EU Plasma-Wall Interaction Task Force meeting November 2006 Lubljana, Slovenia "Interaction of a liquid Gallium jet with ISTTOK's edge plasmas: first experimental results" R. B. Gomes, H. Fernandes, C. Silva, ISTTOK team and the Latvian association Associação EURATOM/IST, Centro de Fusão Nuclear, Av. Rovisco Pais, Lisboa, Portugal.

EU Plasma-Wall Interaction Task Force meeting November 2006 Lubljana, Slovenia Introduction Advantage of liquid metal as plasma facing components. protection capability. power exhaustion capability. Metal candidates (Li, Ga, Sn…). Li : very good compatibility with plasmas (Z=3) Ga: wider temperature range: 30 to ~ 700 ºC (at mBar) Aim of the project: to verify the feasibility of ISTTOK operation with a LM limiter to study the influence of a Gallium jet on the main plasma parameters, incl. impurity content, the plasma stability and confinement; to measure the heat deposited on the LM jet to study dynamic behaviour of liquid metal jets in a magnetic field

EU Plasma-Wall Interaction Task Force meeting November 2006 Lubljana, Slovenia Experimental setup LML design constraints: UHV ambient (10 -6 mBar) Gallium Corrosion Gallium expansion Gallium oxidation Electrical isolation requirements

EU Plasma-Wall Interaction Task Force meeting November 2006 Lubljana, Slovenia Testing of the Liquid Metal Loop outside ISTTOK chamber Aim of this experimental campaign: Assess the operating conditions of the Liquid Metal Loop. Assess the reliability of every components of the system. Detailed characterization of the produced liquid metal jets. Study of the influence of magnetic field gradients on the jet in conditions as close as possible to ISTTOK field. Test conditions: Testing chamber: 33 mm diameter, 276 mm heigth pyrex tube. All the tests are performed with ~1,3 mGa pressure on the nozzle. Nozzle sizes tested: (1.45, 1.80, 2.09 and 2.30 mm). Measured parameters: jet flow rate, BUL and time to reach stability. Magnetic field: 0.25T, 60 ms pulse generated by two coils in the Helmoltz configuration.

EU Plasma-Wall Interaction Task Force meeting November 2006 Lubljana, Slovenia Results of the testing of the LML in the experimental rig Achieved operating conditions compatible with ISTTOK operation. Only non crictical failures in the LML components after one year operation High speed jet movies used to check stability and BUL measurements Stable jet sucessfully produced. 2,3 mm nozzle most suitable for ISTTOK operation: 13 cm BUL, 2.5 m/s flow velocity. Tested magnetic field gradients do not affect the jet.

EU Plasma-Wall Interaction Task Force meeting November 2006 Lubljana, Slovenia Installation of the LML in ISTTOK tokamak ISTTOKs experiment: (R=0.46 m, a=0.085 m, B T =0.45T, I P ~4-8 kA, V loop ~4V). Instalation of the LML from the test facility to the tokamak by modules: colector, injector, pumping + storage circuit. Ga in solid state and under Argon atmosphere to minimize oxidation. Recovery of ISTTOK operating conditions and testing of magnetic field-jet interaction. ISTTOK plasma discharges with Gallium jet interacting with plasma sucessfully performed.

EU Plasma-Wall Interaction Task Force meeting November 2006 Lubljana, Slovenia Plasma-Gallium jet interaction in ISTTOK: first experimental results Comparison of ISTTOKs main parameters and radiated power with and without Gallium jet shows no evidence of strong plasma interaction

EU Plasma-Wall Interaction Task Force meeting November 2006 Lubljana, Slovenia Plasma-Gallium jet interaction in ISTTOK: Power measurement Jet is not as efficient limiter : small area (2.3 mm thick, < ¼ perimeter). Deposit power estimations: q[W/m2]= e T, e = jsat =0.5enc s Copper wire with jet dimensions Power density <2 MW/m2, relevant as q jet q// (B ~ jet surface) 600 W (~5% P in ) for 30 ms <~20 J deposited in the jet 60 ºC increase in Gallium jet. Significant damage in the copper wire

EU Plasma-Wall Interaction Task Force meeting November 2006 Lubljana, Slovenia Plasma-liquid Gallium jet in ISTTOK: Spectroscopy measurements Based on a ½ m imaging spectrograph+CCD camera and multifiber optics for collections: 5 points in the plasma (1,2 cm span) Allows the measurement of Gallium and ions distributions in the plasma. No lines of Gallium appears whithout jet Distribution profiles shows high intensity for Ga in the vicinity of the jet and penetration of ions (Ga + and Ga 2+ ) into the center of the plasma

EU Plasma-Wall Interaction Task Force meeting November 2006 Lubljana, Slovenia Plasma-liquid Gallium jet in ISTTOK: photodiode signals Photosensor at Ø=Ø jet Viewing port Photosensor at Ø=Ø jet +180º Viewing port Interaction of Gallium with plasma appears to be only local

EU Plasma-Wall Interaction Task Force meeting November 2006 Lubljana, Slovenia Conclusions Plasma discharges with Gallium jet interaction doesnt seem to significantly affect plasma performance. Only Local effect. What would happen if Gallium would be the main limiter? (Unable to test in ISTTOK with the current setup). After ~200 discharge of ISTTOK with Gallium there is not yet any clear signal of chamber conditions deterioration. Future work: Absolute measurement of Gallium density profiles measurement by LIF Zeff diagnostic has to be implemented. Measurement of total power exaustion from plasma by jet. More detailed study of the jet-plasma interaction