KAGRA Logbook

IOO (IMC)

koji.nagano - 18:23 Friday 14 July 2017 (3098)

RF QPDs for IMC WFS were brought back to Mozumi

[Nagano, Kokeyama]

For IMC WFS, the resonant frequency of RF QPDs should be tuned.
In order to tune thier resonant frequency to the target frequency, 13.78 MHz used in IMC LSC, we should replace a condencer.
Therefore we brought the RF QPDs back to Mozumi and placed them on the table in Circuit Room (Kairo Shitsu).
We will install them again to IMC REFL Table in the next week after we replace a condencer.

By the way, the RF QPDs do not have S-number. We will assign S-number to them next week.

Comments to this report:

koji.nagano - 18:22 Tuesday 18 July 2017 (3106)

[Nakano, Nagano]

Under Shimode-san's instruction, Nakano-san and I replaced a capacitor of RFQPD for IMC WFS, S_No.016 and 017, which we assigned them.
Specifically, C6 in the circuit diagram was replaced to 330 pF from 270 pF.
This replacement was going to allow us to obtain the resonant frequecy of the about 13.8 MHz.
However, the resonant frequency was measured to be about 19 MHz.
(In this measurement, we used test port.)
Thus, we should use larger capacitance like 680 pF and we will replace C6 and again and install the RFQPD tomorrow.

koji.nagano - 21:31 Thursday 20 July 2017 (3130)

We investigated the reason of the gap between the measured and calculated resonant frequency.
However, we cound not get specific solutions explaining this problem.
Thus we changed our storategy.
We "sweeped" some capacitances.
After some try and error, eventually we could find a good capacitance and tune these RF QPDs' resonsnt frequency to 13.78 MHz.
These RF QPDs were took to IMC REFL table.

keiko.kokeyama - 9:25 Friday 21 July 2017 (3131)

These RFQPDs are placed back on the MC REFL table.