DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2013 EXPERIMENTAL CAMPAIGN Review | Direct submission with log-in | Request submission without log-in
Print this page

Print this page
Title	143: RMP ELM control at low torque
Name:	Richard Moyer moyer@fusion.gat.com	Affiliation:	University of California, San Diego
Research Area:	ELM Control	Presentation time:	Requested
Co-Author(s):	--	ITPA Joint Experiment :	No
Description:	The "worst case" scenario for ITER is that, due to limited torque input, the H-modes will be low torque and low rotation. Recent experimental and 2-fluid modeling work suggests that rotation - specifically, the electron perpendicular rotation = sum of the E x B and electron diamagnetic velocities-plays an important role in determining the plasma response to RMPs. The goal of this experiment is to explore the physics of plasma response to RMPs and the viability of ELM control for ITER-relevant H-modes with balanced torque and low toroidal rotation (limited to the intrinsic rotation level). Demonstration of RMP ELM control or suppression at low tourque would radially enhance the reliability of RMP ELM suppression in ITER. Even if ELM suppression isn't achieved, we will gain substantial information on plasma response and rotational screening in these low torque ELMing H-modes. A side benefit of this experiment will be the development of a high performance, low torque ELMing H-mode target plasma for a variety of ITER-relevant physics studies. If rotational screening models are correct, we should be able to access an ELM suppressed or mitigated regime in ELMing H-modes with low net toroidal rotation (auxiliary heating from balanced NBI plus ECH) using very little I-coil current, possibly only a few hundred amps. This would open a new field of active pedestal control by allowing the use of higher frequency (modulated and/or feedback controlled) RMPs, a first step toward integration of RMP ELM control with other modes of operation, including radiation-enhanced divertor operation, pellet fueling or a hybrid RMP-assisted pellet pacing.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Establish a low net torque/near balanced NBI ELMing H-mode in ISS shape. This will establish a target ELMing H-mode with a zero crossing in the perpendicular velocity (unlike last year's counter NBI cases) but deeper in the core than desired for ELM suppression based on emerging understanding. Apply an n = 3 even parity RMP; this should induce stochasticity in the boundary (foot of the pedestal), and the subsequent radial ion current to maintain ambipolarity with increase the toroidal rotation and move the zero-crossing in the electron perpendicular velocity out toward the top of the pedestal. We will need to use the best error field correction and ECCD to control locking of MHD modes in the core to widen the operating window away from mode locking for this experiment (both techniques were routinely applied in the CY12 campaign. Scan the I-coil current for both phases (0° and 60°) and for both parities (even and odd) to vary the level of resonant vs. non-resonant perturbation applied and it's alignment to the intrinsic error fields. Document plasma response using new magnetics, transport and turbulence changes (especially intermittent transport) and stability.
Background:	Previous atempts have always approached RMP ELM suppression at low torque/low toroidal rotation by starting first with a highly co-rotating ELMing H-mode. Once even a small aount of counter-NBI is applied, the rotation drops until it bifurcates to a locked state starting with at the q = 2 surface. In essence, we keep trying to run these discharges in a controlled manner through the "prohibited" part of the rotation/locking bifurcation curve. It is ill-posed to attempt to "catch and hold" the discharge at the reduced rotation state due to the hard nature of the bifurcaton to locked rotation at the q = 2 surface. In this experiment, we propose to avoid passing through the bifurcation point by starting from a low rotation ELMing H-mode and applying the RMP. We already have a proof-of-principle of ELM control at near zero net toroidal rotation at moderate collisionality in the ITER shape using odd parity (for a lower level of resonant perturbation). This scenario provided an ITER-relevant level of ELM mitigation (replacing ELMs with increased intermittent transport) with little or no pedestal height/width reduction.
Resource Requirements:	Both 210 NBs for counter injection; 30L and 330R beam for balanced torque input. ECCD for control of core MHD modes (NTMs). Additional ECH heating to raise betan.
Diagnostic Requirements:	Ion (CER) and electron profile (ECE, Thomson, reflectometer) diagnostics; Fluctuation diagnostics: swap in 150R for 330R for BES; DBS; FIR, PCI, reciprocating probes. New magnetics SPAs for error field control and n = 3 RMP
Analysis Requirements:	Significant profile analysis, kinetic EFITs, and stability analysis (ELITE); plasma response analysis and comparison to models (M3D-C1; NIMROD,M3D, MARS-F, XGC0) Turbulence and transport analysis
Other Requirements:	--