BTEV VACUUM SYSTEM

1
BTEV VACUUM SYSTEM

• The BTeV Vacuum System, including beam pipes and
  pixel detector vacuum, has been modeled to better
  understand the pressure distribution
• System specifications
• Layout
• Model Input
• Results
• Measured Gas Load
• 10 Mock-Up

2
SYSTEM SPECIFICATIONS

• lt 1e-7 torr in system between RICH detectors
• Determine the source of gas load in system
• Determine adequate pumping speed

3
VACUUM SYSTEM LAYOUT
Clean side Pump 50 L/sec
Dirty side Pump 800 L/sec
Ion Pump 80 L/sec
RICH beam Pipe 1.92 ID
Forward beam Pipe 1.0 ID
4
DETAILS OF PIXEL DETECTOR VACUUM

• Thin metal membrane isolating pixels from beam
  line
• Thin membrane RF shield
• Aperture in membrane allows restrictive flow
  minimizes pressure differential

5
MODEL INPUTS

• Geometry of vacuum system
• Beam pipes
• Clean side of RF shield beam line
• Dirty side of RF shield pixel detector
• Pumping speeds
• Total gas load in beam pipes due to outgassing
• 1e-10 torr-L/cm2/sec (clean, unbaked aluminum
  pipe)

6
MODEL INPUTS (CONTD)

• Total gas load in pixel detector due to
  outgassing
• Initial estimate 1.4 e-2 torr-L/sec
• Based on current measurements 1.5 e-3 torr-L/sec
• Aperture in RF shield 0.5 cm in diameter

7
RESULTS
8
Gas Load Measurement Procedure

• Treat sample by baking and/or cleaning w/ alcohol
• Bake empty stainless steel vacuum chamber for 3
  days
• After cooled, place sample into chamber
• Pump for 3-10 days
• Measure rate-of-rise each day
• Record RGA reading periodically

9
MEASURED OUTGASSING RATES
10
MEASURED GAS LOADS
11
PIXEL VACUUM (DIRTY SIDE) GAS LOADS
Total est. gas load 1.36e-2 Total gas
load 1.44e-3 (w/in 24 hours (3-10 days
pumping) pumping)
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MEASURE GAS LOAD FROM MOCK-UP OF PIXEL DETECTOR

• Assembly that comprises 10 of the total pixel
  detector
• Includes assembly features (virtual leaks)
• Will measure the gas load of assembly
• Good test of assembly temperature control

13
FUTURE PLANS

• Continue long-term gas load measurements
• Continue setting up 10 mock-up
• RF shield test
• Effects of restrictive flow on maintaining vacuum
  pressure differential
• Effects of pressure changes
• Work with Mauro on optimizing design of BTeV
  vacuum system