Resonant magnetic perturbation effect on the tearing mode dynamic

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Resonant magnetic perturbation effecton the
tearing mode dynamic in EXTRAP T2R
L. Frassinetti, P.R. Brunsell, K.E.J. Olofsson,
J.R. Drake Division of fusion plasma physics,
School of electrical engineering, Alfvén
Laboratory, Royal Inst. of Technology KTH,
Stockholm
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OUTLINE

• The reversed field pinch (RFP)
• Resonant magnetic perturbation (RMP)
• what is a RMP?
• why are RMPs important?
• why are RMPs studied in EXTRAP T2R?
• EXTRAP T2R
• the machine
• the feedback system
• the diagnostics
• Experimental results
• TM dynamics with RMP
• Modelling results
• Fitzpatrick theory
• Attempt for explanation of experimental
  results

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THE REVERSED FIELD PINCH

• The toroidal field changes
• direction at the edge
• Poloidal and toroidal magnetic
• fields with similar amplitudes

q(r)
1
wall
r
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RESONANT MAGNETIC PERTURBATION (RMP)
DIII-D example
What is a RMP? 1- A magnetic perturbation
with an helicity resonant in the
plasma. 2- Typically is produced
by a set of external coils.
Fenstermacher, PoP 15, 056122 (2008)
Evans, Nature Phys. 2, 419 (2006)
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RESONANT MAGNETIC PERTURBATION (RMP)
Why are RMPs important?
1- ELM suppression
RMP produces stochasticity in the plasma outer
region
Abdullaev, PoP 16, 030701 (2009)
the pressure gradient is reduced and the ELM
effect mitigated. DIIID Evans, NF 2008,
48 024002 JET Liang, PRL 2007, 98
265004
Evans, NF 2008, 48 024002
2- Neo-classical tearing mode RMP can
interact with the NTM with stabilizing effects
La Haye, PoP 9, 2051 (2002)
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RESONANT MAGNETIC PERTURBATION (RMP)
Why to study RMP in EXTRAP T2R?
1- The mechanisms for ELM mitigation and NTM
stabilization are not yet fully understood
2- There are many theoretical papers that
investigate the interaction between an RMP
and a TM
3- But not many experimental results are available
4- RMPs can be easily produced with EXTRAP T2R
active coils
5- TMs are present in in EXTRAP T2R
The interaction of the RMP with the corresponding
TM can easily studied in EXTRAP T2R
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EXTRAP T2R the device

• R1.24m
• a0.18m
• Ip ? 80kA (standard current plasma)
• ne1019m-3
• Te 200-400eV
• tpulse20ms (w/o FeedBack)
• tpulseup to 90ms (with IS)

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EXTRAP T2R the active coils
shell
by Olofsson E.
Active coils

• tshell6ms
• 4 poloidal x 32 toroidal
• sensor saddle coils (m1 connected)
• located inside the shell
• 4 poloidal x 32 toroidal
• active saddle coils (m1 connected)
• located outside the shell
• Digital controller

Sensor coils
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EXTRAP T2R the feedback
shell
by Olofsson E.
Active coils
Sensor coils
plasma
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EXTRAP T2R the diagnostics
RMP
m1 n-12
br ? 4 poloidal x 32 toroidal sensor
saddle coils (m1 connected) located
inside the shell give the time integrated
signals.
TM
bq ? 4 poloidal x 64 toroidal local
sensors (m1 connected) located inside
the shell give the time derivative of the
signals.
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EXAMPLE
NO RMP
(1,-12)
average of all other helicities
Effect on the rotating TM
1- amplitude larger and modulated
2- velocity modulated
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SOME DETAILS
1- The TM amplitude is so large (compared
to the other TMs) that a magnetic island
appears in core
RMP0.3mT
2- The TM amplitude is correlated with the
phase shift between TM and RMP
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PHENOMENOLOGICAL EXPLANATION
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EFFECT OF RMP AMPLITUDE
The RMP can amplify the corresponding
TM, but are RMP amplitude and TM amplitude
correlated?
How do the TM properties change?
1- The island size
2- The TM dynamic
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TM DYNAMIC WITH HIGH RMP AMPLITUDE
RMP0.5mT
RMP0.3mT
1- Double oscillation during one
poloidal turn
2- TM locking and unlocking
3- After complete suppression, phase
jump to Df0
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MODELLING
Based on Fitzpatrick theory Phys. Plasmas 8 4489
(2001)
3 coupled partial differential equations
1. TM evolution
2. Torque balance
Viscous torque
EM torque
with
braking torque due to interaction of the rotating
TM with the static RMP
braking torque due to eddy currents In the wall
generated by the rotating TM
3. Helical velocity
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APPLICATION OF THE MODEL
tR4ms ne(0)1.5x1019m-3 w030krad/s D
-0.7 brRMP0.25mT n10-10 kg/(ms)
1- The model gives a reasonable explanation
for a low RMP amplitude
2- For high RMP amplitudes, some features like
the double peak are not yet well reproduced
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CONCLUSIONS

• An external RMP can affect the rotating TM and
  the corresponding magnetic island
• The RMP produces TM amplification or
  suppression depending on the phase shift
• The TM rotation is also affected
• The Fitzpatrick model gives a reasonable
  explanation of this phenomenon
• (for low RMP amplitudes)
• Work in progress and future work
• 1- RMP with another helicity
• 2- Improvement of the model