Measurement of LHCD edge power deposition through modulation techniques on Alcator C-Mod

I. C. Faust; D. Brunner; B. Labombard; R. R. Parker; S. G. Baek; M. A. Chilenksi; E. Edlund; A. Hubbard; J. W. Hughes; J. L. Terry; S. Shiraiwa; J. R. Walk; G. M. Wallace; D. G. Whyte

doi:10.1063/1.4936529

Measurement of LHCD edge power deposition through modulation techniques on Alcator C-Mod

I. C. Faust, D. Brunner, B. Labombard, R. R. Parker, S. G. Baek, M. A. Chilenksi, E. Edlund, A. Hubbard, J. W. Hughes, J. L. Terry, S. Shiraiwa, J. R. Walk, G. M. Wallace, D. G. Whyte

Research output: Chapter in Book/Report/Conference proceeding › Conference contribution

Abstract

The efficiency of LHCD on Alcator C-Mod drops exponentially with line average density. At reactor relevant densities (> 1 · 10²⁰ [m^-3]) no measurable current is driven. While a number of causes have been suggested, no specific mechanism has been shown to be responsible for the loss of current drive at high density. Fast modulation of the LH power was used to isolate and quantify the LHCD deposition within the plasma. Measurements from these plasmas provide unique evidence for determining a root cause. Modulation of LH power in steady plasmas exhibited no correlated change in the core temperature. A correlated, prompt response in the edge suggests that the loss in efficiency is related to a edge absorption mechanism. This follows previous results which found the generation of n∥-independent SOL currents. Multiple Langmuir probe array measurements of the conducted heat conclude that the lost power is deposited near the last closed flux surface. The heat flux induced by LH waves onto the outer divertor is calculated. Changes in the neutral pressure, ionization and hard X-ray emission at high density highlight the importance of the active divertor in the loss of efficiency. Results of this study implicate a mechanism which may occur over multiple passes, leading to power absorption near the LCFS.

Original language	English (US)
Title of host publication	Radio Frequency Power in Plasmas
Subtitle of host publication	Proceedings of the 21St Topical Conference
Editors	Robert I. Pinsker
Publisher	American Institute of Physics Inc.
ISBN (Electronic)	9780735413368
DOIs	https://doi.org/10.1063/1.4936529
State	Published - Dec 10 2015
Externally published	Yes
Event	21st Topical Conference on Radiofrequency Power in Plasmas - Lake Arrowhead, United States Duration: Apr 27 2015 → Apr 29 2015

Publication series

Name	AIP Conference Proceedings
Volume	1689
ISSN (Print)	0094-243X
ISSN (Electronic)	1551-7616

Other

Other	21st Topical Conference on Radiofrequency Power in Plasmas
Country/Territory	United States
City	Lake Arrowhead
Period	4/27/15 → 4/29/15

All Science Journal Classification (ASJC) codes

General Physics and Astronomy

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10.1063/1.4936529

Cite this

Faust, I. C., Brunner, D., Labombard, B., Parker, R. R., Baek, S. G., Chilenksi, M. A., Edlund, E., Hubbard, A., Hughes, J. W., Terry, J. L., Shiraiwa, S., Walk, J. R., Wallace, G. M., & Whyte, D. G. (2015). Measurement of LHCD edge power deposition through modulation techniques on Alcator C-Mod. In R. I. Pinsker (Ed.), Radio Frequency Power in Plasmas: Proceedings of the 21St Topical Conference Article 080006 (AIP Conference Proceedings; Vol. 1689). American Institute of Physics Inc.. https://doi.org/10.1063/1.4936529

@inproceedings{6a4492a92117447ea7dcaf838fe453b5,

title = "Measurement of LHCD edge power deposition through modulation techniques on Alcator C-Mod",

abstract = "The efficiency of LHCD on Alcator C-Mod drops exponentially with line average density. At reactor relevant densities (> 1 · 1020 [m-3]) no measurable current is driven. While a number of causes have been suggested, no specific mechanism has been shown to be responsible for the loss of current drive at high density. Fast modulation of the LH power was used to isolate and quantify the LHCD deposition within the plasma. Measurements from these plasmas provide unique evidence for determining a root cause. Modulation of LH power in steady plasmas exhibited no correlated change in the core temperature. A correlated, prompt response in the edge suggests that the loss in efficiency is related to a edge absorption mechanism. This follows previous results which found the generation of n∥-independent SOL currents. Multiple Langmuir probe array measurements of the conducted heat conclude that the lost power is deposited near the last closed flux surface. The heat flux induced by LH waves onto the outer divertor is calculated. Changes in the neutral pressure, ionization and hard X-ray emission at high density highlight the importance of the active divertor in the loss of efficiency. Results of this study implicate a mechanism which may occur over multiple passes, leading to power absorption near the LCFS.",

author = "Faust, \{I. C.\} and D. Brunner and B. Labombard and Parker, \{R. R.\} and Baek, \{S. G.\} and Chilenksi, \{M. A.\} and E. Edlund and A. Hubbard and Hughes, \{J. W.\} and Terry, \{J. L.\} and S. Shiraiwa and Walk, \{J. R.\} and Wallace, \{G. M.\} and Whyte, \{D. G.\}",

