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	273: Sawtooth control via n=1 external magnetic perturbation
Name:	Piero Martin none	Affiliation:	ZZZ
Research Area:	Torkil Jensen Award	Presentation time:	Requested
Co-Author(s):	J. Bialek, D. Bonfiglio. A. Garofalo, G. Jackson, J. Hanson, M. J. Lanctot, E. Lazarus, G. A. Navratil, M. Okabayashi, C. Paz-Soldan, P.Piovesan, E. Strait, F. Turco, A. Turnbull	ITPA Joint Experiment :	No
Description:		ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Even if the original RFX experiment was made in a qedge<2 feedback stabilized regime, exploiting the residual amplitude of the unstable (2,1) mode as perturbation, this might not be the best approach to start with in DIII-D. L-mode The experiment will proceed according to the following steps. a) target plasma. q95<2 operation in DIII-D has in fact been obtained, but not yet in stationary conditions. A more robust target plasma is that developed in 2012 by Turco et al. for the q95<2 campaign, corresponding for example to #150578. These L-mode plasmas have q95=2.2 and are appear to be rather stable, with a nice flat-top. To this target plasma we plan to apply a controlled n=1 external magnetic perturbation and monitor the sawtooth behavior (amplitude and period). b) quick scan with perturbation ramp. Applying an n=1 perturbation ramp, which starts from zero, is a quick approach to check if the effect is present and, if yes, to isolate a range of perturbation amplitude that is effective and not degrade plasma performance. The relatively outer q=1 surface might facilitate the coupling of the external perturbation. c) flat-topped discharges with constant values of the perturbation. Once this is done and an effect similar to RFX is seen, one performs several discharges applying various levels of the perturbation amplitude to demonstrate that flat-topped plasma with very low or no sawtooth can be run in DIII-D. d) q95 scan. In the final step of the L-mode approach, the experiment is repeated using target plasmas with different (and increasing) values of q95, to check whether the process is reproducible as a function of q95. H-mode If the experiment is successful in L-mode, a second stage will aim at reproducing it in H-mode. a) target plasma. if possible, a target plasma with q95=2.2 similar to L-mode will be used. Otherwise higher q95 will be the starting point. b) quick scan with perturbation ramp. As in L-mode. c) flat-topped discharges with constant values of the perturbation. As in L-mode d) giant sawteeth regime. If previous steps are successful, a target plasma with ITER-like equilibria will be produced. Sawteeth of different period/amplitude will be produced controlling the current density profile via ECRH/ECCD, and we will check whether the method is applicable also in this case.
Background:	The experiments in RFX-mod, the simulations by Bonfiglio and Lazarus (see Sect. 4). This proposal is linked to proposal #56 "sawtooth control" submitted to the ROF 2013 by Lazarus et al and detailed in the miniproposal 2012-99-50
Resource Requirements:
Diagnostic Requirements:	Magnetics, MSE, CER, ECE radiometer, density interferometer, Thomson scattering SXR tomography.
Analysis Requirements:	Tomography reconstruction.
Other Requirements: