Jim Warner, Georgia Mansell, Sheila Dwyer

This morning we went back to EY to make some follow up measurements with the electric field meter that Rai brought. (40599 and 40597).  Our main result was to confirm that below 300 Hz the measurements we made on Monday were dominated by acoustic noise from the purge air and clean room, and that some care should be taken to mount the meter so that it has some isolation from acoustic noise and ground motion. It also seems like the line we identified as being from the CPSs on Monday is not actually the CPS line, and we are not currently seeing any signal from the CPSs in the field meter.  

Today the field meter was oriented to measure fields parallel to the beam direction and we did not rotate it.  We first repeated the measurement we did on Monday with the cleanrooms and purge air on.  We then turned off the cleanroom over the BSC chamber (leaving the others alone) and repeated the measurement, then repeated it with the purge air also turned off (top panel of attached plot).  We saw that a line at 33.8kHz was coming from the cleanrooms, and that the noise below 300 Hz was driven both by the cleanroom and purge air motion, as we suspected on Monday after seeing that the spectrum didn't change when we added a tin foil Faraday cage. 

We made a single measurement where we attempted to turn off many of the expected sources of fields in the chamber.  

• We powered off the ISI interface chassis for the GS13s, L4Cs, and CPSs
• We powered off the T240 interface chassis
• We powered off the ISI coil drivers
• We powered off all 4 of the HEPI interface chassis on the HEPI piers
• We powered off the CPS timing fanout chassis
• We took the suspensions to safe and unplugged at satellite amplifiers for all osems (ETM and TMS).  We unplugged the cables from the chassis, not the cables to the flange, and saw that the LEDs were no longer lit.
• We powered off the low voltage driver for the ESD. 
• We unplugged the illuminator power
• We turned off the OpLev laser
• The ring heater chassis was powered off before we started this work, and remained off. 

We repeated the measurement with the clean room and purge air off and saw that powering off all of these items didn't make a difference in our spectrum (bottom panel of attached plot).  To confirm that we had really turned of the CPSs, Jim unplugged one of the cables from the CPS interface that is a silver chassis on the cable tray, no error light lit up when he did this. 

Hugh looked up for us the frequency of the CPS clock signal, which is 25.725kHz.  The second attachment  shows the spectra zoomed in around 25kHz, and you can see that the line we see is at 24.8kHz, so it may be due to something other than the CPSs. 

We will take a break from making these measurements for a few days while the end station alignment work is going on, but if we have an opportunity Rai has requested that we try the measurement with the neutral pin of the power supply grounded to the box and floating.  If possible we would also like to mount the meter so that it is held off of the bench and has some vibration isolation.