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	101: Investigation of n=1 RMP effects on ELMs with pitch-aligned configuration of I-coils
Name:	Jong-Kyu Park jpark@pppl.gov	Affiliation:	Princeton Plasma Physics Laboratory
Research Area:	ELM Control	Presentation time:	Requested
Co-Author(s):	T. E. Evans, R. M. Nazikian, Y. M. Jeon	ITPA Joint Experiment :	Yes
Description:	The goal of this experiment is to test if n=1 RMPs can alter ELMs in DIII-D, when the n=1 configuration of I-coils is adjusted for better pitch-alignment from the nominal configuration that is optimized for error field correction and for the coupling to the kink mode. For this goal, 120-180 poloidal phasing in the n=1 I-coil configuration will be used rather than the typical 240-300 poloidal phasing, and will be applied to ELMing plasmas. Comparison with KSTAR results is also an important goal, and thus target plasmas will be designed to match as closely as possible the operating parameters used in KSTAR RMP experiments. The q95 variation will be particularly important since resonant surfaces are fewer for n=1 and so the location of each surface or the number of resonant surfaces in the pedestal will be critical. Experimental results, whether or not it is successful for ELM alteration, will be very useful to guide RMP physics study and future RMP experiments in other devices including KSTAR.	ITER IO Urgent Research Task :	Yes
Experimental Approach/Plan:	Two different methods of the n=1 I-coil phasing vs. q95 will be used to see if n=1 RMPs can modify ELMs. First, two-step I-coil phasing, either by a pairs (120 phasing to 180 phasing) or (180 phasing to 240 phasing), will be applied depending on q95 of target plasmas (q95=6.5, 5.0, 3.5). Second, the fixed I-coil phasing (120 and 180 phasing) will be applied to q95 varying targets, by changing IP=0.9MA to 1.5MA during the shots. To compare results with KSTAR, NBI power will be also decreased down to PNBI=2.5MW if possible, but the higher heating up to PNBI=7-9MW will be also tested to see if n=1 RMPs can modify ELMs in the low collisionality regime.
Background:	In KSTAR, n=1 RMPs have been successfully used for ELM mitigation and suppression when the coil configuration is optimized for pitch-alignment, 90 phasing. However, another configuration optimized for the kink mode, 180 phasing, locked plasma or caused H-L back transition as typically expected by n=1 fields. In general the KSTAR results imply the importance of the field optimization for edge, regardless of specific toroidal mode n, which can be put to the test in DIII-D using I-coils. Although KSTAR has three rows of coils and DIII-D I-coils are two rows without the midplane array, the coupling to the pitch-alignment by 90 phasing and to the kink by 180 phasing in KSTAR can be similarly produced by 120-180 phasing and 240-300 phasing, respectively, in DIII-D. Nominally DIII-D n=1 I-coils are configured to 240-300 phasing for the kink mode, which may be the reason why n=1 applications were not successful for ELM alteration in DIII-D, as found with 180 phasing in KSTAR. Therefore, it will be interesting to check if the 120-180 phasing of I-coils can mitigate or suppress ELMs. Another important difference between KSTAR and DIII-D experiments is the q-profile. KSTAR had higher q95 when ELMs were suppressed, and the high q95 may be essential in n=1 applications in order to have sufficient number of rational surfaces in the pedestal. So q95 scans in this experiment are also desired. Results of this experiment, whether or not successful, can be compared with KSTAR and will be very useful to understand 3D field effects on ELMs.
Resource Requirements:	Standard RMP ELM control hardware and heating systems.
Diagnostic Requirements:	Standard RMP ELM control diagnostics.
Analysis Requirements:	Kinetic equilibrium reconstructions.
Other Requirements: