[Tanaka, Ushiba]
Abstract:
We tried to increase the laser power more than 10W at PRFPMI_RF_LOCKED state
Laser power once reached 10W but lockoss happened after several minutes due to the oscillation of ETMY pitch oscillation at 1.3Hz.
So, some tuning of local damping control and/or ASC would be necessary.
Detail will be posted later.
Since we finished to check IMC REFL, IMC TRANS, IFO REFL, POP, TMSX, TMSY, and AS table, we started a trial of 10W operation of PRFPMI.
This time, we increase the laser power with the following procedure:
1. Request PRFPMI_RF_LOCKED state to LSC_LOCK guardian.
2. Turn on power nomalization of MICH loop with POP90 signals.
3. Reduce REFL power by rotating IFO REFL HWP with a step of 1 degree until reaching the IFO REFL power close to 1.7 mW while keeping more than 1.7 mW.
4. Increase IMC transmission by rotating PSL HWP with a step of 1 degree until reaching the IFO REFL power close to 2.4 mW while keeping less than 2.4 mW.
5. Repeat 4 and 5 until IMC transmission reaches 10W.
IMC transmission could reach 10W while maintaining PRFPMI_RF_LOCK but ETMY started oscillation several minutes after reaching 10W.
We are not so sure why the ETMY oscillation occured but there are two possibilities:
1. Radiation pressure kicks the suspension resonances; need local damping of the resonances.
2. ASC loop became unstable due to the change of the loop gains due to laser power increase: need ASC loop gain adjustment.
So, we need to check local suspension damping control and/or ASC loop design for stable lock of 10W PRFPMI.