40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log  Not logged in ELOG logo
Message ID: 17140     Entry time: Thu Sep 15 11:13:32 2022
Author: Anchal 
Type: Summary 
Category: ASS 
Subject: YARM and XARM ASS restored 

With limited proof of working for a few times (but robustly), I'm happy to report that ASS on YARM and XARM is working now.


What is wrong?

The issue is that PR3 is not placed in correct position in the chamber. It is offset enough that to send a beam through center of ITMY to ETMY, it has to reflect off the edge of PR3 leading to some clipping. Hence our usual ASS takes us to this point and results in loss of transmission due to clipping.

Solution: We can not solve this issue without moving PR3 inside the chamber. But meanwhile, we can find new spot positions on ITMY and ETMY, off the center in YAW direction only, which would allow us to mode match properly without clipping. This would mean that there will be YAW suspension noise to Length coupling in this cavity, but thankfully, YAW degree of freedom stays relatively calm in comparison to PIT or POS for our suspensions. Similarly, we need to allow for an offset in ETMX beam spot position in YAW. We do not control beam spot position on ITMX due to lack of enough actuators to control all 8 DOFs involved in mode matching input beam with a cavity. So instead I found the right offset for ITMX transmission error signal in YAW that works well.

I found these offsets (found empirically) to be:

  • C1:ASS-YARM_ETM_YAW_L_DEMOD_I_OFFSET: 22.6
  • C1:ASS-YARM_ITM_YAW_L_DEMOD_I_OFFSET: 4.2
  • C1:ASS-XARM_ETM_YAW_L_DEMOD_I_OFFSET: -7.6
  • C1:ASS-XARM_ITM_YAW_T_DEMOD_I_OFFSET: 1

These offsets have been saved in the burt snap file used for running ASS.


Using ASS

I'll reiterate here procedure to run ASS.

  • Get YARM locked to TEM00 mode and atleast 0.4 transmission on C1:LSC-TRY_OUT
  • Open sitemap->ASC->c1ass
  • Click ! Scripts YARM -> Striptool to open a striptool monitor for ASS error signals.
  • Click on ! Scripts YARM -> Dither ON to switch on the dither.
  • Wait for all error signals to have settled around zero (this should also maximize the transmission channel (currently maximizing to 1.1).
  • Click on ! Scripts YARM -> Freeze Offsets
  • Click on ! Scripts YARM -> Offload Offsets
  • Click on ! Scripts YARM -> Dither OFF.
  • Then proceed to XARM. Get it locked to TEM00 mode and atleast 0.4 transmission on C1:LSC-TRX_OUT
  • Open sitemap->ASC->c1ass
  • Click ! Scripts XARM -> Striptool to open a striptool monitor for ASS error signals.
  • Click on ! Scripts XARM -> Dither ON to switch on the dither.
  • Wait for all error signals except C1:ASS-XARM_ITM_PIT_L_DEMOD_I_OUT16 and C1:ASS-XARM_ITM_YAW_L_DEMOD_I_OUT16 to have settled around zero (this should also maximize the transmission channel (currently maximizing to 1.1).
  • Click on ! Scripts XARM -> Freeze Offsets
  • Click on ! Scripts XARM -> Offload Offsets
  • Click on ! Scripts XARM -> Dither OFF.
ELOG V3.1.3-