Elli, Evan

Summary

After Peter and Kiwamu's deep insights into the in-vacuum POP signal chain (LHO#16691), we've transitioned control of the DRMI DOFs from POPAIR to POP with DARM controlled on RF.

Details

First I drove a 1000 ct, 89.1 Hz line into the PRM in order to phase POP. I set the demod phase for POP9 to 90°, making the Q signal a factor of 50 smaller than the I signal. For POP45, I set the phase to 66°, making the Q signal 25 times smaller than the I signal.

With the line still on, I looked at the TFs of the POPAIR/POP signals. For 9I, 45Q, and 45I, POPAIR is weaker than POP by a factor of 0.15 ct/ct, with 0° of phase difference. So I took the POPAIR matrix elements, rescaled them by 0.15, put them into the corresponding POP matrix elements, zeroed the POPAIR matrix elements, and then transitioned.

Then Elli and I remeasured the OLTFs of PRCL, MICH, and SRCL. The PRCL gain was a bit low, so we increased it by 10%. The SRCL gain was a bit high, so we decreased it by 20%. Now the UGFs should be roughly the same as for POPAIR.

The new matrix elements are as follows:

• POP9I → PRCL: 0.035
• POP45Q → MICH: 0.081
• POP45I → SRCL: 0.08
• POP9I → SRCL: 0.005

This last matrix element is just a rescaling of the matrix element for POPAIR9I → SRCL (which itself is just a rescaling of REFLAIR27I → SRCL), so it should be retuned to optimize the PRCL/SRCL subtraction.