PEP ITPA Working Group on RMP ELM Control:

1. PEP ITPA Working Group on RMP ELM Control: 1st Draft Summary Report on Work Plan Progress and Outlook M.E. Fenstermacher (chair) M. Becoulet, C.S. Chang, T.E. Evans, A. Kirk, Y. Liang, A. Loarte, R. Maingi, O. Schmitz, W. Suttrop (members), Pavel Cahyna (new member) Presented at the 16th Pedestal and Edge Physics ITPA MtgApril 23, 2009

2. PEP ITPA Work Plan in RMP ELM Control Contains 7 Elements • Reproduce RMP ELM suppression on at least one tokamak other than DIII-D • Identify the criteria for ELM suppression from experimental data and theoretical models • Quantify the impact of ELM suppression by RMPs on the pedestal pressure and core confinement and develop/validate theoretical models • Quantify the power loading on the wall and divertor with RMP-suppressed ELMs; make recommendations on any requirement for rotating RMPs • Explore the capability to suppress or mitigate ELMs during the current ramp phase (ie. close to the L-H transition threshold, and with time varying q95) • Demonstrate ELM control with ITER-like pellet fuelling • Model the performance of the ITER ELM control coil set, and propose changes to the design as appropriate; likely to require further developments in modeling the plasma response (challenging)

3. PEP ITPA Work Plan in RMP ELM Control Based on 4 Assumptions • Hypothesis: The complete suppression of ELMs on DIII-D by RMPs, while not eg. on JET, is because the DIII-D coils are off-midplane, as presently designed for ITER (Note: ITER design now includes also midplane coils) • Only MAST and DIII-D are presently in a position to test ITER-relevant coils. • AUG will also be in this position from mid-2010 with midplane coils later • Both MAST neutral beams are assumed to be operational early in 2009 to provide reliable ELMing H-modes • Appropriate machine time, experimental and theoretical manpower are made available • The criteria (to be validated) based on a minimum stochastic layer region (width) and alignment of the perturbation with q(r), are the main requirements for ELM suppression • If this proves not to be the case, other model development (including plasma response) and tests will be required. • The target date for input to ITER IO on RMP coil design is Sept 2010, but results will be communicated as they are produced in advance of this date.

4. RMP ELM Control WorkPlan

5. Progress to meet the tasks, highlighting any that could be "closed" (ie. Have a sufficiently complete answer - None) • 1.1 Reproduce RMP ELM Suppression on at least one tokamak other than DIII-D - MAST, and AUG - Internal Off-Midplane Coils - PEP-23 • DIII-D experiments 2009-10 focus on physics understanding • MAST experiments scaling DIII-D conditions in progress 2009-10 • AUG experiments scaling DIII-D conditions could begin in 2011 • 1.1 Reproduce RMP ELM Suppression on at least one tokamak other than DIII-D - JET, NSTX, CMOD, TEXTOR - Midplane Coils - PEP-25 • Joint experiments - planning in progress

6. Progress to meet the tasks, highlighting any that could be "closed" (ie. Have a sufficiently complete answer - None) • 1.2 Identify the criteria for ELM suppression from experimental data - 2009 from DIII-D, MAST, JET, NSTX and TEXTOR • n=3 ELM Suppression: 1) q95 resonance, 2) collisionality, 3) pumpout, 4) beta, 5) core/edge particle and energy transport, 6) RMP in He, 7) island overlap width, 8) aspect ratio, 9) convective cells and pumping (He), 10) shape • n=1 or 2 mitigation: 1) near LH threshold power, 2) first ELM mitigation, 3) q95 resonances, 4) n=2 suppression, 5) RMP for mitigation in He • 1.2 Identify the criteria for ELM suppression from theoretical models • 1) Vacuum field line tracing and Weighted magnetic particle streaming, 2) Neutral and plasma Monte-Carlo fluid, 3) Linear MHD stability, 4) Non-linear MHD with rotation, 5) Turbulence codes with RMPs, 6) NTV, 7) Kinetic modeling

7. There are several proposed candidates for new tasks or objectives • 1.2 Identify the criteria for ELM suppression from experimental data • Evaluate the dependence of ELM suppression on (1) shape differences (eg. low vs. high , squareness variation), (2)  (power), (3) toroidal field at fixed q95 • 1.2 Identify the criteria for ELM suppression from theoretical models • Evaluate whether ideal perturbed equilibria MHD codes are sufficient to explain ELM suppression • 1.4 Quantify the power loading on the wall and divertor … • Measure multi-lobe structures in particle and heat flux for a range of conditions as input to specifications for time response of ITER coils • 1.8 Verify the compatibility of RMP ELM control with ITER operating scenario characteristics • Electron heating dominated plasmas - ECH or ICRF H-modes ?? • Partially detached divertor with SP heat flux reduction • Fueling pellets with shallow penetration (LFS ?)

8. Several changes to the assumptions and/or timescales for answering the tasks have been proposed • Insufficient machine time and manpower to meet work plan schedule • Most of the tasks planned to be completed by Q2-09 are not complete, vis. • 1) Suppress ELMs using RMPs on MAST • 2) Model and compare vacuum RMP field for MAST and DIII-D with suppressed ELMs • 3) Quantify ability to suppress or mitigate ELMs with RMP in current ramp • 4) Explore potential to mitigate/suppress ELMs with midplane coils - can not be completed until suppression achieved ?? • AUG results from high n=3 or 4 RMP with 2 x 8 rows of off-midplane coils delayed one year (to Q3-11) from Work Plan (Q3-10)

9. Several changes to the assumptions and/or timescales for answering the tasks have been proposed • The criteria (to be validated) based on a minimum stochastic layer region (width) and alignment of the perturbation with q(r), are the main requirements for ELM suppression • Debate continues • The target date for input to ITER IO on RMP coil design is Sept 2010, but results will be communicated as they are produced in advance of this date • ITER IO: Sept 2010 target date likely will be delayed • Assume sufficient time before installation decision for data to be available from DIII-D, MAST and AUG n>=3 off-midplane coils • ITER IO: Specification of coil time response (turn-on and frequency) requirements needed soon - mostly P/S issue but some impact on coil design

10. Plan in development to take the work forward over the next 6-12 months • Both DIII-D and JET must finish RMP ELM Control Work Plan work by mid-2010 before long shutdowns • JET power supply upgrades in time for experiments before shutdown • Highest short term priorities for ITER must be weighed against getting sufficient data for physics understanding analysis during the shutdowns • DIFFICULT CHOICES • AUG initial n=2 experiments with 2 x 4 rows of 4 coils will start during DIII-D and JET shutdowns. • NSTX power supply upgrade - improved dynamic EFC (n=3) during RMP (n=2) for reduced locked mode probability

11. Tasks that may not be possible for various reasons (eg insufficient manpower, insufficient machine time, technically too difficult…) • 1.4 Quantify the power loading on the wall and divertor • Explore impact of rotating RMPs on ELM suppression and peak wall/divertor heat flux • Needs device upgrades vis: DIII-D CP coils (2011), MAST upper row of 12 coils (early 2010), AUG 2 x 8 rows (2012)