non-collisional ion heating and magnetic turbulence in mst abdulgader almagri on behalf of mst team...
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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
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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.
€
exp(− k⊥kdis)
€
kdis=0.22cm−1
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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
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Deuterium ions are heated at a sawtooth crash
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Heating level has an ion mass dependence
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Majority ions show nearly square root of mass dependence.
• Minority, Carbon, ion may have a similar mass dependence.• Need to know the density.
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A strong non-collisional ion heating often followed by PPCD to sustain high ion temperature.
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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
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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?
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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)
€
m0.5
€
m0.8
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Magnetic spectrum changes character with m=0 mode
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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
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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
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High frequency magnetic fluctuations are locally resonant
r/a =.92 r/a =.80 r/a =.72
Alfven range
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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
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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
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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.
€
m
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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.