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	305: Scaling Of Pedestal Plasma Transport With RMP I-coil Current
Name:	James Callen jdcallen@wisc.edu	Affiliation:	University of Wisconsin
Research Area:	ELM Control	Presentation time:	Not requested
Co-Author(s):	S. Smith, N. Ferraro, S. Mordijck, R. Moyer	ITPA Joint Experiment :	No
Description:	The basic proposal is to update and expand the exploration, as a function of I-coil current, of the RMP suppression of ELMs in low collisionality DIII-D ISS discharges in the Evans et al, Nucl. Fusion 48, 024002 (2008) paper. Such a set of experiments is very important for developing a better and more quantitative understanding of the effects of RMPs on pedestal plasma transport -- see Background discussion below. Revisiting these experiments is warranted at this time because of the recent upgrading of the edge Thomson scattering system and other diagnostics plus the recent more comprehensive characterization of RMP ELM-suppressed regimes. A new set of I-coil scaling data will provide the key impetus for a new, much more precise round of interpretive transport modeling (via M3D-C1, ONETWO and the flutter transport model module) of RMP effects on pedestal plasma transport.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	In the previous I-coil current scaling discharges (126435-126443) the I-coil current was held constant through the discharge. An alternate approach for determining the I-coil current scaling would be to change the I-coil current in steps, throughout a given discharge, at constant beam power. In addition to fiducial discharges with no RMPs, the I-coil current could also be initiated at a low level (2 kA?) and then stepped up into RMP-suppressed regimes. It would be important to look for any abrupt changes in the plasma transport characteristics in the pedestal region, particularly in the carbon toroidal and poloidal flows and hence the implied radial electric field there, as the ELM suppression I-coil current threshold is exceeded.
Background:	The best, most systematic and comprehensive set of data on RMP suppression of ELMs in low collisionality DIII-D pedestals as a function of I-coil current was provided in the Evans et al, Nucl. Fusion 48, 024002 (2008) paper. This set of data was critical for many papers on pedestal density transport and in particular the development of the RMP-flutter-induced plasma transport model: 1) Saskia Mordijck's Ph.D. thesis, "Particle transport as a result of Resonant Magnetic Perturbations," UCSD, January 2011. 2) J.D. Callen, A.J. Cole, C.C. Hegna, S. Mordijck and R.A. Moyer, "Resonant magnetic perturbation effects on pedestal structure and ELMs," Nucl. Fusion 52, 114005 (2012). 3) J.D. Callen, A.J. Cole and C.C. Hegna, "Resonant-magnetic-perturbation-induced plasma transport in H-mode pedestals," Phys. Plasmas 19, 112505 (2012). 4) J.D. Callen, C.C. Hegna and A.J. Cole, "RMP-Flutter-Induced Pedestal Plasma Transport," San Diego IAEA FEC paper TH/P4-20, 8-13 October 2012. 5) P.T. Raum, S.P. Smith, J.D. Callen, N.M. Ferraro et al., "Comparison of flutter model with DIII-D RMP data," paper currently being written for submission to Nucl. Fusion. The last reference in particular shows relatively good agreement between the ONETWO interpretive results for discharges 126006 and 126443 and the flutter model predictions for the radial electron heat diffusivity and T_e profile at the top of the pedestal when the RMP-induced magnetic perturbations calculated by M3D-C1 which include two-fluid plasma response effects are used. The recent upgrades in the diagnostics and better characterization of ELM-suppression regimes in DIII-D can facilitate the development of a modern, much more precise and comprehensive set of I-coil current scaling data for plasma transport interpretive modeling via M3D-C1, ONETWO and the flutter transport model module that has been developed. A new set of I-coil current scan data should also facilitate exploring the role of the electric field and its effect on the toroidal plasma rotation -- and whether changes in them are critical factors in obtaining ELM suppression, as suggested in Ref. 4) above and Rick Moyer's Providence APS-DPP invited talk.
Resource Requirements:	Mainly a set of similar parameter ELM-suppressed discharges are needed with increasing I-coil current from 0 (for fiducial discharges) to about 6 kA in small steps -- say in units of 1 kA (or less around the threshold for ELM suppression?). Discharges in which the ELM suppression I-coil threshold current is about 2 or 3 kA would probably be best. It would be critical to hold the pedestal in about the same relevant parameter regime (beta, in center of q_95 resonance, core heating etc.) during the changes in I-coil current.
Diagnostic Requirements:	Good Thomson T_e and n_e measurements and CER carbon rotation measurements of the plasma parameters at the pedestal top (0.9 < Psi_N < 0.98) in response to various I-coil currents are critical. More generally, all the critical diagnostics that are needed to facilitate developing good kinetic EFITs should be operative. Measurement of the current profile in the pedestal region with the recently revitalized Lithium beam diagnostic would also be useful both for developing good kinetic EFITs and for exploring the sensitivity of the RMP-induced magnetic perturbations calculated by M3D-C1 to the current density profile in the pedestal.
Analysis Requirements:	Good kinetic EFITs, ONETWO interpretive analysis of the electron density and thermal transport plus plasma toroidal rotation as a function of the I-coil current in ELM-suppressed discharges. Also, M3D-C1 analysis of the magnetic perturbations including flow screening effects will be needed to quantify estimates of the corresponding flutter model predictions for these same discharges.
Other Requirements: