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	11: Investigate in-out density asymmetry at large toroidal rotation
Name:	Keith Burrell Burrell@fusion.gat.com	Affiliation:	General Atomics
Research Area:	Plasma Rotation	Presentation time:	Not requested
Co-Author(s):	C. Chrystal	ITPA Joint Experiment :	No
Description:	The goal of this work is to measure the in-out density variation of various impurities on a flux surface and, from that, to infer the poloidal variation of the electrostatic potential.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Run a plasma which is capable of operating at both low and high rotation speeds and which runs at relatively low density. For example, QH-mode in the ITER shape with the nonresonant magnetic fields would be a good candidate, since it has run at both low and high rotation. Do a rotation scan and use the CER system to investigate the in-out asymmetry in the carbon density. If possible, keep the density profile the same during the rotation scan. Use the low rotation points to cross calibrate the CER chords inside and outside the magnetic axis, since carbon density is expected to be a flux function at zero rotation. Make measurements also with helium and argon since the in-out variation is expected to change strongly with charge. The potential variation determined with all three impurities should be the same for constant plasma conditions; use this as a cross check. To insure that the plasma is the same for all impurity measurements, inject He and Ar on all shots so that plasma composition does not change.
Background:	Lowest order parallel force balance in a rapidly rotating tokamak plasma leads to the prediction that the ion and electron density is not constant on a flux surface because of centrifugal effects. The rapid plasma rotation causes the ions to bunch up on the large major radius side of a flux surface. A poloidal electric field develops to insure charge neutrality. The ultimate poloidal variation of the densities of the various species is due to a balance of the electric field and centrifugal forces. For the 2011 campaign, the CER system was expanded to include measurements both inside and outside the magnetic axis. Using this, we can measure the in-out asymmetry in the carbon density and, from that, infer the poloidal variation of the electrostatic potential. Low density plasmas are preferred for this work both because the neutral beams penetrate better to the high field side of the plasma and because the rotation speeds of low density plasmas are higher. Proper beam modulation is essential to insure good signal from the chords at small major radius because the chords which view the 30 beam at small major radius pass through the 330 beam in the plasma edge.
Resource Requirements:	Reverse Ip for QH-mode. Proper beam modulation to get best CER measurements inside magnetic axis.
Diagnostic Requirements:	All CER chords including those viewing points inside magnetic axis. All profile diagnostics
Analysis Requirements:
Other Requirements: