DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2013 EXPERIMENTAL CAMPAIGN Review | Direct submission with log-in | Request submission without log-in
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Title	83: Establishing stationary I-mode with high performance
Name:	Dennis Whyte whyte@psfc.mit.edu	Affiliation:	Massachusetts Institute of Technology
Research Area:	ELM Control	Presentation time:	Requested
Co-Author(s):	A. Hubbard, M. Fenstermacher, A. White, J. Hughes, S. Gerhardt, R. Maingi	ITPA Joint Experiment :	Yes
Description:	The goal of this proposal is to establish I-mode in a stationary mode (constant heating power, density, etc.) with sufficient energy confinement performance that it can be regarded as a viable burning plasma operating scenario that does not require ELMs for particle and impurity control. The results will be combined with those from Alcator C-Mod (and ASDEX-Upgrade) to help extrapolate I-mode to ITER and to contribute significantly to the 2012 Joint Research Target of OFES.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	The proposal builds on the successes of the 2012 I-mode exploration on DIII-D. Those experiments explored a wide operating space in Ip, q95, density and heating power with ion grad-B drift pointed away from the X-point (the configuration in which I-mode is typically found). An I-mode was tentatively identified (#149908) during the exploration, showing a substantial edge T pedestal, with an L-mode density profile, and significant improvements in confinement (H98 up to 0.8) compared to standard L-mode. There were qualitative indicators of reduced fluctuations in the pedestal during the I-mode phase, however this diagnosis was not optimized. The initial experiment indicated that either shape (triangularity) and/or divertor topology were critical in obtaining I-mode in LSN, with a preference for smaller lower triangularity and the outer strikepoint positioned on the top of the lower divertor baffle. Due to the limited time a full exploration of the effect of shaping was not possible. Also, the I-mode was not maintained in a stationary condition due to the power scan that was present in each discharge. The proposed experiment would use the 2012 results as a starting point for a) establishing the I-mode in a stationary condition with constant heating. b) fully diagnose evolution of edge fluctuation characteristics c) explore the effect of shape/divertor changes on the I-mode operating window (X-point height, total triangularity)
Background:	I-mode is a relatively new operating regime that has been recently explored on C-Mod and ASDEX-Upgrade. At its simplest, I-mode features an edge energy barrier in the form of a temperature pedestal, yet retains L-mode particle confinement with no evident edge density barrier (making it distinct from H-mode). The results on C-Mod and AUG indicate establishment of H-mode energy confinement without the need for ELMs, making it attractive as an alternate operating regime in ITER to avoid ELM-induced damage. Obviously it will be important to compare and contrast I-mode on several devices to determine effects of heating schemes, wall/divertor/plasma geometry, size, etc.
Resource Requirements:	One day of experimental time Reverse-B Beam and ECH heating Divertor cryopumping
Diagnostic Requirements:	Full set of pedestal / boundary fluctuation diagnostics to examine changes in broadband fluctuations and any weakly coherent, high frequency modes often associated with I-mode in other devices.
Analysis Requirements:
Other Requirements: