aLIGO LHO Logbook

H1 ISC (ISC, SEI, SUS)

sheila.dwyer@LIGO.ORG - posted 13:49, Saturday 28 March 2015 - last comment - 09:28, Tuesday 31 March 2015(17561)

Windy Day locking progress

On my drive in I saw a kiddie pool flying across Jadwin Ave, so I knew it would be a good day to work on ALS. The gusts today are up to 45- 50 mph; I can hear the building shake when one hits. While the changes I've made so far aren't enough to lock the IFO under these conditions, there is a lot of progress.

I've switched back to using the IMC VCO to drive the fiber AOM.
Comon tidal feedback is disabled for now (the UGF is set to 0 Hz). This is not needed with the omc vco driving the fiber aom, at least not for locks of tens of minutes
We are now locking ALS COMM first then DIFF, instead of doing them in parallel as we have been. Locking ALS COMM was not a problem today once first two things were done, but DIFF locking was trickier since the PLL was not staying in range for verry long at all. With the IMC VCO driving the fiber AOM, locking COMM means that at low frequecies the Y arm is following the X arm because of tidal. (COMM means that the IMC VCO follows the X arm, using the IMC VCO to drive the fiber AOM means that with Y arm tidal running the Y arm follows the X arm.) Once COMM is locked like this the DIFF PLL stays in range long enough to grab a lock with DIFF.
I increased the bandwidth of the X arm green WFS DOF1 P (to the ETM), the gain changed from -0.003 to -0.01. This goes unstable with a gain of -0.02, but we could think about adding the PUM to increase the bandwith so that we can supress the motion at the 0.45 sus resonance. The higher gain is OK when using all the X arm green WFS loops, so I've left it in.
With the higher bandwidth ETM WFS and the pitch oplev damping engaged (gain -4500, described in alog 16968), we can keep ALS locked for about 10 minutes although the noise is clearly quite high.

One more thing, this morning I opened the X end beam divereter and re did the inital alignment. Now both beam divereters are open. The inital alingment has it's own problems when the wind is this high.

Comments related to this report

sheila.dwyer@LIGO.ORG - 15:17, Saturday 28 March 2015 (17562)DetChar, GRD

Link

Two more comments: For detchar- using the imc vco to drive the fiber aom has the side benefit that we can remove the fixed frequency 79.2 MHz RF from this rack. We know this was contributing to some of the inter modulation products we could see in the IMC spectrum. This won't be done before Tuesday maintence though, and in the meantime there is an extra cable in the rack which is not terminated. For operators- ( or anyone using ALIGN_IFO) I changed the name of the states align sus for als and align sus for full lock to set sus. The original names caused some confusion, these states simply set the suspension to aligned or misaligned as appropriate, they don't run any alignment servos

jeffrey.kissel@LIGO.ORG - 09:28, Tuesday 31 March 2015 (17580)

Link

In hopes to capture graphically what Shiela done in this log as far as switching the Fiber PLL's AOM input from a fixed oscillator at 160 [MHz] to the as-originally-planned IMC VCO input, I've updated the diagram I'd originally put together in G1400519, and Alexa and co. cleaned up / made more accurate / published in P1400105 to form the stand-alone diagram:
The CARM / ALS Electro-Optical Controls Diagram G1500456

I attach a copy of -v1 to this log for easy access.

Focus on the bottom left corner of the diagram, at the input of the red VCO, whose frequency is tuned by the fast output of IMC common mode board. It's output, as currently shown, is how it's configured now -- it's split to head both to the double-passed FSS AOM and to the ALS Fiber PLL AOM. Previously* the path to the ALS Fiber PLL AOM had been replaced with a fixed 80 [MHz] oscillator.

*Recall the history / evolution of this connection: it had always been planned to be this way, and LLO who commissioned their IFO in a more "natural," or serial, fashion always had this connection. However, because LHO had commissioned their ALS system and DRMI in parallel during the HIFO Integration Phase, having the IMC control hooked up to the Fiber PLL would couple them in a distracting detrimental fashion. Thus, the team "temporarily" replaced the IMC VCO output with an independent, fixed oscillator, see E1300659. As with many things in LIGO "temporary" can mean "years," so it's only now that Sheila and Daniel decided that the full IFO was commissioned enough that we could again restore to the original plan.

Non-image files attached to this comment

G1500456-v1_ALS_ElectroOptical_ControlSchematic.pdf