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

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Presentation on theme: "Experimental Measurements of Non- MHD Dynamo Effects Summarized by S.C. Prager."— Presentation transcript:

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

2 many contributors: J. AndersonW. Ding D. BrowerG. Fiksel D. CraigH. Ji D. Den Hartog J. Sarff plus most of MST group

3 || + dynamo = || Dynamotheory status MHDQL, NL comp HallQL Diamagneticvery little KineticRR, 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 Consistent with MHD dynamo 1995

14 Spectroscopic Probe Fiksel, Den Hartog yields local flow velocity

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

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

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

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

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 time (ms) V/m

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

22 3-Wave Polarimeter-Interferometer System MST R 0 = 1.50 m a = 0.52 m I p = 400 kA n e ~ m -3 B 0 ~ 4 kG Faraday rotation/interferometer system

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

24 Current fluctuations increase during dynamo event (kA/m 2 )



27 Hall dynamo large near resonant surface

28 Diamagnetic dynamo: significant at some conditions

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

30 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?

31 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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