Ushiba, YamaT, Tanaka

## Abstract

We modified the OMC lock acquisition sequence by OMC LSC lock because the previous sequence seemed to be not good. Thanks to this modification, we can lock OMC more smoothly even though PRFPMI was locked with 10 W input. After that, we succeeded PRFPMI DC lock with 10 W input by guardian.

## What we did

• We checked the current OMC LSC lock acquisition by the OMC LSC guardain and found two issue as for the lock acquisition. One is the trigger which closes the LSC loop when OMC_TRANS_DC_SUM surpasses LSC_TRIG_THRESHOLD_LO turned on before the ERR signal entered within the linear range (fig.1). Another is that the oscillation occured just after the lock acquisition when CLK_GAIN was 30000 cnts. this oscillation did not occured after CLK_GAIN reduced to 10000 cnts  So the current OMC lock just after the acquisition seems to have too high gain.
• We modified the acquisition sequence so that the trigger activates not by the OMC_TRANS_DC_SUM surpassing the threshlod but by the LSC_ERR_OUT getting within the linear range after passing the peak value. And also we reduced CLK_GAIN to 10000 cnts during this sequence. We made some new states, FIND_RESONANCE_FOR_10W, LOW_BANDWIDTH_FOR_10W, and OMC_LSC_LOCKED_FOR_10W in the OMC_LSC guaridan (fig.1) for the 10W operation in order to be able to switch the 1.2 W lock and the 10 W lock. And also we implemented this procedure in FIND_RESONANCE_FOR_10W. (If you interested in the detail procedure, please see the FIND_RESONANCE_FOR_10W.)
  • On the other hand, the issue of this procedure is too slow because the detection whether the ERR signal is within the linear range is performed by the guardian. If we need to make the procedure more faster, we should implement it in a RT model.
• We tested the procedure with single X-arm lock. Fig. 2 shows the results. The lock seems to become more smoothly.
• After that, we tried to lock OMC with guardian when the input power was 10 W. We adjusted the parameters for the trigger due to many HOMs and 17MHz SB TEM00 but we also succeed in locking OMC in this state (fig.3).
• We modified the LOCKING_OMC_FOR_PRFPMI, HANDDOVER_TRAS_TO_OMCDC states in LSC_LOCK, and the PREP_OMC_BEACON state in OMC_ASC to work with new OMC_LSC states.
• Then, we requested LSC_LOCK to go to the OBSERVATION_WITHOUT_LINES state and succeeded in locking PRFPMI DC with 10 W input automatically.

## Note

The 10 W operation has not become completely automatic because we avoid the conflict with 1.2 W lock. If you want to lock PRFPMI with 10W input, you request the LSC_LOCK guardian to go to PRFPMI_RF_LOCKED -> INCREASING_LAS_POWER -> OBSERVATION_WITHOUT_LINES, in order.