In the following, I will give some info and comments
about the operation performed.
1) Alignment:
- Due to the absence of the autoalignment, the alignment of
the ITF was initially done looking at the north and west
cavity modes and transmitted powers.
- As a complementary information, we used the quadrants
on the west bench, after have tuned the phase of the
photodiode B8. This phase was tuned in order to reproduce
the same behaviour of the B8_ACp and B8_ACq signal during
the C4 run (essentialy same amplitude and same sign for
B8_ACp and B8_ACq. This phase tuning is not optimal for
the longitudinal locking, moreover it allows to lock the
cavity in the lock_acquisition mode. The value of the phase
is B8_Lo = -170
- Due to the changes on photodidoe B7, the transmitted power
was not the same as for the C4 run. The maximum power found
was around 150-160 microW. For the B8 the maximum power
found was around 150 microW.
- Due to the new IB control through the marionetta, now
the beam trasmitted on the north cavity (observed with the
north cavity misaligned) seems to move more than in C4. The
displacement is now visible by eye on the screen B7p.
2) Beam B2
- Locking the recombined ITF in the lock_acquisition state,
but using B1p_ACp instead B2_ACq we observe a big offset
in the signal B2_ACq. The offset is comparable with the fringe
amplitude (see correspondent entry).
Locked with B1p_ACp , the interferomter is stable for
several minutes if well aligned.
- Aligning better the interferometer the offset seems to
be reduced and allow to lock the interferometer in the lock_acquisition state, using B2_ACq.
--> better analysis is needed in order to exclude problems
on the beam B2. In our opinion, this analysis needs the
automatic alignment of the two cavitites, in order to decouple
the problems induced by the Anderson offserts.
3) Locking and frequency stabilization
- It was possible to lock the ITF in the linear state and
in the SSFS state. Then, it was possible to move the BS control
to the NEO100Hz filter. On a separated sequence, the BS control
was moved to the NEO50Hz filter (DSP gain = 2, sensing
GC card = recombined_SSFS 1.1, filtering GC card: recombined_DL_refcav 1.44). The DSP gain = 2 is neeed because
in the recombined_SSFS file we didn't change the Michelson
gain (power is reduced now on B2 by a factor of 2, then the
optical gain in the sensing card should also be reduced).
- It was also possible to switch off the z-damping filters
(zoff) and move the differential control from B1p to B1.
- GPS time of the full ITF operation with the 50 Hz NEO
is around 773414563 (check flags)
- GPS time of the full ITF operation with the 100 Hz NEO
is around 773403662