Today we measured Q for several modes of RCAV and ACAV's suspension the numbers are summarized below.
We removed the insulation foams on both cavities for Q measurement.
We bounce the beam on reference cavity's mirror and used the motion of the reflected beam to
observe the motion of the cavity. For RCAV, we used two PDs for shadow sensing on 2 directions (vertical and horizontal motions)
For ACAV, we use a QPD to observe the beam motion. PSD from 4 signals are taken to identify the peaks
and compared with the beat signal.
fig1,PSD from RCAV H,V motion
fig2, PSD from ACAV, H,V motion
Fig3, beat measurement compared with PSD of ACAV and RCAV motion observed by reflected beams
on the mirrors' surfaces. The PSD is offset for comparison. We still have unknown peaks in the beat to investigate.
Most of the peaks we can excite by white noise on the table do not match with the beat signal
We used PZT attached on the table to excite each mode at its frequency and measured Q.
Beam movement can be observed by eyes for rough identification which suspension mode we excite
RCAV
f Q movement
3.15 Hz 150 -300 N/A
3.73 190 Vertical
4.3 Hz 220 Vertical
4.55 Hz 140 Horizontal
5.1 150 V
7 100 V
ACAV
f Q movement
4.3 Hz 120 V
3.4 N/A H(?)*
For 3.4 Hz horizontal mode, it dies too fast even though we drove at the right frequency,
so Q cannot be measured properly. Its motion is also uncertain. We cannot see by eyes
but the signal on QPD shows that the motion is mostly horizontal at 3.4 Hz.
We will try to get the beat signal and excite each mode we found to check what modes
from which cavities have significant effects on beat signal. Then we will fix the motion of
that cavity. All insulation are back to normal (I misaligned the mirror behind RCAV when I
slide the back panel back, some alignment have to be done later.)
I'll check the temperature and make sure that we can
get both cavities locked for Monday.
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