DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2008 EXPERIMENTAL CAMPAIGN Login | Review | Submit | Logout | Help

Questions about this website? Contact Andrew LeBlanc
Questions about ROF? Contact Chuck Greenfield

Print this page
Title 68: Modulation of Bootstrap Current
Name:C. Craig Petty () Affiliation:General Atomics
Research Area:Heating & Current Drive Presentation time: Not requested
Co-Author(s): B. Hudson
Description: Directly measure the bootstrap current profile near the H-mode pedestal by modulating either (1) the edge ECH heating power, or (2) the I-coil current, and observing the oscillating MSE/LIB response.
Experimental Approach/Plan: (1) Establish QBD discharge using 210 beamline with good MSE and Lithium Beam diagnostics at relatively high field. (2) Aim ECH for power deposition near the top of the H-mode pedestal. Modulate all gyrotrons using several different frequencies (2-10 Hz). (3) Vary some parameter that should effect the magnitude if the bootstrap current (such as q95) and repeat. (4) Try modulating the H-mode pedestal pressure by modulating the I-coil current.
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. The best method of modulating the bootstrap current is to apply 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]. QBD plasmas make good target discharges since the modulation effects of the ELMs are not present and the discharges last a long time.
Resource Requirements: NBI: Co and counter MSE beams, and at least 2 more sources.
EC: Mimimum 5 gyrotrons.
Diagnostic Requirements: MSE is critical.
Analysis Requirements: --
Other Requirements: Modulated I-coil current.