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Collective Thomson Scattering Diagnostics of Confined Fast Ions

Collective Thomson Scattering Diagnostics of Confined Fast Ions. Paul Woskov 1 , S. B. Korsholm 1,2 , H. Bindslev 2 , J. Egedal 1 , F.Leipold 2 , F. Meo 2 , P. K. Michelsen 2 , S. Michelsen 2 , S.K.Nielsen 2 , E. Westerhof 3 , J. W. Oosterbeek 4 , J. Hoekzema 4 , F. Leuterer 5 , D.Wagner 5.

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Collective Thomson Scattering Diagnostics of Confined Fast Ions

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  1. Collective Thomson Scattering Diagnostics of Confined Fast Ions Paul Woskov1, S. B. Korsholm1,2,H. Bindslev2, J. Egedal1,F.Leipold2, F. Meo2, P. K. Michelsen2, S. Michelsen2, S.K.Nielsen2, E. Westerhof3, J. W. Oosterbeek4, J. Hoekzema4, F. Leuterer5, D.Wagner5 1MIT Plasma Science & Fusion Center 2Risø National Laboratory, Technical University of Denmark 3FOM IPP Rijnhuizen 4IPP, Forschungszentrum Jülich 5Max Planck IPP ITPA Diagnostics Meeting, Princeton, March 26 - 30, 2007

  2. CTS Diagnostic Features • CTS diagnostics can diagnose the complete fast ion distribution function, f(v, r, t) • spatially resolved • time resolved • no fundamental limits on energy range • Accessible to plasma core of burning plasmas • Recent experiments in tokamaks have firmly established fast ion CTS • JET (Bindslev et al., PRL 83, 3206, 1999) • TEXTOR (Bindslev et al., PRL 97, 205005, 2006)

  3. Principal of CTS Fast Ion Diagnostics Electromagnetic scattering off microscopic fluctuations, principally in electron distribution, driven by ion motion when the condition between fluctuation wavevector (k) and Debye length (D) is given by: Scattering Geometry In tokamaks Long wavelength sources required for large scat. angles mmwaves for  > 20 receiver laser or gyrotron Projection of ion velocities v along k diagnosed

  4. Tokamak Access for CTS • ECE background restricts access to where the CTS condition (kD)-1 > 1 can be satisfied • Below fundamental ECE resonance, fi < fB • Used at TFTR and proposed for ITER • Between fundamental and first harmonic, fB< fi < 2 fB • Used at JET, TEXTOR, and ASDEX-Up • Not accessible in burning plasmas with Te > 10 keV • Above the highest significant harmonic, fi > > fB • Used at JT-60 with CO2 laser for small angle CTS • Used at Alactor C, TCA, and UNITOR for thermal ion CTS with FIR lasers

  5. Illustrative CTS Spectrum 110 GHz Gyrotron, 160 Scattering Angle Each ion species and electrons contribute to the total CTS spectrum (kD)-1 = 6.7 The fast ions are distinguished in the CTS spectrum by their large Doppler shift above the electron feature

  6. Sensitivity to NBI Ions in ASDEX-Up CTS with 104 GHz Gyrotron, 130 Scattering Angle Te = Ti = 6 keV , ne = 8 x 1019 m-3 100 keV H Beam

  7. Sensitivity to ICRH Ions in ASDEX-Up CTS with 104 GHz Gyrotron, 130 Scattering Angle Te = Ti = 6 keV , ne = 8 x 1019 m-3 100 KeV H ion Maxwellian

  8. Alphas and Beam Ions in ITER Alpha particles can be distinguished in the presence of 1 MW D beam ions in ITER Egedal, Bindslev, Budny and Woskov, NF, 45, 191 (2005)

  9. Alphas and Beam Ions in ITER H-Mode Velocity Space Distribution at Scattering Volume k Direction Projected Velocities Along k Ion Density Profiles

  10. CTS Spectrum ITER H-Mode 60 GHz Gyrotron CTS ion signal proportional to ion charge squared

  11. Alphas and Beams in ITER Reverse Shear Velocity Space Distribution at Scattering Volume k Direction Projected Velocities Along k Ion Density Profiles

  12. CTS Spectrum ITER Reverse Shear 60 GHz Gyrotron

  13. Two Fast Ion CTS Systems Implemented • TEXTOR CTS - Operational • Fast ion measurements being carried out in NBI and ICRH plasmas • Up to 100 CTS spectra per plasma shot to study ion dynamics • ASDEX-Upgrade CTS - Commissioning • makes use of new two frequency gyrotrons • First plasma measurements expected in 2007

