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	61: Energy Transport During Electron-Dominated Heating of ITER-Relevant H-Mode Discharges
Name:	Gary Taylor gtaylor@pppl.gov	Affiliation:	Princeton Plasma Physics Laboratory
Research Area:	Inductive Scenarios	Presentation time:	Requested
Co-Author(s):	N. Bertelli, J.C. Hosea, R.J. Perkins, C.K. Phillips, P.M. Ryan, D.R. Smith, W.M. Solomon	ITPA Joint Experiment :	No
Description:	This experiment will study electron transport and plasma turbulence in DIII-D Advanced Inductive (AI) and ITER Baseline Scenario (IBS) H-mode discharges that are predominantly heated by electron cyclotron (EC) power and it aims to identify the dominant mechanism(s) responsible for enhanced electron transport when EC power is applied to these ITER-relevant scenarios, especially as produced on DIII-D with NBI.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	All discharges should be run with balanced NBI to minimize the applied torque, and they should be run with no beta feedback on NBI power so that the NBI power remains constant. The run plan is as follows: 1.Begin with an AI discharge similar to shot 146571 (the outer gap can be larger since there will be no fast-wave (FW) heating), with sufficient NBI power to transition to and sustain an H-mode. 2.Apply an EC heating pulse that is considerably shorter than the NBI pulse (~1 s). Vary the EC pulse timing and duration. Measure the change in stored energy at the turn-on and turn-off of the EC pulse. 3.Repeat 2 with increasing EC power (eg. 2, 4 and 6 gyrotrons). 4.Repeat 3 with one or possibly two gyrotrons modulated to study electron transport with ECE etc. 5.Repeat 1-4 for an IBS discharge similar to shot 150840 (once again, the outer gap can be larger since there will be no FW heating). Typically the IBS discharges in 2012 had to be run at much higher densities than the AI discharges (~5.5x1019 m-3 for IBS compared to ~ 3.5x1019 m-3 for AI) to avoid NTMs. The higher density in the IBS discharges caused the plasma to go overdense for second harmonic ECE, so the density should be lowered to get core ECE data. If NTM??s appear some of the gyrotron launchers should be configured for ECCD in order to stabilize NTM??s. [NOTE: For the 2013 campaign it is hoped to upgrade at least one, possibly more, of the EC launchers so that they can be changed from ECCD to ECH orientation in 0.5-1 s, compared to ~ 5 s at present.] 6.Compare heating efficiencies for ECCD and ECH for best heating case of 5. Couple EC power from mirrors configured for ECCD followed by coupling power from the mirrors configured for ECH and vice versa. Perform in successive shots, or if possible, using two ECH pulses in the same shot with fast mirror movement or with power configured for ECH and ECCD. 7.Run AI and IBS H-mode discharges with EC heating only (no NBI) at the highest gyrotron power available to assess how well EC heats an ECH-only H-mode discharge.
Background:	ITER will utilize virtually torque-free, fuelling-free, dominant electron heating to generate and sustain plasmas in the H-mode regime. EC heating will play a major role in generating H-mode discharges in ITER. However there is growing evidence for significantly increased electron transport when EC heating is applied to DIII-D ITER-relevant H-mode discharges produced with NBI. Comparison of EC and FW heating of AI H-mode discharges in 2011 showed similar core electron heating and heating efficiency based on the time evolution of stored energy for the first ECH pulse and the FW heating pulse applied on top of the first ECH pulse, whereas very little heating and increase in stored energy was obtained with a second ECH pulse on top of the first (eg. shots 146571 and 146574). In 2012 a saturation of stored energy was observed in DIII-D IBS discharges when increasing levels of EC heating were applied (eg. shots 150840 and 150821). The radiated power observed when the EC power was applied to either the AI or the IBS discharge scenarios was essentially proportional to the total power, suggesting that the observed behavior is due to enhanced electron transport in these scenarios. It is imperative that the dominant mechanism(s) causing the enhanced electron transport are identified so that ITER-relevant scenarios with reduced electron transport during EC heating can be developed.
Resource Requirements:	Machine Time: 1-1.5 days (Steps 1-4 of the run plan for the AI target discharges can be completed in about 0.5 days, similarly Step 5 for the IBS target discharges can be completed in about 0.5 days, and the remaining steps of the run plan may take another 0.5 days) Number of gyrotrons: 6 (7 if available) Number of neutral beam sources: 4, plus beam blips for BES and MSE
Diagnostic Requirements:	ECE, BES, CHERS, , MSE, UCLA reflectometry for oblique angles, and other diagnostics for measuring turbulence
Analysis Requirements:	TORAY, GENRAY, TORBEAM, TRANSP
Other Requirements:	Also submitted to Transport & Turbulence and Steady State Heating and Current Drive - please discuss placement with that group