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(CDP/12) High Frequency Fast Wave Results from the CDX-U Spherical Torus

R. Kaita, R. Majeski, J. Menard, T. Munsat, H. Kugel, P. Efthimion, M. Ono, D. Jens, B. Jones

Plasma Physics Laboratory and Department of Physics, Princeton University, Princeton, New Jersey, USA

D. Stutman, M. Finkenthal

Johns Hopkins University, Baltimore, Maryland, USA

T. Intrator, R. Fonck

University of Wisconsin, Madison, Wisconsin, USA

W.-H. Choe, Y.-S. Hwang

Korea Advanced Institute of Science and Technology, Taejon, Korea

V. K. Gusev, Y. Petrov

Ioffe Institute, St. Petersburg, Russia

T. Seki

National Institute for Fusion Science, Nagoya, Japan

Y. Takase
Tokyo University, Tokyo, Japan

Abstract.  The Current Drive Experiment-Upgrade (CDX-U) is the first spherical torus (ST) to investigate radio frequency (RF) heating and current drive. To address the concern that large magnetic field line pitch at the outboard midplane of ST's could inhibit successful coupling to the high harmonic fast wave (HHFW), a rotatable, two strap antenna was installed on CDX-U. Parasitic loading and impurity generation were discovered to be weak and nearly independent of antenna phasing and angle over a wide range, and fast wave electron heating has been observed. Plasma densities up to about 10¹²cm^{- 3} were obtained with noninductive startup solely with HHFW. New ST diagnostics under development on CDX-U include a multilayer mirror (MLM) detector to measure ultrasoft X-rays, a twelve spatial point Thomson scattering (TS) system, and an Electron Bernstein Wave (EBW) system for both electron heating and electron temperature measurements. Preliminary experiments with a boron low velocity edge micropellet injector have also been performed, and further studies of its effectiveness for impurity control will be conducted with a variety of spectroscopic and imaging diagnostics on CDX-U.

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