Daniel, Kiwamu,

One of the to-do items today was to study how the rotational stage behaves. There have been some suspicion with the rotational stage that:

• It does not go to an exact requested power
• It acts as if the rotational mechanics slipps and therefore it does not come back to a consistent position

Also,

• we wanted to re-calibrate the angle-power relation.

We did a simple test today to study the above issues. It looks that the variation in the adjusted laser power can reach roughly 500 mW at most when the requested power is around 10 W. We also experienced a slipping-like behavior.

(Random walk in requested angle)

To check if it behaves good or bad, I wrote a script which randomly request the angle and automatically collects the resultant power for each random walk. This time I made 200 random steps within +- 90 deg. The result is shown below:

The data points are divided into half i.e. 100 samples each in chronological order. The red dots are the ones from the 1st half and the blue dots from the 2nd half. The difference is that we hit the "search for home button" between the two measurements. Since Daniel incidentally updated and rebooted the rotational stage code during the measurement, we had to hit the "search home" button as the reboot gave us a warning sign. As shown in the above plot, clearly the two data sets have different angle offsets which are visible as sine curves in the bottom residual plot. Because of that, the resultant residuals became bigger and reached 500 mW at most. Probably if I fit only one of the halves, the residuals would be smaller. At the moment, I have no good explanation of why the angle offset seemed to be shifted. I am guessing that it is not from the actual optical hardware as each data set was consistent.

Some notes:

• PMC power = 22.7 W
• ISS first loop on, diffracted power = 8%
• RS_VELOCITY was set to 100 (which is 10 times faster than the nominal operation in order to speed up the measurement)

(Calibration)

See the attached screen shot shown below for some details. Based on all the measured data from the random walk test, I fit the necessary parameters and updated the calibration of the rotational stage. Also the safe.snap in target/h1ecatc1/h1ecatc1plc1epics/burt is updated accordingly.