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

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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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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.