Gas inlet position References Experiment 1) W sputtering experiment Aim: study of W erosion for different plasma conditions by aim of spectroscopy reference.

Page 1

-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.50.0

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no

rmal

ised

inte

nsi

ty [

a.u

.]

distance d to LCFS [cm]

apex position

#113112 phase I

#113112 phase II

#113112 phase III

Te=85eV, n

e=3.0x1018m-3

Te=60eV, n

e=4.3x1018m-3

Te=45eV, n

e=5.3x1018m-3

-4.5 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.50.0

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1.0

distance d to LCFS [cm]

efl

no

rmal

ised

in

ten

sity

[a.

u.]

#115837 r=48.0cm

Te=47eV, n

e=5.5x1018m-3

#115836 r=48.5cm

Te=47eV, n

e=3.8x1018m-3

#115834 r=49.0cm

Te=41eV, n

e=3.2x1018m-3

#115831 r=50.0cm

Te=38eV, n

e=2.5x1018m-3

nozzle positiongas inlet position

References

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400.88 nm / 505 nm

498.26 nm / 505 nm

line

ratio

injection

429.46 nm / 505 nm

line

ratio

Te, edge

[eV]

line

ratio

sputtering

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1.0

distance d to LCFS [cm]

injection W I (400.88 nm) injection W I (505 nm)

rela

tive

inte

nsity

[a.u

.]

sputtering W I (400.88 nm) sputtering W I (505 nm)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 150.0

0.1

0.2

0.3

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efo

ldin

g le

ng

th e

fl [

cm

]

inverse ionisation rate 1/S [10-7 s]

injection

linear fit injection

sputtering

linear fit sputtering

GKU vW = 700 m/s

GKU vW = 2100 m/s

GKU 6 x vW = 700 m/s

GKU 6 x vW = 2100 m/s

Experiment

1) W sputtering experiment

Aim:•study of W erosion for different plasma conditions by aim of spectroscopy•reference experiment to compare to W injection

Experimental realisation:•spherical limiter with W- and C-half•inserting limiter in scrape of layer (SOL), limiter apex 0.5 cm behind last closed flux surface (LCFS)•variation of edge plasma parameters by changing central plasma density and temperature by deuterium fuelling within one discharge (Te, edge = 45 – 85 eV)

2) W injection experiment

Aim:

•simulate W source by calibrated WF6 injection

•realisation of controlled W source in a tokamak experiment•determine proportionality factor between tungsten particle flux ΓW and photon flux ϕW: inverse photon efficiency S/XB (S: ioniSation rate, X: eXcitation rate, B: Branching ratio)• in-situ calibration of spectroscopic method

Experimental realisation:•inserting gas inlet in scrape-off layer 2 - 4 cm behind last closed flux surface•variation of edge plasma parameters by changing radial gas inlet position from discharge to discharge (Te, edge = 38 – 47 eV)

General experimental data:•large radius R = 1.75 m•small radius a = 0.46 m

•plasma current Ip = 0.35 MA

•toroidal magnetic field Bt = 2.25 T

•auxiliary heating power Paux = 1.2 MW

•deuterium fuelling•spectroscopic observation via:

2D cameras equipped with interference filters

setup of high resolution andoverview spectrometers

W s

pu

tter

ing

W in

ject

ion

1)

2)

input for modeling with GKU code [3](collisional-radiative model)

2D camera recordingwith narrowband interference filter

measured / fittedW I (400.88 nm) lines

Comparison of W I line ratios

• similar line ratios for different lines for injected and sputtered W• level population independent from W release process, mainly determined by plasma

parameters

line ratios vs. Te, edgeline ratios sputtering / injection

injection

Comparison with GKU modeling [3]:

•by modifying modeling by a factor of 6 both experimental results can be approximated

•possible reasons for uncertainties: overestimation of ionisation rate coefficients for W I no velocity distribution in modeling included

• broader profiles for lower ne and Te

• maximum moves away from injection hole for lower ne and Te

Radial profiles for W I (400.88 nm) line

ieeefl vn

v

S

v

• efl: e-folding length

• v: W velocity• S: ionisation rate

(including ne and Te)

• <vei>: W I ionisation rate

coefficient (ATOM code [4])

Velocity of injected W:

