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XP 308: Experiment to Optimize the Conversion of EBWs to X-Mode on NSTX

XP 308: Experiment to Optimize the Conversion of EBWs to X-Mode on NSTX. G. Taylor, P. Efthimion, S. Kubota, R. Maingi, W. Peebles, J. Wilgen, R. Wilson New EBW antenna with local, radially adjustable carbon limiter installed on NSTX Two goals for this experiment:

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XP 308: Experiment to Optimize the Conversion of EBWs to X-Mode on NSTX

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  1. XP 308: Experiment to Optimize the Conversion of EBWs to X-Mode on NSTX G. Taylor, P. Efthimion, S. Kubota, R. Maingi, W. Peebles, J. Wilgen, R. Wilson • New EBW antenna with local, radially adjustable carbon limiter installed on NSTX • Two goals for this experiment: • Demonstrate measurement of Te • Demonstrate B-X conversion ≥ 80%

  2. EBW to X-Mode Conversion Efficiency (CBX)Very Sensitive to Ln at Resonant Upper Hybrid Layer • Experiment on NSTX using HHFW antenna tiles shortened Ln and increased CBX from 10%to ~ 50% CBX (%) Ln (cm)

  3. Two 8-18 GHz Quad-ridged Horn Antennas with Radially Adjustable Limiters Installed Near NSTX Bay I/J Midplane • Antenna includes two carbon limiters to control Ln: • Each limiter radially adjustable to be 0-3 cm in front of horns • Local gas feed to adjust density in front of horns • O-mode reflectometer to measure Ln in front of EBW antennas (UCLA) Ion Flow

  4. Antenna Tilted to Align Ridges for X-Mode and O-Mode Ion Flow B

  5. Run Plan • Dedicated run time required only after the new B-X EBW antenna has been fully commissioned: • Need UCLA O-mode reflectometry to measure scrape off density profile routinely • Need remote operation of the radially adjustable carbon limiters • Probably schedule XP no sooner than late March/early April 2003 • XP requires about 20 plasma shots

  6. Run Plan - II Ln scan for maximum B-X conversion, dwell EBW radiometer at frequency ~ 13 GHz (EBW from near axis): • Establish OH plasma using setup from 107975 (Ip = 800 kA LSN), but with Bo = 4.5 kG, not 4 kG (~ 7 shots): - Need ~150 ms Ip flattop, no ne glitches, well-controlled shape - Begin with both limiters A and B retracted (A & B = 0 cm) - Repeat until reproducible & without significant MHD - Acquire MPTS Te(R) and ne(R) profile data during Ip flattop - Measure Ln at the B-X conversion layer and EBW Trad/Te, acquire data on two similar shots • Move limiter B so that B = 1, 2 and 3 cm (6 shots): - Two shots at each position - Limiter B should have the greatest influence on Ln since it is on the ion flow side

  7. Run Plan - III Ln scan for maximum B-X conversion (cont.): • Leave A = 3, move limiter B so that B = 2, 1 and 0 cm: - Two shots at each position (6 shots) Run EBW radiometer in swept frequency mode (11-18 GHz) at maximum B-X conversion: • Set A and B for maximum B-X conversion (2 shots): - EBW Trad/Te vs radius on two similar shots (2 shots) Use HHFW to Suppress Edge Density Fluctuations: • Edge density fluctuations may be reduced when HHFW power is coupled to the plasma • Couple 1-2 MW of HHFW into some shots during the last 50 ms of the current flat top: - assess effect of HHFW on edge density fluctuations and EBW B-X conversion. (piggyback)

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