DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2013 EXPERIMENTAL CAMPAIGN Review | Direct submission with log-in | Request submission without log-in
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Title	334: Measurement of neoclassical response of off-axis beam ions
Name:	Jin Myung Park parkjm@fusion.gat.com	Affiliation:	Oak Ridge National Lab
Research Area:	Steady State Heating and Current Drive	Presentation time:	Not requested
Co-Author(s):		ITPA Joint Experiment :	No
Description:	Measure the local profile of electron shielding of beam ion current for comparison with theory. This is resubmission of 2012 proposal 105.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	(1) Primarily compare two discharges with different Zeff otherwise in similar condition. Reproduce 144265 (off-axis NBCD measurement shot with full power of off-axis beams at max tilt angle) Inject Ne to increase Zeff. Apply ECH for high Zeff case to match beam ion slowing down time. Repeat using on-axis beams (2) Modulate impurity injection (Ne, 10 Hz-10 msec injection). Find the electron shielding profile directly form the periodic response of the MSE signals to the modulation of Zeff created by pulsed impurity injections. We should be able to separate electron response even in the presence of change of beam ion slowing down time due to Zeff modulation (much longer time scale than electron response). (3) Repeat with ECH to increase/decrease Te to test collisionality dependancy of electron shielding
Background:	Measurement of the neoclassical electron response to beam ions is an important next step to complete a validation of the classical model against DIII-D experiments. Slowing down of fast ions by collisions with electrons causes toroidal drift of electrons, which cancels part of the fast ion current (electron shielding). The off-axis NBCD efficiency is as good as on-axis NBCD mainly because the increased fraction of trapped electrons reduces the electron shielding in outer radius region. Nonetheless, the precise profile of electron shielding has never been measured and benchmarked with the models, in particular, the analytic models implemented in NUBEAM. The electron shielding depends mainly on Zeff; JNBCD = Jf [1-(Zb/Zeff)(1-G)], where JNBCD = net NBCD current, Jf = fast ion current, Zb = charge number of beam ion, G = trapped electron correction that depends on Zeff and trapped electron fraction. In principle, the electron shielding profile can be determined by comparing two discharges with different Zeff or by the periodic response of the MSE signals to the modulation of Zeff.
Resource Requirements:	All neutral beam sources with 150 beams at maximum tilt angle. All available gyrotrons to make variation of discharge conditions.
Diagnostic Requirements:	MSE, Neutrons, FIDA spectrometers & cameras, Core spectrometer
Analysis Requirements:
Other Requirements: