In order to try to understand the origin of the inj unlocks which occurred last week (fig. 1 shows an example of ML glitch prior to an unlock), we wanted to check whether we were close to a mode hop of the ML.
Prior to start we measured the SL Transfer Function, finding an UGF of about 298kHz and phase -79° (attached fig. n°7).
Following the procedure reported in the entry 50944, we opened the ML thermal corrections loop (and the corrections kept the constant value of -0.128 V BsX ML TH CORR).
The initial temperature of the ML crystal was 22.7°C. We found a mode hop at 22.2°C and the following at 25.2°C. We decided to increase the crystal temperature from 22.7°C to 24.1°C in order to be better centered wrt the two mode hops.
Moreover, when we tried to realign the beam in the PSTAB AOM we observed strange structure close to the TEM 01 mode of the PMC (#67303). Since we thought it could be a ML mode hop we made the test of changing the ML crystal temperature while scanning the PMC and looking and this structure: no change in shape nor position was observed, so we can exclude that it is linked to a ML mode hop.
| GPS LT | ML crystal temperature | comments | |
| 10:48 LT | 22.7 °C | fig. 2 e 3 - initial temperature setpoint | |
| 10:54:20 LT | 23.2°C | ||
| 10:58:05 LT | 23.7°C | ||
| 11:00:45 LT | 24.2°C | ||
| 11:06 LT | 24.7 °C | ||
| 11:07 LT | 25.2°C | mode hop fig. 4 e 5 | |
| 11:12 LT | 22.5°C | ||
| 11:13 LT | 22.2°C | mode hop | |
| 11:16 LT | 24°C | ||
| 11:19 LT | 24.1°C | final temperature setpoint fig.6 |
