During the beam shift activity, we took the chance to check the newly implemented channels to monitor beam shift on NI/WI.

Dithering lines generated in the Acl_pre process are sent to input marionettes with the following frequencies: WI/NI_TX: 1.5 Hz, WI/NI_TY: 1.3 Hz.

Then B7/B8 are demodulated at the frequency of the lines providing the monitoring signals ASC_{NI,WI}_{TX,TY}_LF_{B7,B8}_{I,Q}_FS

Fig.1 shows such demodulated signals (I and Q), accounting for NI/WI decentering (both horizonal and vertical), during the beam shift.

The demodulation phase has been tuned offline by taking atan(I/Q).

Fig 2. shows the magnitude of the signals. We plan to do a proper calibration of the signals and turn them on on regular basis to monitor the beam shift.

A function to switch on/off the lines has been implemented on ITF_lock_library_HP.py

{WI,NI}_LF_line_toggle (ampl_TX,ampl_TY). The amplitude used today was 1e2.