This morning we tuned the temperature of the crystal of the ML to bring it in a middle of a mode hop range (following log entry https://logbook.virgo-gw.eu/virgo/?r=50870)
The procedure to find the temperatures at which the mode hops appear is attached to this entry.
Here below are the temperature scans that we did.
Times are in local time.
Temperatures are taken on the display of the ML.
10:18
scan SL ok
initial temperature of the ML 24.64
10:20 23.3
10:23 22.6
from 10:23 to 10:24
22.6 -> 23.0
PDH a bit dirty at 23
10:25 10:26
23 -> 24
10:26 10:26:20
24 -> 23.6
PDH dirty at 23.6
10:28
back to 24.6
we increase the temperature
10:29
24.6 -> 25.2
second pdh and first pdh still clean
10:30 25.8
10:31:30 to 10:32
25.8 to 26 back to only one pdh
We decrease the temperature
time?
25.8
The second PDH clearly appeared
10:35:30
25
second PDH disapear
We increase the temperature
a bit dirt from the beginning
25.5 2 PdH
We decrease the temperature
10:39:00
23.7 it starts to be a bit dirty
10:40:00
Kind of dirty while going down till 23 then starts to be clean again.
Decreasing the temperature
10:41:00
22.5 two PDH, clearly
10:43 to 10:44
down to 21.6
second pdh disappear but still a bit dirty
minimum of the ML
Increasing of the temperature
10:44:40
10:45 2 pdh molto chiaro
10:45 22.6 gradi, secondo sparito
keep on increasing the temperature
between 23.2 and 23.7 pdh a bit dirty
10:51:00
24
PDH is clean
keep on increasing the temperature
25.2 second PDH, clearly
10:59 to 11:00:00
25.1 to 24.3
Conclusion:
While decreasing the temperature the mode hop appear at 22.5, while increasing the temperature mode hop appear at 25.2.
The temperature setpoint should then be 23.85.
However we observed that, without clear reasons, the PDH was a bit dirty between 23.2 and 23.7 (plot 1), so to keep it away from that range we set the temperature at 24.3 degrees.