Mhd dynamos in the lab and dynamos beyond mhd
Download
1 / 24

MHD Dynamos in the Lab and Dynamos Beyond MHD - PowerPoint PPT Presentation


  • 131 Views
  • Uploaded on

MHD Dynamos in the Lab and Dynamos Beyond MHD. 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

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'MHD Dynamos in the Lab and Dynamos Beyond MHD' - Antony


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Mhd dynamos in the lab and dynamos beyond mhd l.jpg

MHD Dynamos in the LabandDynamos Beyond MHD


Slide2 l.jpg

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)


In experiment l.jpg
in experiment

E||

j||

radius

additional current drive mechanism (dynamo)


Measure quantities during discrete dynamo event l.jpg
Measure quantities during discrete dynamo event

Toroidal

Magnetic

Flux

(Wb)

MST

time (ms)



The nonlinear dynamo l.jpg
The nonlinear dynamo

instability

energy

source

dynamo

MHD dynamo

analytical quasilinear theory, nonlinear MHD computation


Tasks l.jpg
tasks

  • Measurements of dynamo

  • Active flow drive

  • Connections to more general problem


Mhd dynamo status of past measurements l.jpg
MHD Dynamo: Status of Past Measurements

  • edge measurements with probes,

    core with passive Doppler spectroscopy

  • Important in edge and core, but not full story


Measurement of mhd dynamo l.jpg
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


Mhd dynamo measurements 3 year project l.jpg
MHD Dynamo Measurements(~ 3 year project)

  • Measure spatial profile of <v x B> 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


Sxr imaging of dynamo instabilities l.jpg
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


Active flow drive l.jpg
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


Test experimental feasibility in mst l.jpg
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


Investigate why alpha effect v x b large in lab small in geometrically simpler computation l.jpg
Investigate why alpha effect (<v x B>) large in lab, small in geometrically simpler computation

Specifics of flow pattern?


Dynamo effects beyond mhd l.jpg

dynamo effects beyond MHD in geometrically simpler computation


Effects from two fluid theory l.jpg
Effects from Two-Fluid Theory in geometrically simpler computation

parallel mean-field component,

Linear part,

Using in top eqn,

MHD

Hall

Pressureless MHD

diamagnetic


E dynamo j l.jpg
<E> in geometrically simpler computation|| + dynamo = <j>||

Dynamo theory status

MHD QL, NL comp

Hall QL

Diamagnetic very little

Kinetic RR,

constraints from

Landau resonances


Status of non mhd effects l.jpg
Status of non-MHD effects in geometrically simpler computation

  • Diamagnetic dynamo observed in edge probe measurements under some conditions

  • Hall dynamo observed in MST recently


Hall dynamo measured by laser faraday rotation l.jpg
Hall dynamo measured by laser Faraday rotation in geometrically simpler computation

rotation angle

11-chord

FIR laser

(Ding, Brower, Deng)


Experimental goal l.jpg
Experimental Goal in geometrically simpler computation

Determine locations and conditions at which different dynamo mechanisms dominate


Experimental plans l.jpg
Experimental Plans in geometrically simpler computation

  • 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)


Hall dynamo theory and computation l.jpg
Hall Dynamo Theory and Computation in geometrically simpler computation

  • Expand quaslinear calculation to finite pressure

  • Develop early nonlinear theory

    (Rutherford theory)

  • Develop two-fluid computation for lab plasma (Nimrod)


Related work l.jpg
Related work: in geometrically simpler computation

Two-fluid computation in a box shows Hall dynamo important under some conditions

(Minnini, Gomez, Mahajan)


Ongoing l.jpg
Ongoing in geometrically simpler computation

Assessment of astrophysical relevance of various dynamo effects