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BEAM LOSS MONITORS FOR THE LHC

BEAM LOSS MONITORS FOR THE LHC. E.B. Holzer LHC Specification Committee July 15, 2004 Monitor types Monitor positions Cleaning procedures for monitor production. Monitor Types. Ionization chamber with parallel plate electrodes: faster and more expensive.

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BEAM LOSS MONITORS FOR THE LHC

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  1. BEAM LOSS MONITORS FOR THE LHC • E.B. Holzer • LHC Specification Committee • July 15, 2004 • Monitor types • Monitor positions • Cleaning procedures for monitor production

  2. Monitor Types • Ionization chamber with parallel plate electrodes: faster and more expensive. • Ionization chamber with coaxial electrodes: slower but less expensive. • Secondary emission monitors: gain is ~ 30000 times smaller.

  3. Ionization Chamber - Parallel Plate Design SPS Chamber Gas:N2, Volume: ~ 1 Liter, 30 Al disks of 0.5 mm, Typical bias voltage: 1500 V. New LHC chamber design: Diameter = 8.9 cm, Length 60 cm, 1.5 litre, Filled with Ar + C02 or N2 at 1.1 bar, 61 Al disks of 0.5 mm, Bias voltage: 1500 V.

  4. Ionization Chamber - Coaxial Electrode Design 2 or 3 electrodes from inox or Al, Diameter = 8.9 cm, Length 60 – 150 cm, Filled with Ar + CO2 or N2 at 1.1 bar, Bias voltage: 1500 V

  5. Secondary Emission Monitor Diameter = 8.9 cm, Length 15 cm, 2 electrodes from Al or Ti, 10-5 mbar.

  6. Monitor Positions in Arc Installation of BLMAs on a SSS quadrupole Precise longitudinal position not defined. Installation with a small support and straps or cables on the cryostats Chamber (89 mm) + fixation (8 mm) just fits between the cryostat and the transport space (2 mm space left).

  7. Monitor Positions for BLMS and BLMC BLMS and part of BLMC will be installed on separate stands. The other part of BLMC will be installed on the collimator interconnects: Collimator interconnect with ion pump and BLM (possible positions)

  8. Chamber Gas Purity • Possible problems with ageing: • Electronegative gases (O2, H2O, NH3, …) capture electrons - drift velocity reduced by a factor ~1000  change in signal height and length. • Polymerization (should not pose a problem when properly cleaned and organic materials are avoided in the production process.) • Impurities/additives change the chamber operation characteristics: • Drift velocity, • Recombination losses, • Gain (ionization/cm of charged particle), • Onset of gas amplification, • Flatness of signal vs voltage in the ionization region … • These effects are often used intentionally: • 2% H2 in He to suppress gas amplification, • 5-10% CO2 in Ar to increase drift velocity …

  9. Estimate that electronegative impurities should stay below ppm level. • Calculated for cleaned/baked Al: •  • Thermal desorption acceptable if cleaned according to CERN standard for UHV application and backed in vacuum before filling. • Particle induced desorption: for BLMC glow discharge cleaning during filling process. • Avoid organic material in production process. • Avoid closed volumes in design (from welding, from tubes, …).

  10. Cleaning and Filling Procedure • CERN standard cleaning for UHV procedure • ultrasonic bath of the alkali detergent NGL 17.40 Alu from NGL Cleaning Technologies at 60 degree C • rinsing with cold demineralised water jet (conductivity < 5 uS cm-1) • immersion in hot ultrasonic demineralised water bath • drying with compressed dry nitrogen and afterwards in a hot (80 degree) air oven • Mount (several chambers at same time) • Pump • He leak detection • Bake • He leak detection • For BLMC: glow discharge (Ar at ~10-3 mbar) • Pump • Fill

  11. Cleaning and Filling • Detailed procedures for pumping, baking, glow discharge and filling will be written after the tests on the prototype chambers. • The system for pumping, baking, glow discharge and filling will be built at CERN.

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