LIGO Document E1000088-v1

Qualifying Parts for LIGO UHV Service

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Document type:
E - Engineering documents
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Each part or component intended for service within the LIGO Ultra-High Vacuum (UHV) system shall
be comprised of acceptable materials or components,
be manufactured in accordance with appropriate specifications,
be prepared (cleaned and baked) in accordance with the LIGO specifications, and
be tested to confirm that the surface cleanliness meets requirements.
This document calls out the appropriate specifications to comply with LIGO UHV requirements.
Notes and Changes:
Should add to this document the following Guidance on "Qualification Material Quantity & Preparation":

For polymer materials, or other high rate outgassing elements, which are to be tested for acceptability in the LIGO vacuum system:

* Materials must be prepared in accordance with their proposed processing, i.e. it is not just the inherent material, but also any associated surface treatment and chemical processing which must be qualified.

* Testing composite material assemblies is much preferred over testing individual materials (e.g. best to test a kapton, adhesive, copper flexible circuit assembly than to test each material individually).

* For RGA testing, the amount of material tested should be the larger of either:
~ the intended amount in the vertex vacuum volume (single IFO), or
~ 2 times the intended amount in the end station vacuum volume

The above suggested amounts are based on scaling from test conditions to the LIGO in situ conditions assuming that the RGA background is limited to 2e-11 torr-liters/sec, the RGA chamber pump rate is 10 liters/sec and the target partial pressure for the hydrocarbon sum mass is 6e-14 torr. See T040001 for allocated budget for a more precise estimate.

* For optical contamination exposure cavity testing, the surface area of the material tested should be at least 0.1 times the surface area of the amount intended in a LIGO vacuum volume, preferably 0.3 times this amount (if size and costs allow).

The suggested amount above is based on the measured uncertainty (standard deviation) in the rate of absorption change in time, after one month of testing, 0.4 ppm/yr, compared to the requirement of 0.1 ppm/yr, accounting for the approximate test pump rate of 1/50th of the LIGO pump rate.

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