Experience with turbomolecular pumps
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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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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)


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


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


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


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


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


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


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


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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