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	91: Complete the Development of PCS n=2 Error Field Control Algorithm
Name:	Matthew Lanctot matthew.lanctot@science.doe.gov	Affiliation:	Department of Energy
Research Area:	Stability & Disruption Avoidance	Presentation time:	Requested
Co-Author(s):	C. Paz-Soldan, J.M. Hanson, E.J. Strait, J. King, R.J. LaHaye, A.M. Garofalo, N. Ferraro, J.-K. Park, N. Logan	ITPA Joint Experiment :	No
Description:	Complete compass sweep experiments at two values of q95 in order to obtain the fit coefficients that will allow a PCS algorithm to be implemented. A PCS algorithm has been implemented and will be tested as part of this ½-day experiment. This will establish sufficient n=2 EFC for low beta operation. The experiment naturally incorporates a stringent test of plasma response and NTV theory.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Follows jist of MP 2012-83-09, approved but not given time in 2012) 1. Repeat compass scan at q95=3.4 with reference 149315, but at ne~0.75e13 cm-3 to increase the sensitivity of the plasma to locking, i.e. less n=2 current needed. 2. Perform compass scan also at q95=4.6 3. Compare low-density locked mode limit for both cases to no correction case At least 10 good ohmic shots
Background:	Results from 2012 error field control experiments using the compass sweep technique indicate there is a significant n=2 error field in DIII-D, consistent with in situ vacuum measurements from 2001 and 2003. The inferred control currents are ~50% of the standard n=1 control currents. Using the expected intrinsic error field from SURFMN, plasma response calculations with the IPEC code find that the n=2 pitch-resonant fields are ~5-10x smaller compared to n=1, which suggests the n=2 error field limits performance through non-resonant braking. This is consistent with the experimental observation that the application of a large n=2 I-coil field leads eventually to the onset of an n=1 locked mode. These conditions are ideal for understanding the relative importance of NTV torque in error field compensation metrics compared to kink-resonant and pitch-resonant harmonics.
Resource Requirements:	This low power ohmic experiment does not require auxiliary heating of any kind. We also operate at reduced toroidal field and plasma current. However, it requires all available 3D coil power supplies (4 SPAs and 2 C Supplies) in order to power 6 independent I-coil circuits.
Diagnostic Requirements:	Essential diagnostics are magnetics & CO2 and 288 GHz interferometers
Analysis Requirements:	Standard analysis of compass sweep results. Results Comparisons with plasma response codes: IPEC and M3D-C1
Other Requirements: