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XP 309: Experiment to Optimize the Conversion of EBWs to O-Mode on NSTX

XP 309: Experiment to Optimize the Conversion of EBWs to O-Mode on NSTX. G. Taylor, P. Efthimion, G. Bell, R. Maingi, D. Rasmussen, D. Swain, J. Wilgen, R. Wilson Boron nitride stepped wedge insert installed between HHFW antenna straps to view the oblique B-X-O transmission window

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XP 309: Experiment to Optimize the Conversion of EBWs to O-Mode on NSTX

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  1. XP 309: Experiment to Optimize the Conversion of EBWs to O-Mode on NSTX G. Taylor, P. Efthimion, G. Bell, R. Maingi, D. Rasmussen, D. Swain, J. Wilgen, R. Wilson • Boron nitride stepped wedge insert installed between HHFW antenna straps to view the oblique B-X-O transmission window • Two goals for this experiment: • Broaden the angular transmission window for B-X-O conversion with HHFW BN limiters • Demonstrate B-X-O conversion ≥ 80%

  2. Angular size of B-X-O can be Increased by Reducing Ln at the B-X-O Conversion Layer

  3. BN Stepped Wedge Inserted in Waveguide Between HHFW Antenna Straps Views Oblique B-X-O Emission Window HHFW BN Limiters • Use HHFW antenna Boron nitride limiter tiles to shorten Ln: • Run sequence of shots with increasingly smaller outer gap, shorter Ln • Similar technique used last year to increase B-X conversion (XP-213) Ion Flow

  4. Enhance B-X-O Conversion Using Tiles in HHFW Antenna as Local Limiter to Shorten Lnat UHR • Measure Ln with ORNL X-Mode Reflectometer

  5. Run Plan • XP requires about 10 plasma shots (≤ 1/2 run day) • Setup shot 107975 (Ip = 800kA, Bo = 4kG, LSN) • Need ~100 ms Ip flattop, no ne glitches, well controlled shape • Repeat shot until reproducible and no significant MHD • Need MPTS Te(R) and ne(R) during Ip flattop • Ln at HHFW antenna with ORNL X-mode reflectometer • Determine outer gap from EFIT • Reduce outer gap to ~ 0 cm • Look for steepened Ln and enhanced EBW B-X-O emission

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