effects of external non-axisymmetric perturbations on plasma rotation
DESCRIPTION
Effects of external non-axisymmetric perturbations on plasma rotation. L. Frassinetti, P.R. Brunsell, J.R. Drake, M.W.M. Khan, K.E.J. Olofsson Alfvén Laboratory, Royal Institute of Technology KTH Stockholm. Introduction. Braking of plasma rotation due to non-axisymmetric perturbations - PowerPoint PPT PresentationTRANSCRIPT
Effects of externalnon-axisymmetric perturbations
on plasma rotation
L. Frassinetti, P.R. Brunsell, J.R. Drake, M.W.M. Khan, K.E.J. Olofsson
Alfvén Laboratory, Royal Institute of Technology KTH
Stockholm
OUTLINE
• IntroductionIntroduction Braking of plasma rotation due to non-axisymmetric perturbations - resonant perturbation RMP - non-resonant pert. non-RMP
- Braking due to a RMP (1) helicity resonant close to the axisclose to the axis (2) helicity resonant far from the axisfar from the axis- Braking due to a non-RMP (3) internal non-resonant helicity
• Experimental resultsExperimental results
- The machine and the feedback (quick overview)- Diagnostics
• EXTRAP T2REXTRAP T2R
n=-10
n=-12n=-15
INTRODUCTION
RMPs are an essential tool for ELM mitigation in tokamaks
Do they have only ““positive”positive” effects on the plasma? NO
For example RMPs can produce:
-density pump out
-plasma brakingplasma braking
Present understanding: the braking can be due to two phenomena
(2) Neoclassical toroidal viscosity torque - Toroidal viscous force on plasma fluid as it flows through a non- axisymmetric perturbation
- Collisions and particle drifts in non-axisymmetric field cause a non-ambipolar radial particle flux (radial current) which gives a toroidal force.
RMPRMP
RMP RMP and Non-RMPNon-RMP
From: Y. Sun (FZJ)
(1) Localised electromagnetic torque -interaction between the static RMP and the corresponding TM
EXTRAP T2R
EXTRAP T2R is a RFP with:
• R=1.24m• a=0.18m
• Ip ≈ 80-150kA• ne ≈ 1019m-3
• Te ≈ 200-400eV
• tpulse≈ 20ms (no FeedBack)• tpulse≈ 90ms (with IS)
The device
byOlofsson E.
shell
Sensor coils
Activecoils
• shell≈13.8ms (nominal)• SENSOR COILS 4 poloidal x 32 toroidal sensor saddle coils (m=1 connected) located inside the shell• ACTIVE COILS 4 poloidal x 32 toroidal active saddle coils (m=1 connected) located outside the shell
The feedback
m=1n=-12
Time (ms)
0 20 40 60
b r1,
n (m
T)
0.6
0.4
0.2
0.0
r/a0.0 0.2 0.4 0.6 0.8 1.0
v1,n (
km/s
)
80
60
40
20
0
-20
OIII
OII
OV
OIV
Experimental vi
r/a0.0 0.2 0.4 0.6 0.8 1.0
v1,n (
km/s
)
80
60
40
20
0
-20
Magnetic diagnosticsb 4 poloidal x 64 toroidal local sensors (m=1 connected) located inside the shell.
Plasma flow diagnostics5-channel spectrometer for emissivity profile of impurities
Modelled vi
-30 -25 -20 -15 -10 n
80
60
40
20
0
-20
v1,n (
km/s
)
1,1,
nn dR
vn dt
Poloidal velocity is not considered
0
0
0
0
( ) cos ( ) ( )
cos ( )
x
ixi x
ix
v x x x dxv
x dx
Plasma flow v(r): v(x,) is assumed
Free parameters from minimization of modelled and experimental vi [Cecconello, PPCF 2006]
Spectrometer for Doppler shift of ion lines
OV velocity
Time (ms)0 10 20 30 40 50 60
80
60
40
20
0
VO
V (
km/s
)
I OV
(au)
OV
(au)
brightnessR
econstructedem
issivity
experimentalmodelled
r/a
OV emissivity0.0 0.2 0.4 0.6 0.8 1.0
1.5
1.0
0.5
0.0
0.8
0.4
0.0
velocity profile (magnetics)80
60
40
20
0
-20
vma
g (k
m/s
)
0.0 0.2 0.4 0.6 0.8 1.0r/a
BRAKING DUE TO A RMP
(1,-12)
(1,-12)
(1,-12) most internal TM
Braking occurs for all TMs
Flow braking
0.0 0.2 0.4 0.6 0.8 1.0r/a
0.10
0.08
0.06
0.04
0.02
0.00
-0.02
q(r)
0 20 40 60Time (ms)
80
60
40
20
0
v1,-1
2 (
km/s
)
80
60
40
20
0
vOV (
km/s
)
1.00.8
0.6
0.4
0.2
0.0
b r1,
n (
mT
)
120100
8060
40
200
Ip (
)kA
flow profile (spectroscopy)80
60
40
20
0
-20
flow
(km
/s)
r/a0.0 0.2 0.4 0.6 0.8 1.0
before RMPduring RMP
before RMPduring RMP
Time (ms)20.0 20.05 20.10 20.15 20.20
Pha
se (
1,-1
9)
40.0 40.05 40.10 40.15 40.20
Time (ms)
Pha
se (
1,-1
9)
BRAKING vs RMP amplitude
RMP 0.4mT10ms
RMP 0.6mT 4ms
RMP 0.4 mT braking in 10ms10ms to vv~30km/s~30km/s
RMP 0.6 mT braking in 4ms4ms to v~10km/sv~10km/s (1,-12) is locked to the wall (RMP)but the other TMs still rotate!
