Mitigation of radio frequency sheaths through magnetic field-aligned ICRF antenna design |
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Authors: | ML Garrett SJ Wukitch |
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Affiliation: | Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA, USA |
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Abstract: | One of the primary challenges of auxiliary heating of tokamaks in the ion cyclotron range of frequencies (ICRF) is the reduction of impurities associated with ICRF operation. On Alcator C-Mod, a new magnetic field-aligned antenna was optimized for magnetic flux coupling, power handling, and minimized integrated parallel electric field (E∥). Initial simulations performed using both slab and cylindrical geometry suggested nearly complete cancellation of E∥ in front of the antenna structure for certain toroidal phasings. Using toroidal models, the cancellation of E∥ is more modest, suggesting 3-D geometrical effects are important. Using finite element method simulations with a 3-D toroidal cold plasma model, multiple antenna phases were analyzed: 0, π, 0, π], 0, 0, π, π], 0, π, π, 0], 0, 0, 0, 0], 0, π/6, 0, π/6], and 0, π/2, π, 3π/2]. In each case, the field-aligned antenna had reduced integrated E∥ relative to the existing non-aligned antenna geometry, with the greatest reduction for monopole 0, 0, 0, 0] phasing. |
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