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Title	29: Modulation of Bootstrap Current
Name:	Clinton (Craig) Petty petty@fusion.gat.com	Affiliation:	General Atomics
Research Area:	ELM Control	Presentation time:	Not requested
Co-Author(s):	D. Thomas, H. Stoschus	ITPA Joint Experiment :	No
Description:	Directly measure the bootstrap current profile near the H-mode pedestal by modulating the pedestal gradient using an oscillating I-coil current and measuring the oscillating MSE/LIB response. Ideally this should be done in an ELM-suppressed discharge, but ELMs will be tolerated if they cannot be avoided. It would be useful to make a fiducial comparison by modulating the edge ECH power in place of modulating the I-coil current.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	(1) Establish RMP ELM-suppressed discharge with q_95=3.5 with good MSE and Lithium Beam diagnostic coverage at relatively high field. (2) Modulate the I-coil current at 5-20 Hz to vary the pedestal gradients. Make the modulation depth as large as possible without having ELMs return. (3) Make the I-coil modulation depth 100% even if ELMs return. (4) Repeat previous step with q_95 out of the ELM suppression window. Changing q_95 should vary the bootstrap current. (5) Aim ECH for power deposition near the top of the H-mode pedestal. Modulate all gyrotrons using several different frequencies (5-20 Hz).
Background:	The bootstrap current profile near the H-mode pedestal strongly effects the plasma stability. If the bootstrap current density can be modulated, then the flux surface average value of the oscillating component can be determined by Fourier analyzing the pitch angles measured by MSE/LIB via the poloidal flux diffusion equation. This can be exploited to determine if the modifications in the pedestal gradients caused by the RMP really result in a change in the edge pressure-driven currents. The best method of modulating the bootstrap current is therefore to modulate the I-coil current. To check the method, it would be good to obtain a fiducial by applying modulated ECH near the H-mode pedestal [core ECH is not as desirable owing to (a) pulse pile up and (b) electron-ion collisional exchange].
Resource Requirements:	NBI: Co and counter MSE beams, and at least 2 more sources. EC: 6 gyrotrons.
Diagnostic Requirements:	MSE and Li Beam are critical.
Analysis Requirements:
Other Requirements: