ohmic plasmas limited on HFS (see also ID 141 by T. Evans of this ROF) and produce both regimes with n=3, study transition behavior. Go to limiter H-mode and study the effect of the two settings obtained before on the limiter H-mode performance, elongate plasma and study impact, go to pol. div. settings and try to establish the improved confinement with RMP. See if here PO can be produced also (linked to TF ELM control). Check if with the improved confinement settings - if found - the H-mode performace can be affected. | ||
| Background: | At TEXTOR-DED two particle confinement regimes were found. On the one hand an improved particle confinement was obtained shifting the plasma towards the perturbation source (see also ID 141 by T. Evans, this ROF). The preliminary conclusion was that the equilibrium was optimzed such that just the next resonant island chain was destroyed when shifting the plasma. This leads to a short cut between these island's x-points and therefore for a change in the sheath potential and by that of the radial electric field. Accordingly an increase of the poloidal rotation was seen when the density steps up. These density steps are correlated to changes in the heat and particle flux on the DED target, indicating that the heteroclinic tangles of the next deeper island chain connect at this point. In contrast a controlled degradation of the particle confinement - the particle pump out - was found by shifting the plasma with constant edge q away from the perturbation source. A candidate for the mechanism is that the perturbed field lines don't reach the wall but lead to an ergodic domain with diffusive transport characteristics and enhanced radial transport. Fuelling the plasma with glas blow was hardly possible. Very recently we could resolve the transition between both regimes at fixed position just increasing the perturbation strength. Here a pronounced 4/1 island dissapears and we get immediately the transition from pump out to the improved confienemt. The characteristics of this transition should be studied with different base mode (n=3) and with the facility to elongate the plasma changing the steepness of the q profile. Here the resonant layers and accordingly the islands created come closer together and the resulting change in the transition shall be elevated. This will contribute to the understanding of the island overlapp criterium and might be also a method to check it comparing to the SURFM results. Going to the poloidally diverted configuration shall enhance the information if there is a smooth transition and how it evolves. The question if there can be an improved confinement produced by RMP in pol. div. L-mode plasmas is very interesting (see ID 141 of T. Evans again). | ||
| Resource Requirements: | L-mode plasmas limited on HFS, beam blips if possible for L-mode (CER), developement of this scenario and the limiter H-mode (beams accordingly), I-coils in n=3, EFC with C-coils
For this experiments the n=3 internal coils and the facility to elongate the plasma and go to pol. div. configuration is unique at DIII-D | ||
| Diagnostic Requirements: | fast probes, full TS capability, CER beam box, DiMES TV camera set to inner wall, possibly also IR camres with this view, any high resolution edge diagnostic (BES-Li beam) | ||
| Analysis Requirements: | SURFM and TRIP-3D post experiment, kinetic EFITS for improved magnetic reconstruction | ||
| Other Requirements: | -- | ||
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