Diagnostic of the plasma-wall transitionregion in a divertor-like system

G. Popa, C. Costin, S. Teodoru, C. Lupu,V. Anita, M. Solomon, C. Agheorghiesei

Faculty of Physics, “Al. I. Cuza” University IasiAssociation EURATOM - MEdC

FOM Institute for Plasma Physics “Rijnhuizen”, The Netherlands, Association EURATOM-FOM

Theoretical Plasma Physics Group & Department for Ion Physics, Innsbruck University, Austria, Association EURATOM-ÖAW

Castor Tokamak, Institute of Plasma Physics, Prague, Czech Republic, Association EURATOM/IPP.CR

Collaborations

Achievements

Numerical modelling for PILOT-PSI

2D fluid model

PIC model

Electrical diagnostic of PILOT-PSI plasma beam

Future plans

Evolution of the charged space sheath

Secondary electron emission induced by electron bombardment

Probe plasma diagnostic on Castor Tokamak

Multi-channel analyser (MCA). Experiments on PILOT-PSI

Evolution of the charged space sheath

Evolution of the charged space sheath

Time evolution of the collector potential for different values of the angle θbetween the magnetic field and the normal direction to the wall surface

-70

-60

-50

-40

-30

-20

-10

0

10

θ = 90 [ deg ]θ = 70 [ deg ]

θ = 30 [ deg ]V

[ V

]θ = 10 [ deg ]

0.00 1.50x10-10 3.00x10-10 4.50x10-10 6.00x10-10-60

-50

-40

-30

-20

-10

0

V [ V

]

t [ s ]0.00 1.50x10-10 3.00x10-10 4.50x10-10 6.00x10-10

t [ s ]

Evolution of the charged space sheath

Spectrum of the potential oscillations at the collector for (a) constant B = 1T and different θ,(b) constant θ = 30° and different B

Secondary electron emission induced by electron bombardment

Measured current-voltage characteristics

-800 -600 -400 -200 0

-12

-6

0

ni = 4.313*1017m-3 nf/ni = 3.98*10-4

Te= Ti= 20 eV Tf= 10 eV Esh= 500 eV

Vp(V)

simulation without SEE simulation with SEE theory

j (10

2 A/m

2 )

Current-voltage characteristic for Deuteriumplasma, simulation (1D-PIC) and theory

Probe plasma diagnostic on Castor TokamakMeasurements of the diffusion coefficient

Katsumata probe – schematic representation

Castor Tokamak: R = 40 cm, a = 8.5 cm, B = 1.2 T and Ip =10 kA

Probe plasma diagnostic on Castor TokamakMeasurements of the diffusion coefficient

Fluctuation power spectra for different collector position h [mm] (r = 65 mm)

Probe plasma diagnostic on Castor TokamakMeasurements of the diffusion coefficient

Radial decay of the spectrumat different frequencies

Dependence of 1/L2 on the frequency

2

14Df

Lπ=

Probe plasma diagnostic on Castor TokamakMeasurements of the diffusion coefficient

Radial profile of the measured diffusion coefficient (black points) and of the Bohm one (red line)

Probe plasma diagnostic on Castor TokamakIon temperature measurements by Katsumata probe

I-V characteristic of the collector;linear scale (top) and logarithmic scale (bottom)

(h = -0.5 mm, r = 80 mm)

Probe plasma diagnostic on Castor TokamakIon temperature measurements by Katsumata probe

Radial profile of the Ti for two positionsof the collector h = -0.5 and -0.3 mm

Ion temperature measured with Katsumata and Tunnel probe

Multi-Channel Analyser (MCA)

B

dp = 10 mm dc1 = 0.9 mmdc2 = 0.6 mmdc3 = 0.3 mm

PILOT-PSI device

PILOT-PSI MCA measurements

0.1 0.2 0.3 0.4 0.5

10-4

10-3

10-2

10-1

H2, Ti = 2 eV H2, Ti = 4 eV Ar, Ti = 2 eV Ar, Ti = 4 eV H2 exp H2+Ar exp Ar exp

f = I/

I 0

R (mm)

2 2 2 2 2

2(1 )1 2

8 (1 sin )

0 0 0

1 1i

i i

q B R xkT m xIf e xdxd

I

πϕ ϕ

π⊥

−−

−⎡ ⎤⎢ ⎥= = −⎢ ⎥⎣ ⎦

∫ ∫

Fraction f of the collected current versus channel radius R

theory

experiment

-30 -20 -10

-800

-600

-400

-200

Ar, Isource = 80 A, B = 0.4 T

I plat

e (m

A)

Uplate (V)

-250 -200 -150 -100 -50

-300

-200

-100

H2, Qv=1 l/min, Vf = -11,2 V, VfB = - 79 V

I plat

e (μA

, mA)

Uplate (V)

B = 0.0 T, I (μA) B = 0.4 T, I (mA)

Current-voltage characteristics of MCA plate

PILOT-PSI measurements

-40 -30 -20 -10 10 20 30 40-20

20

40

60

80

100

120

Ar, Isource = 90 A, B = 0.4 T, p = 0.03 mbar

I targ

et (A

)

Utarget (V)

-40 -30 -20 -10

-40

-30

-20

-10

Ar, B = 0.4 T, p = 0.03 mbar

I targ

et (A

)

Utarget (V)

I = 90 A I = 120 A I = 150 A

Current-voltage characteristics of the target (Carbon)

Publications [1] R. Schrittwieser, C. Ionita, J. Adamek, J. Stockel, J. Brotankova, E. Martines, G. Popa, C. Costin, L. van de Peppel and G. van Oost, “Direct measurements of the plasma potential by katsumata-type probes”, Czech. J. of Phys. 56 (2006), Suppl. B, pp B145 – B 150

[2] J. Brotankova, J. Adamek, J. Stockel, E. Martines, G. Popa, C. Costin, R. Schrittwieser, C. Ionita, G. van Oost and L. van de Peppel, “A probe-based method for measuring the transport coefficient in the tokamak edge region”, Czech. J. of Phys. 56 (2006), pp. 1321–1328

[1] C. Costin, L. Grigoras and G. Popa, “Multi-channel analyser and perpendicular ion energy distribution in magnetised plasma”, 33rd European Physical Society (EPS) Conference on Controlled Fusion and Plasma Physics, 19-23 June 2006, Rome, Italy (poster)

[2] J. Brotankova, E. Martines, J. Adamek, J. Stockel, G. Popa and C. Costin, “A new-probe based method for measuring the diffusion coefficient in the tokamak edge region”, 33rd European Physical Society (EPS) Conference on Controlled Fusion and Plasma Physics, 19-23 June 2006, Rome, Italy (poster)

[3] R. Schrittwieser, J. Adamek, C. Ionita, J. Stockel, E. Martines, J. Brotankova, C. Costin, G. Popa, G. van Oost and L. van de Peppel, “Direct measurements of the plasma potential by Katsumata-type probes”, 33rd European Physical Society (EPS) Conference on Controlled Fusion and Plasma Physics, 19-23 June 2006, Rome, Italy (poster)

[4] C. Lupu, D. D. Tskhakaya sr., S. Kuhn, D. Tskhakaya jr. and G. Popa, “Floating sheath formation in a collisional magnetised plasma”,33rd European Physical Society (EPS) Conference on Controlled Fusion and Plasma Physics, 19-23 June 2006, Rome, Italy (poster)

[5] J. Adamek, J. Stockel, R. Panek, M. Kokan, E. Martines, R. Schrittwieser, C. Ionita, G. Popa, C. Costin, J. Brotankova, G. van Oostand L. van de Peppel, “Simultaneous measurements of the parallel and perpendicular ion temperature by Katsumata and segmented tunnel probe”, 9th Workshop on the Electric Fields, Structures and Relaxation in Edge Plasma, 26-27 June 2006, Rome, Italy (oral presentation)

[6] J. Brotankova, E. Martines, J. Adamek, J. Stockel, G. Popa, C. Costin, R. Schrittwieser, C. Ionita and G. van Oost, “A probe-based method for measuring the transport coefficient in the tokamak edge region”, 9th Workshop on the Electric Fields, Structures and Relaxation in Edge Plasma, 26-27 June 2006, Rome, Italy (oral presentation)

Conferences

Future plans

Numerical modelling for PILOT-PSI

2D fluid model

PIC model

Electrical diagnostic of PILOT-PSI plasma beam

Numerical modelling for PILOT-PSI

Scheme of the device

Numerical modelling for PILOT-PSI

( ) , ,ss s iz e

n n v f n s e it

∂+∇⋅ = =

∂

ur

( ) ( )ss s s s s s s s

vm n v v q n E v B Pt

⎡ ⎤∂+ ⋅∇ = + × −∇ −⎢ ⎥∂⎣ ⎦

urur ur ur ur ur

1 e izs s ms s

s ms

n fm n f vn f

⎛ ⎞+⎜ ⎟

⎝ ⎠

ur

( ) ( )e ee e e e e e

n n v E ntε ε θ∂

+∇ ⋅ = −Γ ⋅ −∂

ur uur ur

2D Fluid model

( ) /ee e e e e e e e e men v n E D n n v fμΓ = = − −∇ − ×Ωuur ur ur ur ur

eff

i i i i i i in v n E D nμΓ = = − ∇uur ur ur

( )eff

eff e imi iz

i i i

nE f E E ft n n μ

Γ∂= − −

∂

uururur ur

Numerical modelling for PILOT-PSI

Particle fluxes

Poisson equation

0

( )i ee n nVε−

Δ = −

12e e en v⊥Γ = < >

14

effi i thi i in v n Eδμ⊥ ⊥Γ = +

|| 0 , ,s s e i nΓ = =12e e e en vε ε⊥Γ = < >

|| 0eεΓ =

Numerical modelling for PILOT-PSI

Boundary conditions

walls

source

target secondary electron emission is consideredimposed V

0n⊥Γ =

, ,simposed s e i n and V⊥Γ =

0V =

Electrical diagnostic of PILOT-PSI plasma beam

- Langmuir probe (self-emissive probe)- emissive probe

Electrical diagnostic of PILOT-PSI plasma beam

I-V characteristics of a self-emissive probein a magnetron discharge

Electrical diagnostic of PILOT-PSI plasma beam

- Multi-channel end-plate

Thank you for your attention!

Assumptions: -Only the ions enter into the channels, the electrons are rejected.-2R < the sheath thickness formed in front of the MCA ~ a few Debyelengths.

Example:-Hydrogen plasma, n0 = 1021 m-3, Te = 2 eV, Ti = 4 eV (working conditions for Pilot) Debye length is ~ 0.3 μm.-B = 1 T ion Larmor radius ~ 0.3 mm.

MCA + grid

-Hydrogen plasma, Te = 2 eV, Ti = 4 eV, R = 0.15 ÷ 0.45 mm Debye length ~ 0.1 mm n0 ≤ 1016 m-3.

-B = 0.4 T ion Larmor radius ~ 0.7 mm.

Multi-Channel Analyser (MCA)