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Message ID: 6262     Entry time: Thu Feb 9 13:04:11 2012
Author: Koji 
Type: Summary 
Category: IOO 
Subject: PMC/IMC alignment 

There has been no lock of input MC for more than 5days. WTF???

I have fixed a loose mirror of the PMC input and the alignment of the MC2 Yaw.

- The PSL mech-shutter was closed. It has been opened.

- Then, I checked the MC suspensions. Mainly MC2 Yaw has kept drifting. (Fig.1)
In fact, there was no WFS actions during this drift.

Anyway, now MC2 Yaw was aligned and the lock was restored.

- It was very unsatisfactory for me that the PMC alignment kept drifting.
The trend of the PMC REFL and PMC TRANS for a year suggests that:

  • Occasional drifts exist since a year ago (or probably since we built this new PMC setup in 2010 Sep)
  • The drift has got frequent for the recent four months, and got more for the recent one month.

I went into the PMC setup and tapped several optics in order to find any loose optic.
Immediately I found that the mirror before the AOM was loose. Basically any mild tapping was enough
to misalign the mirror such that the caivty loose the TEM00 mode.

I tightened the retainer set screw of the optic and aligned the PMC again. It looks OK now as I can not
misalign this optic by the tapping anymore. But if it still remains drifting, we need to replace the mount.

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