@inproceedings{04c0071b605a4d509e204e2c315ebc03,
title = "Operating the upgraded NSTX HHFW antenna array in an environment with Li-coated surfaces",
abstract = "The single-feed, end-grounded straps of the NSTX 12-strap HHFW antenna array have been replaced with double-feed, center-grounded straps to reduce the voltages in the vicinity of the Faraday shield (FS) for a given strap current. The strap spacings to the FS and to the back plate were increased by 3 mm to decrease the electric fields for a given voltage. The electric fields near the FS have been roughly halved for the same strap currents, permitting a direct examination of the roles that internal fields play in determining antenna power limits in plasmas. Extensive RF/plasma conditioning of the antenna was required to remove enough of the evaporated Li deposits from prior wall conditioning to permit coupling in excess of 4 MW to L- and H-mode plasmas in 2009. Most arcs were associated with expulsion of Li from the FS/antenna frame surfaces. The center-grounded straps were less susceptible to arcing during ELMing H-mode plasmas. Reliable operation above 2 MW was difficult after the installation of the Liquid Lithium Divertor (LLD) in 2010. Li-compound {"}dust{"} was found in the antennas after this run and is believed to have contributed to the reduced power limit.",
keywords = "RF Heating and Current Drive, Spherical Torus",
author = "Ryan, \{P. M.\} and R. Ellis and Hosea, \{J. C.\} and Kung, \{C. C.\} and Leblanc, \{B. P.\} and Pinsker, \{R. I.\} and G. Taylor and Wilson, \{J. R.\}",
year = "2011",
doi = "10.1063/1.3664938",
language = "English (US)",
isbn = "9780735409781",
series = "AIP Conference Proceedings",
pages = "101--104",
booktitle = "Radio Frequency Power in Plasmas - Proceedings of the 19th Topical Conference",
note = "19th Topical Conference on Radio Frequency Power in Plasmas ; Conference date: 01-06-2011 Through 03-07-2011",
}