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Title	74: Optimize TBM error field correction against field penetration in low NBI torque H-modes
Name:	Holger Reimerdes reimerdes@fusion.gat.com	Affiliation:	CRPP-EPFL
Research Area:	Stability & Disruption Avoidance	Presentation time:	Requested
Co-Author(s):	J. Hanson, R. La Haye, M. Lanctot, N. Oyama, C. Paz-Soldan, J. Snipes	ITPA Joint Experiment :	No
Description:	This experiment seeks to evaluate the potential of low n external fields to ameliorate TBM effects in ITER relevant slowly rotating H-modes, where error fields can limit operation either by causing field penetration or triggering an NTM. This is achieved by optimization EFC currents by maximizing the n=1 error field tolerance and/or minimizing the NBI torque required for stable operation. Low density locked mode experiments suggest that n=1 correction alone could be sufficient to restore the resilience against field penetration, which would be a favourable result for ITER.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	One possible approach is a measurement of the tolerance to an n=1 proxy error in compass scans. Comparing origin and radii of the circles of maximum tolerable proxy field in discharges with and without TBM field yield correction currents and quantifies the detrimental effect of the TBM using optimized EFC currents. Another approach is based on measuring the minimum tolerable NBI torque for various correction currents. This approach requires more discharge since each discharge only yields a measurement for one n=1 I-coil current. The approaches are complementary.
Background:	The limited effectiveness of n=1 EFC in ameliorating the TBM induced rotation decrease in rotating H-modes [H. Reimerdes, et al., IAEA 2012] contrasts its ability to fully recover a low locking density in L-modes [M.J. Schaffer, et al., Nucl. Fusion 51 (2011) 103028]. This suggests that the components of the external field that cause braking at higher beta and higher rotation (presumably through non-resonant braking) differ from the components that cause field penetration (presumably through resonant braking). If rotation is key to the successful recovery of the locking density, EFC should also be more effective in ITER relevant slowly rotating H-modes.
Resource Requirements:	- TBM mock-up coil - 5 co-NBI, 2 ctr-NBI
Diagnostic Requirements:
Analysis Requirements:
Other Requirements: