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