Absorption of lower hybrid waves in the scrape off layer of a diverted tokamak

Absorption of lower hybrid waves in the scrape off layer of a diverted tokamak

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The goal of the Lower Hybrid Current Drive (LHCD) system on the Alcator C-Mod tokamak [ Hutchinson et al., Phys. Plasmas 1, 1511 (1994) ] is to investigate current profile control under plasma conditions relevant to future tokamak experiments. Experimental observations of a LHCD “density limit” for...

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Bibliographic Details
Main Authors: Wallace, Gregory Marriner, Parker, Ronald R., Bonoli, Paul T., Hubbard, Amanda E., Hughes, Jerry W., LaBombard, Brian, Meneghini, Orso-Maria Cornelio, Schmidt, Andrea Elizabeth, Shiraiwa, Shunichi, Whyte, Dennis G., Wright, John C., Wukitch, Stephen James, Smirnov, A. P., Wilson, J. R.
Other Authors: Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science
Format: Article
Language:en_US
Published: American Institute of Physics 2011
Online Access:http://hdl.handle.net/1721.1/67355
https://orcid.org/0000-0002-9001-5606
https://orcid.org/0000-0003-4432-5504
https://orcid.org/0000-0002-7841-9261
https://orcid.org/0000-0002-1620-9680
Description
Summary:The goal of the Lower Hybrid Current Drive (LHCD) system on the Alcator C-Mod tokamak [ Hutchinson et al., Phys. Plasmas 1, 1511 (1994) ] is to investigate current profile control under plasma conditions relevant to future tokamak experiments. Experimental observations of a LHCD “density limit” for C-Mod are presented in this paper. Bremsstrahlung emission from relativistic fast electrons in the core plasma drops suddenly above line averaged densities of 10[superscript 20] m[superscript −3] (ω/ω[subscript LH] ~ 3–4), well below the density limit previously observed on other experiments (ω/ωLH ∼ 2). Electric currents flowing through the scrape off layer (SOL) between the inner and outer divertors increase dramatically across the same density range that the core bremsstrahlung emission drops precipitously. These experimental x-ray data are compared to both conventional modeling, which gives poor agreement with experiment above the density limit and a model including collisional absorption in the SOL, which dramatically improves agreement with experiment above the observed density limit. These results show that strong absorption of LH waves in the SOL is possible on a high density tokamak and the SOL must be included in simulations of LHCD at high density.

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