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Experience with Turbomolecular Pumps

Experience with Turbomolecular Pumps. for LHC Insulation Vacuum Systems D. Convers*, P. Cruikshank, R. Gavaggio, B. Heywang**, N. Hilleret, A. Grimaud***, W. Maan , G. Moranne*, L. Mourier. *Adixen by Alcatel Vacuum Technology, Annecy (FR) **40-30, Seyssinet-Pariset (FR)

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Experience with Turbomolecular Pumps

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  1. Experience with Turbomolecular Pumps for LHC Insulation Vacuum Systems D. Convers*, P. Cruikshank, R. Gavaggio, B. Heywang**, N. Hilleret, A. Grimaud***, W. Maan, G. Moranne*, L. Mourier • *Adixen by Alcatel Vacuum Technology, Annecy (FR) • **40-30, Seyssinet-Pariset (FR) • ***Air Liquide DTA, Sassenage (FR)

  2. Contents • LHC insulation vacuum system. • Technical specification for turbomolecular pump supplies & procurement. • Integration of the turbomolecular pump into different pumping group systems. • Failures and some remedies……. W. Maan

  3. LHC Insulation Vacuum Systems • QRL & Magnet insulation vacuum system • Continuous arc cryostats subdivided into insulation vacuum subsectors or volumes: • 112 magnet and 72 QRL insulation vacuum subsectors • ~ 80 m3 (214 m magnets and 428 m QRL) • ~200 m2/m Multi Layer Insulation • 128 permanently installed and from distance controlled Turbomolecular 300l/s pumping systems • ~400 positions to attach a mobile pumping system (rough and turbomolecular) • Stand alone cryostats (one insulation vacuum volume or subsector) • 50 volumes/sectors • Average of 4 m3 • 66 permanently installed and from distance controlled Turbomolecular 60l/s pumping systems • High Vacuum system; • ~10-3 mbar at room temperature before cooldown, ~10-7 mbar at cold • Internal process line leak tightness requirement <10-8 mbarl/s He at warm • Important quantities of water vapour during initial pumpdown • Not very “clean” vacuum (variety of materials, dust, particles, swarfs…) W. Maan

  4. Technical specification for turbomolecular pump supplies • Invitation to tender ( March 2002) for the supply and maintenance of Turbomolecular Pumps and their power supplies • High pumping speed (>200 l/s N2 eq and >180 l/s He eq) • High compression required to pump possible He leaks from cryo systems (>108 for N2 and 104 for He) • Radiation resistant up to 200 Gy (20 Gy per year) • Forced air cooling to ensure operation up to 35ºC ambient air temperature (lower temperature limit not specified) • Remotely controlled (on/off, rotation, nominal speed, failures) • Maintenance for permanent installed turbomolecular pumps included in offer: • Preventive (executed by CERN but materials to be foreseen within contract or executed fully by contractor on the CERN premises) • Corrective (all defective pumps should be replaced immediately to ensure the functionality of the LHC; i.e. replacement pumps and power supplies to foreseen. Repair of damaged pumps can be done at CERN two times a year) • Operation according to specification up to 43 khours during the LHC life W. Maan

  5. Procurement • The order was placed for: • 300 l/s Hybrid Turbomolecular Pump (up to the total of 168 units) • Sealed bearings for minor maintenance constraints… • Special developed power supply (more than 170 units) • High radiation resistance due to simple traditional electronics • High power output to drive turbo with extended cables (>100m) • Maintenance contract to guarantee the performance W. Maan

  6. Integration of turbomolecular pumps into pumping systems • Several Turbo Molecular pumps have been stored (>6 months) before being integrated into a pumping system and put into service. • 128 permanently installed and remotely controlled. • 40 mobile turbo pumping systems (installation, commissioning and interventions) W. Maan

  7. Power cable Control cable Failures and remedies on the Turbomolecular pumping systems • Turbo powering difficulties over long distance (>100m) deported power supply. • CERN developed a cabling configuration where the power to run the motor of the turbo is transferred via one cable and all the control signals (rotation speed, temperature) in a separate second cable. • Charge independent speed oscillations (Conceptual error in pump temperature treatment). • CERN started to by-pass the temperature readings. • On request of the supplier, CERN has to implement additional logic on our pumping group control level (using rotation speed signal) to protect the turbomolecular pump • Bearing failures on both mobile and permanently installed turbomolecular pumps. W. Maan

  8. Bearing failures on both mobile and permanently installed turbomolecular pumps. • 168 pumps (128 permanently installed and 40 mobile pumping systems) • 72 pumps (43%) failed and have been returned for revision • 6 pumps (8%) failed a second time after revision • 56% of the failures appears before 4000 hours of operation (10% of the required number of running hours for the LHC) W. Maan

  9. What caused the bearing failures? • Pumps? • Usage? • Storage? • Environment? • Actual status: • The LHC is starting up and we encounter about 6 bearing failures a month. • The maintenance contract with the supplier needs to be revised. • 43 pumps awaiting bearing change to re-enter the guarantee and maintenance contract with the supplier (due to storage). W. Maan

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