KAGRA Logbook

VIS (General)

tomohiro.yamada - 3:29 Saturday 16 November 2019 (11571)

Rolling off high frequency for cryopayload damping filter (except for EX)

[Ushiba, Yamada]

We modified damping filters to lower roll-off frequency in EY, IX and IY.
[EY]
- MN_MNOLDAMP_Y
- MN_PSDAMP_L
(IM_TMOLDAMP_P has been already implemented by UT.)
[IX]
- IM_TMOLDAMP_P
- MN_MNOLDAMP_Y
[IY]
- IM_TMOLDAMP_P
- MN_MNOLDAMP_Y
- MN_PSDAMP_L

In the 8th figure, you can find which filter bank is used.

Points to be noted:

- same UGF
- same gain in low frequency
- 30 degree phase margin at least.

These modified filters are currently working well.
Measured spectum is attached.

We hope some improvements in the sensitivity.

Images attached to this report

Comments to this report:

tomohiro.yamada - 5:41 Saturday 16 November 2019 (11573)

I slightly modified ITMY_MN_MNOLDAMP_Y.

Images attached to this comment

yoshinori.fujii - 12:25 Saturday 16 November 2019 (11579)

K. Tanaka, Y. Fujii,

At ITMX suspension, we temporarily teaked MNYoplev2MNY loop gain, just total gain.

we found that ITMX was oscillating in Yaw at ~80mHz larger than like yesterday.
by increasing the total gain of MNYoplev2MNY, the residual was suppressed to the usual one. this time the gain was changed from 1 to 1.8.
- I did this since the gain of the modified FM looked a bit smaller than the original one according to the attachment and I was not sure which FM gain should be modified.
- Figure 1 is the time series of TMY as an example of gain tweaking.
- I note that this gain tweaking is done just for Tanaka-kun's today's measurement. still it is not optimized.

Can someone check the total gains are same before/after this work?
If I was going to wrong direction, please correct me, thanks!

Images attached to this comment

tomohiro.yamada - 16:37 Monday 18 November 2019 (11604)

I also implemented roll off for ETMX_MN_MNOLDAMP_Y.
It is currently working well.

Images attached to this comment