Measurement of LHCD edge power deposition through modulation techniques on Alcator C-Mod
Name
Den Whyte Faust - 21st RF Power in Plas Conf - AIP 2015.pdf
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Author(s)
Parker, R. R.
Chilenksi, M. A.
Faust, Ian Charles
Brunner, Daniel Frederic
Labombard, Brian
Baek, Seung Gyou
Edlund, Eric Matthias
Hubbard, Amanda E
Hughes Jr, Jerry
Terry, James L
Date Issued
December 2015
Journal
AIP Conference Proceedings
Publisher
American Institute of Physics (AIP)
Citation
Faust, I. C., D. Brunner, B. LaBombard, R. R. Parker, S. G. Baek, M. A. Chilenksi, E. Edlund, et al. “Measurement of LHCD Edge Power Deposition through Modulation Techniques on Alcator C-Mod.” AIP Conference Proceedings 1689, 080006 (2015).
Version
Final published version
Abstract
The efficiency of LHCD on Alcator C-Mod drops exponentially with line average density. At reactor relevant densities (> 1 · 1020 [m[-3 superscript]]) no measurable current is driven. While a number of causes have been suggested, no specific mechanism has been shown to be responsible for the loss of current drive at high density. Fast modulation of the LH power was used to isolate and quantify the LHCD deposition within the plasma. Measurements from these plasmas provide unique evidence for determining a root cause. Modulation of LH power in steady plasmas exhibited no correlated change in the core temperature. A correlated, prompt response in the edge suggests that the loss in efficiency is related to a edge absorption mechanism. This follows previous results which found the generation of n||-independent SOL currents. Multiple Langmuir probe array measurements of the conducted heat conclude that the lost power is deposited near the last closed flux surface. The heat flux induced by LH waves onto the outer divertor is calculated. Changes in the neutral pressure, ionization and hard X-ray emission at high density highlight the importance of the active divertor in the loss of efficiency. Results of this study implicate a mechanism which may occur over multiple passes, leading to power absorption near the LCFS.
MIT Department
Massachusetts Institute of Technology. Department of Mathematics
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
Massachusetts Institute of Technology. Department of Physics
Massachusetts Institute of Technology. Plasma Science and Fusion Center
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DOI of Published Version
https://doi.org/10.1063/1.4936529