velocity profile (magnetics)
0.0 0.2 0.4 0.6 0.8 1.0r/a
80
60
40
20
0
-20vm
ag (
km/s
)
0 20 40 60Time (ms)
80
60
40
20
0
v1,-1
2 (
km/s
)
80
60
40
20
0
vOV
(km
/s)
before RMPduring RMP
(1,-12)
1, 12magv
Average during RMP(each dot corresponds a different shot)
60
40
20
00.0 0.2 0.4 0.6 0.8 1.0
brRMP (mT)
V
(km
/s)
OVspecv
The flow seems to brake
with a lower rate
0.0 0.2 0.4 0.6 0.8
r/a
vm
ag (
km/s
)
10
0
-10
-20
-300.0 0.2 0.4 0.6 0.8
r/a
BRAKING DUE TO A RMP FAR FROM THE AXIS
Any difference between
-12 and -15?YES
(1,-15)
(1,-15)
(1,-15) resonant at r/a~0.4
80
60
40
20
0
v1,-1
2 (
km/s
)
80
60
40
20
0
vOV (
km/s
)
1.00.8
0.6
0.4
0.2
0.0
b r1,
n (
mT
)
120100
8060
40
200
Ip (
)kA
0 10 20 30 40 50 60Time (ms)
RMP (1,-12)
velocity profile (magnetics)
0.0 0.2 0.4 0.6 0.8
r/a
velocity profile (magnetics)
before RMPduring RMP
RMP (1,-15)
before RMPduring RMP
0.0 0.2 0.4 0.6 0.8
r/a
80
60
40
20
0
-20
vma
g (
km/s
)
0.0 0.2 0.4 0.6 0.8 1.0r/a
0.10
0.08
0.06
0.04
0.02
0.00
-0.02
q(r)
region ofmax v
1, 15risr
1, 12risr
BRAKING DUE TO A RMP FAR FROM THE AXIS
Average during RMP(each dot corresponds a different shot)
1, 12magv
1, 15magv
Comparison of braking due to RMP (1,-15)RMP (1,-15) and RMP (1,-12)RMP (1,-12)
velocity profile (magnetics)
before RMPduring RMP
(1,-12)
0.0 0.2 0.4 0.6 0.8 1.0
r/a
80
60
40
20
0
-20
vma
g (
km/s
)
before RMPduring RMP
(1,-15)
0.0 0.2 0.4 0.6 0.8 1.0
r/a
80
60
40
20
0
-20
vma
g (
km/s
)
60
40
20
0
Vm
ag
(km
/s)
0.0 0.2 0.4 0.6 0.8 1.0 1.2
brRMP (mT)
0.0 0.2 0.4 0.6 0.8r/a
vm
ag (
km/s
)
10
0
-10
-20
-30
-40
-500.0 0.2 0.4 0.6 0.8
r/a
10
0
-10
-20
-30
(1,-10)(1,-10)
BRAKING DUE TO A non-RMP(1,-10) non-resonant(1,-10) non-resonant
Not a significantNot a significantdifferencedifference80
60
40
20
0
v1,-1
2 (
km/s
)
80
60
40
20
0
vOV (
km/s
)
1.00.8
0.6
0.4
0.2
0.0
b r1,
n (
mT
)
120100
8060
40
200
Ip (
)kA
0 10 20 30 40 50 60Time (ms)
0.0 0.2 0.4 0.6 0.8 1.0r/a
0.10
0.08
0.06
0.04
0.02
0.00
-0.02
q(r)
velocity profile (magnetics)
0.0 0.2 0.4 0.6 0.8r/a
80
60
40
20
0
-20
RMP (1,-12)RMP (1,-12)
velocity profile (magnetics)
0.0 0.2 0.4 0.6 0.8r/a
80
60
40
20
0
-20vm
ag (
km/s
)
non-RMP (1,-10)non-RMP (1,-10)
1, 12magv
OVspecv
RMP (1,-12)RMP (1,-12)
0.0 0.2 0.4 0.6 0.8
brRMP (mT)
Average during RMP(each dot corresponds a different shot)
non-RMP (1,-10)non-RMP (1,-10)
1, 12magv
OVspecv
0.0 0.2 0.4 0.6 0.8
60
40
20
0
V
(km
/s)
brRMP (mT)
BRAKING vs non-RMP amplitude
before RMPduring RMP
(1,-12)
0.0 0.2 0.4 0.6 0.8 1.0r/a
0.0 0.2 0.4 0.6 0.8 1.0r/a
80
60
40
20
0
-20
vma
g (k
m/s
) (1,-12)
Not a significantdifferences so far
0 10 20 30 40 50 60Time (ms)
60
40
20
0
V1,
-12
(km
/s)
vOV
(km
/s)
60
40
20
0
0.8
0.6
0.4
0.2
0.0
b r1,
n (
mT
)
In this region the RMP
is very perturbative
CONCLUSIONS
MAIN CONCLUSION: clear evidence of plasma rotation braking due to external perturbations
RMPRMP
(close to axis)(close to axis)
RMPRMP
(far from axis)(far from axis)
non-RMPnon-RMP
(1,-10)(1,-10)
Plasma flow(from spectroscopy)
Braked Braked Braked
Mode velocity(from magnetics)
Braked Braked Braked
Velocity profile Globally affected Globally affected Globally affected
Velocity variation Peaked at the resonance
(on axis)
Peaked at the resonance
(off axis)
Peaked on the axis
Role of the perturbation amplitude
Braking increases
with RMP amplitude
Braking increases with RMP amplitude
Braking increases with non-RMP amplitude