First operation of the XFEL linac with the 2K cryogenic system T.Paetzold2, B. Petersen1, T. Schnautz1, C. Ueresin3 & J.Zajac3 1Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany 2Linde Kryotechnik/Engie, Hamburg, Germany 3Linde Kryotechnik, Pfungen, Switzerland How to edit the title slide Upper area: Title of your talk, max. 2 rows of the defined size (55 pt) Lower area (subtitle): Conference/meeting/workshop, location, date, your name and affiliation, max. 4 rows of the defined size (32 pt) Change the partner logos or add others in the last row.

Cold compressors Overview (General) challenges Requirements on XFEL cold compressors Cold compressor bypass operation Mass flow compensation Temperature adjustment Stand alone operation Pressure Stability Current Problems Summary Outlook Before you start editing the slides of your talk change to the Master Slide view: Menu button “View” > Slide Master: Edit the following items: 1. On the Title slide (second master slide) a) Click to add title of your talk b) Click to add subtitle (conference, location, name of the speaker, date) 2. On the Slide Master (first master slide) a) The 1st row in the violet header: Delete the existent text and write the title of your talk into this text field b) The 2 rows in the footer area: Delete the text and write the information regarding your talk (same as on the Title Slide) into this text field. If you want to use more partner logos position them left beside the DESY logo in the footer area. Close Master View

Cold compressors Operational challenges Cold compressors are turbomachines and hence very sensitive towards massflow-, temperature- and pressure- changes in the 2K-return flow (but the massflow-stability is most important) Surge line Choke operation: Should be avoided as cryo capacity decreases Surge operation: Not possible - breakdown of operation

Cold compressors Requirements Requirements on XFEL 2K cold compressor system: 2K Pressure stability: < 1% High availability Exchange of cold compressor motors for maintenance after 16.000hrs. Suction pressure: 24mbar - 1000mbar Set-pressure shall be regulated automatically 30% turn down capacity Discharge pressure: 700mbar - 1000mbar… … by reducing the suction pressure of warm screw compressors Before you start editing the slides of your talk change to the Master Slide view: Menu button “View” > Slide Master: Edit the following items: 1. On the Title slide (second master slide) a) Click to add title of your talk b) Click to add subtitle (conference, location, name of the speaker, date) 2. On the Slide Master (first master slide) a) The 1st row in the violet header: Delete the existent text and write the title of your talk into this text field b) The 2 rows in the footer area: Delete the text and write the information regarding your talk (same as on the Title Slide) into this text field. If you want to use more partner logos position them left beside the DESY logo in the footer area. Close Master View

Cold compressors Requirements Required abilities to optimize operational issues Cold compressor system shall allow: Easy adaption on different operation modes Extension of the specific operation field Stand alone operation Re-connection of XFEL Linac/injector at sub atmospheric pressure Reduction of recovery time Cold compressor bypass system can fulfill these requirements Cold compressors CB44 CC-bypass XFEL Linac & Injector Refrigerating plant Before you start editing the slides of your talk change to the Master Slide view: Menu button “View” > Slide Master: Edit the following items: 1. On the Title slide (second master slide) a) Click to add title of your talk b) Click to add subtitle (conference, location, name of the speaker, date) 2. On the Slide Master (first master slide) a) The 1st row in the violet header: Delete the existent text and write the title of your talk into this text field b) The 2 rows in the footer area: Delete the text and write the information regarding your talk (same as on the Title Slide) into this text field. If you want to use more partner logos position them left beside the DESY logo in the footer area. Close Master View

Cold compressors Bypass operation Bypass operation: Massflow compensation and temperature adjustment 2K supply (~4.5K) 2K supply (linac) Cold compressors (require ~106g/s) Cold compressor bypass Mass flow compensation Temperature adjustment Stand alone operation Cold compressor bypass functions:

Cold compressors Operational challenges Bypass operation: Massflow compensation and temperature adjustment 2K return flow: 70g/s 2K supply (~4.5K) 2K supply (linac) 2K return (linac) Cold compressors (require ~106g/s)

Cold compressors Operational challenges Bypass operation: Massflow compensation and temperature adjustment 2K return flow: 70g/s 2K supply (~4.5K) 2K supply (linac) 2K return (linac) Cold compressors (require ~106g/s) 20K return (coldbox)

Cold compressors Operational challenges Bypass operation: Massflow compensation and temperature adjustment 2K return flow: 70g/s 2K supply (~4.5K) 2K supply (linac) 2K return (linac) Cold compressors (require ~106g/s) 20K return (coldbox) CC-bypass has to produce: 30g/s

Cold compressors Operational challenges Bypass operation: Massflow compensation and temperature adjustment Real CC mass flow: 2K return flow + CC-bypass flow 2K return flow: 70g/s 2K supply (~4.5K) 2K supply (linac) 2K return (linac) Cold compressors (require ~106g/s) 20K return (coldbox) CC inlet temperature is adjusted by use of two heat exchangers in CC-bypass CC-bypass has to produce: 30g/s

Cold compressors Mass flow compensation Bypass operation: Massflow compensation 22.02.2017 (12:00) 25.02.2017 (10:00) 110 g/s 50 g/s 70 g/s 20.03.2017 (06:00) 20.03.2017 (12:00) 110 g/s 50 g/s 70 g/s Required massflow Real massflow Bypass flow 2K return flow Surge shutdown Required massflow Real massflow = (2K return flow + bypass flow) Bypass flow Massflow bypass 2K return flow (linac & injector) Conclusion: CC-bypass operation delivers reasonable reactions on changes in 2K return flow Extent of changes in 2K return determines limits of massflow compensation

Cold compressors Recovery after shutdown / stand alone (bypass) operation Bypass operation: Recovery after shutdown Normal operation configuration Warm He pumps AMTF XFEL Coldbox Distribution box XLVB XFEL Linac & Injector Cold compressors CB44 CC-bypass 2K return flow 1000mbar 29mbar

Cold compressors Recovery after shutdown / stand alone (bypass) operation Bypass operation: Recovery after shutdown Operation configuration after surge – beam operation not possible, but linac can be kept cold at 30mbar 1000mbar 29mbar Warm He pumps AMTF Cold compressors CB44 CC-bypass XFEL Coldbox Distribution box XLVB XFEL Linac & Injector 2K return flow 1000mbar 1000mbar Sudden shutdown!

