Transcript Inductive Current Profile Control and Sustainment in the RFP

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 exp( k ) where k  0.22cm much
k
smaller, stronger dissipation, than classical resistive and viscose theoretical
predictions.
1

dis
dis


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 msec, Ti per and par. equilibration time is short, about 10 msec
Energy flow
Energy released
from mean fields
(0,1) mode
Low n Tearing
Mode grow
Cascade
What is the
dissipation
mechanism?
High n
50< f(kHz) <600
Modes grow
Dissipation
Mass dependent ion heating
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 m0.5
G. Fiksel et al., Phys. Rev. Lett. 103, 145002 (2009).

• Ion cyclotron damping in a turbulent cascade predicts m0.8
V. Tangri, et. al. Phys. Plasmas 15, 11250 (2008)

Magnetic spectrum changes character with m=0 mode
Low frequency magnetic spectrum changes character with m=0
mode
214 sawtooth events with n=1
55 sawtooth events without n=1
13-apr-2006
05-may-2006
n=1
n=6
n=7
n=8
n=9
n=10
n=11
n=12
n-spectrum
n=13
n=14
n=15
with n=1
without n=1
before ST
time (ms)
time (ms)
time (ms)
n
Small scale magnetic turbulence is strongly anisotropic with
respect to mean field.
5 < f(kHz) < 50
Tearing
50 < f(kHz) < 350
Alfven
At r/a = 0.92
350 < f(kHz) < 2000
Ion cyclotron
High frequency magnetic fluctuations are locally resonant
r/a =.92
r/a =.80
Alfven range
r/a =.72
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
k
exp(  ),k  0.22cm1
dis
k
dis
Theoretical analysis show that the observed dissipation in MST is
Stronger than can be accounted for by classical resistivity or viscosity
P.W. Terry, and V. Tangri, Phys. Plasmas 16, 82305 (2009)
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
•
The minority ions may have a simmilar mass dependence.
m 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.
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.