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	112: 2D imaging of small ELMs
Name:	Benjamin Tobias tobias@lanl.gov	Affiliation:	Los Alamos National Laboratory
Research Area:	ELM Control	Presentation time:	Requested
Co-Author(s):		ITPA Joint Experiment :	No
Description:	Produce small ELMs appropriate for 2D ECE-Imaging and BOUT++ simulation.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	This experiment can take any number of forms and still meet its stated goals, and so the specifics of the discharges depend more upon selecting a small ELM regime that is of interest to a broader range of experiments. The only obvious exception being that we do not want to do this during discharges where the ELMs have been artificially modified by one of the other mitigation techniques, i.e. pellet pacing, RMPs, etc. Certainly the experiment can be done as a piggy-back if there are other experiments with an interest in either Type-III or other small ELM regimes.
Background:	In the past we've put much effort into characterizing and modeling large Type-I ELMs for the purpose of validating BOUT++ simulations [Fenstermacher, M., et al., Fast Pedestal, SOL and Divertor Measurements from DIII-D to Validate BOUT++ Nonlinear ELM Simulations. 2012.] . The large ELMs selected from previous campaigns present a variety of challenges to modeling, and so there is interest in attempting to model small ELMs in the hopes that the code will produce more consistent results. From the perspective of the experimentalist, there are a number of reasons why large, Type-I ELMs become the most challenging to draw detailed measurements from. Of course, the ELM evolution is rapid, and there is often little or no hint of any precursor or evolving linear mode. Aside from this, ECE diagnostics have special difficulties imaging these modes on DIII-D. Strong mm-wave bursting of unknown origin obscures the ELM structure in these discharges [Yu, L., et al., Characterization of Intense Bursts of mm-wave Emission Using New RF Spectrometer on the DIII-D Tokamak. Bulletin of the American Physical Society, 2012. 57, B. Tobias, et. al., Intense millimeter wave radiation from the H-mode pedestal on DIII-D at ITER relevant collisionality, 39th EPS]. The fact that this bursting is not observed under the higher collisionality conditions at AUG and KSTAR suggests that it will not be a complication for imaging small ELM regimes. If this is successful, and we are able to get good imaging data for an ELM not obscured by mm-wave bursting, there will be a wide range of opportunities to compare this to modeling and also to results obtained on other machines. In particular, we are motivated to touch base with the results reported last year on ASDEX, where small ELM regimes were accompanied by both coherent and broadband fluctuations with much shorter poloidal wavelength than edge fluctuations routinely observed on DIII-D by our ECE-Imaging system [Boom, J., et al., Characterization of broadband MHD fluctuations during type-II edge localized modes as measured in 2D with ECE-imaging at ASDEX Upgrade. Nuclear fusion, 2012. 52(11): p. 114004.].
Resource Requirements:
Diagnostic Requirements:	ECE-Imaging MIR desirable (expected avail. nlt June 2013)
Analysis Requirements:
Other Requirements: