As a preparation for Schnupp asymmetry measurement, diaggui template was copied in
/users/Commissioning/data/MICH/2020/0615/.
Measurement principle is Izumi method.
Othere references: klog4946, klog4960.
We expect the measurement will be much better this time as we now have ISS and the Michelson is short where the alignment fluctuation is thousand times shorter. It will be measured next week.
[Kokeyama, Nakano]
We tried to measure the schnupp asymmetry. Although each measurement seems to have good SNR, but the calculated result was 0.56 m far from the designed value of 3.34m.
We might have a stupid mistake, so we will check it again tomorrow.
Measurement procedure.
-
Lock the MICH at the mid fringe.
The MICH was locked with REFLDC and ASDC. The VERTEX guardian can lock it in MICH_MID state. The UGF is about 20 Hz. -
Optical gain measurement of the MICH loop
The transfer function from BS_ISCINF to MICH_IN1 was measured. By using the actuator efficiency (klog14516), BS_ISCINF can be calibrated to m, so we can obtain the optical gain of the MICH in cnts/m. The first attached file shows this measurement data. Top is raw data of the TF and bottom is the calibrated one. and you can see the optical gain has less than 1 % fluctuation during this swept sine measurement. -
Excite laser frequency and measure the response to the MICH error signal
The laser frequency was excited by using DGCARM port. The configuration of the DGCARM path is as follows:
- LSC-DGCARM: gain 1, INPUT off, OUTPUT on, No FM is on.
- SUMMING NODE CMS: EXCA is on, no filter is engaged
- CARM CMS: IN2 is enabled with 0dB gain, FAST path is engaged with gain of 11 dB,
- IMC servo: IN2 is enabled with -32 dB gain.
Excite DGCARM with 621 Hz 3000 cnts signal. Laser frequency excitation can be calibrated with K1:IMC-SERVO_SLOW_DAQ_OUT. This channel is calibrated in V and we have a PZT efficiency of the laser PZT 3 MHz/V (klog13012), so it can be calibrated in Hz. By using the optical gain we got in the privious measurement, we can measure the response from the freqeuncy fluctuation to the MICH signal as 2.0e-15 m/Hz. - Schunupp asymmetry can be derived as 2.0e-15 * (3e8/1064e-19) = 0.56 m
[Nakano, Kokeyama]
I did a measurement for BS TM actuator efficiency completely independently. At 1Hz, 5.4e-11 [m/cts]. It is 1 order different from the known value measured by Darkhan. I think it s a typo on his post.
I did an old school method:
A = G / (Cmi/Servo) [m/cts]
where G is a meauserd open loop gain. Mesured and fitted plots are attached.
Cmi is an optical gain (including the sensor and ADC) measured by free swinging, which was 1.05e+7 [cts/m].
Servo is a digital MICH servo (taken from foton).
Measurements were done with the mid fringe lock.
See the attachment for the full result. You can also see /users/kokeyama/MICH for calculations and /users/Commissioning/data/MICH/2020/0616/ for data.
With the modified parameters, Schnupp asymmetry is 5.6m!!