Mathew C. Wright January 26, 2009 Improving Helium Refrigeration Plant Reliability at Jefferson Laboratory Mathew C. Wright January 26, 2009

Definitions Jefferson Lab Cryo Operations Three Cryo Plants 4600W @ 2.1K (Accelerator) 1500W @4.5K (Experimental Halls) 750W @ 4.5K (Test Facility) 24/7/365 Continuous unattended operations 2K operations started in 1994 Typical major maintenance cycle every 5 years Only once LINAC has been warmed up Hurricane Isabel

Definitions Down-time Any time loss to scheduled beam operations due to the cryogenics system and back to data collecting Accounts for the restoration of the entire machine The amount of time to recover from an outage is exponential to the amount of time that the cryogenic plant is down Cryo down-time resulting in stopped physics 1999 through 2008 ~ 1.57% average down time November 2008 major down time of ~60 hours 2008 down time ~ 2.6% Main compressor failure without redundancy

History Original Conditions 4 GeV (235 g/s at 2K – design with margin) Forced cryo plant to run at max design point No redundant equipment (compressors or turbines) Improvements made Implemented Ganni cycle Replaced the old 2K Cold Box with Jefferson Lab design (1998) Added the Stand-by Refrigerator (SBR) Present conditions 6 GeV max load (235 g/s) 4 GeV turn down (190 g/s)

Major Contributions to Down Time Utilities Failures Electrical Power Power spikes Phase imbalance Cooling Water Cooling tower accumulates debris Pumping system failures Instrument (control) air Faulty / failure of pneumatic control valves due to moisture contamination

Major Contributions to Down Time Control systems (CAMAC) Old technology, uses lots of power, generates lots of heat (more heat, higher failure rates). Laboratory grade hardware, not designed for industrial environment. Highest failure rates in control system; electric valve cards, crate controllers, power supplies. Replacement components are getting harder to find. Aging system Control cards Carbon purification systems Compressors Carbon Steel components Vacuum Jackets Water Piping

Contamination Dirty Sources (mostly Air & H2O) Helium introduced into the system is always scrubbed Clean gas from vendors is not always clean Contamination can be found in Liquid dewars Liquid dewars have been used as a source of clean helium Loads from different users Magnets Cryogenic targets (sometimes sub-atmospheric) Sub-atmospheric cryomodules

Contamination Oil carryover Improperly sized oil coalescers 10 cm/s max velocity Saturated carbon resulting in oil breakthrough to the cold box Oil coats heat exchangers and reduces effectiveness Can result in months to years of down time

System Cycle Ganni cycle reduces how hard the system has to run Invalidates the traditional philosophy that the design (‘TS’) condition is the optimal operating condition for as-built hardware and load The traditional philosophy Controls to the design T-s condition by adding heat, throttling valves and/or bypass of flow to maintain a fixed (design) load. Utilizes a floating pressure system A constant pressure ratio system that maintains a constant efficiency for a variable load

Redundancy Up to 5.5 GeV using the Ganni cycle SBR 2nd stage compressor (1/2 size of main compressor) can be used instead of one of the three main 2nd stage compressors The SBR compressor can be run while maintenance on one of the main compressors is performed Only two 1st stage compressors are required compared to the three needed to reach the operating condition The SBR can be used to keep 4K liquid helium in the LINACs during scheduled physics down-time Opportunity to replace charcoal in oil removal system of main machine and any other maintenance requiring the main machine to be down

Preventative Maintenance (PM) Do not over maintain The longer the process piping is open, the higher the probability of contaminating the system Oil has a high affinity to absorb moisture from surrounding atmosphere Mistakes can be made when performing PM Jefferson Lab runs compressors for 74,000 hours between maintenance Vendor recommends 25,000 hours on helium compressors

Conclusion To minimize down-time and keep reliability up Keep system free of contamination Do not over drive the system Have redundant systems for backup Do not over maintain the system Pay your cryogenics operators more Attention Money Compliments