note = "Publisher Copyright: {\textcopyright} 2015 AIP Publishing LLC.; 21st Topical Conference on Radiofrequency Power in Plasmas ; Conference date: 27-04-2015 Through 29-04-2015",

year = "2015",

month = dec,

day = "10",

doi = "10.1063/1.4936529",

language = "English (US)",

series = "AIP Conference Proceedings",

publisher = "American Institute of Physics Inc.",

editor = "Pinsker, \{Robert I.\}",

booktitle = "Radio Frequency Power in Plasmas",

}

Faust, IC, Brunner, D, Labombard, B, Parker, RR, Baek, SG, Chilenksi, MA, Edlund, E, Hubbard, A, Hughes, JW, Terry, JL, Shiraiwa, S, Walk, JR, Wallace, GM & Whyte, DG 2015, Measurement of LHCD edge power deposition through modulation techniques on Alcator C-Mod. in RI Pinsker (ed.), Radio Frequency Power in Plasmas: Proceedings of the 21St Topical Conference., 080006, AIP Conference Proceedings, vol. 1689, American Institute of Physics Inc., 21st Topical Conference on Radiofrequency Power in Plasmas, Lake Arrowhead, United States, 4/27/15. https://doi.org/10.1063/1.4936529

Measurement of LHCD edge power deposition through modulation techniques on Alcator C-Mod. / Faust, I. C.; Brunner, D.; Labombard, B. et al.
Radio Frequency Power in Plasmas: Proceedings of the 21St Topical Conference. ed. / Robert I. Pinsker. American Institute of Physics Inc., 2015. 080006 (AIP Conference Proceedings; Vol. 1689).

Research output: Chapter in Book/Report/Conference proceeding › Conference contribution

TY - GEN

T1 - Measurement of LHCD edge power deposition through modulation techniques on Alcator C-Mod

AU - Faust, I. C.

AU - Brunner, D.

AU - Labombard, B.

AU - Parker, R. R.

AU - Baek, S. G.

AU - Chilenksi, M. A.

AU - Edlund, E.

AU - Hubbard, A.

AU - Hughes, J. W.

AU - Terry, J. L.

AU - Shiraiwa, S.

AU - Walk, J. R.

AU - Wallace, G. M.

AU - Whyte, D. G.

PY - 2015/12/10

Y1 - 2015/12/10

N2 - The efficiency of LHCD on Alcator C-Mod drops exponentially with line average density. At reactor relevant densities (> 1 · 1020 [m-3]) no measurable current is driven. While a number of causes have been suggested, no specific mechanism has been shown to be responsible for the loss of current drive at high density. Fast modulation of the LH power was used to isolate and quantify the LHCD deposition within the plasma. Measurements from these plasmas provide unique evidence for determining a root cause. Modulation of LH power in steady plasmas exhibited no correlated change in the core temperature. A correlated, prompt response in the edge suggests that the loss in efficiency is related to a edge absorption mechanism. This follows previous results which found the generation of n∥-independent SOL currents. Multiple Langmuir probe array measurements of the conducted heat conclude that the lost power is deposited near the last closed flux surface. The heat flux induced by LH waves onto the outer divertor is calculated. Changes in the neutral pressure, ionization and hard X-ray emission at high density highlight the importance of the active divertor in the loss of efficiency. Results of this study implicate a mechanism which may occur over multiple passes, leading to power absorption near the LCFS.

AB - The efficiency of LHCD on Alcator C-Mod drops exponentially with line average density. At reactor relevant densities (> 1 · 1020 [m-3]) no measurable current is driven. While a number of causes have been suggested, no specific mechanism has been shown to be responsible for the loss of current drive at high density. Fast modulation of the LH power was used to isolate and quantify the LHCD deposition within the plasma. Measurements from these plasmas provide unique evidence for determining a root cause. Modulation of LH power in steady plasmas exhibited no correlated change in the core temperature. A correlated, prompt response in the edge suggests that the loss in efficiency is related to a edge absorption mechanism. This follows previous results which found the generation of n∥-independent SOL currents. Multiple Langmuir probe array measurements of the conducted heat conclude that the lost power is deposited near the last closed flux surface. The heat flux induced by LH waves onto the outer divertor is calculated. Changes in the neutral pressure, ionization and hard X-ray emission at high density highlight the importance of the active divertor in the loss of efficiency. Results of this study implicate a mechanism which may occur over multiple passes, leading to power absorption near the LCFS.

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U2 - 10.1063/1.4936529

DO - 10.1063/1.4936529

M3 - Conference contribution

AN - SCOPUS:84984532161

T3 - AIP Conference Proceedings

BT - Radio Frequency Power in Plasmas

A2 - Pinsker, Robert I.

PB - American Institute of Physics Inc.

T2 - 21st Topical Conference on Radiofrequency Power in Plasmas

Y2 - 27 April 2015 through 29 April 2015

ER -

Measurement of LHCD edge power deposition through modulation techniques on Alcator C-Mod

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