Background

This procedure is designed to map out the flexure of the gratings as a function of rotator angle. The flexure is a function of the rotator angle in two ways. First as the instrument rotates the flexure changes (obvious), second, the rotator angle at which the grating is clamped may also impact the flexure curve.

Understanding these two components help us determine where we can and cannot correct for flexure especially when clamping the grating. The test below clamps the grating at many rotator angles and then rotates the instrument.

Primary script

The script that is used to acquire DEIMOS flexure curves at various orientations on clampup can be run as any DEIMOS account on any of the DEIMOS Linux hosts:

      slider_flexure_curves_for_various_clampups n

where n is the slider number. This script clamps up the grating at the following rotator angles: -270, -180, -90, 0, -315, -225, -135 and -45.

The sccript generates the following log and data files are created in the /s/sdata1004/flexure_curves directory:

      slider_flexure_curves_for_various_clampups_slider_4_2020oct24.log
      slider_flexure_curves_for_various_clampups_slider_4_2020oct24.dat

Procedure

The procedure to generate the flexure curves for one grating requires about 3 hours of time and the FCS Cu lamp will be on most of the time so run during the day if necessary. These are the steps to follow:

Contact the summit crew to check if it is ok to rotate DEIMOS.
If you have not started all DEIMOS GUIs, make sure that DEIMOS is ready to take images by typing deimos start obsapps on a polo terminal.
Configure DEIMOS for acquring spectra with a default wavelength of 7500.
On the DEIMOS control GUI, click on Init/Stow → Details... → Return to default → Apply default config
Run the FCS tracking software from the VNC background menu DEIMOS Control Menu → Subcomponents... → Start fcstrack
Insert any slitmask
Make sure that the rotator mode is Pos by selecting on the DEIMOS control GUI → Rotator → Details... → Manual mode → Rotator mode: → Pos
Acquire FCS reference images for the current spectroscopy setup using the FCS → Details... → Prepare for reference [New], followed by Take a reference
Do NOT start FCS tracking.
In an xterm on any DEIMOS linux host run slider_flexure_curves_for_various_clampups [2|3|4]

Analysis Procedure

This procedure describes how to generate the flexure curves once the data acquisition has been completed.

The output data file (e.g. slider_flexure_curves_for_various_clampups_slider_4_2020oct24.dat) contains the following colums:

Clampup rotator angle
Initial frame number
Final frame number
Location of FCS log file

For instance:

      # /s/sdata1004/flexure_curves/slider_flexure_curves_for_various_clampups_slider_4_2020oct24.dat
      -270    428     465     /sdata1005/deimos10/2020oct23/fcs/fcsref.600ZD.slider4.at.7500.022461.OG550.log
      -180    466     502     /sdata1005/deimos10/2020oct23/fcs/fcsref.600ZD.slider4.at.7500.022461.OG550.log
      -90     503     540     /sdata1005/deimos10/2020oct23/fcs/fcsref.600ZD.slider4.at.7500.022461.OG550.log
      0       541     577     /sdata1005/deimos10/2020oct23/fcs/fcsref.600ZD.slider4.at.7500.022461.OG550.log
      -315    578     614     /sdata1005/deimos10/2020oct23/fcs/fcsref.600ZD.slider4.at.7500.022461.OG550.log
      -225    615     651     /sdata1005/deimos10/2020oct23/fcs/fcsref.600ZD.slider4.at.7500.022461.OG550.log
      -135    652     688     /sdata1005/deimos10/2020oct23/fcs/fcsref.600ZD.slider4.at.7500.022461.OG550.log
      -45     689     725     /sdata1005/deimos10/2020oct23/fcs/fcsref.600ZD.slider4.at.7500.022461.OG550.log

Create the directory /s/sdata1004/flexure_curves/fcsref_logs/YYYYMMDD
Copy the fcsref.log file from the FCS directory to /s/sdata1004/flexure_curves/fcsref_logs/YYYYMMDD

In any terminal on any of the DEIMOS Linux hosts, run the script PlotDeimosFlexureCurve as follows:

	  PlotDeimosFlexureCurve /s/sdata1004/flexure_curves/ slider_flexure_curves_for_various_clampups_slider_4_2020oct24.dat 20201024 -30 30 -30 30

The following plot will be created in /s/sdata1004/flexure_curves:
```
	  flexure_curves_slider_4_2020oct24.png
	
```
which can be visualized wit the eog script.

Sample of flexure curves

The following two figures show the flexure curves for slider 3 and 4 taken on August 26 and September 16, 2022, respectively. The flexure is within the FCS correction range at all rotator angles for slider 3, but it is outside the range at -135 and -45deg clampup angles for Slider 4.