Georgia, Keita, Jenne (Peter F, Seb, Slawek)
Summary & motivation
Today I went through the PI and OMC drumhead medm screens and populated the bandpass filters and matrix elements so we can monitor and actuate on our 10.4 kHz modes. In the 10.4 kHz region we have two sets of modes for each test mass: the drumhead and butterfly (flower) modes. We want to identify each of these modes for each test mass, but top priority is ETMY as we believe a mode on this test mass went unstable a few weeks ago. To discern the flower mode from the drumhead mode we can drive diagonal ESD quadrants in and out of phase and see which configuration excites which mode. After this we want to measure the Q- factor of these modes, exciting them with the ESD (at 2 W IFO input power so we aren't influeced by the optical mode), and looking at the ring down. While the infrastructure is in place to monitor and damp PI modes, the frequencies had not been updated to match our new test masses.
Recap
A few weeks ago we rang up the 10.43 kHz mechanical mode of a test mass, see second attachment to Andy's comment here. The next day Sheila, TJ and Ed took a large step on ETMY's ring heater, increasing the power from 0.2 W to 1.2 W on both the upper and lower elements. They observed a shift in frequency of two neighbouring modes (10.4305 kHz and 10.4271 kHz), see first attachment comparing red and yellow traces, so we strongly suspect these are two different mechanical modes of ETMY. The high power on RH_Y caused another mechanical mode at 10.2105 kHz, see second attachment to Andy's other comment here. We have since backed off the ring heaters to 0.4 W, so our arm-cavity second-order higher order mode is sitting between these two mechanical modes. We have not encountered any parametric instabilities since setting the ETM ring heaters.
Details
Today I added many bandpass filters around the 10.4kHz modes so we can monitor them with the TR QPDs, DCPD's and actuate on them with the ESD. The channels and modes refrenced below can be found on the PI overview medm screen.
- I added 10-10.8 kHz bandpasses to channel 8 of the TRX QPD, TRY QPD, and DCPD paths (down conversion filters). Following the same convention of existing filters, these are 4th order elliptical band passes
- I set the local oscillator to be 10 kHz for channel 8 of TRX, TRY, and the DCPDs
- I populated the channel2mode matrix, sending the 10kHz mode seend on TRX, TRY, and the DCPDs to mode 8, 16, and 24 respectively
- I updated the bandpasses in SUS_PROC_PI for these modes, adding 420-440 Hz bandpasses. This covers both modes, might want to make these filters narrower in the future
- I did not touch the mode2channel matrix for the TR QPD channels
- I updated the mode2channel matrix element for mode24, sending it to channel 8 of ETMY
- I updated the bandpass filter and local oscillator of ETMY mode 8 (up conversion filters) to match the down conversion filters
In the PI-drumhead infrastructure I updated the D (EY) control filters:
- I updated the OMC-ASC_BEACON_D_BANDPASS, and OMC-ASC_BEACON_D_CLOCK_RECOVER to be 429-432 Hz (the mode is downconverted before this control filter). This is focused in on the higher frequency mode - if we identify that mode to be the flower mode rather than the drumhead we will want to shift this bandpass filter.
- I populated the beacon drive matrix
The second attachment is the safe SDF diffs, I accepted them.
During tomorrow's commissioning time Keita and I will try and identify which mode is which on ETMY, using the deacon.
