TMS Meeting Minutes, April 1, 2021

Attendees: Andrew, Breann, Heejoo, John, Olga, Trenton, Yang (Zoom Meeting)


TMS Active Mode Data Collection 2021.03.29
  • TMS data collected last Sunday night for 3 hours (2021.03.29 on Google Drive)
  • One problem came up with the software (no reply from Etalon yet, Kai is away)
    • TMS spit out error at time 6.5 UT and was down for 20 minutes
    • After restart, TMS worked fine
    • Z4 over time shows a substantial arc in LBC blue focus, while LBC red was monotonically increasing
    • Olga generated these plots by running FPIA offline after the fact
  • Andrew notes that there is an issue with disentangling three radially symmetric Zernike terms, Z4, Z11, and Z22
    • FPIA is semi-reliable in this particular use case
    • Olga suspects there is some issue with higher order Zernikes intermingling with lower orders
    • Around the time of the turnover of the LBC blue focus Z4, the estimated seeing started to fall below the threshold for calculating Z11 and Z22
    • Blue wasn't calculating spherical aberration up until the point at T=6.5hrs
    • Even though FPIA isn't sending anything, the measured Z11 and Z22 are incorporated into the matrix
    • There is an issue with the blue side where there is sometimes a fuzzy edge around the pupil
    • The focus calculation only depends on the diameter, and the diameter has a seeing correction
    • THEN, FPIA multiplies Z11 and Z22 into the crosstalk matrix, which affects the overall system focus
  • Why do we see a ramp in red focus over T=5.2hrs to T=7.8hrs?
    • dZ of 37.5 microns on M1 corresponds to 1000 nm's of Z4, according to Andrew (some disagreement on this point)
    • Temperature was flucuating early in the night, and then stabilized later (a few points of a degree change over 3 hours)
    • 0.1 K gives 4 microns of surface focus, front to back gradient, according to Buddy Martin
    • The temperature corrections were not turned off in the collimation model
    • For Z, Yang's code adjust everything except the instrument offsets that TCS sets
    • Don't want TMS servo to have to work ten times harder than it needs to
    • The thermal collimation model brings us close, and then TMS brings us closer in
    • At the beginning of the night, the relationship between the mirror and the hub is set by the reference
    • TMS is working to hold the necessary Z positioning, but we still see a monotonic focus change on LBCr over time
    • Could be an interesting next step to attribute this monotonic rise to thermal focus on the mirror (according to Buddy Martin's estimate) and see what that nets us
  • Barring the above software glitch, the TCP/IP glitch has not reoccured, which is encouraging; the software is not failing nearly as often as it was before
  • Overall, the functionality of Yang's software seems to be rather good! Doesn't seem that it would negatively affect the TO's night in any real way.
  • Andrew proposes we run the experiment a few more times, gather data sets, and see how well we can correct residual errors with glass therms; Andrew thinks we can do even better, putting our best foot forward
    • This would also give us more experience running in this current smooth mode
  • John notes that it would be great to have TMS usable for science right now, as you could three times as long between FPIA runs
  • Would be great to propose this to the LBT science community after we figure out where the residual drift is from
  • PI's who propose to do imaging with LBC would like sub-arcsec imaging (we aren't there yet)
  • Would be nice to have a couple more three hour slots, seeing where we stand at that point, and then prepare a proposal

TMS Testing Scenarios
  • Olga: One scenario could be to slew to an object, observe for a short while, then slew to a new object, without having to run FPIA every time
  • If we could demonstrate multiple slews with well controlled collimation and pointing using TMS, that could be huge
  • Andrew: could slew from target to target using FPIA to hold blue, and TMS to hold red, running VFast Extra the whole time to see image quality on slewing
  • This method could show the efficiency gain in not having to run FPIA
  • Another gain would be under poor conditions, with a changing thermal environment
  • Could be very useful for transit measurements, where a defocussed star must have the PSF held over a period of time
  • We can probably extract glass therm fitting data from our passive observing with LBC
  • Could use the continuous TMS measurements along with the FPIA corrections to pull out information about the thermal gradients

Engineering Night
  • Next engineering night is on the 28th of April (29th UT)
  • LBC planned for the start of tonight, though the weather is not looking too great
  • In general, it would be great to get passive TMS data to build up a dataset on the residual focus

Heejoo's Next Visit on April 11th - 13th
  • Bringing laser tracker for survey
  • Planning to bring the custom Thorlabs collimators, if they are done in time
  • Could be nice to bring a platinum wire thermal sensor

Software Updates
  • John moved the LBC primary mirror movement check from the lbc_tms.py code
  • Yang updated the data extraction utility to show the number of times channels drop

-- TrentonBrendel - 01 Apr 2021
Topic revision: r1 - 01 Apr 2021, TrentonBrendel
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