PERSISTENT SURVEILLANCE FOR PIPELINE PROTECTION AND THREAT INTERDICTION International Plan for ELM Control Studies Presented by M.R. Wade (for A. Leonard) Presented at IEA Large Tokamak Meeting June 3, 2008

Status of ELM Control R&D Program R&D program has demonstrated in current devices: Complete ELM suppression at ITER collisionalities through enhanced pedestal transport by the application of Resonant Magnetic Perturbations Reduced ELM size and increased ELM frequency, by a factor of 2, through pellet injection triggering of ELMs. ELM-free H-mode operation (QH-mode) at ITER collisionality through the use of counter-plasma current neutral beam injection heating Greatly reduced ELM size (Grassy ELMs), > factor of 20, in low collisionality high poloidal beta regimes Numerous ELM control techniques (toroidal ripple, toroidal rotation, cyclic vertical displacement, edge localized heating and current drive) and small ELM regimes that hold promise (Type III ELMs, EDA, Type II and Type IV ELMs).

Strategy for ELM control plan development for ITER ITER will need ELM control as soon as H-mode is achieved. While there is reasonable confidence that ELM control techniques can be successfully applied to ITER, an understanding of the physics that governs these techniques and regimes remains incomplete. In view of these uncertainties, the strategy for ELM control in ITER has to be based in a portfolio of approaches, whose further development and detailed application to ITER requires an aggressive R&D programme

R&D plan seeks to develop improved physics basis of ELM control for use on ITER Address outstanding physics uncertainties through –Exploitation of the capabilities of the existing experiments –Execution of coordinated experiments to determine dimensionless or/and dimensional scaling laws describing the expected performance in ITER. Address the key compatibility issues of the ELM control techniques and/or small ELM regimes with other scenario requirements in ITER –Core plasma confinement and plasma density –Control of stationary heat loads, He exhaust, etc. Develop new strategies that can be implemented in ITER within its baseline design or minor modifications of it to be implemented at a later stage. Coordinated data analysis and modeling to develop a physics-based evaluation of the expected requirements and performance of the proposed ELM control methods in ITER and for the access to small ELM regimes, etc.

ELM Control via RMP Goal: Determine edge magnetic field perturbation and plasma conditions required for ELM control and integration with requirements for ITER high fusion gain scenarios Physics basis for ELM control by edge magnetic field perturbation –Dependence of enhanced pedestal transport and ELM control/suppression on edge plasma collisionality and/or plasma density –Plasma response to edge magnetic field perturbation : edge magnetic field screening, effect on plasma rotation/rotation shear, influence of pedestal and/or total plasma β –Influence of edge magnetic field spectrum on pedestal transport and ELM control/suppression : dependence on edge q, plasma shape, resonant versus non resonant spectra, etc. –Effect of edge magnetic perturbation on edge plasma stability

ELM Control via RMP (continued) Operational issues and integration with overall requirements for ITER high fusion gain scenarios –Effect on average pedestal pressure in H-modes with controlled/suppressed ELMs by edge magnetic perturbation –Compatibility of ELM-control/suppression with gas/pellet fuelling and (DT, He) exhaust requirements –Compatibility of ELM-control/suppression with a high density radiative divertor for stationary target plate heat flux control –Interaction of edge magnetic field perturbations with other detrimental MHD activity expected in ITER scenarios (NTMs, RWMs, locked modes, …) –Effect edge magnetic field perturbations on plasma rotation –Effect of edge magnetic field perturbations on H-mode plasmas with Pedge/PL-H < 2 –Application of ELM control by edge magnetic field perturbation to transient phases of the discharge such as H-mode current ramp up/down and H-mode phases in the current flat top before and after full performance phase

ELM Control via RMP (continued) Participating devices and timescales –JET (2008) –DIII-D ( ) –ASDEX-Upgrade ( ) –MAST ( ) –NSTX ( ) –TEXTOR ( ) –Alcator C-mod ( )

Pellet Pacing Program Plan Physics basis: –Determine physics processes leading to the triggering of ELMs by pellets in Type I H-mode plasmas –Plasma energy and particle transport during and following high- frequency pellet-triggered ELMs Operational and integration issues –Determine maximum ELM frequency enhancement (with respect to the natural ELM frequency) achievable while maintaining the Type I ELMy H- mode regime –Determine minimum pellet size and depth of penetration required to trigger an ELM –Evaluate effects on the average pedestal pressure in H-modes of control of ELMs by pellet injection –Compatibility of ELM control by pellet injection with gas/pellet fuelling and (DT, He) exhaust requirements –Compatibility of ELM control by pellet injection with maintaining a high density radiative divertor for stationary target plate heat flux control

ELM Control via Pellet Pacing (continued) Participating devices and timescales –JET (2008) –DIII-D ( ) –ASDEX-Upgrade ( ) –MAST ( )

Alternative H-mode regimes with small or no ELMs Determine physics processes responsible for edge harmonic oscillation (EHO) and resulting QH-mode (plasma rotation/rotational shear, fast ion loss, etc.) and implications for low collisionality/high density operation in ITER Analysis of the role of plasma edge stability (including plasma shaping and q95) and plasma conditions for the Grassy ELM regime and its extraplation to conditions required for advanced regimes in ITER Determine role of plasma edge stability (including shaping and q95) and edge plasma collisionality for high collisionality regimes with small or no ELMs ( Type IV, Type II, EDA, etc. ) and possible extension towards lower q95 and lower edge plasma collisionality conditions Characterize Type III ELMy H-mode regimes both in conditions of low and high collisionality (high density/high radiative fraction) and evaluation of the pedestal pressure degradation with respect to Type I ELMy H-mode. Evaluate plasma edge/core transport and overall confinement properties of the alternative ELM regimes considered for ITER

Alternative Small ELM Regimes (continued) Participating devices and timescales –JET (2008) –DIII-D ( ) –ASDEX-Upgrade ( ) –MAST ( ) –NSTX ( ) –Alcator C-mod ( ) –TCV ( )

Alternative ELM Control Techniques Determine effect of toroidal ripple on ELM losses and pedestal pressure and dependence on plasma density/collisionality Determine effect of plasma rotation magnitude/direction on ELM losses and pedestal pressure and their dependence on plasma density/collisionality Development of cyclic plasma displacement as a technique for ELM control within the technical limitations and scenario requirements for its application in ITER Demonstrate ELM control by stationary modification of the edge current distribution such as : edge plasma heating and current drive, modification of edge plasma distribution function leading to changes of the bootstrap current, etc., which can be achieved by external heating methods in ITER, such as ECRH Development of ELM control by pellet pacing with solid low-Z pellets to minimise plasma convective losses associated with ELM Evaluate of the effect of the ELM-control/suppression techniques developed on the overall plasma confinement properties

Alternative ELM Control Techniques (continued) Participating devices and timescales –JT-60U (2008) –JET (2008) –DIII-D ( ) –ASDEX-Upgrade ( ) –MAST ( ) –NSTX ( ) –Alcator C-mod ( ) –TCV ( )

Alternative Small ELM Regimes (continued) Participating devices and timescales –JET (2008) –DIII-D ( ) –ASDEX-Upgrade ( ) –MAST ( ) –NSTX ( ) –Alcator C-mod ( ) –TCV ( )