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Title	93: Active Control of the EHO in Quiescent H-modes
Name:	Matthew Lanctot matthew.lanctot@science.doe.gov	Affiliation:	Department of Energy
Research Area:	Plasma Control	Presentation time:	Requested
Co-Author(s):	H. Reimerdes, K.H. Burrell, A.M. Garofalo, J.M. Hanson, P.B. Snyder, W.M. Solomon, B. Tobias, L. Yu	ITPA Joint Experiment :	No
Description:	This experiment will test the feasibility of actively driving the edge harmonic oscillation, which is the essential feature of the Quiescent High confinement mode regime. The EHO is a naturally occurring edge-localized mode in the 5-10 kHz range that enhances particle transport without degrading the thermal transport barrier. This continuous mode provides density control with H-mode confinement without the deleterious effects of edge-localized modes. The prevailing theory of the EHO posits that it is a saturated kink-peeling mode driven by shear in the edge rotation. This rotation shear requirement limits the QH-mode operating space, which might be extended if external control of the EHO is possible. In this initial experiment, we will attempt to couple to a pre-existing saturated EHO using externally applied fields. We will also attempt to drive the mode at the boundary of the operating regime. Following such a demonstration, future experiments will focus on expanding the QH-mode operating regime and probing the stability of the EHO.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	This plan for a Thursday evening experiment requires access to QH-mode. Therefore, it should be conducted following a full-day experiment that will operate in the QH-mode regime. Shot 1. Reproduce a counter-rotating QH-mode. Use magnetics, BES, and ECEI to measure natural EHO amplitude and frequency. In the second half of the QH-mode phase, slowly decrease the neutral beam power to find the threshold where the ELMs return (expect ~ 3MW). Note changes in EHO structure and frequency during power scan, if any. Shot 2. This shot has two phases: one with sufficient beam power to access QH-mode, and the other with the NBI power epsilon-smaller than the threshold found in shot 1. Throughout the shot, apply a magnetic perturbation with the I-coil at the EHO frequency. Measure I-coil induced changes in the EHO amplitude during QH-mode phase. Look for any I-coil enhanced D-alpha emission. Observe if EHO is driven to finite amplitude and ELMs avoided when beam power is below the threshold for QH-mode. Shot 2a. If there is evidence for active control of the EHO, repeat shot 2 with half the I-coil current. Note change in driven EHO amplitude, if any. Shot 2b. If there is evidence for active control of the EHO, repeat shot 2 with a smaller outer gap during the second phase to vary the plasma-coil distance. Shot 2c. If there is evidence for active control of the EHO, repeat shot 2 with a programmed triangle waveform in the I-coil frequency during the second phase. Shot 3. Reproduce a counter-rotating QH-mode. In the second half of the QH-mode phase, puff gas to raise the density until ELMs return. Shot 4. Repeat shot 3 with I-coil field. Observe if EHO is driven to finite amplitude and ELMs avoided when the density exceeds the threshold identified in shot 3. Shot 4b. If there is evidence for active control of the EHO, repeat shot 4 with even higher density.
Background:	The EHO is a key feature of the QH-mode. It provides the sufficient particle transport to allow the plasma to reach a transport steady state at edge parameters below the explosive ELM limit. Previous experiments have demonstrated that external fields can influence the toroidal mode number of the EHO using odd parity n=3 NRMF. One of the most fascinating observations is the switch of the EHO from n=1 to n=3 when odd parity NRMF is applied. This is evidence that external fields can interact with the EHO, although this interaction may be indirect, i.e. via changes in the kinetic profiles. Examples of direct interaction between magnetic fields and other MHD modes are well documented. For example, internal saddle coils have been used on JET to drive global Alfven waves in the range from 30-70 kHz, and on DIII-D to drive marginally stable RWMs in the range from -40 to +60 Hz (the sign denotes the direction w.r.t. the plasma rotation). If the EHO is indeed a kink-peeling mode, then, in principle, it should be possible to drive this MHD mode to finite amplitude when it is close to marginal stability provided there is sufficient coupling between the I-coil field and the stable EHO.
Resource Requirements:	I-coils with audio-amplifiers, preferably with two parallel amplifiers powering pairs of I-coils. Because of this special I-coil patch panel, this experiment is unlikely to be done during a dedicated QH-mode experiment.
Diagnostic Requirements:	3D magnetics, BES, and other diagnostic for kinetic equilibrium reconstructions
Analysis Requirements:	--
Other Requirements:	--