Initial experiments with liquid target materials in PSI-2 and TEXTOR

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1 Member of the Helmholtz Association Initial experiments with liquid target materials in PSI-2 and TEXTOR B. Unterberg, J.W. Coenen, A. Kreter, V. Philipps, M. Reinhart, G. Sergienko, A. Terra and T. Wegener Institut für Energie- und Klimaforschung Plasmaphysik Forschungszentrum Jülich, Ass. EURATOM- Forschungszentrum Jülich, Trilateral Euregio Cluster, D Jülich, Germany 4th IEA International Workshop on Plasma Material Interaction Facilities for Fusion Research (PMIF 2013), Oak Ridge, TN, USA, September 9th 13th 2013

2 Program on liquid targets in Jülich After assessment of alternative target concepts, FZJ concentrates on alternatives to Li in CPS configuration, in the frame of the co-ordinated EU fusion program (EFDA-PEX) and in TEC collaboration with FOM- DIFFER Development of samples for exposure in PSI-2 and TEXTOR Ø Report on initial experiments with tin B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 2

3 Optimization of temperature window motivates work on alternative materials Temperature limit Lower limit Melting Wetting Upper limit Evaporation flux: impact on plasma performance, redeposition, migration to remote areas Chemistry (e.g. LiH formation), corrosion / alloy formation (large window for Li, show stopper for Ga) Evaporation rates [R. Majeski, "Liquid metal walls, lithium, and low recycling boundary conditions in tokamaks" AlP Conf. Proc. vol. 1237, 122.] B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 3

4 Re-Deposition Factor 10 increase in redepostion enhances T window by <100 K Ø Re-deposition - while allowing for potentially higher surfaces temperatures is not necessarily allowing for high-heat flux operation due to re-deposition of energy B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 4

5 Material compatibility of tin with mesh metals SST/Ga SST/Sn Mo/Sn W/Sn SST show a strong ability to form alloys with all investigated liquid metal candidates. Mo alloys with liquid Sn but in very small amounts. EDX analysis shows small inclusions (<1µm) in the liquid Sn with under 1 atm.% Mo. W solubility of W in lquid Sn is very low at 2273 K 0,001 at% 2 B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 5

6 Wetting Wetting - contact angle < 90 Mo/Sn 950 C 10-6 mbar Adhesion > Cohesion Clean metal surfaces are normaly wettable with liquid metals BUT they nearly always have oxide layers which reduce the wettability of the surface! No Wetting - contact angle > C 10-6 mbar W/Sn 1mbar H2 950 C W/Sn Adhesion < Cohesion B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 6

7 Overview of wetting characteristics Contact angle B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 7

8 Linear plasma device PSI-2 Coils Target manipulator Plasma source TEAC Side-fed manipulator 3m Periphery level Plasma conditions (deuterium plasmas), with target biasing q = MW m-2, simulation of transients by laser irradiation (120 J / 4 ms) ne = m-3 Te up to 20 ev (Ti~ 0.5 Te) Eion = ev (biasing) Γion = m-2s-1 F = 1027 m-2 in 4 h Δflow channel ~ 6 cm B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 8

9 Target holder in PSI-2 B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 9

10 Setup Tungsten Mesh: d= mm molybdenum disk & mounting plate B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 10

11 Exposure Infra-red visible IR-Camera Pyrometer Pyrometer B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 11

12 Exposed samples Empty Before After B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 12

13 Material Cuts B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 13

14 Exposure characteristics Plasma characteristics Total exposure time (D2- plasma): 64 min. Plasma parameters in front of target: n e = 8x10 17 m -3 /T e = 9 ev Plasma flux density: 5x10 21 m -2 s -1 Surface temperature Heat flux density: 60 kwm -2 (no biasing) Equilibrium reached after ~900s IR-cam: temperature variation across sample ±100 C B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 14

15 Sn mass loss in during exposure Total loss: 240 mg (of 1139mg) Surface temperature needed for evaporation of 240 mg: 1120 C (full area) effective erosion yield : Y=0.15 >> Y sputter Penetration depth of Sn atoms: λ= 1.7 cm, E kin =1.5 ev >> E kin =0.15 ev (evaporated Sn) Ø Indicating sputtered particles SnI intensity rising during increase of target temperature, indication of temperature enhanced erosion? Intensity distribution SnI (380 nm) target B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 15

16 TEXTOR experiment: Aims A: Tin Evaporation Temperature Evolution Tin Spectroscopy Liquid Metal Stability under quiescent Plasmas B: Stability of Liquid Tin Layers under Disruptive Events DMV triggered disruptions And be prepared for suprises B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 16

17 Setup Tungsten Mesh filed with Tin TZM Holder filled empty Heatable Limiter-Setup B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 17

18 Conditions Tin surface The Limiter is preheated to 300 C, to allow liquid Tin to be present at all times Position at the Bottom of TEXTOR TZM Graphite 49cm, LCFS ~ 47cm 1MW NBI heated (1-4.5s) BT=2.25 T, Ip=350 ka B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 18

19 Exposure Before B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 19

20 Wetted surface After B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 20

21 Wetting Loss After B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 21

22 Camera View B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 22

23 3 frames # Strong droplet mission # B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 23

24 Fast Camera Single Frames 3000fps # frames 50 frames 500 frames B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 24

25 Droplets B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 25

26 Disruptions 14 frames before 6 frames during Droplets do not originate from mesh during disruption B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 26

27 Mass Loss in TEXTOR Droplets sizes seem to be in the µm range in sized r=10µm--> 30ng Sn Mass available 2.12g Mass Loss: *10-3 g ~ Droplets Consistent with numbers extrapolated from fast CCD Mechanism not yet understood Differences PSI-2 TEXTOR to be assessed: Plasma temperature / ion energies Carbon background in TEXTOR (coating of Sn surface) Magnetic field strength B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 27

28 Summary and outlook Tin has been studied as liquid target material alternative to Lithium within the concept of a the capillary porous system. Tungsten has been found as optimum mesh material, wetting improved under hydrogen atmosphere. Exposure in PSI-2: mass loss could not be explained by physical sputtering / evaporation temperature enhanced sputtering? Exposure in TEXTOR: mass loss dominated by strong droplet emission, mechanism unclear to date Next exposure in PSI-2: target biasing to increase ion energy to come close to TEXTOR conditions and to assess temperature enhanced erosion Next exposure in TEXTOR: positioning of targets in erosion dominated zone to prevent carbon deposition B. Unterberg Institut für Energie- und Klimaforschung Plasmaphysik, Forschungszentrum Jülich Nr. 28