Non-collisional ion heating and Magnetic Turbulence in MST Abdulgader Almagri On behalf of MST Team...
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Transcript of Non-collisional ion heating and Magnetic Turbulence in MST Abdulgader Almagri On behalf of MST Team...
Non-collisional ion heating and Magnetic Turbulence in MST
Non-collisional ion heating and Magnetic Turbulence in MST
Abdulgader Almagri
On behalf of MST Team
RFP Workshop • Padova, Italy • April 2010
Motivation.
• During a magnetic reconnection event ions are transiently heated to as high as 3 keV, often exceeding the electron temperature.
• High frequency small scale magnetic turbulence is anisotropic in wave number.
• Magnetic fluctuation has a power law dependence (Cascade) and an exponential
law (dissipation). The dominate fluctuation is where much smaller, stronger dissipation, than classical resistive and viscose theoretical predictions.
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exp(− k⊥kdis)
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kdis=0.22cm−1
Outline.
• Non-collisional ion heating during reconnection event.
1. Ion heating and mass dependence.
2. Strong ion heating and sustainment with current profile control
• Magnetic turbulence.
1. Magnetic anisotropy.
2. Exponential low and dissipative mechanism
Deuterium ions are heated at a sawtooth crash
Heating level has an ion mass dependence
Majority ions show nearly square root of mass dependence.
• Minority, Carbon, ion may have a similar mass dependence.• Need to know the density.
A strong non-collisional ion heating often followed by PPCD to sustain high ion temperature.
An anisotropy in the minority ions develops at high density
Ti is sampled every 100 sec, Ti per and par. equilibration time is short, about 10 sec
Energy flow
Energy released from mean fields
(0,1) mode
Low n TearingMode grow
High n50< f(kHz) <600
Modes grow
Mass dependent ion heating
Dissipation
Cascade
What is the dissipation
mechanism?
Why does the heating depend on mass?
Ion heating mass dependence, theory
We have two models that predict similar mass dependence
• A theoretical model based on a randomly varying electric field predicts G. Fiksel et al., Phys. Rev. Lett. 103, 145002 (2009).
• Ion cyclotron damping in a turbulent cascade predicts V. Tangri, et. al. Phys. Plasmas 15, 11250 (2008)
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m0.5
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m0.8
Magnetic spectrum changes character with m=0 mode
Low frequency magnetic spectrum changes character with m=0 mode
214 sawtooth events with n=155 sawtooth events without n=1
13-apr-200605-may-2006
n=1 n=6 n=7 n=8
n=9 n=10 n=11 n=12
n=13 n=14 n=15
before ST
without n=1
with n=1
time (ms) time (ms) time (ms) n
n-spectrum
Small scale magnetic turbulence is strongly anisotropic with respect to mean field.
5 < f(kHz) < 50Tearing
50 < f(kHz) < 350Alfven
350 < f(kHz) < 2000Ion cyclotron
At r/a = 0.92
High frequency magnetic fluctuations are locally resonant
r/a =.92 r/a =.80 r/a =.72
Alfven range
The small scale turbulence having a radial standing wave structure
Radial Coherence Radial phase
Higher frequency modes have smaller radial width
High frequency modes show sudden phase change from 0 to π, which is consistent with a radial standing wave structure
The dominant magnetic turbulence has an exponential law,dissipation
€
exp(−k⊥kdis
),kdis −0.22cm−1
P.W. Terry, and V. Tangri, Phys. Plasmas 16, 82305 (2009)
Theoretical analysis show that the observed dissipation in MST is Stronger than can be accounted for by classical resistivity or viscosity
Summery of Results
• Ions , majority and minority, are heated to new record values, 3 keV, by unknown non-collisional process.
• The heating level has an ion mass dependence.
• The majority ions show nearly dependence.
• The minority ions may have a simmilar mass dependence.
• The non-collisional ion heating occurs only when there is an m=0 activity, during sawtooth.
• The minority ions heating is asymmetric. At low density, both of the parallel and the perpendicular ion temperature increases. At high density the parallel temperature is unaffected.
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m
Summary continued
• Magnetic spectrum changes character with m=0 mode.
• Low frequency magnetic spectrum changes character with m=0 mode.
• Small scale magnetic turbulence is strongly anisotropic with respect to mean field.
• High frequency magnetic fluctuations are locally resonant.
• The small scale turbulence having a radial standing wave structure.
• The dominant magnetic turbulence has an exponential law, dissipation.