Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 In-situ studies of H/D interaction with W, Ta and Cu Progress report on: WP09-PWI-05/03a/MHEST – BS 0.35ppy+PS 0.15ppy Reflection and re-emission of excited H 2 and D 2 molecules from high-Z surfaces Iztok Čadež, Sabina Markelj, Primož Pelicon, Zdravko Rupnik Association EURATOM-MHEST Jožef Stefan Institute, Ljubljana, Slovenia EU TF PWI - SEWG High Z Materials and Liquid metals (05)

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Outline 1.Introduction and objectives 2.Comments on previous results 3.Work performed in Work plan for the rest of Work proposed for 2010

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October Introduction and objectives 2.Comments on previous results 3.Work performed in Work plan for the rest of Work proposed for 2010

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Present WP09-PWI-05-03a/MHEST: Reflection and re-emission of excited H 2 and D 2 molecules from high-Z surfaces is a continuation of two tasks from WP08, PWI-08-TA-07/MHEST/BS/02 In-situ ERDA studies of hydrogen and deuterium interaction with tungsten, and PWI-08-TA-10/MEHST/BS/01 Production and reflexion of vibrationally excited hydrogen molecules at material surfaces (W) We also proposed continuation of this program for WP2010: Interaction of excited H 2 and D 2 molecules with high-Z surfaces

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 The general objective of our work is to quantitatively characterize production and relaxation of excited particles on high-Z metals, in particular vibrationally excited H 2 and D 2 molecules on W. WP09-PWI-05-03a/MHEST: Reflection and re-emission of excited H 2 and D 2 molecules from high-Z surfaces Task objectives: Detailed understanding of processes leading to emission of neutral vibrationally excited hydrogen molecules (H 2 and D 2 ) (VEH) from plasma facing components and reactor vacuum vessel wall. Milestone 1: Determination of vibrational distribution of emitted molecules from W and Ta – final report by the end of Milestone 2: Determination of H and D content on high Z metals subjected to the flow of hydrogen atoms and molecules.

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Motivation and background Rich experience on production of vibrationally excited hydrogen molecules (VEH) by atom recombination on surfaces was gained during our previous work. Following this, we have constructed a unique experimental tool for vibrational spectroscopy of hydrogen molecules (different isotopologues) based on dissociative electron attachment. It is easy to operate and thus allow original experiments to be performed. Having at the same time in our laboratory Ion beam analytical (IBA) methods ERDA (Elastic Recoil Detection Analysis) and RBS (Rutherford Back Scattering) triggered us to join this two experimental sets of techniques and perform deeper studies of hydrogen recombination process on surfaces. Vibrational spectrometer allows us to do some specific studies of surface reactions but also of some volume collision processes.

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Relevance to PWI studies Providing data (reaction rates, cross sections) for modelling codes (edge plasma, erosion and deposition, negative ion sources, neutral vapour cushion in transient phenomena (?)) on processes involving VEH – importance of these is well documented in some cases and feedback on particular needs would be most welcomed. Understanding energy exchange by neutrals between wall and edge plasma. Search for new phenomena involving VEH and impurity or seeding particles (e.g. production of VEH by thermal dissociation of hydrocarbon on hot tungsten, production of other excited particles at hot tungsten surface).

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October Introduction and objectives 2.Comments on previous results 3.Work performed in Work plan for the rest of Work proposed for 2010

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Hydrogen vibrational spectroscopy is based on the detection of negative ions produced by the dissociative electron attachment (DEA) in hydrogen through the 4 eV resonance state: AB (X 1 g +,v) + e AB - (X 2 u + ) A - + B where A and B stands for any of hydrogen isotopes, H, D or T. Method was first developed at LDMA, UPMC, Paris in 80-ties. Vibrational distribution of studied target gas is determined by deconvolution of measured yield of low energy A - ions as a function of electron energy in eV. Experimental techniques/1 – vibrational spectrometer

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Homogeneous magnetic field (B 60G) is used for guiding electron beam and for ion extraction. Experimental set-up developed recently Efficient zero-energy ion collection is achieved by combined action of weak electrostatic penetration field and guiding magnetic field. Sufficient mass selectivity to distinguish H - from D -. Vibrational distribution of hydrogen molecules in interaction region is obtained from H- (D-) ion yield variation with electron beam energy in the range from 0 to 5 eV by S. Markelj et al., Int. J. Mass Spectrom. 275 (2008) 64 By changing electrode polarity, the positive ions are detected what allows determination hydrogen atom concentration by the same set-up!

