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Title	291: Trigger-less onset of NTMs with P_EC and NTV effects on rotation regime
Name:	Filomena Nave mfn@ipfn.ist.utl.pt	Affiliation:	Instituto Superior Tecnico, Lisboa, Portugal
Research Area:	Stability & Disruption Avoidance	Presentation time:	Not requested
Co-Author(s):	E.Lazzaro,O.Sauter, S.Nowak, M.F. Nave et al.	ITPA Joint Experiment :	No
Description:	Test that modified rotationat rational surfaces in the regime predicted by the latest version of the theory [CONNOR, J.W. WAELBROECK F. L. and WILSON, H. R. Phys. Plasmas 8 (2001) 2835], causes NTMs even in the absence of triggers. This would be the first genuinely trigger-less mechanism for NTM onset and has an obvious relevance to ITER. Experiments on TCV show that NTMs can occur without seed island formation, in regimes of non-steady rotation caused by ECH near central power absorption and non-steady pressure and current density profiles [E. Lazzaro, S. Nowak, O. Sauter et al,Proc. FEC-IAEA 2012 , paper EX/P4-32]. The onset of the NTM is also apparently consistent and concomitant with the instability condition associated with the ion polarisation current (IPC). The growing tearing modes contribute a nonlinear magnetic braking that consistently modifies the rotation profile. This would be the first genuinely trigger-less mechanism for NTM onset and has an obvious relevance to ITER.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Prepare a sawtooth-free target marginally stable (i.e., with beta slightly below critical) against 2/1 and 3/2 NTMs. Use n=3 RMPs to suppress ELMs, if necessary. Also make sure that fishbones or other NTM triggers are absent. Ramp down the toroidal rotation by means of balanced injection or magnetic braking. If successful, repeat with reverse Bt (but normal Ip), which would decouple the toroidal and poloidal rotation effects. As recently observed on TCV (Lausanne) injection of P_EC upstream of the q=3/2 surface, may both drive a 3/2 mode and a strong effect on plasma rotation. Even in absence of triggers subsequently a 2/1 NTM can appear, associated with local flattening of the rotation shear, and modification of 2/1 rotation that enters the IPC unstable regime. [LA HAYE R. J., PETTY., C. C., STRAIT E. J., WAELBROECK F. L., AND WILSON H. R., Phys. Plasmas 10 (2003) 3644] Therefore it is proposed to test: a)A direct effect of P_EC (~ P_Ohm) on (N)TM stability through modification of J profile (upstream of q=m/n) (1 good shot with ECH , 1 good shot with ECCD) b)An indirect effect of P-EC on (N)TM stability through direct effect on rotation. A simple theory involving mode rotation in the presence of NTV effects (due to the static applied RMP and the TM modes themselves) will help designing the magnetic braking aspects of the experiment. Note that braking could be in place anyway, if RMPs will be used for ELM control.
Background:	The transverse ion polarization current (IPC) can be stabilizing or destabilizing for NTMs, depending whether the rotation is faster or slower than a reference "natural' value of the order of the ion diamagnetic drift frequency [E. Lazzaro, Proc.36th EPS Conference, Sofia (Bulgaria) 2009, paper P1.125]. Thus,varying the rotation of a q=m/n surface around that value can cause NTM onset even in absence of triggers (sawteeth, ELMs , fishbones...).
Resource Requirements:	In case of success of the first day or half day, possibility of a second day or half day with reverse Bt or Ip.
Diagnostic Requirements:	Magnetics, MSE(optional), ECE (both radiometer and Michelson), TS, Interferometer, CER.
Analysis Requirements:	EFIT, Tearing mode stability codes, optional reconstruction of NBI beam momentum deposition (TRANSP?), CXSR measurement of rotation.
Other Requirements:	--