Thomas Härtl, IPP, Measurement of Gas Retention in AUG, WP10-PWI /II/BS, 19. July Measurement of Gas Retention in ASDEX Upgrade - A Technical View - Thomas Härtl, ASDEX Upgrade Team Max-Planck-Institut für Plasmaphysik, EURATOM Association

Thomas Härtl, IPP, Measurement of Gas Retention in AUG, WP10-PWI /II/BS, 19. July Outline Methods of Measurement Reasons for Retention Gas Sources - Sinks Ideal Gas Law Options of Measurement Status of Gas-Balance Measurement Torus Pumping System (TPS) Concepts of Measurement Summary

Thomas Härtl, IPP, Measurement of Gas Retention in AUG, WP10-PWI /II/BS, 19. July Methods of Measurement Measurement retention: 2 options Direct => Post-Mortem-Analyses Analyses of components Average of long time period with many different events Single events may change whole campaign Indirect => Gas-balance Measurement of inflow Measurement of outflow Small difference of big numbers

Thomas Härtl, IPP, Measurement of Gas Retention in AUG, WP10-PWI /II/BS, 19. July Reasons for Retention Reasons for retention Adsorption Absorption Deep implantation Trapping Co-deposition In vessel cryo-pump Liquid Nitrogen and liquid Helium panel High capacity High pumping speed (100,000 l/s) Dependent on gas species No pumping speed for Helium and Hydrogen Different conductance Consideration of black box is not sufficient Metal wall Tungsten coated tiles Cables …

Thomas Härtl, IPP, Measurement of Gas Retention in AUG, WP10-PWI /II/BS, 19. July Gas Sources - Sinks Many different sources and sinks has been investigated

Thomas Härtl, IPP, Measurement of Gas Retention in AUG, WP10-PWI /II/BS, 19. July Ideal Gas Law n - Amount of Substance [mole] P - Pressure [Pa] V - Volume [m 3 ] T - Temperature [K] R - Gas constant Measurement error V - Vessel volume 1m 3 (1m ±1mm) ± 0.3% P - Accuracy 0.1% F.S. (use at 10% F.S.) ± 1% T - Accuracy 1K (Room temp. 300K) ± 0.3% homogenous in volume V

Thomas Härtl, IPP, Measurement of Gas Retention in AUG, WP10-PWI /II/BS, 19. July Options of Measurement P- Most common pressure gauges based on indirect principles (Pirani, Penning, Bayard-Alpert, SRG) very imprecise, dependent of gas composition Baratron, F.S … > 1000 mbar only 3 decades /device) V- Different ways of measurement static or dynamic system T- Many methods: response time feedback on system n- Mass, dependent to gas species

Thomas Härtl, IPP, Measurement of Gas Retention in AUG, WP10-PWI /II/BS, 19. July Status of Gas-Balance Measurement Calculate Retention Determine overall inlet is necessary in all cases Cryo-pump Pumping speed (PS) * pressure - PS not constant, dependent of species Conductance dependent of plasma scenario Applied standard Mass of cryo sorbate - Dependent of gas composition - Marginal compared to cryo-pump Not applicable Regeneration of cryo sorbate, no pumping to outside, Pressure, volume (Alcator C-Mod) - Temperature not homogeneous Measurement system outside

Thomas Härtl, IPP, Measurement of Gas Retention in AUG, WP10-PWI /II/BS, 19. July Torus Pumping System (TPS) Gas transfer pumping system In vessel base pressure mbar Compression stage pumping system Gate valve Turbo molecular pump (TMP) (14) Operational range: mbar … mbar Compression (depending of gas species and pressure): >10 5 Pumping speed 2000 l/s ( l/s) Roots pump (1) Operational range: mbar … 3 mbar Compression: (depending of pressure): <10 1 Pumping speed 7500 m 3 /h (2.000 l/s) Rotary vane pump (2) Operational range: mbar … mbar Compression: 10 6 Pumping speed 250 m 3 /h (140 l/s) Torus 10E-7 Gate valve TMP Roots pump Rotary vane pump Atmosphere

Thomas Härtl, IPP, Measurement of Gas Retention in AUG, WP10-PWI /II/BS, 19. July Concepts of Measurement Pumping speed (PS) Requirement on PS constant over wide range Independent of gas Requirement on pressure measurement Precise Independent on gas Requirement on T measurement Fast Little feedback Very little modification No influence on operation No restriction on gas amount Flow rate Requirement on device Wide measuring range Independent on gas Volume counter Characteristic Need pressure difference up to 5 mbar Counts n-times a definite volume Few modification Little influence on operation Little restriction on gas amount

Thomas Härtl, IPP, Measurement of Gas Retention in AUG, WP10-PWI /II/BS, 19. July Concepts of Measurement Typical amount of gas in AUG shots Shot: ca. 1.5 bar l 50 bar l /d, 150 bar l /w GDC: ca. 5 barl /each, 10 / d 50 bar l /d Ver.1/2: Store at p 1E-1 mbar not possible p AUG > p Strorage Ver.3: Store at p 10 mbar V Storage 5,000l Ver.3: Store at p 100 mbar V Storage 500l Ver.4: Store at p 1000 mbar V Storage 50l Storage in volume Requirements: Volume not to large, max. 1…2 m 3 static compression independent of gas combination Modification is necessary Influence on operation Gas amount is design criteria

Thomas Härtl, IPP, Measurement of Gas Retention in AUG, WP10-PWI /II/BS, 19. July Details: Storage in Volume Storage in volume Standard operations End pressure, P Torus < 1E-7 mbar K FV > 10E4 GDC, P Torus 3E-3 mbar S >1500 l/s at 2E-2 mbar Regenerate cryo-pump PV TMP < 3E-1 mbar Volume of fore vacuum line buffers

Thomas Härtl, IPP, Measurement of Gas Retention in AUG, WP10-PWI /II/BS, 19. July Details: Storage in Volume Storage in volume Standard operations End pressure, P Torus < 1E-7 mbar K FV > 10E4 GDC, P Torus 3E-3 mbar S >1500 l/s at 2E-2 mbar Regenerate cryo-pump PV TMP < 3E-1 mbar Volume of fore vacuum line buffers Regenerate cryo-pump after long operations (>50 bar l) Bypass TMPs Bypass first (second) stage All scenarios could be handled New fore vacuum system necessary

Thomas Härtl, IPP, Measurement of Gas Retention in AUG, WP10-PWI /II/BS, 19. July Concepts of Measurement Storage at constant pressure Requirements: Constant ambient pressure Δp 5 mbar V Storage 50 l (for 1 day operation) Independent to pumping system No feed back to system Established reference standard also for H 2

Thomas Härtl, IPP, Measurement of Gas Retention in AUG, WP10-PWI /II/BS, 19. July Summery Pumping speed Good accuracy at higher pressure Difficult at low pressure, long time measurement Temperature measurement imprecise Flow rate Very precise at operational range (0.3 %) Uncertain at high and very low flow rate Temperature may vary at very high flow rate Storage in volume Precise pressure measurement Continues compression may influence temperature Modification of pumping system necessary Storage at constant pressure Very precise (< 0.3 %) Constant conditions for P, T Independent of nature of pumping system