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Pressure: 9x10 -4 mbar. Impinging rate (H 2 equivalent): 9.9x10 17 cm -2 s -1. H 2 flow rate: 1.8x10 17 molecule/s (0.4 sccm). Impinging rate of H-atoms on the sample (center): 1.7x10 15 atoms/(cm 2 s). Vibrational distribution of hydrogen molecules created by atom recombination on W. T V = 3700 ± 100 K for H 2. T V = 3400 ± 100 K for D 2. Rotational temperature is lower, 500K and 300K assumed for fitting for H 2 and D 2 respectively. Importance of impurities remains to be studied. I. Čadež et al., J. Nucl. Mater (2009) 520 (PSI 2008)

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Beam: MeV 7 Li 2+ - very good separation of H and D surface peaks MeV 1 H + for few RBS measurements. Geometry: Sample tilted 75°, RBS detector at 160°, ERDA detector at 30°. ERDA particle filter: 11 µm Al foil Dose calibration: mesh charge integrator (tungsten mesh, open area of 77.4 %). Standard irradiation dose for single spectrum recording (on sample) – 4.4 C (1.4x Li atoms). P. Pelicon et al., NIM B 227 (2005) 591 Experimental techniques/2 – Li-ERDA

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Experimental development for in-situ studies of neutral hydrogen - metal interaction Old set-up for in situ ERDA studies of hydrogen-material interaction Sample is exposed to neutral, partially dissociated hydrogen atmosphere created by hot tungsten filament. S. Markelj et al., NIM B 259 (2007) 989

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October Introduction and objectives 2.Comments on previous results 3.Work performed in Work plan for the rest of Work proposed for 2010

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Experimental development for in-situ studies of neutral hydrogen - metal interaction Hydrogen atom beam is directed to the sample mounted on the temperature controlled holder. 4.2 MeV 7 Li 2+ beam is hitting the surface at 15 o. ERDA and RBS detector are positioned at 15 o and 30 o respectively with respect to the sample surface. New set-up for in situ ERDA studies of hydrogen-material interaction was installed on reconstructed ERDA/RBS beam line of 2MV tandem accelerator during MeV 7 Li 2+ beam RBS detector ERDA detectorHABS Sample on the heater

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Studied sample material and sample holders Two Tungsten samples were studied: PCW - Tokamak grade obtained from IPP, Garching (produced by Plansee) - PCW HRW - Hot rolled tungsten from Goodfellow - HRW Measurements were performed also with Ta and OFHC Cu and also with thin layer of hard amorphous hydrogenated carbon (a-C:H) (in collaboration with IPP Garching). Two sample holders were constructed: - holder with ceramic heater (Boralec) 80 o C – 1200 o C (left) - holder with resistive heater and water cooling 10 o C – 400 o C (right)

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 ERDA measurements influence sample due to: - sample heating - projectile implantation - build-up of vacuum oil deposit Surface roughness (by STM) Power deposited in the target is 10 mW in 14 mm 3 for 5nA of 4.2MeV 7 Li 2+ beam spread over 4mm x 4mm area. Number of implanted 7 Li during continuous 1 h irradiation: 5.6x10 13 (n W = 6.3x10 16 at/mm 3 ) HRW – RMS: 14nm PCW – RMS: 4nm

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Hydrogen atom source We use a commercial hydrogen atom source, HABS from MBE- Komponenten GmbH described in detail by Tschersich et al., J.Appl.Phys. 104 (2008) Constant heating conditions were used during experiment: - Heating current 13A; heating power 173W; capillary temperature 2000 K. - Driving H 2 and D 2 pressure: typically mTorr ( Pa). - Hydrogen dissociation rate 40%. - From a-C:H erosion calibration measurements: - Central H flux density at the sample: 1.6x10 15 at/cm 2 s (124 mTorr driving P) - Central D flux density at the sample: 1.0x10 15 at/cm2s (143 mTorr driving P)

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Exposure of a-C:H film to hydrogen beam at angle 24 o to the surface normal, distance capillary-sample 7.85 cm Sample temperature 550 K 20 K, erosion yield at this temperature Y=0.012 [Schluter et al., JNM 376 (2008), Schwartz-Selinger et al., J. Vac. Sci. Technol A 18 (2000)] Driving pressure 124 mTorr Atom flux density on the sample Hydrogen Atom Beam Source (HABS) - beam profile calibration

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Performed experiments from till HRW PCW Ta Cu Calibration: (kapton, a-C:H) (with break)

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Measurements with PCW First heating and exposure to H 2 : Initial room temperature [H] ~20x10 15 cm -2. Heating to 1100 o C and [H] reduced to ~5. After start of exposure to H with no heating (~85 o C) first sudden jump of [H] observed (spec# 9,10) to Then steady [H] increase with rate the rate of 5.6x10 12 at./cm 2 s. Clear displacement of W-edge RBS spectrum towards lower energy. indicating layer buildup to 170! New layer unstable and [H] decreases as soon as exposure stops and also under successive exposures to 120. However next morning same value of [H].

