Reflectometer Sensing of RF Waves in front of the HHFW antenna on NSTX

Conference · Sun Jan 01 00:00:00 EST 2006

OSTI ID:1110836

Wilgen, John B ^[1]; Ryan, Philip Michael ^[1]; Hanson, Gregory R ^[1]; Swain, David W ^[1]; Bernabei, Stefano ^[2]; Greenough, Nevell ^[2]; DePasquale, Steve ^[2]; Phillips, Cynthia ^[2]; Hosea, Joel ^[2]; Wilson, Randy ^[2]

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1. ORNL
2. Princeton Plasma Physics Laboratory (PPPL)

The ability to measure RF driven waves in the edge of the plasma can help to elucidate the role that surface waves and Parametric Decay Instabilities (PDI) play in RF power losses on NSTX. A microwave reflectometer has recently been modified to monitor RF plasma waves in the scrape-off layer in front of the 30 MHz High Harmonic Fast Wave (HHFW) antenna array on NSTX. In RF heated plasmas, the plasma-reflected microwave signal exhibits 30 MHz sidebands, due to the modulation of the cutoff layer by the electrostatic component of the heating wave. Similarly, electrostatic parametric decay waves (when present) are detected at frequencies below the heating frequency, near 28, 26, MHz, separated from the heating frequency by harmonics of the local ion cyclotron frequency of about 2 MHz. In addition, a corresponding frequency matched set of decay waves is also detected near the ion cyclotron harmonics, at 2, 4, MHz. The RF plasma-wave sensing capability is useful for determination of the PDI power threshold as a function of antenna array phasing (including toroidal wavelength), outer gap spacing, and various plasma parameters such as the magnetic field and the plasma current.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1110836
• Resource Relation: Conference: 16th Topical Conference on High-Temperature Plasma Diagnostic (HTPD), Williamsburg, VA, USA, 20060507, 20060511
• Country of Publication: United States
• Language: English