  14. Balcony CTS cabinet with DAQ & electronics CTS receiver CTS port Liner CTS quasi-optical transmission line Copper bellow Liquid N2 TEXTOR CTS

  15. Steerable mirror 1 CC waveguide TEXTOR CTS Receiver Optics inside TEXTOR

  16. ASDEX-Upgrade CTS Towards the tokamak MOU box supporting frames Gyrotron 1 MOU box Quasi-optical CTS transmission line CTS receiver and electronics cabinet

  17. Exit to CTS Receiver Polarizer Plates Moveable Mirror ASDEX-Upgrade CTS MOU Box #2 Optics CTS Receiver From Tokamak MOU Box #1 MOU Box #2 CTS Receiver CTS Horn

  18. co-NBI ICRH Frq/GHz CTS ECE+CTS ECE TEXTOR CTS Measurements Shot # 100477 with ICRH and NBI • Gyrotron modulated 2 ms on / 2 ms off • Signal from off times (blue) used to determine background (green) to subtract from on times (red) to obtain CTS signal

  19. CTS receiver Probe Scattering volume Establishing CTS Beam Overlap • Receiver scanned in toroidal direction during Ohmic shot # 100467 • Receiver and probe beams go through overlap for a variation of 5 in toroidal angle • Corresponds to scat. volume width of 4 cm perpendicular to figure • k to B angle 110

  20. 45 B B 80 vcts vcts Observations of NBI Fast Ion Anisotropy Shot # 97982 NBI 1 Shot # 97984 NOTCH FILTER

  21. Other Ion CTS Observations at TEXTOR • Sawteeth fast ion dynamics localized in space and orientation, and to lower ion velocities1 • NBI fast ion relaxation after turn off in good agreement with Fokker-plank modeling1 • Toroidal rotation of thermal ion population observed 1Binslev et al., PRL 97, 205005, 2006

  22. Requirements for CTS to Work Understood • Low background electron cyclotron emission (ECE) • Spectrally narrow, clean, and stable probe beam radiation • Sensitive, wideband receiver with deep notch filter for stay light rejection • Receiver robust against gain compression • Well defined, overlapping probe and receiver beams

  23. Gyrotron Spectral Adjustments 110 GHz TEXTOR gyrotron adjusted for clean spectrum Initial Spectrum After Tuning Gyrotron Frequency Gyrotron Frequency Probe signal P(gyro) = 100% 5% 100% 5% 100% Noise level Time (sec) 5% 100% 5% 100% GainCompression 6.5 GHz 6.5 GHz Channel (frequency) Channel (frequency) Careful gyrotron operating parameter adjustment achieves clean spectrum for CTS.

  24. Precision Gyrotron Frequency Measurements ASDEX-Up Gyrotron Measurements • Precision Gyrotron Frequency Measurements Allow: • Optimization of receiver notch filters • Optimization of receiver blocking switch • Improved data analysis • Higher frequency resolution measurements • Bulk ion feature • Plasma rotation • Ion Bernstein waves (fuel ratio) • Other plasma resonances Continuous Modulated

  25. 600 109.62 GHz 500 400 300 200 400 109.54 GHz Spectral power density (eV) 350 300 250 200 109.38 GHz 350 250 150 50 2.4 2.45 2.5 2.55 2.6 2.65 Time (s) Gain Compression Red: gyrotron on, Blue: off Without Gain Compression With Gain Compression Compensation Strategies • Multiplex IF with narrow central band (TEXTOR 2.56 GHz, ASDEX-UP 1.0 GHz) • Use stiff IF amplifiers (Higher output power compression point) • Carefully characterize receiver electronics (Eliminate cross talk)

  26. Beam Alignment and Mapping Micro-rig • Receiver view profile measurements insure well defined view with no side lobes. • Locate view position to help facilitate obtaining overlap with gyrotron probe beam

  27. Summary • CTS diagnostics can make possible a complete determination of the fast ion distribution function f (v, r, t) in burning plasmas • Experiments at TEXTOR and ASDEX-Upgrade are proving fast ion CTS diagnostics • Practical requirements for making fast ion CTS work in burning plasmas are understood and tractable • A basis for a CTS confined alpha particle diagnostic has been established

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