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Title: Towards identifying the mechanisms underlying field-aligned edge-loss of HHFW power on NSTX

Abstract

Fast-wave heating will be a major heating scheme on ITER, as it can heat ions directly and is relatively unaffected by the large machine size unlike neutral beams. However, fast-wave interactions with the plasma edge can lead to deleterious effects such as, in the case of the high-harmonic fast-wave (HHFW) system on NSTX, large losses of fast-wave power in the scrape off layer (SOL) under certain conditions. In such scenarios, a large fraction of the lost HHFW power is deposited on the upper and lower divertors in bright spiral shapes. The responsible mechanism(s) has not yet been identified but may include fast-wave propagation in the scrape off layer, parametric decay instability, and RF currents driven by the antenna reactive fields. Understanding and mitigating these losses is important not only for improving the heating and current-drive on NSTX-Upgrade but also for understanding fast-wave propagation across the SOL in any fast-wave system. This talk summarizes experimental results demonstrating that the flow of lost HHFW power to the divertor regions largely follows the open SOL magnetic field lines. This lost power flux is relatively large close to both the antenna and the last closed flux surface with a reduced level in between, somore » the loss mechanism cannot be localized to the antenna. At the same time, significant losses also occur along field lines connected to the inboard edge of the bottom antenna plate. The power lost within the spirals is roughly estimated, showing that these field-aligned losses to the divertor are significant but may not account for the total HHFW loss. To elucidate the role of the onset layer for perpendicular fast-wave propagation with regards to fast-wave propagation in the SOL, a cylindrical cold-plasma model is being developed. This model, in addition to advanced RF codes such as TORIC and AORSA, is aimed at identifying the underlying mechanism(s) behind these SOL losses, to minimize their effects in NSTX-U, and to predict their importance in ITER.« less

Authors:
 [1];  [2];  [1];  [1];  [1];  [1];  [3];  [2];  [4];  [1];  [1];  [1];  [1];  [2];  [2];  [1];  [1];  [2];  [5];  [1] more »;  [1];  [1] « less
  1. Princeton Plasma Physics Laboratory (PPPL)
  2. ORNL
  3. Oak Ridge National Laboratory (ORNL)
  4. XCEL
  5. Columbia University
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1150378
DOE Contract Number:  
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1580
Country of Publication:
United States
Language:
English

Citation Formats

Perkins, R. J., Ahn, Joonwook, Bell, R. E., Bertelli, Nicola, Diallo, A., Gerhardt, S., Gray, T. K., Green, David L, Jaeger, E. F., Hosea, J., Jaworski, M. A., LeBlanc, B, Kramer, G., McLean, Adam G, Maingi, Rajesh, Phillips, C. K., Podesta, M., Ryan, Philip Michael, Sabbagh, S. A., Scotti, F., Taylor, G., and Wilson, J. R. Towards identifying the mechanisms underlying field-aligned edge-loss of HHFW power on NSTX. United States: N. p., 2013. Web.
Perkins, R. J., Ahn, Joonwook, Bell, R. E., Bertelli, Nicola, Diallo, A., Gerhardt, S., Gray, T. K., Green, David L, Jaeger, E. F., Hosea, J., Jaworski, M. A., LeBlanc, B, Kramer, G., McLean, Adam G, Maingi, Rajesh, Phillips, C. K., Podesta, M., Ryan, Philip Michael, Sabbagh, S. A., Scotti, F., Taylor, G., & Wilson, J. R. Towards identifying the mechanisms underlying field-aligned edge-loss of HHFW power on NSTX. United States.
Perkins, R. J., Ahn, Joonwook, Bell, R. E., Bertelli, Nicola, Diallo, A., Gerhardt, S., Gray, T. K., Green, David L, Jaeger, E. F., Hosea, J., Jaworski, M. A., LeBlanc, B, Kramer, G., McLean, Adam G, Maingi, Rajesh, Phillips, C. K., Podesta, M., Ryan, Philip Michael, Sabbagh, S. A., Scotti, F., Taylor, G., and Wilson, J. R. Tue . "Towards identifying the mechanisms underlying field-aligned edge-loss of HHFW power on NSTX". United States.
@article{osti_1150378,
title = {Towards identifying the mechanisms underlying field-aligned edge-loss of HHFW power on NSTX},
author = {Perkins, R. J. and Ahn, Joonwook and Bell, R. E. and Bertelli, Nicola and Diallo, A. and Gerhardt, S. and Gray, T. K. and Green, David L and Jaeger, E. F. and Hosea, J. and Jaworski, M. A. and LeBlanc, B and Kramer, G. and McLean, Adam G and Maingi, Rajesh and Phillips, C. K. and Podesta, M. and Ryan, Philip Michael and Sabbagh, S. A. and Scotti, F. and Taylor, G. and Wilson, J. R.},
abstractNote = {Fast-wave heating will be a major heating scheme on ITER, as it can heat ions directly and is relatively unaffected by the large machine size unlike neutral beams. However, fast-wave interactions with the plasma edge can lead to deleterious effects such as, in the case of the high-harmonic fast-wave (HHFW) system on NSTX, large losses of fast-wave power in the scrape off layer (SOL) under certain conditions. In such scenarios, a large fraction of the lost HHFW power is deposited on the upper and lower divertors in bright spiral shapes. The responsible mechanism(s) has not yet been identified but may include fast-wave propagation in the scrape off layer, parametric decay instability, and RF currents driven by the antenna reactive fields. Understanding and mitigating these losses is important not only for improving the heating and current-drive on NSTX-Upgrade but also for understanding fast-wave propagation across the SOL in any fast-wave system. This talk summarizes experimental results demonstrating that the flow of lost HHFW power to the divertor regions largely follows the open SOL magnetic field lines. This lost power flux is relatively large close to both the antenna and the last closed flux surface with a reduced level in between, so the loss mechanism cannot be localized to the antenna. At the same time, significant losses also occur along field lines connected to the inboard edge of the bottom antenna plate. The power lost within the spirals is roughly estimated, showing that these field-aligned losses to the divertor are significant but may not account for the total HHFW loss. To elucidate the role of the onset layer for perpendicular fast-wave propagation with regards to fast-wave propagation in the SOL, a cylindrical cold-plasma model is being developed. This model, in addition to advanced RF codes such as TORIC and AORSA, is aimed at identifying the underlying mechanism(s) behind these SOL losses, to minimize their effects in NSTX-U, and to predict their importance in ITER.},
doi = {},
journal = {AIP Conference Proceedings},
number = ,
volume = 1580,
place = {United States},
year = {Tue Jan 01 00:00:00 EST 2013},
month = {Tue Jan 01 00:00:00 EST 2013}
}