PEP ITPA Working Group on RMP ELM Control: 1 st Status Report on Work Plan Progress

1. PEP ITPA Working Group on RMP ELM Control: 1st Status Report on Work Plan Progress 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) Conference Call by H.323 Remote ParticipationMarch 19, 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. 1.1 Reproduce RMP ELM suppression on at least one tokamak other than DIII-D - MAST and AUG Internal Off-Midplane Coils • Initial attempts on MAST have not shown ELM suppression yet • Five different shapes - 4 near DN • Pumpout and turbulence change with RMP in L-mode (with even parity resonant) • ELMs change in H-mode with one beam - compound ELMs and dithering • No effect with 2 beams even for overlap width comparable to DIII-D ELM suppression • Future plans include shape variation, beam power variation • High bN at lower Ip plus 2 beams • Key issues may be geometric coupling to coils (shape), plasma beta and pitch alignment of RMP

6. 1.1 Reproduce RMP ELM suppression on at least one tokamak other than DIII-D - MAST and AUG Internal Off-Midplane Coils • AUG off-midplane internal coils project continues to make progress • Preferential support from Brussels granted July 2008 • Call for tender completed by Jan 2009 • Contract in place to build upper and lower rows with initially 4 coils each • Projected installation in Summer-Fall 2010 including DC P/S • Plasma operations with 2 x 4 RMP coils to begin earliest Sept 2010 or Jan-Feb 2011 • Allows both odd and even parity n=2 RMP • Remaining 2 x 4 off-midplane coils installed mid to late 2011 • 8 in-vessel midplane coils installed 2011-12 with up to 3 kHz AC capability

7. 1.1 Reproduce RMP ELM suppression on at least one tokamak other than DIII-D - JET and NSTX External Midplane Coils • Experiments at JET and NSTX with external, midplane EFCC have not shown ELM suppression • JET - No ELM suppression (n=1 or 2 on midplane ) with maximized chir>1 = 0.915 (high collisionality) • Compensation of ne pumpout by gas • ELM mitigation tested with toroidal field ripple • Multiple resonances in ELM freq for n=1 and n=2 • Strong rotation braking • Compound to Type-I ELM transition with n=1 • Future plans must be completed in C27 before ILW • Higher coil current and longer pulse length from new PS allows tests of RMP effects: (1) Before vs after 1st ELM, (2) on L-H transition, (3) Try complete suppression with n=2, (4) stationary ELM control, (5) q95 resonances • NSTX - Several days in 2008 with n=3 on midplane showed ELM stability modified (ELMs larger) but no suppression • Magnetic ELM pacing with 8-10 ms square wave n=3 pulses in Li-enhanced ELM-free H-modes - 75% effectiveness • Controls density build-up and radiated power

8. 1.2 Identify the criteria for ELM suppression from experimental data and theoretical models • (Very) Recent DIII-D experiments support resonance of ELM suppression with pitch alignment of RMP fields • ELM suppression windows in q95 obtained with ramps of Ip up, Ip down, and BT down • NSTX - Several days in 2008 with n=3 on midplane showed ELM stability modified (ELMs larger) but no suppression • IPEC showed n=2+3 best overlap, but no suppression for q95>=7 • 2009 run day at q95 < 6 with n=2+3 will attempt suppression • Convective cell hypothesis for edge island particle transport explored • Reciprocating probes through islands in TEXTOR and DIII-D • Collisionality dependence of ELM suppression and density pumpout last week on DIII-D • MAST experiments with island overlap width similar to DIII-D do not yet show ELM suppression • Splitting of particle flux (D emission) at SP • Vacuum-like in DIII-D and TEXTOR • Not observed in JET, MAST, NSTX (?)

