Benno W, Rick S, Michael R

We swapped out the ISS PDs with our spare set to correct for noise we were seeing in the out of loop PD. This swap helped, but we were still seeing some noise, so we tried disconnecting cables, tightening the screws holding the ISS box to the table, which all helped. We were able to lower our out of loop PD noise to below what it was after installation. In this configuration, the QPD and DC output cables are disconnected from the rack outside the PSL and from the ISS box. Currently we have the QPD cables disconnected from the rack, and PDB DC is hooked into the outer loop PD input. Additionally, we were able to get rid of a peak at ~78 kHz by adjusting the gain from -1.7 to -2.1. UGF is 46 kHz with phase margin of 32 degrees.

We adjusted the aligment of the DBB to lower the higher order modes. After optimizing the aligment, we realized the power on the RPD was too low, and compensated by adjusting DBB_M3 to get more light.

Plots (in order they appear):

DBB mode scan on 3/7 (pre-alignment)

DBB mode scan on 3/9 (post alignment)

ISS rpn on 3/7 - old PDs, QPD cables connected to ISS box and rack, DC output cables connected to ISS box only

ISS rpn on 3/9 - new PDs, QPD cables connected to ISS box and rack, DC output cables connected to ISS box, PDB DC connected to outer loop input, cover on, all screws tightened

ISS rpn on 3/9 - new PDs, QPD and DC cables disconnected from rack and ISS box, all screws tightened