•slope ratio of linear fits

velocity ratio Rv = <vsput>/vinj = 3

•with <vsput> = 2122 m/s

(assuming Thompson distribution) vinj = 707 m/s

•vinj too high to be understood from dissociation energy release

dissociation path length must be taken into account

vinj has to be considered as effective parameter with dimensions of velocity

plasma center

plasma center

sputtering

ne, edge and Te, edge behave inversely

for comparison of both experiments ionisation rates must be consideredT

e, e

dg

e, n

e, e

dg

e

Te

, ed

ge

ne

, ed

ge

Introduction

Penetration Depths of Injected/Sputtered W in the Plasma Edge Layer of TEXTOR

M. Laengnera*, S. Brezinseka, J.W. Coenena, A. Pospieszczyka, D. Kondratyeva,D. Borodina, H. Stoschusb, O. Schmitza, V. Philippsa, U. Samma and the TEXTOR team

 aInstitute of Energy and Climate Research - Plasma Physics, Forschungszentrum Jülich GmbH, Association EURATOM-FZJ, Partner In the Trilateral Euregio Cluster, Jülich, Germany

bOak Ridge Institute for Science Education, Oak Ridge, Tennessee 37830, USA

Summary and ConclusionsTungsten (W) is foreseen as the plasma-facing material in the ITER divertor due to its beneficial properties like high melting temperature, low physical sputtering yield and small fuel retention. However, only a small amount of W (~10-5 W/D) can be tolerated in the core plasma as it can cause strong radiation losses and hamper the fusion burn. Thus, it is of high importance to understand W as an impurity source and to determine the W source distribution. In this context two aspects are essential:

• in-situ determination of the W source strength by spectroscopy means• characterisation of the interaction of W with the plasma by the penetration depths.

To address these aspects two experiments have been set up at the tokamak TEXTOR:

1)The first experiment was performed to study the erosion of W under different plasma conditions.

2)A WF6 injection experiment was performed with the aim to

• realise a controllable W source• determine the inverse photon efficiencies, the so-called S/XB values [2] for different W I

and W II lines to finally convert photon fluxes into W particle fluxes.

By the comparison of both experiments with respect to

• W particle velocities• energy level population

a conclusion can be drawn in which way injected W bears similarities to sputtered W and how far it can be applied to simulate a source of sputtered W.

1) W velocities and e-folding lengths:• velocity ratio for injected / sputtered W about a factor of 3

• vinj = 707 m/s dissociation path must be taken into account

• measured e-folding lengths approximated by GKU by assuming a modification of a factor of 6: ionisation rate coefficients used in GKU might be overestimated no velocity distribution of particles included in modeling

2) Energy level population:similar line ratios for W I for injected and sputtered W• indication for same energy level population• level population independent from W release process, mainly determined by plasma

parameters

• effective S/XB values from WF6 injection can be applied for sputtered W

3) Modeled S/XB values:GKU can reproduce curve shape for (S/XB)eff vs.Te but measured values are systematically lower

4) Measured effective S/XB values:values from multimachine fit including weight loss, W(CO)6 and WF6 calibration applied for first erosion measurements at JET (see G.v. Rooij I3)

20th International Conference on Plasma Surface Interactions 2012 | Mai 21 — 25, 2012 | Eurogress Aachen, Germany

*[email protected]

[1] S. Brezinsek et al 2011 Phys. Scr. T145 (2011) 014016[2] Pospieszczyk A et al 2010 J. Phys. B: At. Mol. Opt. Phys. 43 144017[3] Vainshtein L et al 2007 Plasma Phys. Control. Fusion 49 1833[4] Vainshtein L et al 2011 J. Phys. B: Atom. Mol. Opt. Phys. 44 125201[5] http://physics.nist.gov/PhysRefData/ASD/lines_form.htm

Penetration depth of W: analysis for W I at 400.88 nm

Measured effective S/XB values for W I linesmultimachine fit W I (400.88 nm) [6,7,8]

• effective S/XB values systematically lower than modeled by GKU

• consistent with assumption of overestimated ionisation rates

• values from multimachine fit including WF6 calibration with density scan applied for first erosion measurements at JET (see G.v. Rooij I3)

W I (400.88 nm) and (522.47 nm)

NIST W I energy level diagram [5]

[6] Geier A et al 2002 Plasma Phys. Control. Fusion 44 2091[7] Nishijima D et al 2011 Phys. Plasmas 18 019901[8] Steinbring J, Spektroskopische Untersuchung von zerstäubtem Wolfram in einer linearen Plasmaanlage, diploma thesis, 1997, university of Berlin

P2-070

NIST tables version 3

energy level configuration

wav

e n

um

ber

[cm

-1]

[nm]

tokamak experiment

TEXTOR

position ofgas inlet /

limiter

limiter / gas inlet design

side view

top view

WF6

injection

0 20 40 60 80 1000

10

20

30

40

50

60

70

80

90

100

0

250

500

750

1000

1250

1500

TEXTOR, W I (400.88 nm)

effe

ctiv

e S

/XB

W I

(400

.88

nm)

Te, edge

[eV]

GKU, W I (400.88 nm), TW = 0.3 eV

522.47 nm

effe

ctiv

e S

/XB

W I

(522

.47

nm)

TEXTOR, W I (522.47 nm)

400.88 nm

GKU, W I (522.47 nm), TW = 1.0 eV

Results