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raman_mgi_icc2011_paper.pdf2011-09-12 11:42:51Roger Raman
raman_disruptionmitigation.pdf2011-08-31 10:44:09Roger Raman

Disruption Mitigation Studies in NSTX

Author: Roger Raman
Requested Type: Consider for Invited
Submitted: 2011-05-31 09:56:31

Co-authors: S.P. Gerhardt, T.R. Jarboe, H.W. Kugel, D. Mueller

Contact Info:
University of Washington
AERB 352250
Seattle, WA   98195
USA

Abstract Text:
Predicting and controlling disruptions is an important and urgent issue for ITER. Reactors based on the ST and Tokamak concepts are expected to carry several MA of plasma current and therefore have the potential for disruption and the generation of substantial amounts of run-away electrons. While work is in progress to avoid disruptions, some may be unavoidable. For these cases, a fast discharge termination method is needed to minimize the deleterious effects of the disruption.
At present Massive Gas Injection (MGI) is the most promising method for safely terminating discharges in ITER. NIMROD simulations for C-MOD and DIII-D have shown that the cold front from the edge, which has been cooled by a massive gas injection pulse, needs to reach the q=2 surface for the onset of rapid core cooling to occur. On ITER, because of the large minor radius of the device, the long transit times for the slow moving neutral gas, and the large scrape-off-layer flows, it is not known if a simple MGI pulse from multiple locations would be adequate. Insight into ways for reducing the total amount of injected gas and optimizing the injection locations would further help with the design of a reliable system for ITER. NSTX can offer new data by injecting gas into the private flux and lower x-point regions to determine if this is a more desirable location for massive gas injection.
Injection from this new location has two advantages. First, the gas is injected directly into the private flux region, so that it does not need to penetrate the scrape-off-layer. Second, because the injection location is located near the high-field side region, the injected gas should be more rapidly transported to the interior as known from high-field side pellet injection research and from high-field side gas injection on NSTX. By comparing gas injection from this new location to results obtained from injecting a similar amount of gas from the conventional outer mid-plane, NSTX results on massive gas injection can provide additional insight, a new database for improving computational simulations, and additional knowledge to disruption mitigation physics using massive gas injection.
A brief summary of disruption mitigation physics will be presented in addition to any available experimental results from NSTX.

This work supported by U.S. DOE Contracts DE-AC02-09CH11466 and DE-FG02-99ER54519 AM08

Characterization: A4

Comments:
At present there is no experimental data from NSTX. We think that by the time of the ICC meeting we will have initial results from the first test of the MGI system in late July or early August.

University of Washington

Workshop on Innovation in Fusion Science (ICC2011) and
US-Japan Workshop on Compact Torus Plasma
August 16-19, 2011
Seattle, Washington

ICC 2011