Experimental evidence of lower hybrid wave scattering in Alcator C-Mod due to scrape off layer density fluctuations

E. H. Martin; C. Lau; G. M. Wallace; S. Shiraiwa; R. T. Mumgaard

doi:10.1088/1741-4326/ab16a2

Experimental evidence of lower hybrid wave scattering in Alcator C-Mod due to scrape off layer density fluctuations

E. H. Martin, C. Lau, G. M. Wallace, S. Shiraiwa, R. T. Mumgaard

Research output: Contribution to journal › Article › peer-review

18 Scopus citations

Abstract

Novel experimental measurements of the lower hybrid (LH) wave electric field vector, E _LH, obtained in Alcator C-Mod using dynamic Stark spectroscopy are presented. Three key results were obtained by comparison with 3D full-wave COMSOL simulations using the cold plasma dielectric tensor and reflectometry-measured density profiles. (1) As a function of space and LH power, the magnitude of E _LH was found to agree with the full-wave simulation result. (2) The direction of E _LH was found to have a substantial poloidal component and is in strong disagreement with the nearly radial full-wave simulation result. (3) The addition of scrape off layer density fluctuations to the density profile implemented in the full-wave simulations can be used to explain the E _LH direction discrepancy. It is concluded that diffraction and scattering by turbulence-driven scrape off layer density fluctuations is the responsible mechanism behind the modification in the direction of E _LH. These results further support the previously reported proposition that edge turbulence is an important mechanism behind the strong anomalous drop in LH current drive efficiency for diverted plasmas in the high-density regime.

Original language	English
Article number	076006
Journal	Nuclear Fusion
Volume	59
Issue number	7
DOIs	https://doi.org/10.1088/1741-4326/ab16a2
State	Published - May 23 2019

Funding

The authors would like to thank P. Bonoli for his guidance and M. Umansky for suppling the BOUT simulation results of [41]. This work was supported under US Department of Energy contract nos. DE-AC05-00OR22725 and DE-FC02- 99ER54512. Alcator C-Mod is a DOE Office of Science User Facility. This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy. gov/downloads/doe-public-access-plan).

Funders	Funder number
U.S. Department of Energy

Keywords

Electric field vector
Lower hybrid current drive
Turbulence

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

Access to Document

10.1088/1741-4326/ab16a2

Cite this

@article{c7a225fdc4e44430b169c09f10bcb0a7,

title = "Experimental evidence of lower hybrid wave scattering in Alcator C-Mod due to scrape off layer density fluctuations",

abstract = "Novel experimental measurements of the lower hybrid (LH) wave electric field vector, E LH, obtained in Alcator C-Mod using dynamic Stark spectroscopy are presented. Three key results were obtained by comparison with 3D full-wave COMSOL simulations using the cold plasma dielectric tensor and reflectometry-measured density profiles. (1) As a function of space and LH power, the magnitude of E LH was found to agree with the full-wave simulation result. (2) The direction of E LH was found to have a substantial poloidal component and is in strong disagreement with the nearly radial full-wave simulation result. (3) The addition of scrape off layer density fluctuations to the density profile implemented in the full-wave simulations can be used to explain the E LH direction discrepancy. It is concluded that diffraction and scattering by turbulence-driven scrape off layer density fluctuations is the responsible mechanism behind the modification in the direction of E LH. These results further support the previously reported proposition that edge turbulence is an important mechanism behind the strong anomalous drop in LH current drive efficiency for diverted plasmas in the high-density regime.",

keywords = "Electric field vector, Lower hybrid current drive, Turbulence",

author = "Martin, {E. H.} and C. Lau and Wallace, {G. M.} and S. Shiraiwa and Mumgaard, {R. T.}",

note = "Publisher Copyright: {\textcopyright} 2019 IAEA, Vienna.",

year = "2019",

month = may,

day = "23",

doi = "10.1088/1741-4326/ab16a2",

language = "English",

volume = "59",

journal = "Nuclear Fusion",

issn = "0029-5515",

publisher = "IOP Publishing",

number = "7",

}

TY - JOUR

T1 - Experimental evidence of lower hybrid wave scattering in Alcator C-Mod due to scrape off layer density fluctuations

AU - Martin, E. H.

AU - Lau, C.

AU - Wallace, G. M.

AU - Shiraiwa, S.

AU - Mumgaard, R. T.

PY - 2019/5/23

Y1 - 2019/5/23

N2 - Novel experimental measurements of the lower hybrid (LH) wave electric field vector, E LH, obtained in Alcator C-Mod using dynamic Stark spectroscopy are presented. Three key results were obtained by comparison with 3D full-wave COMSOL simulations using the cold plasma dielectric tensor and reflectometry-measured density profiles. (1) As a function of space and LH power, the magnitude of E LH was found to agree with the full-wave simulation result. (2) The direction of E LH was found to have a substantial poloidal component and is in strong disagreement with the nearly radial full-wave simulation result. (3) The addition of scrape off layer density fluctuations to the density profile implemented in the full-wave simulations can be used to explain the E LH direction discrepancy. It is concluded that diffraction and scattering by turbulence-driven scrape off layer density fluctuations is the responsible mechanism behind the modification in the direction of E LH. These results further support the previously reported proposition that edge turbulence is an important mechanism behind the strong anomalous drop in LH current drive efficiency for diverted plasmas in the high-density regime.

AB - Novel experimental measurements of the lower hybrid (LH) wave electric field vector, E LH, obtained in Alcator C-Mod using dynamic Stark spectroscopy are presented. Three key results were obtained by comparison with 3D full-wave COMSOL simulations using the cold plasma dielectric tensor and reflectometry-measured density profiles. (1) As a function of space and LH power, the magnitude of E LH was found to agree with the full-wave simulation result. (2) The direction of E LH was found to have a substantial poloidal component and is in strong disagreement with the nearly radial full-wave simulation result. (3) The addition of scrape off layer density fluctuations to the density profile implemented in the full-wave simulations can be used to explain the E LH direction discrepancy. It is concluded that diffraction and scattering by turbulence-driven scrape off layer density fluctuations is the responsible mechanism behind the modification in the direction of E LH. These results further support the previously reported proposition that edge turbulence is an important mechanism behind the strong anomalous drop in LH current drive efficiency for diverted plasmas in the high-density regime.

KW - Electric field vector

KW - Lower hybrid current drive

KW - Turbulence

UR - http://www.scopus.com/inward/record.url?scp=85069055263&partnerID=8YFLogxK

U2 - 10.1088/1741-4326/ab16a2

DO - 10.1088/1741-4326/ab16a2

M3 - Article

AN - SCOPUS:85069055263

SN - 0029-5515

VL - 59

JO - Nuclear Fusion

JF - Nuclear Fusion

IS - 7

M1 - 076006

ER -

Experimental evidence of lower hybrid wave scattering in Alcator C-Mod due to scrape off layer density fluctuations

Abstract

Funding

Keywords

UN SDGs

Access to Document

Other files and links

Fingerprint

Cite this