[RTakahashi, Washimi]

Yesterday, we constructed a test stak (3 steps) at NAOJ Mitaka, TAMA West-end.
Used rubbers were Hs=80 for the top and middle (3rd and 2nd) steps and Hs=84 for the bottom (1st) step.
In this test, we used Cu-gaskets and standard bolts (head thickness = 4mm). The tightening torque was not cared.
It took about 2 hours.

After this construction test, we added some weights and measured the gap-changing.
The result is plotted and fitted.
The final weight was 183kg, which is enough larger than the actual value in the OMC (total 457kg / 3 stacks = 152 kg/stack).

I measured the gaps throughout the weekend, with constant weight (183 kg).
Waiting 24 hours looks enough to stabilize.

[R.Takahashi, Washimi]

We measured the gap change for the top and middle steps when the weight decreased.

I calculated the spring constant for the Hs=80 rubbers, from the adding test (on 24) and removing test (on 27).
spring constant [N/mm] = [kg/mm] * 9.8 m/s2 (grav. acc.) / 3 (# of parallel rubbers)

The results were 469 N/mm (adding test) and 572 N/mm (removing test).

[RTakahashi, Hirata, Washimi]

We measured the Horizontal -> Horizontal vibration transfer function of the test stack (3 steps) using a shaking stage, by changing the load weight.

The lower accelerometer was TEAC707LFZ (10 mV/(m/s2), amp gain = 100) and the upper accelerometer was TEAC710 (300 mV/(m/s2), amp gain = 10 or 20).
In the plot, the calibration factor and the amplification gain are already canceled.

Changing the resonant frequencies is seen.
The amplitude was larger than 1 below 40 Hz. The shape looks healthy, but is this amplification OK for KAGRA?

Do you have any idea on the large peak in the green curve around 120Hz?

I guess it is due to the resonant of the top weights, 3 thin metal plates.

[RTakahashi, Washimi]

Yesterday we investigated some issues for the H->H TF.

We found a strange factor of 2.5 was multiplied for the TF amplitudes of the weight-loaded measurements (due to the GUI application, for plot zooming up).
After canceling it, the DC gain goes to 0 dB. (somehow +63kg data goes below 0 dB)

We also performed additional measurements, with loading +155 kg (without thin plates).

In this result, the strange peaks over 100 Hz are disappeared.

[RTakahashi, Washimi]

Yesterday we constructed a vertical shaking setup and tried to measure the transfer functions.
However, the shaking amplitude was very small and SNR was not good, even though we set the signal amplifier gain to be 500 (for lower ACC) and 50  (for upper ACC).

We will try it again in the next week.

I compared the recent results (without additional weight) to the TAMA paper (Rev. Sci. Instrum. 73, 2428–2433 (2002)).

The Q-value is larger (due to harder rubber?) in the recent test and the resonant peaks are sharp.
Also, the number of peaks is in the recent test, but why? (the ancient test should also be a 3-steps stack).

Takahashi-san suggested the additional peaks may be the yaw modes.

[R.Takahashi, Washimi]

We tried to measure the vertical transfer function of the test stack at Mitaka again.
The changed points from last week are the following:

• using a jig (a UFO-like shape) specified for the vertical shaking
• inserting rubbers between the shaker and the plate the stack stands
• (making an Al-frame jig to avoid a turnover accident. It was not touched to the stack and the weights during measurements)

The results look better (smoother) than last week's results, but still, we can see a shape peak around 100Hz...
We left the setup weight pressing through tonight and will check the difference tomorrow.

[RTakahashi, Washimi]

We developed an Al-frame jig to avoid a turnover accident. It looks like it is working well.

[R.Takahashi, Washimi] work on June 4th @ Mitaka

We measured the TF(V) of the test stack after ~20 hours of continuous loading weight (+155 kg), without any other changes.
Measurements just after removing the weight were also performed.

In the results, the TF with additional weight was shifted to a higher frequency.
The TF without additional weight was not changed so much.

The structure at high frequency should be due to the deformation of the rubbers of the jig.

work on June 4th @ Mitaka

I measured the TF(V, +155kg) with the portable shaker (broad-band injection) and a datalogger (GL980).
Good SNR was found in the ASD and the coherence plots.

I evaluated the TFs from these data and compared them to the result of the shaking table test (swept sine).
The results of the potable shaker tests were consistent with each other, but some discrepancy between the two methods is found.
One possibility is the deformation of the jig-plate was not the same.