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MIF (ITF Control)
kiwamu.izumi - 1:16 Wednesday 12 December 2018 (7339) Print this report
Continuing work on noise investigation for ALS X

Yutaro, Kiwamu,

This is a report on a follow-up measurement of 7317.

Conclusion: PSL Koach filters and precision AC give broadband noise in a few - 100 Hz band while the FFU give a line (sometime a broad line) at around 17 Hz.

We conducted the same noise measurement as done yesterday (7317) where the ALS PDH was used to witness residual frequency noise while the IR laser was directly stabilized with respect to the arm cavity (7289). This time we switched off the PLL Koach filters and shut one and half of the precision air units (7255) while leaving the FFU units running as normal. We were able to see broadband noise going down to a level as low as what we saw yesterday when all the relevant fans were off. This directly means that Kach and precision ACs actually affect the ALS performance as opposed to what we reported yesterday (7317). This is consistent with what we have experienced in this past month or so. So we believe this result.

By the way, according to our eye-ball calibration, multiplying a factor of 1500 to MIXER IN brings it to the units of Hz/Hz1/2 for 1064 nm.

However, we are still not sure how this noise couples to residual frequency noise. Is this through the fiber or free-space light?

Comments to this report:
shinji.miyoki - 9:47 Wednesday 12 December 2018 (7340) Print this report
The precision air generator has combined modes, cooling and warming. I am not sure whether vibration level of the presision air filter itself is different in cooling mode and warming mode. The amount of air flow is same in both modes.

However, during KOACH operation, the main air flow on the optical bench is dominated by the only KOACHs.

If you turn off only KOACHs, the air flow becomes slower but complicated air flow is expected on the optical bench because the injected air from the presicion air generator hit on the ceiling structure above the optical bench and dose not directly hit the optical bench itself. It will go to the optical bench area mainly from the open side, partially through inside the unoperated KOACHs.

Anyway, during observation, we originally plan to stop KOACHs at least. While the precision air generator operation consults with sensitivity.
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