1. gas inlet position References 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 ( T e, edge = 45 – 85 eV) 2) W injection experiment Aim: simulate W source by calibrated WF 6 injection realisation of controlled W source in a tokamak experiment determine proportionality factor between tungsten particle flux Γ W and photon flux ϕ W : 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 ( T e, edge = 38 – 47 eV) General experimental data: large radius R = 1.75 m small radius a = 0.46 m plasma current I p = 0.35 MA toroidal magnetic field B t = 2.25 T auxiliary heating power P aux = 1.2 MW deuterium fuelling spectroscopic observation via:  2D cameras equipped with interference filters  setup of high resolution and overview spectrometers W sputtering W injection 1) 2) input for modeling with GKU code [3] (collisional-radiative model) 2D camera recording with narrowband interference filter measured / fitted W 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. T e, edge line 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 n e and T e maximum moves away from injection hole for lower n e and T e Radial profiles for W I (400.88 nm) line l efl: e-folding length v: W velocity S: ionisation rate (including n e and T e ) : W I ionisation rate coefficient (ATOM code [4]) Velocity of injected W: slope ratio of linear fits  velocity ratio R v = /v inj = 3 with = 2122 m/s (assuming Thompson distribution)  v inj = 707 m/s v inj too high to be understood from dissociation energy release  dissociation path length must be taken into account  v inj has to be considered as effective parameter with dimensions of velocity plasma center sputtering n e, edge and T e, edge behave inversely  for comparison of both experiments ionisation rates must be considered T e, edge, n e, edge T e, edge n e, edge Introduction Penetration Depths of Injected/Sputtered W in the Plasma Edge Layer of TEXTOR M. Laengner a*, S. Brezinsek a, J.W. Coenen a, A. Pospieszczyk a, D. Kondratyev a, D. Borodin a, H. Stoschus b, O. Schmitz a, V. Philipps a, U. Samm a and the TEXTOR team a Institute of Energy and Climate Research - Plasma Physics, Forschungszentrum Jülich GmbH, Association EURATOM-FZJ, Partner In the Trilateral Euregio Cluster, Jülich, Germany b Oak Ridge Institute for Science Education, Oak Ridge, Tennessee 37830, USA Summary and Conclusions Tungsten (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 WF 6 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 v inj = 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 WF 6 injection can be applied for sputtered W 3) Modeled S/XB values: GKU can reproduce curve shape for (S/XB) eff vs.T e but measured values are systematically lower 4) Measured effective S/XB values: values from multimachine fit including weight loss, W(CO) 6 and WF 6 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 *m.laengner@fz-juelich.de [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.htmhttp://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 lines multimachine 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 WF 6 calibration with density scanapplied for first erosion measurementsat 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 wave number [cm -1 ] Dl [nm] tokamak experiment TEXTOR position of gas inlet / limiter limiter / gas inlet design side view top view WF 6 injection Results