First, I measured the spectrum with excitation.
Fig.1 - Fig.6. showed the results compared with the Aug 2024
We adjuseted NBDAMP filters (L1,2,3, and 5)
- L1: changed the filter from FM3(pink) to FM1(red)
- L2: changed the filter from FM3(brown) to FM1(red)
- L3: checked FM3(original one) and FM1(300K one). As FM3(brown) looks better than FM1(red), we keep using FM3.
- (L4: not be closed at LOCK_AQUISITION)
- L5: Measured TF had too large gain peaking. So we comment out the line which closes this loop in the guardian code.
After this work, we checked the ETMX suspension can reach the LOCK_AQUISISION state and back to ISOLATED state. (The L5 loop was not closed as we expected.)
The current temperature of ETMX is 270K.
We adjusted T1-T3 NBDAMP filters.
- T1: Changed from FM3(pink) to FM1(cyan), and adjusted FM1(red)
- T2: Changed from FM3(brown) to FM1(red)
- T3: Copied FM3(cyan) to FM5 and modified FM5(5.336, 271K) for the adjustment.
(Wide)
MN DAMP L
MN DAMP T
(NB)
P1
Y1, Y2, Y3 and Y4 (with spectrum of the IM Y photo sensor)
NBDAMP
L1, L2, L3
T1, T2, T3
MNDAMP
L, T
MNOLDAMP
R, P, Y
Even after tuning the following filters, the ETMX suspension started oscillating around 1.67 Hz.
I changed the MNOLDAMP R, P notch fireqencies (1.685 -> 1.67) and turned off the ACALIGN matrix K1:VIS-ETMX_MN_ACTALIGN_6_5 (P->Y) from 0.017 to 0 (temporary)
The oscillation can be stopped(at least 1 hour).
So, next step would be ALS DARM lock!
Since MN_DAMP_L gain seems slightly smaller than the nominal value and it takes a long time to damp longitudinal mode due to it, I increased the gainf MN_DAMP_L by a factor of 1.6.
This gain is implemented into FM3 (LOCK+ELP9).
After that, OLTF was measured and notch position seems not good.
So, I modified the notch filter frequency from 2.40 Hz to 2.52 Hz in FM8 (notch).
Figure 1 shows the OLTF after the modification.
Green line shows OLTF only modifying the gain and red line represents the OLTF after changing gain and notch frequency.
The gain peaking around 2.5Hz was reduced, so the new setting seems better.
Note:
OLTF measurements were performed when the suspension was at LOCK_ACQUISITION state, so the several struture of OLTF is different from the original post.
