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	153: Controlling VH-mode with RMPs and comparison to NSTX EPH-mode
Name:	John Canik canikjm@ornl.gov	Affiliation:	Oak Ridge National Lab
Research Area:	ELM Control	Presentation time:	Requested
Co-Author(s):	R. Maingi, S.P. Gerhardt	ITPA Joint Experiment :	No
Description:	The goal of this experiment is to extend the duration of the VH-mode by applying RMPs, and to perform a comparison of the edge characteristics to those of the EPH-mode observed in NSTX, which has some features in common with VH, as part of the FY13 JRT. This is partially motivated by the recent progress in understanding ELM suppression via RMP application, and if successful will guide later experiments on NSTX aiming to control and extend the duration of the EPH-mode. The comparison to EPH-modes includes kinetic profiles, the structure of the ExB profiles will be documented, and the edge fluctuation characteristics. The measurements will be supplemented by analysis of the macro- and micro-stability properties of the edge plasma.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	The first step in this experiment is to establish a robust, high quality VH-mode. To facilitate comparison to NSTX, this will be done in a DN shape with high triangularity. Once established, a sufficient number of shots will be taken to thoroughly measure the edge kinetic profiles and turbulence characteristics. Finally, n=3 RMP will be applied following the transition to VH-mode in order to attempt to extend the ELM-free VH phase. This will likely require tuning based on recent DIII-D analysis, including q-ramps to search for resonant windows and to place appropriate rational surfaces near the pedestal top in order to halt its inward growth.
Background:	The FY13 JRT is targeted at developing and understanding stationary enhanced confinement regimes without large ELMs. To date the VH-mode is not stationary, ending due to a large ELM and exhibiting a ramping density. However, the application of RMPs may allow stationary conditions to be achieved in VH, by suppressing the first large ELM as well as providing particle control via the routinely observed density pump-out. While this has been tried in DIII-D in the past, the understanding of RMP ELM-suppression has grown significantly since then, and the divertor geometry has been altered to improve pumping at high triangularity, so that new experiments are more likely to be successful. Further, the Enhance-Pedestal (EP) H-mode observed in NSTX experiments has several features that are similar to VH-mode (although there are also some differences). In particular, the EPH-mode exhibits a substantially wider edge region with significant ExB shear, along with a widening of the pedestal and higher pedestal-top temperatures; this results in higher confinement times (up to ~4 times L-mode scaling). Access to EPH-mode is also facilitated by achieving low-recycling conditions (at NSTX accomplished through lithium coatings applied to the PFCs), and shows reduced particle confinement compared to ELM-free H-modes. Part of the goal of the proposed experiment is to directly compare edge profiles and turbulence in EPH and VH-modes to explore these commonalities further. This effort will have a broad impact in developing these improved confinement regimes (both VH and EPH) towards steady-state.
Resource Requirements:	~1 day, RMPs, cryopump
Diagnostic Requirements:	TS, CER (esp. edge), BES, reflectometry
Analysis Requirements:	Profile analysis, edge stability (ELITE), edge microstability (GS2/GENE), transport (ONETWO/TRANSP)
Other Requirements: