1. 1 NSTX Electron Bernstein Wave Emission Measurements Gary Taylor NSTX Results Review September 20-21, 2004

2. 2 Antennas on NSTX Measured EBW Emission via Conversion to X-Mode and O-Mode During 2004 Campaign "X-mode" EBW coupling requires steep density gradient at EBW conversion layer:  need L n ~ 2-3 mm for ~100% EBW conversion on NSTX  need limiter to maintain steep L n  very sensitive to L n fluctuations  measured very low (~%) EBW conversion  local reflectometry showed plasma underdense in front of antenna New oblique viewing "O-mode" EBW antenna less sensitive to fluctuations in L n at EBW mode conversion layer B

3. 3 Modeling Predicts Efficient EBW Coupling with Oblique, Circularly Polarized, “O-Mode” Launch EBW coupling at 14 GHz modeled with OPTIPOL/GLOSI [Mark Carter, ORNL] EBW Coupling Efficiency 80% 60% 40% 20%

4. 4 New Obliquely Viewing Antenna Installed at Bay G on NSTX Measures “O-Mode” EBW Emission Two 8-18 GHz radiometers simultaneously measure orthogonal polarizations with quad-ridged antenna:  compare emission results to OPTIPOL/GLOSI coupling predictions Focusing lens optimized for 16-18 GHz EBW emission Antenna views along 35 degree B field pitch, suitable for NSTX plasmas with I p ~ 1 MA at B t (0) ~ 4.0 kG Adjustable Limiters

5. 5 Radiometers Measuring Orthogonally Polarized Emission Detect Similar EBW T rad EBW Emission Frequency = 16.5 GHz B t (0) = 4 kG 113544 800 Reflectometer Interference

6. 6 Ray Tracing Calculations Show 16.5 GHz EBW Emission is Generated Locally at r/a = 0.4 CompX EBW Emission Frequency = 16.5 GHz B t (0) = 4 kG GENRAY t = 325 ms Shot 113544 OPTIPOL/GLOSI L n = 1 cm, f = 14 GHz Poloidal Angle (deg.) Toroidal Angle (deg.) -90900 0 -90 90 > 90% EBW Coupling 10% B Approx. Antenna Acceptance Angle GENRAY ray tracing uses EFIT equilibrium and T e (R) & n e (R) from Thomson scattering Antenna acceptance angle much larger than predicted 90% EBW conversion region

7. 7 EBW T rad /T e ~ 70%, Consistent with Theory; Radiometer Signal Ratios Consistent with Near-Circular Polarization Freq. = 16.5 GHz Emission fluctuations due to fluctuation in L n at EBW conversion layer Radiometer signal ratio ~ 1.3 ± 0.3, consistent with near-circular polarization predicted by modeling:  need additional measurements to confirm polarization

8. 8 Obliquely Viewing 20-40 GHz EBW Radiometer to be Installed on NSTX Next Year Larger vacuum window & higher frequency should allow much better collimation:  current 16-18 GHz antenna has ± 12 degree acceptance angle, 20-40 GHz antenna should achieve less than ± 5 degrees Detailed 28 GHz coupling study using OPTIPOL/AORSA1D and realistic EBW launcher model planned for 2005:  compare to 28 GHz emission measurements

9. 9 Summary Initial emission results at 16-18 GHz via EBW conversion to “O-mode” look promising & consistent with theory X-mode emission measurements with local limiter had very low (~%) EBW conversion; plasma underdense in front of antenna Next year measure 20-40 GHz EBW emission via “O-mode” conversion & compare to theory