1 Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics NYU ORNL PPPL PSI SNL UC Davis UC Irvine UCLA UCSD U Maryland U New Mexico U Rochester U Washington U Wisconsin Culham Sci Ctr Hiroshima U HIST Kyushu Tokai U Niigata U Tsukuba U U Tokyo Ioffe Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching U Quebec E.J. Synakowski PPPL Alcator C-Mod Ideas Forum December 2-3, 2004 Flow perturbations & impact on ITB formation & sustainment

2 Use a rapid (but small ~ mm) change in X-point balance to induce a V  pulse from the edge into the core. Presumably, a perturbed velocity shear pulse will move inward, yielding a radially propagating ExB shear layer Questions: –What is impact on an established core barrier in stationary state? –What is impact on formation conditions? Idea: induce core flow perturbations in plasmas at formation and during sustained ITB phase by modifying the edge radius VV

3 The observation that edge rotation may drive core flows may give C-Mod a control knob on core ExB shear If ExB shear is playing a role in barrier formation and dynamics, modifying the edge rotation may allow the barrier width, position, or existence to be modifed Also, expore if the power requirement for barrier formation can be reduced or increased in the presence of a V  pulse Velocity propagation assocatied with outward- to-inward barrier formation? Wukitch, 2002 PoP

4 Recall that TFTR ERS plasmas were keenly sensitive to changes in V  and its shear Illustrated that control of some ITBs is possible, in principle, if a control knob on flow shear is available Demonstrating the control/modification of an ICRF ITB with edge variations might have deep implications

5 Proposed: document the effect of a V  perturbation on existing internal barriers as well as on formation conditions Study an existing double barrer –USN with 4 MW or more –Induce a V  pulse with a prompt change from USN to LSN, hopefully maintaining the edge barrie characte (include ELMing nature). Monitor core response, if any. Wiggle of core P gradient? Collapse? Expansion? Nothing? –At the least: should obtain a measure of differences in momentum transport in plasmas with and without ITBs. Study ITB formation conditions with a target plasma w/out a core barrier, in USN and near the core ITB power threshold –Induce a core V  perturbation and see if a core barrier can be triggered –If successful, reduce the applied power in steps