LIGO Document E1800020-v1

Optical Contamination Test resuits: EPO-TEK 302-3M adhesive

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Document type:
E - Engineering documents
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This test will reveal the optical effects (absorption and scatter) at 1064 nm wavelength due to outgassing from EPO-TEK-301-3M adhesive in vacuum when properly prepared/mixed and cured at room temperature. The optical cavity load consists of twelve (12) 25mm X 45mm mircroscope slides coated on one side with EPO-TEK-302-3M adhesive.
They were put in VBO "D" Baked for 48 HRs @ 50C. See Link to ICS bake-8859 below in Other publication information.

The EPO-TEK 302-3M adhesive is currently planned to be used, with the addition of graphite powder, for the Acoustic Mode Damper (AMD) device. For the final AMD application, the total epoxy volume is only ~1 micron x 0.090 cm^2, or ~0.01 mg per AMD. Moreover the exposed surface area for outgassing is only ~1 micron x 1.2 cm = 0.0001 cm^2 per AMD. In the final AMD application we may have 4 AMDs per test mass.

An initial AMD trial is planned before observation run O3 where AMDs are bonded to the end test masses using EPO-TEK 301-3M instead of silicate bonding. This AMD-to-barrel bond was *assumed* to be thicker than the bond within the AMD assembly. If we assume the AMD-to-barrel bond is much thicker, say 10x, then the total bond surface area for this AMD trial will be ~10 x 4 x .0001 cm^2 = ~.004 cm^2 per ETM chamber.

N.B.: The AMD base to barrel bond is in fact just as thin as the graphite-loaded bonds to the PZT. It turns out that the viscosity of the bond changes when we add graphite, therefore it requires a lot of pressure to obtain a thin bond (2microns) between the PZT and the base. Far less pressure is required to obtain the same thickness with pure epoxy, which explains the small force applied in situ.

(FWIW we have approved EPO-TEK 353ND, another EPO-TEK "optical" epoxy (see E960050, E1300653 and E1300654) which also passes NASA low outgas testing. However EPO-TEK 353ND was cured at 80C for 30 minutes, whereas the epoxy for the AMD is proposed as a room temperature cure.)

Files in Document:
Epoxy EPO-TEK Glue
Notes and Changes:
After 48 days of testing, the absorption in the test cavity appears to increase at 0.4 +/- 0.5 ppm/yr (1 sigma) and the scatter appears to increase at 28 +/- 20 ppm/yr (1 sigma). When the proposed amount of material is scaled to the LIGO vacuum system the predicted loss rate is within requirements (at the 2 sigma level).
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