Today I spent sometimes setting up the calibration filters for LSC DARM in h1oaf. It should be functional now.

What I did:

• checked the suspension responses
  • There had already been some suspension filters in the DAM calibration path in oaf. It seems that the ones installed in OAF are more damped, compared with the latest damped suspension model. I did not try to change the existing filters this time as I did not think it was crucial.
  • The suspension model I used for the comparison was generated by a matlab function, generate_QUAD_Model_Production with a damping by dampingfilters_QUAD_2013-06-14.mat in SVN.
  • See the first attached png and fig files for the comparison. The dashed lines represent the suspension models and the solid lines for the ones actually installed in oaf.
• adjusted the DC gain of each suspension stage.
  • ESD gain was adjusted by using the new definition of alpha (e.g. T1500036-v1). I used the following equation to derive the force coefficient
  • dF/ dV = 2 x alpha x G^2 Vbias
  • where alpha = 2e-10, G=40, Vbias =9.5
  • The DC gain of the rest of the stages were also adjusted such that they match the suspension models.
• adjusted the DARM error signal path.
  • Currently the cavity pole is set to 389 Hz. We should correct it once we measure the actual cavity pole with the interferometer fully locked.
  • The DC gain of the DARM error path is set to 1e-6 as it was already calibrated into um for ALS diff.

Also, the second attached png is a screen shot of the latest DARM calibration setup. This is set up for a single ETM configuration where either ETMX or ETMY is not in use. If one wants to feed DARM back to both ETMs, an extra factor of two should be added somewhere. Note that the L1 (UIM) stage currently has a gain of 0.5 as shown in the screen shot n order to simulate the digital gain in SUS-ETMX_L1_LOCK_L_GAIN.