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

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

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

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

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

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

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


Failures and remedies on the turbomolecular pumping systems

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

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

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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