Cold compressors Recovery after shutdown / stand alone (bypass) operation Bypass operation: Recovery after shutdown Operation configuration after surge – beam operation not possible, but linac can be kept cold at 30mbar 1000mbar 29mbar Warm He pumps AMTF Cold compressors CB44 CC-bypass XFEL Coldbox Distribution box XLVB XFEL Linac & Injector 2K return flow 1000mbar 1000mbar → 29mbar Stand alone bypass operation - Internal pump down

Cold compressors Recovery after shutdown / stand alone (bypass) operation Bypass operation: Recovery after shutdown Normal operation configuration after internal pumpdown and re-connection of XFEL linac/injector 1000mbar 29mbar Warm He pumps AMTF XFEL Coldbox Distribution box XLVB XFEL Linac & Injector Cold compressors CB44 CC-bypass 2K return flow 1000mbar 29mbar Re-connection of linac at sub atmospheric pressure Conclusion: The recovery time after a cold compressor shutdown is minimized by the possibility of the stand alone CC-bypass operation and the re-connection of the XFEL linac/injector at sub atmospheric pressure (5 hours, 2-3 well trained cryo operators).

Cold compressors Pressure stability Specified pressure stability: 1% (30.6 mbar +/- 0.3 mbar) Cascaded regulation for pressure adjustment in 2K circuit is used The pressure controller of the linac determines the set point of another pressure controller, which regulates the suction pressure of the cold compressors Automatic heat load compensation (AHLC) is used: Changes in the 2K return flow – caused by dynamic RF operation - are determined automatically and compensation takes place in the linac by automatic heating in the 2K liquid helium. Sudden RF-shutdown (10 GeV) Required massflow for CCs 30.9 mbar Real massflow (2K return flow + bypass massflow) 2K pressure 30.6 mbar Massflow bypass 1% - pressure stability 30.3 mbar 2K return flow from linac 05.04.2017 (09:00) 05.04.2017 (16:00) 05.04.2017 (09:00) 05.04.2017 (16:00) Conclusion: Cold compressors deliver a pressure stability better than 0.3%, which is much better than internally specified. Heat load changes –caused by dyn. RF operation- can be compensated perfectly well by AHLC

Cold compressors Motor failures Current problems/challenges with cold compressors: CC-motor failures CC-motors are equipped with ceramic ball bearings Three of four motors show bearing problems Specification: lifetime of cold compressor motors of at least 16000 hrs. Observed average lifetime of the (three) motors is far below specification Due to the bearing failures, the specified lifetime could not yet be achieved New motor design has been tested successfully at manufacturer and is currently in operation at DESY for > 2200 hrs. without failures Root cause analysis by Linde Kryotechnik Conclusion: Downtime, caused by cold compressor issues, has to be reduced significantly Duration of interruption in case of motor failure: 2.5 days New CC-motor design is very promising, impact on lifetime has to be verified

Cold compressors Summary XFEL cryogenic system: Summary Most promi Cold compressors deliver very high 2K pressure stability (0.3%) Dynamic procedures in the XFEL linac can be compensated quite well by CC-bypass operation Most promi Sensibility of cold compressors could be eased by Bypass operation in combination with automatic heat load compensation Even a sudden RF-shutdown from 10 GeV does not affect the stability of the cold compressor operation Most promi Recovery time after shutdown is optimized by the possibility … … to use of warm helium pumps to keep the linac at 30mbar (static) … of stand alone CC-bypass operation (internal pumpdown) … to re-connect XFEL linac/injector to the cold compressors at sub atmospheric pressure Problem solving related to lifetime of CC-motors is ongoing New motor design seems to increase lifetime of CC-motors → more experience must be gained

Cold compressors Outlook XFEL 2K cold compressors: Outlook Most promi Dynamic procedures have to be (partly) automated Dynamic procedures at XFEL cryo are still very complicated, time consuming and personnel-intensive Pumpdown Restart of cold compressors Cryo operators have to be trained intensively Operators not only need to know how to operate the plant, they also have to understand why they have to do it in a certain way Operating instructions have to be optimized Different compressor-wheels will be defined to match the real 2K return flow Required massflow for cold compressors will be reduced Operational costs will be reduced

Cold compressors Outlook XFEL 2K cold compressors: Outlook Most promi Dynamic procedures have to be (partly) automated Dynamic procedures at XFEL cryo plant (e.g. restart of cold compressors) are still very complicated, time consuming and personnel-intensive Cryo operators have to be trained intensively Operators not only need to know how to operate the plant, they also have to understand why they have to do it in a certain way Operating instructions have to be optimized Different compressor-wheels will be defined to match the real 2K return flow Required massflow for cold compressors will be reduced Operational costs will be reduced

Thank you for your attention Acknowledgements In particular, we thank: Linde Kryotechnik (C. Ueresin, L. Decker, K. Rautert, …) Linde/Engie cryo operating team (J. Zajac, T. Paetzold, …) Hecht cryo & gas experts (H. Hecht, …) Many more… Thank you for your attention