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MHD Dynamos in the Lab and Dynamos Beyond MHD

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MHD Dynamo: Status of Past Measurements. edge measurements ... If good absorption, then model with MHD computation, implement in MST and MRX ... MHD effects ... – PowerPoint PPT presentation

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Title: MHD Dynamos in the Lab and Dynamos Beyond MHD


1
MHD Dynamos in the LabandDynamos Beyond MHD
2
  • The lab plasma dynamo does
  • Generate current locally
  • Increase toroidal magnetic flux
  • Conserve magnetic helicity
  • Act through alpha and other effects
  • Arise from fluctuations superposed on the mean
    field
  • Achieve a nonlinearly saturated steady state
  • (with full backreaction)
  • The lab plasma dynamo does NOT
  • Generate magnetic field from a small seed field
  • Increase magnetic energy (it redistributes
    magnetic field)

3
in experiment
?E?
??j?
radius
additional current drive mechanism (dynamo)
4
Measure quantities during discrete dynamo event
Toroidal Magnetic Flux (Wb)
MST
time (ms)
5
The MHD Dynamo
6
The nonlinear dynamo

instability
energy source
dynamo
MHD dynamo
analytical quasilinear theory, nonlinear MHD
computation
7
tasks
  • Measurements of dynamo
  • Active flow drive
  • Connections to more general problem

8
MHD Dynamo Status of Past Measurements
  • edge measurements with probes,
  • core with passive Doppler spectroscopy
  • Important in edge and core, but not full story

9
Measurement of MHD dynamo
0
Volts m
r/a 0.9
-10
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
10
MHD Dynamo Measurements( 3 year project)
  • Measure spatial profile of ltv x Bgt in MST
  • good progress in CHERS for v - now debuting
  • laser Faraday rotation improving (B)
  • motional Stark effect in several years (B)
  • probes for edge
  • Measure dynamo and helicity changes in MRX
  • probes

11
SXR imaging of dynamo instabilities
information on 3D structure of magnetic
field, collaboration with RFX team (P. Franz, P.
Martin, L. Mirelli)
spatial resolution being improved
12
Active Flow Drive
  • Present experiments
  • Flow drive experiments

Exploratory flow drive via neutral beam
injection, inject 25 keV beam of neutral
atoms, transfers momentum to plasma
13
Test experimental feasibility in MST
Beam installed momentum transfer tested in few
months
from Novosibirsk
If good absorption, then model with MHD
computation, implement in MST and MRX
14
Investigate why alpha effect (ltv x Bgt) large in
lab, small in geometrically simpler computation
  • Specifics of flow pattern?

15
dynamo effects beyond MHD
16
Effects from Two-Fluid Theory
  • parallel mean-field component,
  • Linear part,
  • Using in top eqn,

MHD
Hall
Pressureless MHD
diamagnetic
17
ltEgt dynamo ?ltjgt
  • Dynamo theory status
  • MHD QL, NL comp

Hall QL
Diamagnetic very little
Kinetic RR, constraints from Landau
resonances
18
Status of non-MHD effects
  • Diamagnetic dynamo observed in edge probe
    measurements under some conditions
  • Hall dynamo observed in MST recently

19
Hall dynamo measured by laser Faraday rotation
rotation angle

11-chord FIR laser
(Ding, Brower, Deng)
20
Experimental Goal
  • Determine locations and conditions at which
    different dynamo mechanisms dominate

21
Experimental Plans
  • Measure diamagnetic dynamo
  • (probes in MST and MRX, explore Thomson
    scattering for pe)
  • Measure ve x B ( v x B j x B/ne)
  • (explore laser Fizeau effect for ve,)
  • Measure Hall dynamo with improved spatial
    resoluton
  • (Faraday rotation, MSE, probes)

22
Hall Dynamo Theory and Computation
  • Expand quaslinear calculation to finite pressure
  • Develop early nonlinear theory
  • (Rutherford theory)
  • Develop two-fluid computation for lab plasma
    (Nimrod)

23
Related work
  • Two-fluid computation in a box shows Hall dynamo
    important under some conditions
  • (Minnini, Gomez, Mahajan)

24
Ongoing
  • Assessment of astrophysical relevance of various
    dynamo effects
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