9. 1.2 Identify the criteria for ELM suppression from experimental data and theoretical models • Estimates using vacuum field line dispersion • Heat transport larger than experiment - no splitting measured • Particle flux smaller than measured • Changes in density during RMP in TEXTOR He plasmas not determined by wall sources - particle balance analysis suggests transport effects • Pump-out and strong gas consumption in TEXTOR He RMP plasmas • Beta (power) threshold - Empirical evidence • Dependence on shape (triangularity, squareness) - Empirical evidence • Ratio of resonant to non-resonant spectra - nothing new to report • Dependence on rotation (screening or amplification) - nothing new to report

10. 1.2 Identify the criteria for ELM suppression from experimental data and theoretical models • Neutral and plasma Monte-Carlo fluid - useful to scale transport physics based on vacuum picture from DIII-D to ITER • Adapted to poloidal divertor geometry and numerically validated • L-mode plasma validation very satisfactory at TEXTOR • L-mode and H--mode validation ongoing for DIII-D LSN plasmas • Linear MHD stability: • Beta (power, Shafranov shift) threshold effects, Shape (d, squareness) • Non-linear MHD with rotation: • Screening of RMPs by toroidal or poloidal rotation • Challenge: realistic collisionality • Turbulence codes with RMPs • Drift fluid with self-consistent evolving equilibrium • Blobby transport and Resistive Ballooning turbulence • Challenges: non-circular cross section, rotation effects, diamagnetic effects, H-mode transition • Kinetic modeling • Reproduces density transport • Uses ad-hoc screening factor due to rotation

11. 1.3 Quantify the impact of ELM suppression by RMPs on the pedestal pressure and core confinement and develop/validate theoretical models • Comparison of pedestal height and width on DIII-D, MAST and NSTX both with and without RMPs • starting • Comparison of measured pedestal height during RMP with EPED1 predictions • will start in the next few weeks • Demonstrate ability (or not) to maintain edge density during ELM suppression • Some data from DIII-D experiments in April focused on collisionality (density) dependence of RMP ELM suppression • Quantify impact of RMP on core transport and H-factor • Nothing new to report

12. 1.4 Quantify the power loading on the wall and divertor with RMP-suppressed ELMs; make recommendations on any requirement for rotating RMPs • Quantify impact of RMP-suppressed ELM regimes on divertor power loading • Jakubowski NF paper from IAEA08 • Good data from fast IRTV in recent DIII-D experiments - analysis in progress • MAST IRTV shows effect of coil (splitting ?? - resolution limited) in L-mode with pumpout, no effect yet in H-mode • Make recommendations on need to rotate RMPs • Loarte estimates of 4 Hz requirements for ITER • Explore impact of rotation of RMPs on ELM suppresion • Waiting for DIII-D CP coils, MAST rotating RMP expts (if 6 more coils installed in one row), AUG rotatable RMPs in future

13. 1.5 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) • Quantify the ability to suppress or mitigate ELMs with RMP in current ramp • Nothing to report • Possible experiments in DIII-D for 2010 • Quantify ability to suppress or mitigate ELMs close to L-H transition • Experiments proposed in JET for C27 campaign • Possible experiments in DIII-D for 2010

14. Other Work Plan Elements • 1.6 Demonstrate ELM control with ITER-like pellet fuelling • DIII-D experiments in April focus on collisionality (density) dependence of RMP ELM suppression - used HFS pellet fuelling • JET pellet fueling for compensation of density pumpout during ELM mitigation • 1.7 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) ] • Major review (8 hours) of internal ITER coil set held April 3

15. 1st Inter-ITPA Meeting of RMP ELM Control WG Included Discussion of Work Plan Modifications and Assumptions • Proposals to Modify RMP ELM Control Work Plan • In Section 1.2 Criteria for ELM Suppression add: • Evaluate the dependence of ELM suppression on shape differences (eg. low vs. high , squareness variation) • Evaluate dependence of ELM suppression on  (power) • Evaluate the dependence on toroidal field at fixed q95 • Evaluate whether ideal perturbed equilibria MHD codes are sufficient to explain ELM suppression • Comments on Assumptions Used to Develop Work Plan • DIII-D: not enough machine time and manpower to meet work plan schedule • ITER IO: Sept 2010 target date likely will be delayed • ITER IO: Specification of coil time response (turn-on and frequency) requirements needed soon - mostly P/S issue but some impact on coil design • JET: concern that coil current requirements based on DIII-D experiments with single spectrum in n=3

16. 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)

17. 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.