effect of 3d fields on flows in rfps
DESCRIPTION
EFFECT OF 3D FIELDS ON FLOWS IN RFPs L. Frassinetti, P. Brunsell, S. Menmuir, K.E.J. Olofsson and J.R. Drake Association EURATOM-VR , School of Electrical Engineering, Royal Institute of Technology KTH, Stockholm. OUTLINE. Experimental tools : - EXTRAP T2R - The feedback system - PowerPoint PPT PresentationTRANSCRIPT
EFFECT OF 3D FIELDS ON FLOWS
IN RFPs
L. Frassinetti, P. Brunsell, S. Menmuir, K.E.J. Olofsson and J.R. Drake
Association EURATOM-VR , School of Electrical Engineering, Royal Institute of Technology KTH, Stockholm
Experimental toolsExperimental tools:
- EXTRAP T2R - The feedback system - External magnetic perturbations
Plasma flow and Tearing Modes (TM) braking with - non-Resonant Magnetic Perturbations (non-RMP) (m=1, n=-10)(m=1, n=-10)
- Resonant Magnetic Perturbations (RMP) (m=1, n=-12)(m=1, n=-12) (m=1, n=-15)(m=1, n=-15)
TM dynamics on short time scale (0.1ms) with RMP and non-RMP
Modelling and viscosity profile estimation
0 0.5 1.0 1.5 2.0Te (keV)
100
75
50
25
0
flow
(km
/s)
RFX-modRFX-mod
EXTRAP T2REXTRAP T2RTM velocity 20-80 km/s
TM mainly wall locked
R/a=1.24m/0.183m Ip < 150kA tpulse≈ 0.1 s
-15
-12-13
-14
-16
(m=1 n<-12) are resonant
EXTRAP T2R safety factor
TM velocities: 4x64 local sensors for b
Plasma flow: Passive Doppler spectroscopy for OV, OIV, OIII, OII
-10-12
-15
shellshellshellshell≈≈13.8ms 13.8ms
(nominal)
active active coilscoils
sensor sensor coilscoils
The system is composed of:
- Sensor coilsSensor coils 4 poloidal x 32 toroidal located inside the shell
- Digital controller
- Active coilsActive coils 4 poloidal x 32 toroidal located outside the shell
0 10 20 30 40 50 60 70Time (ms)
1.0
0.8
0.6
0.4
0.2
0.0
br(
mT)
No Feedback
LCFS
(cm)
0 10 20 30 40 50 60 70Time (ms)
1.0
0.8
0.6
0.4
0.2
0.0
br(m
T)
Intelligent Shell
LCFS
(cm)
With the Intelligent Shell: - RWMs- RWMs - Error fields- Error fields are suppressedsuppressed
The LCFS is much smoother
It is useful to apply only a single external harmonic in order to have an easier interpretation of the results
0 10 20 30 40 50 60 70Time (ms)
1.0
0.8
0.6
0.4
0.2
0.0
br(m
T)
Measured spectrum at the plasma surface
Measured spectrum at t=25ms
(cm)
LCFSat t=25ms
0.15
0.10
0.05
0
-0.05
-0.10
-015
harmonic (1,-12)from 10ms to 30msamplitude 0.4mT
The feedback needs to: suppress error fields suppress RWMs apply the perturbation consider the plasma response to the external perturbation
The work done by the active coils is not obvious:
n
n
time (ms)
time (ms)
Measured br spectrum
Applied current spectrum
[Olofsson et al., Fus. Eng. Des. 2009][Olofsson et al., PPCF 2010][Frassinetti et al., IAEA 2010]
[Frassinetti et al., submitted to NF]
time (ms) 0 20 40 60
4
3
2
1
0
I 1,-
12 (
A)
br1,-12
I1,-12
time (ms) 0 20 40 60
phas
e (1
,-12
) br1,-12
I1,-12
flowTM velocity (1,-12) (1ms smoothed)
NO PERTURBATION
