Experimental Measurements of Non-MHD Dynamo Effects
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Transcript of Experimental Measurements of Non-MHD Dynamo Effects
many contributors:
J. Anderson W. Ding
D. Brower G. FikselD. Craig H. JiD. Den Hartog J. Sarff
plus most of MST group
<E>|| + dynamo = <j>||
Dynamo theory statusMHD QL, NL comp
€
˜ v × ˜ B
€
˜ j × ˜ B
€
˜ B ⊥∇˜ p ⊥
€
˜ B r ˜ p ||
Hall QL
Diamagnetic very little
Kinetic RR, constraints fromLandau resonances
Three Effects from Two-Fluid Theory
parallel mean-field component,
Linear part,
Using in top eqn,
€
E + v × B −j × B
ne−∇pe
ne= ηj
€
E||+ ˜ v × ˜ B
||+
˜ j × ˜ B ||
ne= η j
||
€
˜ v −˜ j
ne≈
˜ E × B
B2 −
∇˜ p e × B
B2
€
E||+
˜ E ⊥˜ B ⊥
B2 +
(∇⊥˜ p e ) ˜ B ⊥
B2 = η j
||
MHD Hall
Pressureless MHD
diamagnetic
The “kinetic dynamo”radial transport of parallel current along stochastic magnetic field
for electrons, the flux of parallel momentum
or
€
Γr =r Γ || • ˆ r = Γ||
r B
B• ˆ r =
˜ Γ || ˜ B rB
€
Γr =˜ p ||e ˜ B r
B
Experimental Observations
To my knowledge,
Only in RFP(some MHD dynamo measurements in SPHEX spheromak)
Dynamo Measurements
• MHD: some detailed measurements
• Hall: some detailed measurements
• Diamagnetic: one measurement
• Kinetic: no measurements
All measurements are ongoing;
Diagnostics being expanded
in experiment
-0.5
0.5
1.0
1.5
2.0
V/m
0.0
0.0 0.2 0.4 0.6 0.8 1.0ρ/a
E||
neo J||(Zeff = 2)
€
E ≠ η j
E||
j||
radius
additional current drive mechanism (dynamo)
MHD dynamo in edge
€
˜ E ̃ B By Langmuir and magnetic probes
€
˜ v × ˜ B By spectroscopic and magnetic probes
time (ms)
r/a = 0.9
€
⟨ ˜ v × ˜ B ⟩
€
⟨ j⟩− ⟨E⟩
MHD dynamo dominant at some radii, not everywhere
r/a = 0.8
Measurement of MHD dynamo
0
-10
-20
0
-20
-10
Volts m
Volts m
-0.5 0 0.5time (ms)
r/a = 0.9
r/a = 0.8
-25
-20
-15
-10
-5
0
5
-1 -0.5 0 0.5 1 1.5 2
Hall dynamo (V/m)
Time from crash (ms)
Hall term is significant at r/a = 0.8 Fiksel, Almagri
ongoing
time (ms)
V/m
€
⟨ ˜ j × ˜ B ⟩ne
Core measurements of Hall Dynamo
E vector of injected laser rotates by angle
€
~ nBdl∫
Wave phase-shifted by angle
€
~ ndl∫
Can infer
€
˜ B , ˜ j
W. Ding, D. Brower, B. Deng UCLA 2003
3-Wave Polarimeter-Interferometer System
MST R0 = 1.50 ma = 0.52 mIp = 400 kAne ~ 1019 m-3
B0 ~ 4 kG
Faraday rotation/interferometer system
Faraday rotation angle: detects mean B, fluctuating B, sawteeth
6
4
2
0
-2
-4
x=-17 cm
-9
-2
6
13
21
m=1 activity
1.0
0.5
0.026.025.525.024.524.0
[ ] Time ms
external magnetic coil
Current fluctuations increase during dynamo event
120
100
80
60
40
20
-2 -1 0 1 2
Time [ms]
(1,6) mode current fluctutaion
€
˜ j T(kA/m2)
Kinetic dynamo
•No direct measurement
•In ZT-40, fast electrons detected in edge may imply transport from core
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?