Speaker
Rory Perkins
(Princeton Plasma Physics Laboratory)
Description
We propose a new model for the anomalous loss of high-harmonic fast-wave (HHFW) heating power to the scrape-off layer (SOL) of the National Spherical Torus eXperiment (NSTX). A significant fraction, up to 60%, of the coupled HHFW power can be lost along scrape-off layer field lines [1], creating bright spirals of heat deposition on the upper and lower divertor regions [2]. It is important to determine the underlying mechanism because, with 20 MW of ICRF power planned for ITER, a similar loss of ICRF power may erode the divertor and produce unacceptable impurity levels. We hypothesize that the SOL losses are caused by a two-step process. First, the radiofrequency (RF) field amplitude becomes quite high in the SOL when the right-hand fast-wave cutoff layer is positioned too close to the HHFW antenna [1-4]. Second, these RF fields setup far-field RF sheaths on the divertor tiles and drive an enhanced heat flux into the divertor [5]. We present results from a cylindrical cold-plasma model that demonstrate a class of modes that conduct a significant fraction of their wave power in the peripheral plasma [6]; these modes appear when roughly a quarter radial wavelength fits into the SOL. Experimental evidence for RF rectified voltages and currents is presented, and our analysis suggests that they could produce additional heat fluxes consistent with infrared camera measurements of the HHFW heat flux within the spirals. This suggests that the SOL losses can be minimized, and heating efficiency maximized, through tailoring of SOL density and antenna phasing, which will be an important consideration for high-power long-pulse ICRF heating on fusion devices, such as ITER.
This work was supported in part by DOE Contract No. DE-AC02-09CH11466.
[1] J. C. Hosea et al., Phys. Plasmas 15 (2008) 056104.
[2] J. C. Hosea et al., AIP Conf. Proc. 1187 (2009) 105.
[3] D. L. Green et al., Phys. Rev. Lett. 107 (2011) 145001.
[4] N. Bertelli et al., Nucl. Fusion 54 (2014) 083004.
[5] R. J. Perkins et al., Phys. Plasma 22 (2015) 042506.
[6] R. J. Perkins et al., 41th EPS Conference on Plasma Physics (2015) P-1.011.
| Country or International Organization | USA |
|---|---|
| Paper Number | EX/P4-42 |
Primary author
Rory Perkins
(Princeton Plasma Physics Laboratory)
Co-authors
Dr
Adam McLean
(Lawrence Livermore National Laboratory)
Dr
Ahmed Diallo
(PPPL)
Dr
Benoit LeBlanc
(Princeton Plasma Physics Laboratory)
Mr
Gerrit J. Kramer
(Princeton Plasma Physics Laboratory)
Dr
James Wilson
(Princeton Plasma Physics Laboratory)
Dr
Joel Hosea
(Princeton Plasma Physics Laboratory)
Dr
Joon-Wook Ahn
(Oak Ridge National Laboratory)
Dr
Lane Roquemore
(Princeton Plasma Physics Laboratory)
Dr
Michael Jaworski
(Princeton Plasma Physics Laboratory)
Dr
Nicola Bertelli
(Princeton Plasma Physics Laboratory)
Dr
Rajesh Maingi
(Princeton Plasma Physics Laboratory)
Dr
Ronald Bell
(Princeton Plasma Physics Laboratory)
Dr
Stefan Gerhardt
(Princeton Plasma Physics Laboratory)
Dr
Steven Sabbagh
(Columbia University)
Dr
Taylor Gary
(Princeton Plasma Physics Laboratory)
Dr
Travis Gray
(Oak Ridge National Laboratory)