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 By assuming build-up of a carbon surface layer it was possible to reproduce well RBS edge displacement using SIMNRA modelling tool.

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 When sample is exposed to D-beam, sharp [D] rise is observed but not corresponding [H] decrease as was the case with HEC. By sample heating to o C and exposure to D beam it was possible to clean the surface.

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Long term exposure to D-beam. Mainly rise of [D] is observed and only weak [H]. [C] increase is slower than for the case of exposure to H-atoms: only about 3x10 12 Cat./cm 2 s as compared to 8x10 12 Cat./cm 2 s. Possible reasons: different sample temperature, different atom flux, different atom velocities. Again, weak isotope exchange when H-beam is switched on.

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Layer produced by long term exposure to D was stable next day and again very weak isotope exchange was observed when H-exposure was performed even at higher temperature.

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 After gaining experience with other samples (in particular with a-C:H) we performed final study of sample cleaning at higher temperature. By p-RBS it was possible to follow [C] decrease with temperature and then by exposure to H-beam. Final low values of [H] and [D] were confirmed by last measurements being Li-ERDA/RBS.

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Measurements (mainly by the end of 2008 but calibration and final PCW in January 2009) 7 Li ERDA and p-RBS. Detailed data evaluation has been initiated. All measurement data are available for discussion to interested colleagues. Work performed in 2009 until September 30 th Problem: Main reason for slow advance of our study on H 2 (v) production is observation that metal surface is strongly changing under H and/or D bombardment in HC contaminated environment. This produces non reproducible results but stimulates further work.

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 First chamber: 14 x 25 mm Filament: 0.2 mm W Channel: 4 x 10 mm Second chamber: 16 x 15 mm Exit Aperture: 6 mm Material: OFHC cupper Typical hydrogen flow: 6.7x10 -3 mbar*lit/s Vibrational distribution as well as a fraction of (still) present atoms in the beam are experimentally determined. A simple source of VEHs has been developed for some particular experiments. C x H y interaction with hot tungsten/1

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 C x H y interaction with hot tungsten/2 Production of H 2 (v) molecules by thermal dissociation of C 2 H 4 and C 2 H 6 but not of CH 4 on tungsten filament was observed and studied to some extent. Quantitative evaluation of data is under way.

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October Introduction and objectives 2.Comments on previous results 3.Work performed in Work plan for the rest of Work proposed for 2010

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Further experimental data evaluation. New experiments will be performed in the second half of 2009 with HABS equipped with newly acquired hydrogen purifying filter, All data evaluation will be performed before the end of 2009 and conclusions drawn. Plan for the rest of year 2009

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October Introduction and objectives 2.Comments on previous results 3.Work performed in Work plan for the rest of Work proposed for 2010

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 TA: PWI in a full-W device Proposal: WP10-PWI-05-xx/MHST - BS Interaction of excited H 2 and D 2 molecules with high-Z surfaces Studies of interaction of vibrationally excited hydrogen molecules from materials for PFC initiated in previous two years will be continued. Measurements will be performed with ITER-wall relevant materials, in particular W but some other high-Z metals such as Ta and Mo will be studied as well. We will upgrade vibrational spectrometer for hydrogen molecules (H 2, HD, D 2 ) by incorporating differential pumping of detector chamber and improving energy and mass selectivity. This instrument is unique of its kind thus allowing original studies not possible elsewhere. Surface reactions occurring under simultaneous bombardment by different neutral particles (atoms, cold and hot hydrogen molecules, impurity molecules) will be studied by IBA methods ERDA and RBS. Our recent experiments have revealed important synergistic effects of H(D) atoms, hydrocarbon impurities and possibly hot molecules on the build-up of carbon layers on W, Ta, Cu at room temperature. We plan to work on detailed understanding of formation and destruction of mixed layers at high-Z metals and possible role of seed impurities, in particular N 2, will be studied.

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October Energy resolution of the e-beam. - Differential pumping of detector's chamber. - Mass selectivity D vs. H. - Adaptation for the possible use on other experiments. Improvements of vibrational spectrometer

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 In our measurements we regularly observe a detector nose dependent on W temperature and in the presence of hydrogen – metastable atoms or molecules or UV photons? Background detected from the hydrogen atomic source - Activation energy: 3.05±0.15 eV Solving an old and still open question (at least for us!) – emission of excited particles from hot W when exposed to hydrogen.

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October TA proposed to SEWG Material migration on carbon erosion/deposition. - Influence of surface created VEHs on optical emission from magnetized hydrogen plasma. - MC modelling of gas cell containing atoms and VEHs (in collaboration with UNG). Within our Association MHEST project the following activities are also planned in 2010:

Joint meeting of SEWG 05 and 07 of EU TF PWI, Ljubljana, Slovenia, October 2009 Thank you for your attention!