Module%20Gas%20Leak

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• Module Gas Leak
• Chiho Wang
• Duke University

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Gas leak requirements

• Operating condition
• ionization gas at 1 atm with 70 Xe
• purging gas at 1 atm with 100 CO2
• allow 10 volume / year of Xe loss
• Measurement simulates Xe loss with
• Same gas (or different gases assuming both are
  ideal gas) in each gas volume
• Slight over pressure of ionization gas volume
• monitoring pressure change over time
  (indifference of composition change)
• Present requirement at Duke/IU
• lt 0.1 mBar/Bar/minute

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Module leak test setup
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Module leak test setup
Reference Volume
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Leak Measurement

• Measurement procedure
• pressurize/equalize module and reference tank
  pressure to 20mB above room atm
• isolate module from reference tank
• monitor pressure change between reference tank
  and module over time
• Leak rate is calculated dP/P/T
• dP pressure difference
• Tank - Module (mBar)
• P module pressure vs room (Bar)
• T elapsed time (minute)

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Module 2.07 mechanical

• 42 hrs, Leak rate -0.007 mB/B/min

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Measurement Accuracy

• Affecting factors
• Temperature may swing 2ºC during measurement.
• The measurement assumes module and reference tank
  responds to temperature change equally.
• Suppose theres a 10 mismatch in their
  responses, the error in dP measurement would be
• 10 2/3001013 0.68 mB
• To wash out temperature effect with time to
  0.05mB/B/min would be
• 0.05 0.68(mB) / 0.02(Bar) / T (minute)
• T 675 minutes 11.3 hours
• Room pressure may swing 10s of mBar and affect
  module P used in calculating leak rate
• This, however, can be corrected by taking average
  P or integrating P over time.

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Module leak measurements

• measured at mechanical completion

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Summary

• Modules built are leak tight
• Continue to improve leak measurement and
  understand the measurement error
• Added barometer to obtain absolute module
  pressure
• Try to understand temperature dependence of dP
  between module and tank
• Try different method of leak rate calculation,
  e.g. using P/T nR/V without using reference
  tank.