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Flow perturbations & impact on ITB formation & sustainment

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

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Flow perturbations & impact on ITB formation & sustainment

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  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 Flow perturbations & impact on ITB formation & sustainment E.J. Synakowski PPPL Alcator C-Mod Ideas Forum December 2-3, 2004

  2. Idea: induce core flow perturbations in plasmas at formation and during sustained ITB phase by modifying the edge • Use a rapid (but small ~ 5 - 10 mm) change in X-point balance to induce a Vf 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? Vf radius

  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 Vf pulse Wukitch, 2002 PoP Velocity propagation assocatied with outward-to-inward barrier formation?

  4. Recall that TFTR ERS plasmas were keenly sensitive to changes in Vf 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 Vf perturbation on existing internal barriers as well as on formation conditions • Study an existing double barrer • USN with 4 MW or more • Induce a Vf 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 Vf perturbation and see if a core barrier can be triggered • If successful, reduce the applied power in steps

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