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Experimental Measurements of Non-MHD Dynamo Effects

Experimental Measurements of Non-MHD Dynamo Effects. Summarized by S.C. Prager. many contributors:. J. Anderson W. Ding D. Brower G. Fiksel D. Craig H. Ji D. Den Hartog J. Sarff plus most of MST group. <E> || + dynamo = <j> ||. Dynamo theory status MHD QL, NL comp.

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Experimental Measurements of Non-MHD Dynamo Effects

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  1. Experimental Measurements of Non-MHD Dynamo Effects Summarized by S.C. Prager

  2. many contributors: J. Anderson W. Ding D. Brower G. Fiksel D. Craig H. Ji D. Den Hartog J. Sarff plus most of MST group

  3. <E>|| + dynamo = <j>|| Dynamo theory status MHD QL, NL comp Hall QL Diamagnetic very little Kinetic RR, constraints from Landau resonances

  4. Three Effects from Two-Fluid Theory parallel mean-field component, Linear part, Using in top eqn, MHD Hall Pressureless MHD diamagnetic

  5. The “kinetic dynamo” radial transport of parallel current along stochastic magnetic field for electrons, the flux of parallel momentum or

  6. Experimental Observations To my knowledge, Only in RFP (some MHD dynamo measurements in SPHEX spheromak)

  7. Dynamo Measurements • MHD: some detailed measurements • Hall: some detailed measurements • Diamagnetic: one measurement • Kinetic: no measurements All measurements are ongoing; Diagnostics being expanded

  8. in experiment E|| j|| radius additional current drive mechanism (dynamo)

  9. Dynamo occurs in bursts Toroidal Magnetic Flux (Wb) MST time (ms)

  10. MHD Dynamo (exists, but not the whole story)

  11. Early measurement, passive Doppler spectroscopy (1995)

  12. MHD dynamo in edge By Langmuir and magnetic probes By spectroscopic and magnetic probes

  13. 1995 Consistent with MHD dynamo

  14. Spectroscopic Probe Fiksel, Den Hartog yields local flow velocity

  15. Measurement of MHD dynamo 0 Volts m -10 r/a = 0.9 r/a = 0.9 -20 Volts m 0 -10 r/a = 0.8 r/a = 0.8 -20 time (ms) -0.5 0 0.5 time (ms) MHD dynamo dominant at some radii, not everywhere

  16. Hall Dynamo • Edge: magnetic probes • Core: laser Faraday rotation

  17. Fluctuation Power Spectra B probes at edge Shen et al 1993 j Frequency (kHz)

  18. Correlation between j and B phase coherence Frequency (kHz)

  19. Result at r/a ~ 0.9,Hall term accounts for less than 25% of the total current

  20. Hall term is significant at r/a = 0.8 Fiksel, Almagri ongoing V/m time (ms)

  21. Core measurements of Hall Dynamo W. Ding, D. Brower, B. Deng UCLA 2003 E vector of injected laser rotates by angle  Wave phase-shifted by angle  Can infer

  22. 3-Wave Polarimeter-Interferometer System Faraday rotation/interferometer system MST R0 = 1.50 m a = 0.52 m Ip = 400 kA ne ~ 1019 m-3 B0 ~ 4 kG

  23. Faraday rotation angle: detects mean B, fluctuating B, sawteeth

  24. Current fluctuations increase during dynamo event (kA/m2)

  25. Hall dynamo large near resonant surface

  26. Diamagnetic dynamo: significant at some conditions

  27. Kinetic dynamo • No direct measurement • In ZT-40, fast electrons detected in edge may imply transport from core

  28. Summary • Evidence for importance of MHD and Hall dynamos • Some indications that diamagnetic dynamo may be important • Would not be surprised if kinetic dynamo was important. Evidence for stochastic transport of particles, energy - why not electron momentum?

  29. Goal: understand what mechanisms are important, under what conditions • Possibly dynamo always relaxes plasma toward preferred MHD state - specific mechanisms vary with conditions • Experimental dynamo program is active, with new diagnostics.

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