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

Abstract

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 amore » 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.« less

Authors:

Faust, I. C. ^[1]; Brunner, D.  ^[1];

• Search DOE PAGES for author "Brunner, D."
• Search DOE PAGES for ORCID "0000-0002-8753-1124"

LaBombard, B. ^[1]; Parker, R. R. ^[1]; Terry, J. L.  ^[1];

• Search DOE PAGES for author "Terry, J. L."
• Search DOE PAGES for ORCID "0000-0003-4255-5509"

Whyte, D. G. ^[1]; Baek, S. G. ^[1]; Edlund, E. ^[1]; Hubbard, A. E. ^[1]; Hughes, J. W.  ^[1];

• Search DOE PAGES for author "Hughes, J. W."
• Search DOE PAGES for ORCID "0000-0003-4802-4944"

Kuang, A. Q. ^[1]; Reinke, M. L. ^[2]; Shiraiwa, S. ^[1]; Wallace, G. M. ^[1]; Walk, J. R. ^[1]

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+ Show Author Affiliations

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

Publication Date:

Fri May 20 00:00:00 EDT 2016

Research Org.:

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

Sponsoring Org.:

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

OSTI Identifier:

1894447

Alternate Identifier(s):

OSTI ID: 1420674

Grant/Contract Number:  

FC02-99ER54512; FC02- 99ER54512-CMOD

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 23; Journal Issue: 5; Journal ID: ISSN 1070-664X

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; plasma confinement; plasma waves; cameras; thermoelectricity; magnetic fields; hybrid energy system; wave power; tokamaks; plasma diagnostics; RF waves