Jeff K., Krishna V.

The pressure at the Turbo was 1.2E-6 torr this morning. The transfer function measurements have been less than convincing today. For now, I think d may be (+12.5 +/- 5) microns. I think cross-couplings (twist to tilt) may be introducing larger errors in this measurement than what I'm used to in the lab, where I have a much sturdier platform. The above value of d gives a displacement rejection of (9E-5 +/- 4E-5) rad/m. 

I have attached an ASD plot of 10k seconds of data from late last night/early morning, showing a very quiet ground, at the level of 0.1 nrad/rt(Hz). The blue curve, labeled tilmeter, is the measured tilt and the reference mirror curve is a ~ proxy for the autocollimator noise. We were hit with a dust storm around 4 PM this afternoon which produced lots of tilt noise, shown in the second graph, which was taken from ~5:25-6:30 PM. The noise near 0.1-0.5 Hz appears to be a factor of 10-100 worse. Wind speeds in that time frame were in the 30-40 mph range.

The pump has been turned off and I'm doing another overnight measurement. Tomorrow we will decide how much mass to add to try and reduce d as much as possible.