This morning there was a chance to check the PRM suspension.

I set it to the ALIGNED state and then back to MISALIGNED state in order to check what Guardian was doing with the actuation offsets.  With the exception OPTIC ALINED in pitch, all the other offsets reported in the commented entry seem to be set on purpose to achieve the misalignment of the optic,so pressing CLEAR HISTORY was not going solve the problem.

It seems the orientation of the optic has to be tuned again when the suspension becomes available again.

With Kokeyama-san

From what I was able to gather from a couple of klog entries, Kokeyama-san and the medm screen, a suitable description of the MISALIGNED state in PRM requires specifying the actuation in three diffferent medm blocks and, additionally, the orientation of the optic must fulfill two requirements.

The requirements are clearly written in entry 11234:

• The beam should go into the beam dump as shown in the third picture in entry 8303 and
• The position sensitive device (PSD) must indicate the beam is reaching its central area.

In order to achive such a condition the strategy is to apply actuation offsets in three differen blocks when having the oplev control loop onto the IM off:

• OL DAMP: floated actuation corresponding to the DC offset needed in ALIGNED state (very likely this is for a suitable recovery of the ALIGNED state).
• TEST FILTER: offset for misalignment in pitch and partially in yaw (see entry 9056).
• BF TEST FILTER: offset for partial misalignment in yaw (too much actuation at the IM brings the IM too close to IRM; see entry 9056).

So far I haven't found any entry reporting all these numbers together but only one or two, so I write again the currently used ones (which yield an incorrect MISALIGNED orientation):

• BF yaw test: 15,000 cnt per entry 9056,
• IM yaw test: -7,500 cnt per entry 9056,
• IM pitch test: -4,500 cnt,
• IM OL DAMP pitch: 4732 cnt (varies slightly each time the MISALIGNED state is requested),
• IM OL DAMP yaw: 170 cnt (varies slightly each time the MISALIGNED state is requested).

Additionally to the symptoms reported in entry 11234, against our expectations we found that when the optic is in ALIGNED state the beam reaches the central area of the PSD. So it seems it was accidentally moved.

The beam reaches the beam dump (see picture with 5e5 exposure) in the following conditions:

• BF yaw test: 0 cnt,
• IM yaw test: -4000,
• IM pitch test: -4,500 cnt,
• IM OL DAMP pitch: 4732 cnt,
• IM OL DAMP yaw: 170 cnt.

Pending authorization from PR experts, what we should do next is the following:

• Change the Guardian settings to the values above for BF yaw test and IM yaw test.
• Move the PSD to an appropriate position.

Reference entries: 11234, 9056, 8303, 8449, 10849.

With Yamamoto-kun.

• The changes proposed above were commited.
• Using SDF we created a snapshot for the MISALINED state.

From seeing the picture I posted Kokeyama-san pointed out that the beam was not going into the beam dump, therefore, I changed again the orientation of the mirror.

• With respecto to the previous position the beam clearly moved to the right of the view shown in the picture and the intensity decreased in an obvious way.
• With the current offset value of the IM yaw actuation (-7000 counts) the IM is close to the limit of it's free moving range. When using -8000 counts it was definitively touching. I checked this by injecting a sinusoidal signal 100 counts in amplitude and 100 mHz ans checking the IM was following.
• I had to apply actuation in BF yaw, pretty much what we had before: 15,000 counts.
• There seem to be stray light which is not reaching the beam dump.
• I didn't move the optic all the way to the other side to see the beam emerging at the other side of the dump, that would require a very large actuation in BF yaw.
• I updated the snapshot.
• The acompanying picture was produced with 1e6 units of exposure.

The amount of actuation used was

• BF yaw test: 15,000 cnt,
• IM yaw test: -7000 counts, (the limit is before -8000 counts)
• IM pitch test: -4,500 cnt,
• IM OL DAMP pitch: 4745 cnt (varies slighty each time MISALIGNED state is requested).
• IM OL DAMP yaw: 106 cnt (varies slighty each time MISALIGNED state is requested).