0 20 40 60 80time (ms)
60
40
20
0
velo
city
(km
/s)
br (
mT
)
1.0
0.8
0.6
0.4
0.2
0
flowTM velocity
60
40
20
0
velo
city
(km
/s)
br (
mT
)
1.0
0.8
0.6
0.4
0.2
0
0 20 40 60 time (ms)
WITH PERTURBATION (m,n)=(1,-12)
TMs rotate with velocities comparable to the flow
with the perturbation: - reduction of the TM velocity - reduction of the plasma flow
velocity profile (TM)
t=40mst=20ms
r/a
toro
ida
l vel
ocity
(km
/s)
(1,-15)
RMP (far from axis)
0.0 0.1 0.2 0.3 0.4 0.5 0.6r/a
0.10
0.05
0.00
q(r)
0.0 0.1 0.2 0.3 0.4 0.5 0.6r/a
v (
km/s
)
0
-5
-10
-15
-20
-25
RMP (far from axis)
(1,-15)
shot 22624
0.0 0.1 0.2 0.3 0.4 0.5 0.6r/a
v (
km/s
)
0
-5
-10
-15
-20
-25
0.10
0.05
0.00
q(r) (1,-12)
RMP (close to axis)
(1,-12)
Different RMP harmoniccDifferent RMP harmonicc produce different velocity brakingdifferent velocity braking
Maximum brakingMaximum braking located at the radius where theradius where the RMP harmonic is resonantRMP harmonic is resonant
RMP (close to axis)
0.0 0.1 0.2 0.3 0.4 0.5 0.6r/a
shot 22623
0.0 0.1 0.2 0.3 0.4 0.5 0.6r/a
v (
km/s
)
0
-5
-10
-15
-20
-25
(1,-10)
non-RMP
(1,-10)
non-RMP
shot 22668
0.10
0.05
0.00
q(r)
0.0 0.1 0.2 0.3 0.4 0.5 0.6r/a
n (harmonic of external perturbation)
v (
km/s
)MAX velocity variation
non-RMPRMP
Set of 13 shots with different harmonic of the perturbation n but same amplitude: br
n0.4mT
n (harmonic of external perturbation)
v (
km/s
)
TM velocity variation
non-RMPRMP
OV velocity variation
non-RMPRMP
n (harmonic of external perturbation)
v (
km/s
)
Set of 13 shots with different harmonic of the perturbation n but same amplitude: br
n0.4mT
flowTM velocity (1ms smoothed)ve
loci
ty (
km/s
)br
(m
T)
RMP
flowTM velocity (1ms smoothed)ve
loci
ty (
km/s
)br
(m
T)
non-RMP
0.1ms
TM velocity (not smoothed)
time (ms)
(mT
)(k
m/s
)
TM amplitude
With RMPRMP clear clear correlation correlation between velocity and TM amplitudevelocity and TM amplitude
0.1ms
[Frassinetti, NF 2010]
(mT
)(k
m/s
)
time (ms)
TM velocity (not smoothed)
TM amplitude
Island width: amplification and suppression Island velocity: acceleration and deceleration
depending of relative phase between TM and RMP
Static RMPStatic RMP
Rotating TMRotating TM
Island with RMP
LCFS(1,-12) island
0.1ms
• The island is not simplynot simply slowed downslowed down• It has strong strong velocity modulationsvelocity modulations
RMP n=-12RMP n=-12
n=-12 island
t=tt=t00
t=tt=t00+2µs +2µs t=tt=t00+4µs +4µs t=tt=t00+6µs+6µs
0.0 0.2 0.4 0.6r/a
TM
ve
loci
ty (
km/s
)
80
60
40
20
0
velo
city
(km
/s)
br (
mT
)
time (ms)
time (ms)
velo
city
(km
/s)
velocity variation
-10 -5 0 5 10 15 20time (s)
r/a
• The island is not simplynot simply slowed downslowed down• It has strong strong velocity modulationsvelocity modulations
RMP n=-12RMP n=-12
n=-12 island
t=tt=t00
t=tt=t00+2µs +2µs t=tt=t00+4µs +4µs t=tt=t00+6µs+6µs
0.0 0.2 0.4 0.6r/a
TM
ve
loci
