Thomas Jefferson National Accelerator Facility Page 1 CEBAF Cryo & SRF Workshop April 3, 2014 Jonathan Creel Electrical / Cryogenics Engineer Cryogenics CEBAF Cryogenics and SRF Workshop Jefferson Lab April 3, 2014

Thomas Jefferson National Accelerator Facility Page 2 CEBAF Cryo & SRF Workshop April 3, 2014 Outline System Overview CHL1 and CHL2 Systems Cold Compressor Pumpdowns Starting at 4K (warm pumpdown) Starting at 2K (cold pumpdown) CHL Performance Capacity Pressure Stability Efficiency Loads Calculated verses “measured” Summary Conclusion

Thomas Jefferson National Accelerator Facility Page 3 CEBAF Cryo & SRF Workshop April 3, 2014 CHL1 and CHL2 Systems CHL1-SCM-NL Warm compressors HP high pressure HP low pressure 4K Cold Box 4 Turbines Stages 2K Cold Box (SCM) 5 Cold Compressor Stages 190 g/s at atm Pressure stability +/ atm 6+ MW (before floating pressure implementation) 4.2 MW and 300 gal/hr LN2 Efficiency CHL2-SCN-SL/FEL Warm compressors HP high pressure HP medium pressure HP low pressure 4K Cold Box 7 Turbine Stages 2K Cold Box (SCN) 5 Cold Compressor Stages 195 g/s at atm Pressure stability +/ atm 3.1 MW and 300gal/hr LN2 Efficiency Value $500K per MW-Year

Thomas Jefferson National Accelerator Facility Page 4 CEBAF Cryo & SRF Workshop April 3, 2014 Cold Compressors Wheel & Diffuser LN2 Cooled Motor CC1 & CC4/5 WheelsSide View Max Hz Max RPM Wheel Dia Inch CC CC CC CC CC

Thomas Jefferson National Accelerator Facility Page 5 CEBAF Cryo & SRF Workshop April 3, 2014 Warm Pumpdown Process of pumping LINAC vapor space from 1 atm to atm Without violating individual cold compressor constraints Motor / variable frequency drive current overload limits Wheel surge / stall characteristics and CC inlet conditions (P, T, mass flow) Head pressure capacity verses tip speed Without violating maximum flow returning to 4K cold box

Thomas Jefferson National Accelerator Facility Page 6 CEBAF Cryo & SRF Workshop April 3, 2014 Cold Pumpdown Cold pumpdowns are incredibly fast and unstable Liquid inventory overflow starts earlier (smaller volume and higher JT positions) Liquid inventory starts near lambda (less boil off vapor available) Cold compressors have trouble speeding up fast enough to support the head pressure requirements without return flow exceeding 4K CB capabilities Return line liquid flashing and fast changing inlet conditions One of the cold compressors loses its grip on the helium (stall)

Thomas Jefferson National Accelerator Facility Page 7 CEBAF Cryo & SRF Workshop April 3, 2014 “Heat” Loads North LINAC Expected capacity 190 g/s * 22 J/g = 4180 W (RF 2750W) + (Electric 2000W) + (Static 900W) = 5650 W 4180W – 5650W = -1470W South LINAC + FEL Expected capacity 200 g/s * 22 J/g = 4400 W (RF 2350W) + (Electric 1350W) + (Static 1200W) = 4900W 4400W – 4900W = -500W Expected verses “reported” do not match

Thomas Jefferson National Accelerator Facility Page 8 CEBAF Cryo & SRF Workshop April 3, 2014 LINAC Heat Compensation North LINAC South LINAC Too much electric heat added Too much electric heat removed RF turned off RF turned on

Thomas Jefferson National Accelerator Facility Page 9 CEBAF Cryo & SRF Workshop April 3, 2014 LINAC Heat Compensation Autoheat Divides up excess heat evenly among all cryomodules 2L24 and 2L25 have been removed from autoheat control and the heat request values sometimes get set lower than the expected RF heat in order to allow the cavities to be brought up in gradient Forces larger heat deltas to other cryomodules Prevents RF verses electric heat compensation from working Should consider moving toward SNS type heater control system

Thomas Jefferson National Accelerator Facility Page 10 CEBAF Cryo & SRF Workshop April 3, 2014 Uncontrolled Loss of LINAC Heat 1.Lost electric heat in 2L22, 23, 24, 25, 26 when breaker tripped Tunnel pressure falls as remaining heaters ramp to maximums 2.Tunnel pressure begins to stabilize 3.Lost another CM worth of electric heat when 2L18 blew a fuse Tunnel pressure continues falling to a pressure ratio > 41 (norm ~ 33) 4.Electric heat control returns and pressure stabilizes

Thomas Jefferson National Accelerator Facility Page 11 CEBAF Cryo & SRF Workshop April 3, 2014 Conclusion Completed Successful automated warm pumpdowns Successful operation of both LINACs at 2K In Process More work on automated cold pumpdowns Future Tests MOPS heat readback verses measured current and voltage MOPS heat verses JT position for every module Can be used to cross check RF heat calculations Low and high flow subatmospheric cold box testing

Thomas Jefferson National Accelerator Facility Page 12 CEBAF Cryo & SRF Workshop April 3, 2014 Appendix

Thomas Jefferson National Accelerator Facility Page 13 CEBAF Cryo & SRF Workshop April 3, 2014 Appendix

Thomas Jefferson National Accelerator Facility Page 14 CEBAF Cryo & SRF Workshop April 3, 2014 Appendix