The MC2 suspension occasionally ran into a situation where some part of the suspension was kicked intermittenly for some unknown reason. I noticed this behavior this morning. I could not identify what was kicking.

The worst part is that the kicks (or glitches) seem to be gone since sometime around 14:14 local. Very bad.

The symptoms are:

• Once it runs into a glitchy period, the suspension glitches mostly in yaw. This is visible in the witness sensors and even in the IMC REFL camera.
  • Usually not big enough to unlock the IMC. However, very bad for lock acquisition which relies on the stability of the laser power.
• According to the witness sensors at the bottom stage, glitches are as large as 20 urad in yaw in pk-pk and 5 urad in pitch.
• This happened even when all the active loops were off (LSC, ASC, and damping loops).
  • Note that I left the static alignment biases on -- so there were some finite constant DAC counts at the top stage.
• When it came back to the nominal situation where no glitches, the actual alignment changed roughly by 5 urad in yaw.
• Evan also noticed a similar behavior yesterday evening for the first time.
  • Maybe this issue is new and started happening very recently ?

(Checking various channels)

Apparently this behavior is different from the two DAC issues we have seen in this past week (alog 18453 outputting a high constant voltage, alog 18569 outputting a nonlinear signal). As mentioned above, I disabled ail the active loops including the LSC, ASC and the top stage damping loops. Even in this condition, the suspension still kept being kicked interminttently. I looked at VOLMONs on all the stages, but did not find any suspicious activities. Also, I checked motions of the HAM3 ISI in L, P and Y using the suspension-coordinate-witness-signals (i.e. SUS-MC2_M1_ISIWIT_L(P, Y)MON), but did not  find such a fast signal. In addition, I checked the bottom stage witness sensors of PR2 as well to see if this is some kind of table motion, but the PR2 was very quiet and no glitches were found at the time when MC2 was glitching.

(A test without LSC or ASC signals)

I attach a second trend of some relevant channels. This is a two-hours trend, with the top stage damping loops fully on and with no LSC or ASC signals. You can see that the wintess sensors of the bottom stage showed glitches in the first 1/3 of the trend and suddenly stopped. Since the damping loops were engaged during this periode, the VOLMONs showed some reaction of the loops and I think they are just reactions and not the cause of the glitches.

Actually, now the top stage RT OSEM makes me think this is it. Its VOLTMON showed a noticable discrete jump (by 14 counts) in the attached trend right around the time when glitches stopped.