Title: MHD Dynamos in the Lab and Dynamos Beyond MHD
1MHD 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)
3in experiment
?E?
??j?
radius
additional current drive mechanism (dynamo)
4Measure quantities during discrete dynamo event
Toroidal Magnetic Flux (Wb)
MST
time (ms)
5The MHD Dynamo
6The nonlinear dynamo
instability
energy source
dynamo
MHD dynamo
analytical quasilinear theory, nonlinear MHD
computation
7tasks
- Measurements of dynamo
- Active flow drive
- Connections to more general problem
8MHD Dynamo Status of Past Measurements
- edge measurements with probes,
- core with passive Doppler spectroscopy
- Important in edge and core, but not full story
9Measurement 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
10MHD 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
11SXR 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
12Active 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
13Test 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
14Investigate why alpha effect (ltv x Bgt) large in
lab, small in geometrically simpler computation
- Specifics of flow pattern?
15dynamo effects beyond MHD
16 Effects from Two-Fluid Theory
- parallel mean-field component,
- Linear part,
- Using in top eqn,
MHD
Hall
Pressureless MHD
diamagnetic
17ltEgt dynamo ?ltjgt
- Dynamo theory status
- MHD QL, NL comp
Hall QL
Diamagnetic very little
Kinetic RR, constraints from Landau
resonances
18Status of non-MHD effects
- Diamagnetic dynamo observed in edge probe
measurements under some conditions - Hall dynamo observed in MST recently
19Hall dynamo measured by laser Faraday rotation
rotation angle
11-chord FIR laser
(Ding, Brower, Deng)
20Experimental Goal
- Determine locations and conditions at which
different dynamo mechanisms dominate
21Experimental 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)
22Hall Dynamo Theory and Computation
- Expand quaslinear calculation to finite pressure
- Develop early nonlinear theory
- (Rutherford theory)
- Develop two-fluid computation for lab plasma
(Nimrod)
23Related work
- Two-fluid computation in a box shows Hall dynamo
important under some conditions - (Minnini, Gomez, Mahajan)
24Ongoing
- Assessment of astrophysical relevance of various
dynamo effects