LIGO Document T1900786-v1
- A quick formulation of the condensation rate for water in rarefied environments.
At 10^-8 Torr partial pressure of water, ice deposits at ~100 nm/day on surfaces colder than 137 K. The rate is roughly linear with pressure until the saturation pressure.
If any ice is accumulated on a 124 K surface (saturation pressure of 10^-11 torr), at best it will thermally evaporate at 6 nm/month.
The presence of a cryo shield and cold beam tube can loosen the requirements for no ice accumulation on the test mass by a factor of 10^3. However, to reach this water partial pressure we might still need to wait until the ion pumps are engaged.
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