Speaker
Bart Van Compernolle
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1051.pdf
Fast wave experiments at LAPD in support of fusion
B. Van Compernolle1, M. Martin1, T. A. Carter1, W. Gekelman1, P. Pribyl1, D. Van Eester2,
K. Crombe3, R. Perkins4, C. Lau5, E. Martin5, J. Caughman5, S.K.P. Tripathi1, S. Vincena1
1
University of California, Los Angeles, United States, 2 LPP, Royal Military Academy,
Brussels, Belgium, 3 Ghent University, Ghent, Belgium, 4 Princeton Plasma Physics
Laboratory, Princeton, United States, 5 Oak Ridge National Laboratory, United States
Recent work on ICRF physics at the Large Plasma Device (LAPD) at UCLA has focused on
deleterious near-feld antenna efects, such as RF rectifcation, sputtering, convective cells
and power lost to the plasma edge. Plasma parameters in LAPD are similar to the scrape-of
layer of current fusion devices. The machine has a 17 m long, 60 cm diameter magnetized
plasma column with typical plasma parameters ne ~ 1012 – 1013 cm-3, Te ~ 1 – 10 eV and B0 ~
1000 G. A new high-power (~150 kW) RF system and fast wave antenna have been
developed for LAPD, enabling the generation of large amplitude fast waves. Evidence of
rectifed RF sheaths is seen in large increases (~ 10 Te) in the plasma potential on feld lines
connected to the antenna, and in copper deposition on plasma facing components due to
sputtering at the antenna. The rectifed potential scales linearly with antenna current. The
rectifed RF sheaths set up convective cells of local E x B flows, measured indirectly by
potential measurements, and measured directly with Mach probes. At high antenna powers
substantial modifcations of the density profle were observed after the RF antenna is
powered up. The density rearrangement is asymmetric with a decrease in plasma density
near the top of the antenna and an increase near the bottom. The plasma density profle
initially exhibits transient low frequency oscillations (~10 kHz) and settles into a quasi-
steady state profle for the remainder of the RF pulse. RF antenna current is constant during
the pulse. In preliminary experiments at low antenna powers, the parasitic coupling to slow
waves in the low density region in front of the antenna is being studied. Detailed wave feld
measurements show coupling to both the short wavelength slow wave and the long
wavelength fast wave if the density at the antenna is low enough. Coupling to lower hybrid
waves was demonstrated for a range of normalized frequencies, from 1 < f / fci < 30.
M. J. Martin et al, Phys. Rev. Lett. 119, 205002 (2017)
Supported by NSF/DOE at BaPSF
