Measurements of the parallel wavenumber of lower hybrid waves in the scrape-off layer of a high-density tokamak

Baek, S. G.; Wallace, G. M.; Shinya, T.; Parker, R. R.; Shiraiwa, S.; Bonoli, P. T.; Brunner, D.; Faust, I.; LaBombard, B. L.; Takase, Y.; Wukitch, S.

doi:10.1063/1.4948555

Title: Measurements of the parallel wavenumber of lower hybrid waves in the scrape-off layer of a high-density tokamak

Journal Article · Fri May 06 00:00:00 EDT 2016 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4948555· OSTI ID:1471068

Baek, S. G. ^[1]; Wallace, G. M. ^[1]; Shinya, T. ^[2]; Parker, R. R. ^[1]; Shiraiwa, S. ^[1]; Bonoli, P. T. ^[1]; Brunner, D. ^[1]; Faust, I. ^[1]; LaBombard, B. L. ^[1]; Takase, Y. ^[2]; Wukitch, S. ^[1]

Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). MIT Plasma Science and Fusion Center
Univ. of Tokyo (Japan)

In lower hybrid current drive (LHCD) experiments on tokamaks, the parallel wavenumber of lower hybrid waves is an important physics parameter that governs the wave propagation and absorption physics. However, this parameter has not been experimentally well-characterized in the presentday high density tokamaks, despite the advances in the wave physics modeling. Here in this article, we present the first measurement of the dominant parallel wavenumber of lower hybrid waves in the scrape-off layer (SOL) of the Alcator C-Mod tokamak with an array of magnetic loop probes. The electric field strength measured with the probe in typical C-Mod plasmas is about one-fifth of that of the electric field at the mouth of the grill antenna. The amplitude and phase responses of the measured signals on the applied power spectrum are consistent with the expected wave energy propagation. At higher density, the observed k_II increases for the fixed launched k_II, and the wave amplitude decreases rapidly. This decrease is correlated with the loss of LHCD efficiency at high density, suggesting the presence of loss mechanisms. Evidence of the spectral broadening mechanisms is observed in the frequency spectra. However, no clear modifications in the dominant k_II are observed in the spectrally broadened wave components, as compared to the measured k_II at the applied frequency. It could be due to (1) the probe being in the SOL and (2) the limited k_II resolution of the diagnostic. Future experiments are planned to investigate the roles of the observed spectral broadening mechanisms on the LH density limit problem in the strong single pass damping regime.

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Research Organization:: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

Sponsoring Organization:: USDOE

Grant/Contract Number:: FC02-99ER54512

OSTI ID:: 1471068

Alternate ID(s):: OSTI ID: 1251642

Journal Information:: Physics of Plasmas, Vol. 23, Issue 5; ISSN 1070-664X

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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Cited by: 5 works

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References (22)

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Modified propagation path and expanded coupling regime of lower hybrid fast wave by n ∥-upshift via wave scattering in VEST Jo, JongGab; Wang, J.; Kim, S. C. Physics of Plasmas, Vol. 26, Issue 1 https://doi.org/10.1063/1.5055294	journal	January 2019
Experimental investigation on spectral broadening of lower hybrid waves with different frequencies in the EAST long-pulse plasmas Li, M. H.; Ding, B. J.; Liu, F. K. Plasma Physics and Controlled Fusion, Vol. 61, Issue 6 https://doi.org/10.1088/1361-6587/aaf9da	journal	April 2019
Review of recent experimental and modeling advances in the understanding of lower hybrid current drive in ITER-relevant regimes Ding, B. J.; Bonoli, P. T.; Tuccillo, A. Nuclear Fusion, Vol. 58, Issue 9 https://doi.org/10.1088/1741-4326/aad0aa	journal	July 2018

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