ty (
km/s
)
80
60
40
20
0
RMP n=-15RMP n=-15n=
-15 island
t=tt=t00
t=tt=t00+2µs +2µs t=tt=t00+4µs +4µs t=tt=t00+6µs+6µs
0.0 0.2 0.4 0.6r/a
80
60
40
20
0TM
ve
loci
ty (
km/s
)
0.1ms
velo
city
(km
/s)
br (
mT
)
time (ms)
time (ms)
velo
city
(km
/s)
velocity variation
-10 -5 0 5 10 15 20time (s)
r/a
velocity variation
-5 0 5 10 15 20 25 30time (s)
• The island is not simplynot simply slowed downslowed down• It has strong strong velocity modulationsvelocity modulations
• The velocity perturbationperturbation is mainly located located at the island positionat the island position• But then it “spreads” to “spreads” to the surrounding plasmathe surrounding plasma
RMP n=-12RMP n=-12
n=-12 island
t=tt=t00
t=tt=t00+2µs +2µs t=tt=t00+4µs +4µs t=tt=t00+6µs+6µs
0.0 0.2 0.4 0.6r/a
TM
ve
loci
ty (
km/s
)
80
60
40
20
0
RMP n=-15RMP n=-15n=
-15 island
t=tt=t00
t=tt=t00+2µs +2µs t=tt=t00+4µs +4µs t=tt=t00+6µs+6µs
0.0 0.2 0.4 0.6r/a
80
60
40
20
0TM
ve
loci
ty (
km/s
)
[Frassinetti et al., IAEA 2010]
0.1ms
velo
city
(km
/s)
br (
mT
)
time (ms)
time (ms)
velo
city
(km
/s)
velocity profile with RMP n=-15
[Frassinetti et al., APS 2010]
SIMULATED DATA
time (µs)r/
a
,
3
1
4
m nEM
s
Tr r r
t r r r R r
Data are modelled using the torque balance equation. [Fitzpatrick et al. PoP 7, 3610 (2000)]
[Guo et al. PoP 9, 4685 (2002)]
Reasonable agreementReasonable agreementbetween modelled and
experimental data
velocity profile with RMP n=-15
EXPERIMENTAL DATA
time (µs)
r/a
,
3
1
4
m nEM
s
Tr r r
t r r r R r
exp. data
model
0( ) 1r cr
The viscosity profile is modelled using 3 free parameters
The free parameters are determined by comparing simulated and experimental velocity using a n=-15 RMP.
RMP n=-15
viscosity profile
10
-7 (
kg/m
∙s)
Viscosity is 1010-7-7kg/(mkg/(m∙∙s)s)
This corresponds to a momentum confinement time:
MM a a22 1ms 1ms
The observed plasma rotation braking is compared with simple empirical model:
[R.J. La Haye et al, PoP 9 (2002)2051]
- momentum confinement time
eff- effective frequency
Experimental data are well fitted with
3ms3ms and
eff = 4x106 s-1
2
0 2
1 reff
M
dV bV V V
dt B
br (
mT
)flo
w (
km/s
)
non-RMP (1,-10)
[Brunsell et al., EFDA MHD TG meeting 2010]
External magnetic perturbations produce plasma flow and TM brakingExternal magnetic perturbations produce plasma flow and TM braking
RMPs:RMPs: - The maximum braking is located in the position where the RMP is resonant - The island has phases with amplification-suppression and acceleration-deceleration - The estimated viscosity is approximately 10-7 kg/(m∙s) [M1ms]
Non-RMPsNon-RMPs
- The maximum braking is located in the core
- The estimated momentum confinement is M3ms
What happens if a RMP is applied to RFX-mod?
TMs are wall locked, do we still see a flow braking?
Do we see a transition in the flow braking from RMP to non-RMP?
TM velocity variation
n
v (
km/s
)
non-RMPRMP
?