Max-Planck-Institut für Plasmaphysik 1 ICEC 26- ICMC 2016 March 7-11, 2016, New Delhi, India Michael Nagel Cryogenic commissioning, cool down and first magnet operation of Wendelstein 7-X Presented by Michael Nagel M. Nagel, C.P. Dhard, H. Bau, H.-S. Bosch, U. Meyer, S. Raatz, K. Risse, T. Rummel Max-Planck-Institut für Plasmaphysik Wendelsteinstraße 1, Greifswald, Germany 24 th ICEC26 – ICMC 2016

Max-Planck-Institut für Plasmaphysik 2 Michael Nagel ICEC 26 - ICMC 2016 March 7-11, 2016, New Delhi, India 1. Overview W7-X Outer cryostat wall Plasma vessel Coil support structure Machine base 50 non-planar coils nominal current 17.6 kA at 4 K 20 planar coils nominal current of 16 kA at 4 K Characteristic values Magnetic field energy: 620 MJ Magnetic peak field: 6.7 T (on plasma axis 3 T) 7 electrical circuits 5 non-planar coil circuits 2 planar coil circuits with 10 coils each in serial Schematic view of W7-X cryostat Plasma

Max-Planck-Institut für Plasmaphysik 3 Michael Nagel ICEC 26 - ICMC 2016 March 7-11, 2016, New Delhi, India 1. Overview W7-X Plasma vessel sector with thermal shield Module of coils 10 non-planar + 4 planar coils Support structure Outer vessel + thermal shield Cross section of cryostat

Max-Planck-Institut für Plasmaphysik 4 Michael Nagel ICEC 26 - ICMC 2016 March 7-11, 2016, New Delhi, India 1. Overview W7-X Diagnostics, supply piping and scaffolding cover the cryostat surface! View on W7-X cryostat

Max-Planck-Institut für Plasmaphysik 5 Michael Nagel ICEC 26 - ICMC 2016 March 7-11, 2016, New Delhi, India 2. RefrigeratorLayout No.Device 7 kWRefrigerator power at 4.5 K 2Screw compressors 1.6 MW electrical power 1212 Oil removal system Dryers 3Pressure levels 1.1; 3-4;11-17 bar 7Turbines in cold box 1Phase separator 2Sub coolers with cold compressors 4Cold circulators 1LHe - dewar 5Different consumers Screw compressor Coalescer + adsorber Dryer Cold box Cold pump LHe- dewar

Max-Planck-Institut für Plasmaphysik 6 Michael Nagel ICEC 26 - ICMC 2016 March 7-11, 2016, New Delhi, India 2. RefrigeratorDistribution from sub cooler to W7-X cryostat Cooling W7-X: Forced flow supercritical helium  cold circulators and / or JT-flow Sub cooler baths: 1 cold compressor in operation  3.9 K 2 cold compressors in operation  3.4 K 1.1 bar 0.63 bar 0.37 bar Cold compressors

Max-Planck-Institut für Plasmaphysik 7 Michael Nagel ICEC 26 - ICMC 2016 March 7-11, 2016, New Delhi, India 3. Preparation of cryogenic system Cryogenic system: refrigerator, supply lines to cryostat, piping inside the cryostat, current leads, quench gas exhaust system Verification that assembly and tests had been done successfully Flushing procedure: - filling to 3 bars, rapid expansion, gas was filtered - at least three times - inside cryostat pressure increased from 3 to 12 bars Pumping and filling of the single cooling circuits (three times): - evacuated to 30 mbar - filled to 1 bar with helium Cleaning using the dryer and cold adsorber of refrigerator - first cleaning of single circuits, than all circuits together - impurity less than 10 vpm for nitrogen - 4 weeks cleaning time Inside the cryostat: - helium leak rate better than 3*10 -5 mbar *l/s (warm condition) - vacuum 2*10 -4 mbar before cool down

Max-Planck-Institut für Plasmaphysik 8 Michael Nagel ICEC 26 - ICMC 2016 March 7-11, 2016, New Delhi, India 4. ResultFirst cool down of cryostat Parallel cool down of cryostat and refrigerator Visual checks, no ice formation or water condensation on cryostat or components No vibrations or fluctuations Check of flow distribution in circuits Check of displacement sensors at coils, at GFK-supports at magnet structure and at CL  Displacements within predicted range! Smooth cool down in 4 weeks cold mass 456 tons max(ΔT) = 40 K cool down rate 1 K/h cryostat pressure mbar (warm) mbar (cold) helium leak rate at 4 K ≈ 5*10 -5 mbar*l/s

Max-Planck-Institut für Plasmaphysik 9 Michael Nagel ICEC 26 - ICMC 2016 March 7-11, 2016, New Delhi, India 4. Result * design value for refrigerator performance Heat load on components and flow conditions SSM = short stand by mode SM = standard mode ModeSM (3.9 K)SSM (<10 K) Coil housing and structure Conductor cooling Shield cooling Coil conductor, housing and structure Feed temperature [K] Flow rate [g/s] Heat Load [W] Design value for heat load [W] * Pressure drop [mbar] Specified mass flow rates achieved Pressure drop within limits Average thermal loads on shield 4 W/m² Average thermal loads on cold structure 0.55 W/m² Conductor outlet temperatures between 4.0 to 4.7 K

Max-Planck-Institut für Plasmaphysik 10 Michael Nagel ICEC 26 - ICMC 2016 March 7-11, 2016, New Delhi, India 4. Result Current load steps for single coil circuit Functionality test of single coil circuits with load steps Non-planar coils: 12.8 kA, planar coils: 5.0 kA

Max-Planck-Institut für Plasmaphysik 11 Michael Nagel ICEC 26 - ICMC 2016 March 7-11, 2016, New Delhi, India 4. Result 30 A/s Slow discharge Fast discharge He-inlet Coil outlets Coil current [kA] Non-planar coils: 12.8 kA, planar coils: 5.0 kA Cooling with helium flow (3.7 bar, 3.9 K) Helium cooling during current load steps

Max-Planck-Institut für Plasmaphysik 12 Michael Nagel ICEC 26 - ICMC 2016 March 7-11, 2016, New Delhi, India 4. ResultPressure increase during fast discharge Pressure increase over time in ring manifolds for the casing and conductor cooling. 70 coils in operation 12.8 kA NPC 5 kA PLC Fast discharge of current with time constant 5 s  pressure increase  trip of cold compressor  trip of cold circulators

Max-Planck-Institut für Plasmaphysik 13 Michael Nagel ICEC 26 - ICMC 2016 March 7-11, 2016, New Delhi, India 4. ResultCoil temperature during magnet operation Helium outlet temperature of the coil conductor cooling Current ramp 15 A/s from 0 to 12.8 kA in the NPC  Maximum 200 mK temperature increase due to eddy currents Stable current operation with 12.8 kA  in the average ΔT = 50 mK for conductor cooling  ΔT = 10 mK for coil housing cooling  low ohmic heating, good quality of joints Helium outlet temperature of coil housing cooling 50 mK 10 mK

Max-Planck-Institut für Plasmaphysik 14 ICEC 26- ICMC 2016 March 7-11, 2016, New Delhi, India Michael Nagel Cool down within 4 weeks Thermal shield works well  5.6 kW Cold structures (coil / casing)  682 W Conductor temperatures allow save magnet operation Successful magnet operation (12.8 kA NPC, 5 kA PLC) First Plasma Summary: