The glitches are clear on B1p and originate by Tx marionette control.
- The SLED source does not seem the main cause., as the same unit is used for Tz.
- The amplifier was replaced with a new one a week ago.
- The glitches are not related magnetic disturbances in CD.
=> probably control boards (driving ?) can be checked
=> the optical line can be re-checked (fibre BS)
=> PSD substitution (at last)
The MCH port statistics that log board to board communication problems have been checked and seem to exclude hardware issues. Moreover the keep sample policy is used in both MIR and MAR boards. We will continue the investigation.
A series of tests both open loop and closed loop has been performed on BS. The open loop data show (see figure) that the glitches are still present in the signals genereated with PSDm (tx,ty) but not on those obtained with PSDt (ty_t, tz). We can therefore exclude problems related with the DSP boards. In order to make the debugging easier we changed BS MAR coil configuration: both ty and tz correction are now applied using the MAR board while tx and mirror signals are sent using MIR board.
PROVIDED that :
(L.E. 41575) the glitches seem not related to control path as they use to appear also in open loop
SUMMARY of what hierarchically I revised :
> Replacement PSD Amplifier building absolute asymmetries => through this check also the dynamics of the LN sensing was re-tuned
> Spare beams check on the PSD sensor => through this check the reflection of the other OpLev (roll, Tz) was slightly repositioned.
> +-15V Supply of the PSD amplifier, by swapping the voltage with another one (SR,Tz)
> Viewport cleaning from air side => indeed it was incredibly dirty of dust, believe me !
> replacement of a 2"Lens => indeed it was so dirty to appear opaque
> Check of the viewport used to inject the lever (at the vacuum side in/out viewports are both clean) => that port, from the air side was rather clean
> Replacement of the Hamamatsu PSD sensor.
NOTICE that :
very reasonably it is not the SLD source because the same light, once split through the optfiber is used for TZ, where there aren't glitches
THE GLITCHES are still there
WHAT remains:
> Collimator
> in-line BS used to split the SLD light
> internal scratches on the mirror used to reflect (easy, it can be checked by displacing a bit the impinging point)
> Ext disturbance: the area appears relatively clean but hidden sources can be present, only magnetic probes have been checked without any culprit evidence. Yesterday I checked that refilling-line
gate relays during maintenance can produce disturbances of the same amplitude and timescale, but repeated, they have different characteristics.
It was proposed to push on Full BW AA implementation on BS. PLS resist. We will do it later on.