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EXPERIMENTS OF ACTIVE QSH CONTROL IN EXTRAP-T2R. L. Frassinetti, P.R. Brunsell, E.K.J Olofsson and J.R. Drake. OUTLINE. INTRODUCTION (1) The device and the feedback system (2) Diagnostics for MHD modes (3) Spontaneous QSH in EXTRAP T2R EXPERIMENTAL RESULTS (1) Open loop experiments - PowerPoint PPT Presentation
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EXPERIMENTS OF ACTIVE QSHEXPERIMENTS OF ACTIVE QSHCONTROL IN EXTRAP-T2R CONTROL IN EXTRAP-T2R
L. Frassinetti, P.R. Brunsell, E.K.J Olofsson and J.R. Drake
• INTRODUCTION
(1) The device and the feedback system
(2) Diagnostics for MHD modes
(3) Spontaneous QSH in EXTRAP T2R
• EXPERIMENTAL RESULTS
(1) Open loop experiments
(2) Close loop experiments
• CONCLUSIONS
OUTLINE
EXTRAP T2R – the device
• R=1.24m• a=0.18m
• Ip 80kA (standard current plasma)
• ne≈1019m-3
•Te ≈200-400eV
• pulse≈20ms (w/o FeedBack)• pulse≈up to 90ms (with IS)
EXTRAP T2R – the feedback
• shell≈6ms
• 4 poloidal x 32 toroidal sensor saddle coils (m=1 connected) located inside the shell
• 4 poloidal x 32 toroidal active saddle coils (m=1 connected) located outside the shell
• Digital controller
Sensor coils
Activecoils
shell
byOlofsson E.
EXTRAP T2R – algorithmsAt present, three algorithms are routinely used in EXTRAP T2R:
• Open Loop• Intelligent Shell (close loop) IS• Mode Control (close loop) MC
Active coils
plasmaSensor
coils
external helical magnetic
perturbations
Open Loop (OL)Open Loop (OL)
shell
byOlofsson E.
Active coils
plasmaSensor
coils
external helical magnetic
perturbations
Close Loop (MC)Close Loop (MC)
shell
Digitalcontroller
bc
b1,n bcVc(t) V1,n(t)=-Knp[ref-b1,n(t)]
Fourier harmonics in real time
inputto active coils
DIAGNOSTICS
Magnetic perturbations:
br 4 poloidal x 32 toroidal sensor saddle coils (m=1 connected) located inside the shell give the time integrated signals.
TM RWM-12 -13-14
Raw signals
b 4 poloidal x 64 toroidal local sensors (m=1 connected) located inside the shell give the time derivative of the signals.
SPONTANEOUS QSHs IN EXTRAP T2R
QSH example in EXTRAP T2R
MH Ns>2QSH Ns<2 SH Ns=1
Average duration QSH≈0.1ms
Fraction of the discharge characterized by QSHs:
1%QSHQSH
pulse
P
The dominant mode is the first resonant. With the typical equilibrium: nDOM=-12n=-12
vacuum
OPEN LOOP EXPERIMENTS
Active coils
plasmaSensor
coils
external helical magnetic
perturbations
Open Loop (OL)Open Loop (OL)
shell
Basic idea:
• Apply a static helical perturbation (n=-12)
plasmaV=1.4VV=1.2VV=1.0VV=0.8VV=0.6VV=0.4VV=0
Average between5ms-end of discharge
• Study the plasma behaviour
OPEN LOOP EXPERIMENTS
A staticstatic helical field with n=-12 is applied at the plasma boundary.
What happen to the corresponding rotatingrotating TM?
“Often”, the TM is larger than “usual”
in the sense thatmore and longer QSHs
are generated
But the TM still rotates!
spontaneous QSH
induced QSH
OPEN LOOP EXPERIMENTS
More QSHs when the external helical perturbation is used
But when br-12 is too large,
even secondary modes increase
120 QSHs are considered
Amplitude of dominant TM during QSHs
Is the amplitude of the rotating TM during QSH affected
by the external helical perturbation?
spon
tane
ous
QSHQSH
pulse
P
Dominant TM
Secondary TMs
CLOSE LOOP EXPERIMENTS (MC)
Active coils
plasmaSensor
coils
external helical magnetic
perturbations
Close Loop (Mode Control)Close Loop (Mode Control)
shell
Digitalcontroller
bc
b1,n bcVc V1,n=-Kpn b1,n
Fourier harmonics in real time
Calculates inputto active coils
The mode suppression is controlled by kp
-12 Each can be controlled separately.
One mode free to growAll other modes suppressed
n=-12
Secondary modes
CLOSE LOOP EXPERIMENTS (MC)
Amplitude of dominant TM during QSHs
210 QSHs are considered
Are QSH and rotating TMs affected?
The gain of mode n=-12 is reduced
All m
odes suppressed
…20
Gain reduction
br-12 increase
-12
CLOSE LOOP EXPERIMENTS (MC)
Using the optimal kp-12, F is scanned
to test the dependence of PQSH.
PQSH is clearly dependent on F
This is mainly due to a changein the position of the resonant radius.
(1,-11)
(1,-12)
(1,-13)
(1,-14)
(1,-15)
Dependence of resonant radii with F
MH std
CONCLUSIONS
(1) A static helical perturbation can affect the corresponding rotating TM
- Higher QSH probability- The TM velocity is affected- But NOT the TM mode amplitude during the QSH
(2) With the MC better results are obtained
- QSH probability higher than in Open Loop- QSH are more “pure” (i.e. lower secondary modes)- The amplitude of the rotating TM is affected
QSH OL
MH MC
QSH MC
OPEN LOOP EXPERIMENTS
Is the TM velocityvelocity affected by the external perturbation?
Fitzpatrick model [NF 33, 1049 (1993)]