Lower hybrid wave edge power loss quantification on the Alcator C-Mod tokamak

Faust, I. C.; Brunner, D.; LaBombard, B.; Parker, R. R.; Terry, J. L.; Whyte, D. G.; Baek, S. G.; Edlund, E.; Hubbard, A. E.; Hughes, J. W.; Kuang, A. Q.; Reinke, M. L.; Shiraiwa, S.; Wallace, G. M.; Walk, J. R.

doi:10.1063/1.4951736

Lower hybrid wave edge power loss quantification on the Alcator C-Mod tokamak

Journal Article · Fri May 20 00:00:00 EDT 2016 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4951736· OSTI ID:1894447

Faust, I. C. ^[1]; ^[2]; LaBombard, B. ^[2]; Parker, R. R. ^[2]; ^[2]; Whyte, D. G. ^[2]; Baek, S. G. ^[2]; Edlund, E. ^[2]; Hubbard, A. E. ^[2]; ^[2]; Kuang, A. Q. ^[2]; Reinke, M. L. ^[3]; Shiraiwa, S. ^[2]; Wallace, G. M. ^[2]; Walk, J. R. ^[2]

Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center; OSTI
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

For the first time, the power deposition of lower hybrid RF waves into the edge plasma of a diverted tokamak has been systematically quantified. Edge deposition represents a parasitic loss of power that can greatly impact the use and efficiency of Lower Hybrid Current Drive (LHCD) at reactor-relevant densities. Through the use of a unique set of fast time resolution edge diagnostics, including innovative fast-thermocouples, an extensive set of Langmuir probes, and a Lyα ionization camera, the toroidal, poloidal, and radial structure of the power deposition has been simultaneously determined. Power modulation was used to directly isolate the RF effects due to the prompt (t<τ_E) response of the scrape-off-layer (SOL) plasma to Lower Hybrid Radiofrequency (LHRF) power. LHRF power was found to absorb more strongly in the edge at higher densities. It is found that a majority of this edge-deposited power is promptly conducted to the divertor. This correlates with the loss of current drive efficiency at high density previously observed on Alcator C-Mod, and displaying characteristics that contrast with the local RF edge absorption seen on other tokamaks. Measurements of ionization in the active divertor show dramatic changes due to LHRF power, implying that divertor region can be a key for the LHRF edge power deposition physics. These observations support the existence of a loss mechanism near the edge for LHRF at high density (n_e>1.0×10²⁰ (m^-3)). Results will be shown addressing the distribution of power within the SOL, including the toroidal symmetry and radial distribution. Finally, these characteristics are important for deducing the cause of the reduced LHCD efficiency at high density and motivate the tailoring of wave propagation to minimize SOL interaction, for example, through the use of high-field-side launch.

View Accepted Manuscript (DOE)

Research Organization:: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center

Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Grant/Contract Number:: FC02-99ER54512

OSTI ID:: 1894447

Alternate ID(s):: OSTI ID: 1420674

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

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

Country of Publication:: United States

Language:: English

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Multiple striated heat fluxes patterns on the EAST first wall generated by lower hybrid wave absorption in the scrape-off layer Gan, K. F.; Li, M. H.; Gong, X. Z. Physics of Plasmas, Vol. 26, Issue 7 https://doi.org/10.1063/1.5088156	journal	July 2019
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Experimental evidence of lower hybrid wave scattering in Alcator C-Mod due to scrape off layer density fluctuations Martin, E. H.; Lau, C.; Wallace, G. M. Nuclear Fusion, Vol. 59, Issue 7 https://doi.org/10.1088/1741-4326/ab16a2	journal	May 2019
Full-wave model for the lower hybrid wave electric field vector with synthetic turbulence on Alcator C-Mod Lau, C.; Martin, E. H.; Shiraiwa, S. Nuclear Fusion, Vol. 60, Issue 3 https://doi.org/10.1088/1741-4326/ab6481	journal	January 2020
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