EMAS Vacuum TestingJune 2, 2011

Last 2 slides added after Feb 28, 2012 getter initiationMike Watson

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E-MAS Vacuum Testing

Convectron vacuum gauge

• Assembled empty vacuum chamber

• All accessories• Butyl orings• Installed ion gauge on

vacuum valve• Window• Connectors

• Precision cleaned internals• Conducted bakeouts until rate-of-

rise testing indicated we were only seeing oring permeation

• Bakeouts at ~70C• Initiated pumping with barium

tube getter• Monitored pressure for ~2 weeks

Barium tube getter

Vacuum valve

Ion gauge

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E-MAS Vacuum Testing• Getter Initiation

• The getter tube has an indium seal that must be melted to start pumping.

• Initiation can only be verified by monitoring vacuum to see the rate-of-rise change

• Apply focused heat from a small torch to melt the indium (~160C). Notice the small discolored area just below the swagelok nut.

• Can also apply heat with a heat gun but precautions must be taken to ensure heat does not damage the nearby orings.

• Pictures below shows the front screen cut away and the indium melted in the bottom about an inch behind the screen.

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E-MAS Vacuum Testing(2 day scale)

3 successive tests with identical pressure transients indicate we are seeing only oring permeation. Note: this permeation rate is ~30% of what was predicted

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E-MAS Vacuum Testing(15 day scale)

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E-MAS Vacuum Testing• Results

• Pressure rises to ~10 mTorr after 15 days. • Hard to forecast a pressure after 90 days:

• Pumping speed of tube getter is not constant and varies for each gas

• Individual gas permeation will slow as it approaches partial pressure equilbrium across o-ring seal

• Test secured before capacity of getter tube could be determined• Test does not account for outgassing of all internal components

• Certainly, we will not meet the specified requirement 30mTorr after 90 days with the current design.

• However, it is apparent that the getter tube will help keep system pressure low enough to allow the cryocooler to operate efficiently during an extended period of time.

• If addition pumping is necessary, another tube getter mounted in parallel could be used.

• If turbo pumping is readily available, the getter tube can be kept in standby or not mounted/used at all.

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EMAS Delivery Getter Initiation• Getter Tube initiated immediately before system packed for

delivery• Tube took ~30seconds of torch heat until system indicated that the

indium seal was melted and getter pumping was initiated• Before getter started, the system was isolated from the turbo and

allowed pressure to rise to ~1mTorr.• Rate-of-rise during this period closely matched the rate-of-rise

demonstrated during an empty, fully baked out EMAS system.• Indicates minimal system contamination or outgassing• Indicates that oring permeation is fairly repeatable and at a

reasonable level

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E-MAS Vacuum Testing

Matches earlier RoR testing at best conditions

Getter started ~1hr mark