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.
