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Diagnostic techniques for measuring suprathermal electron dynamics in plasmas

Diagnostic techniques for measuring suprathermal electron dynamics in plasmas. Centre de Recherches en Physique des Plasmas. EPFL, Association Euratom-F é d é ration Suisse, Lausanne, Switzerland. S. Coda. The elusive Maxwellian distribution. RHESSI hard X-ray solar images:

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Diagnostic techniques for measuring suprathermal electron dynamics in plasmas

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  1. Diagnostic techniques for measuring suprathermal electron dynamicsin plasmas Centre de Recherches en Physique des Plasmas EPFL, Association Euratom-Fédération Suisse, Lausanne,Switzerland S. Coda

  2. The elusive Maxwellian distribution RHESSI hard X-ray solar images: March 25, 2008 flare S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  3. Outline • origin and interest of suprathermal electrons • comparison of diagnostic techniques • hard X-rays • electron cyclotron radiation • other techniques • conclusions and outlook S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  4. Origin and interest of fast electrons • External drives: e.m. waves, electric fields (laboratory - strongly driven, non-equilibrium systems) • Internal drives: magnetic reconnection, e.m. instabilities (laboratory, solar corona, aurora) Study of fast electrons brings understanding of drives  important for MHD, current drive, runaways, etc. S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  5. Diagnostic techniques Hard X-rays • good spatial resolution • poor time resolution • energy deconvolution only through modeling Electron cyclotronradiation • good time resolution • energy and space convolved Spectroscopy • good space and time resolution • difficult anisotropy deconvolution Probes,energy analyzers • good space and time resolution • limited to low temperature S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  6. - g + also thick-target bremsstrahlung (JT-60, ASDEX, …) Hard-X-ray bremsstrahlung electron-ion collisions  photons up to hn = Eelectron S. von Goeler et al, RSI 65, 1621 (94) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  7. HXR • initially driven by mirror machines, runaways,LHCD • scintillation detectors (NaI, CsI, BGO) + photomultipliers, intensifiers ST, PLT, PBX-M,Alcator-C, TEXTOR,WT-3, ASDEX, JET, … PBX-M S. von Goeler et al, FED 34-35, 97 (97) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  8. HXR HXR used to determine LHCD profile peaked off-axis peaked on-axis PBX-M S. Jones et al, PPCF 35, 1003 (93) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  9. Alcator-C HXR • electron distribution function cannot be derived in general • parametric model widely used for LHCD PBX-M, Alcator-C, WT-3, JFT-2M, … S. Texter et al, PLA 175, 428 (93) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  10. 0.15 0.30 0.60 m2/s HXR suprathermal electron transport with LHCD:generally negligible (<1 m2/s) w.r.t. collisional slowing-down data model ASDEX R. Bartiromo et al, NF 33, 1483 (93) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  11. HXR • laser fusion requires speed:fast plastic scintillators + microchannel plates/PMTs • fast electron generation preheats target, reducing compression and probability of direct-drive ignition OMEGA C. Stoeckl et al, RSI 72, 1197 (01) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  12. LH+EC LH HXR hardware developments: solid-state detectors (Ge, Si) JFT-2M H. Kawashima, JJAP 33, 3590 (94) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  13. HXR The advent of ECRH early measurements (T-10) suggested reduced ECCD efficiency but suprathermal transport still negligible Compass-D, RTP, T-10, TCV,Tore Supra, TJ-II, HSX, LHD, … T-10 V.V. Alikaev et al, NF 32, 1811 (92) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  14. HXR sawteeth have no effect on LHCD suprathermals • further hardware developments: high-Z,room-temperature solid-state detectors (CdTe, CZT) • tomography(Tore Supra) • also wire chamber (mainly SXR) 20-40 keV 40-60 keV 60-80 keV Tore Supra, TCV, HSX, MST, FTU, T-10, Alcator C-Mod, ADITYA, HT-7, HL-1M TORE SUPRA F. Imbeaux, Y. Peysson, PRL 84, 2973 (00) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  15. HXR High-power-density ECCD: suprathermal transport becomes significant  current profile broadening, less efficiency enhancement TCV S. Coda et al, NF 43, 1361 (03) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  16. HXR MHD: electrons acceleration by reconnection (sawteeth, disruptions) T-10 JET, T-10, TCV, … P.V. Savrukhin, PPCF 48, B201 (06) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  17. HXR ADITYA The last generation P.K. Sharma et al, FED 81, 41 (07)  HgI2 detectors on HL-1M  Real-time control on Tore Supra  Full tomography proposed forTCV (S. Gnesin poster N1 @10:30) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  18. g - Electron cyclotron emission w = nwce/g + v//k// sensitive to suprathermals if • HFS perpendicular to B-field • oblique LFS measurement potential in • multiple harmonics(emission  v2n) • X+O polarizations(v direction dependence) v// v S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  19. ECE Vertical HFS ECE: R  energy • Averagepitch-angle distribution derived • Early applications to LHCD, runaways Alcator-C, PLT,TEXT-U, TCV, WT-3, … PLT T. Luce et al, RSI 59, 1593 (88) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  20. a) no turbulent diffusion b-c) magnetic turbulence magn. + e.s. turb. ECE Vertical ECE Study fast electron transport w. ECRH by fit toFokker-Planck model TEXT-U G. Giruzzi et al, PPCF 38, 1593 (96) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  21. ECE ECE ECCD HFS ECE to probe suprathermal dynamics bi-Maxwellian modelto deconvolve R and energy TCV S. Coda et al, PPCF 48, B359 (06) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  22. ECE Oblique LFS ECE geometry  Rmin resonance  Rmax  localization PBX-M PBX-M,TORE SUPRA, JET, FTU, TCV S. Preische et al, RSI 68, 409 (97) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  23. ECE Oblique LFS ECE Co- vs counter-ECCD  v// asymmetry ECE asymmetry CO COUNTER TCV T.P. Goodman et al, ECA 31F, 2.147 (07) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  24. ECE Synchrotron radiation from runaways (infrared) TEXTOR I. Entrop et al, PPCF 40, 1513 (98)  Related technique: Čerenkov emission (runaways) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  25. Electron cyclotron absorption oblique vertical propagation: resolves v// Versator II LHCD Versator II,TORE SUPRA, TdeV R. Kirkwood et al, PFB 2, 1421 (90) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  26. Plasma polarization spectroscopy light emitted by excited atoms preserves memory of electron velocity distribution R. Fischer, V. Dose, PPCF 41, 1109 (99) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  27. Other techniques • Langmuir probes • derive electron distribution from first and second derivatives of probe current (e.g. JFT-2M) • In-situ electron spectrometers • electrostatic analyzers, electron multipliers • Indirect methods: • Pyrobolometers and optical pyrometers: determination of energy flux (e.g. MST, laser fusion) • Radio waves converted from plasma instabilities excited by suprathermals (e.g. radio bursts from solar corona) S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

  28. Conclusions and outlook • From space to laboratory,non-Maxwellian electron distribution functions are the norm • Suprathermal electrons play a fundamental role incurrent drive, reconnection, disruptions, MHD, etc. proper diagnosis important for understanding • Several mature diagnostic techniques:particularly based on X-rays and cyclotron radiation • Many challenges still: • reliable deconvolution of local energy distribution tomography, imaging • increasingly sophisticated model-based analysis constraints • real-time control S. Coda, 17th HTPD Conf., Albuquerque, NM, 11-15 May 2008

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