Continued the recovery of the Injection after the work on the optical components and on the control electronics for the new EOM and the new PSTAB.

Found IMC locked, alignment close to what we left yesterday (kudos to suspensions)

• The noise on IMC_TRA_seems to be a high 50Hz, while PSTAB_PD2_AC shows 15Hz and many harmonics. Anyway, the PSTAB loop cannot be engaged in these conditions, needs to be investigated.

• Our colleagues of the EGO Electronics Group warned us that while installing the hardware for the 81MHz in the Piscina, they found a loose knob on the phase shifter for the 22MHz (rack closer to laser lab). They have fixed it but told us that probably we had to retune the phase for the IMC loops. I have turned the knob of phase shifter in the piscina - output 3. Saw that changing the phase I caused a loop oscillation in the IMC freq, so I increased the attenuation of the error signal input to the rampeauto to kill the oscillation.

  • New parameters: potentiometer of phase shifter output 3 is at 6.50 (was 3.0); attenuation is 13dB (was 6dB).

• Pstab still plagued by low frequency lines and it is impossible to us. Will postpone the diagnostic after the work by Artemis team on the PSTAB

• Yesterday we did not manage to implement the AA on IMC, so today a new injection was performed on the mirror/bench (report attached) after being sure that the alignment of the IMC was compatible with small offsets coming from demodulated RF quadrants.The sensins matrix calculation takes into account the sign of the RF quadrants, but for the BsX_X loop which lives in the DSP. For the latter, a flip of sign was needed after the tuning of the 22MHz phase. This was implemented in ISYS_ACL (see screenshot) for the INJ_IMC_QD_FF_I_H channel.

  • Test with FF_I_H flipped sign in ISYS_ACL (line 59: was -1 -> +1)

  • Drift control works, not optimal, but survived several lock acquisitions

    • Tried to reduce the gain on vertical tilt sensing, but when switching in full bandwidth it breaks the lock

    • RFC locked without problems

Several attempts have been also made to engage the full bandwidth  AA, but an oscillation on vertical tilts regularly breaks the lock, to be further tuned.

Overall, INJ subsystem has been restored to minimal functionality. We need to engage full bandwith in AA, and PSTAB loops. The completion of the recovery (and the full characterization) will be performed after the work on PSL scheduled in the next days.

EIB loop was ringing this morning, cured by disabling and then enabling the PID on the VPM.

From GPS 1352967980 to GPS 1352968700 clean scan of the RFC. Data will be analyzed offline.

I have analyzed the INJ throughput losses before and after the EOM installation.

The analysis before the installation is the following (1st to 16th of November):

In Fig. 1 we can see that the mismatch (left upper graph) was oscillating around 8%, while the throughput losses (right upper graph) of the IMC cavity were arounf 16%.

In Fig. 2 it is shown in the bottom graph the PSL to ITF throughput, which were around 65% (i.e., the ratio between the calculated power at the output of the PMC (we have estimated 7% losses from the output of the PMC to the output of EIB) and the power at the input of the interferometer (which is estimated to be 7.5% less w.r.t the output of the IMC due to SIB1 losses)).

After the EOM installation we have (from Nov 19th to 21st):

Fig. 3 shows that the mismatch improved a little bit, to 7.4%, and the throughput losses dropped to 11.3% after Nov 20th.

In Fig. 4 we can see that the PSL to ITF throughput increased and it is now around 69.5%.

As a conclusion we can say that the mismatch and the IMC cavity losses improved by 0.6% and 4.7%, respectively. Also the PSL to ITF throughput has improved roughly by 4.5%.

On the bottom right-hand corner of the figure attached, one can see the unsual behavior of the photodiode read by the channel PSTAB_PD2_DC (linear decrease between 50s5 and 50s6). After this moment this photodiode stop working.

This morning we checked the tuning of the RF quadrants for the IMC automatic alignment.

We followed the same procedure as reported in eLog #44643

- IMC NF quadrant tuning --> maximizing the 2 Hz line injected on IB MAR TZ (plot 1)

- IMC FF quadrant tuning --> maximizing the 2 Hz line injected on MC TX (plot 2, the red is the old value)

The phases were already quite good we only did a fine tuning.  We measured the sensing matrix :

PR_SUM_CH MC_ty 19.70 MCT_h_err 0.00 FF_ACh_err 0.00 NF_ACh_err

PR_SUM_CH IB_ty 34.50 MCT_h_err 0.00 FF_ACh_err 1.08 NF_ACh_err

PR_SUM_CH MC_tx 12.11 MCT_v_err -0.58 FF_ACv_err 0.17 NF_ACv_err

PR_SUM_CH IB_tx 42.76 MCT_v_err -0.48 FF_ACv_err 0.14 NF_ACv_err

PR_SUM_CH IB_tz 10.59 MCT_v_err -0.18 FF_ACv_err -0.82 NF_ACv_err

Injection time (duration = 120 s)

MC ty gps = 1353235522.00

IB ty gps = 1353235035.00

MC tx gps = 1353235378.00

IB tx gps = 1353234869.00

IB tz gps = 1353235207.00

We finally closed the alignment in full bandwidth (plot 3, blue in full and pink is drift control)

RFC PDH was found heavily mistuned (first plot: in-phase and quadrature error signal have the same amplitude), and this yelded some extra frequency noise at low/intermediate frequency (second plot).

We tuned the SIB2_RFC demodulation phase while scanning the RFC via the MC F0 z position as usual (third plot), via python console:

/users/optics/ISC_scripts

In [8]: run LSC_init.py

 SIB2.RFC_6MHz_phi0.AcParamGet()
cm_send('SIB2_Photodiodes', 'AcParamGet', 'RFC_6MHz_phi0')
Received AcParam message from SIB2_Photodiodes

# nameOut - unit - rampTime(s) - sampling frequency(Hz) - value - flag
ACL_CONST_CH RFC_6MHz_phi0   "rad" 0 10000 3.46 0

 SIB2.RFC_6MHz_phi0 = 3.46 - 2*pi /6
cm_send('SIB2_Photodiodes', 'AcConstChSet', 'RFC_6MHz_phi0', 2.4128024488034026)

and then saved the phase to ACL (line 147) of https://vpm.virgo.infn.it:40000/editor.html?editable=SIB2_Photodiodes

The result is shown in plot 4. Not that big a reduction of noise, just some slight improvement of RMS.

I updated the value in the configuration file of the INJ Automation, and corrected a typo in the Acl configuration file (swap of value/ramptime).

The value has also been updated online, as it was still 3.46 (the old one).

Indeed, after Diego made the tuning happen in the real world (thank you!), some effect on the RFC loop is visible (see first plot). Now it is like it was before the intervention on INJ.

The modulation index of the 56MHz in this scan (20th of November) is ~ 0.12