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Sawtooth Behavior Modification in Alcator C-Mod via Lower Hybrid Current Drive. P.T. Bonoli, E. Marmar, M. Porkolab, R. Granetz, A. Hubbard, Y. Lin, R. Parker, P. Phillips, J.R. Wilson, S.J. Wukitch. Alcator C-Mod Ideas Forum December 2-3, 2004. Motivation.
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Sawtooth Behavior Modification in Alcator C-Mod via Lower Hybrid Current Drive P.T. Bonoli, E. Marmar, M. Porkolab, R. Granetz, A. Hubbard, Y. Lin, R. Parker, P. Phillips, J.R. Wilson, S.J. Wukitch Alcator C-Mod Ideas Forum December 2-3, 2004
Motivation • Lower hybrid current drive (LHCD) system will be on-line in FY05: • Want to propose a series of experiments to qualitatively test J//(r) modification by LHCD. • Idea is to examine sawtooth behavior modifications induced with co- and counter- LHCD. • Possible benefit to plasma confinement if sawteeth can be stabilized in low density H-mode operation.
Physics of Sawtooth Behavior Modification via LH Current Profile Control • Counter - LHCD at 0 < r < rrinv : • Lower J//(r) locally with counter JLH (n// ≈ 2). • This raises q(r) > 1 and stabilizes sawteeth. • Co - LHCD at r rinv : • Broaden the profile of J//(r) with off-axis JLH (n// ≈ 3). • At fixed total Ip this lowers J//(r) in the core, thus raising q(r) > 1. • In both schemes check for either sawtooth stabilization or a change in the sawtooth period.
Outline for Experiment • Set up either a low density H-mode or L-mode plasma: • For both co - and counter - LHCD: • Scan n// from 2.0 - 3.0 • Scan ne • Scan PLH • Diagnostics required: • GPC for Te(r,t) • Thomsen scattering and VBE for density
