Sheila, Camilla, Naoki

After alog74223, we engaged the SQZ phase dither servo as shown in the first attached figure. After we engaged the dither servo, the error signal (SQZ-PHASE_DITHER_DEMOD_I_OUTPUT) goes to 0 and the SQZ phase (SQZ-CLF_REFL_RF6_PHASE_PHASEDEG) goes to around optimal value. 

Detail

First we checked the error signal of dither servo by scanning SQZ phase as shown in the second attached figure. The dither error signal is SQZ-PHASE_DITHER_DEMOD_I_OUTPUT shown in gray. You can see the two zero crossing points where the BLRMS4 (SQZ-DCPD_SUM_RMS4_MON) is minimum and maximum.

Then we made a new state in SQZ_MANAGER guardian named ADJUST_SQZ_ANG to adjust the SQZ phase using dither servo. The servo is engaged with cdu.Servo and it uses the SQZ-PHASE_DITHER_DEMOD_I_OUT16 as readback channel and the SQZ-PHASE-OUTMTRX_1_1 as control channel. We cannot use the SQZ phase (SQZ-CLF_REFL_RF6_PHASE_PHASEDEG) as control channel since it is a discrete number (SQZ-CLF_REFL_RF6_PHASE_DELAYSTEP must be an integer). So we stored the value of the DELAYSTEP in the unused output matrix element (SQZ-PHASE-OUTMTRX_1_1) and used it as control channel. The DELAYSTEP itself is controlled by rounding the value of SQZ-PHASE-OUTMTRX_1_1 to an integer. 

Note: Although the SQZ phase dither servo seems to work, the SQZ phase the servo ended up (152.7 deg) is not exactly optimal value (145.47 deg). We needed to adjust the SQZ phase manually to really optimize the SQZ BLRMS.