1. DCOPS Readout before and during MTCC
DCOPS Data
DCOPS Readout before and during MTCC
James Bellinger
13-September-2006
V1.0

2. Outline
Layout
DCOPS readout
Results
Further Efforts

3. Review of Layout
The DCOPS laser system as implemented in the MTCC consisted of
1) 6 half SLM lines at the ME+1 position
2) 3 full SLM lines at each of the ME+2, ME+3, and ME+4 positions. Each has two lasers, one at each end.
2 partial transfer lines, consisting of 1 laser and DCOPS at the ME+4/3/2/1 and YE+2/+0/-0/-2 positions (4 others had the ME+ positions, and one of those a YE+2 as well).

4. DCOPS
Each DCOPS has channel CCD's arranged in a square, with light filters in each face to try to equalize the light intensity.
The HSLM's have 1 reference DCOPS and 3 mounted on chambers.
The ME+2/3 SLM's have 2 reference DCOPS and 8 mounted on chambers
The ME+4 SLM's have 2 reference DCOPS and 4 mounted on chambers.
The Transfer Lines have 12 DCOPS, one on each reference plate.

5. Usage The transfer plates represent knowable points in the system.
We ideally can measure the Z distance from one to the next, measure the angle the steel on which they are mounted bends using inclinometers, and use the laser transfer lines to establish the radial positions of each plate.

6. Usage
When the disk bends, DCOPS near the center where the steel bulges forward will record different positions for the laser beam. If the laser were always normal to the Z axis you could easily measure the displacements.
The edge of the disk bends backwards, though, and so each laser points in a new direction.
We should be able to determine the new direction, and from this the new DCOPS positions, using the laser on the other side as a reference, using inclinometers, or using assumptions about how uniformly the disk bends.

7. Unfortunate Limitation
We discovered after mounting and carefully aligning the lasers so that they would pass through the DCOPS along the SLM lines, that the green framework was not where it was thought to have been, and almost all the lasers had to be dismounted for closing and then remounted again after the disks closed.
There was not time enough to realign all of the lasers once remounted, and the lack of access and visibility made the job even slower.
It turned out that the DCOPS on-board generation of an average was not adequate.

8. First a reminder
Before I go on, I need to emphasize that a great many of our beam profiles look like this. These look great, and the onboard calculation of the average is probably just fine for them

9. Simple Averaging Doesn't work
Some need a little help. A different on-board algorithm could probably deal with these. Until we test and install one, we have to read back the entire spectrum and fit it.
I chose to fit it online, rather than store the spectrum. That may have been a mistake.

10. Hardware status
Some of the exceptionally low signals may be due to shadowing, or possibly damaged filters, and at least in principle are fixable: in the first case by adjusting upstream apertures and in the second by repair.
Some lasers were broken, and at least four DCOPS was broken during disk assembly. We hope that better care will prevent this from happening again.

11. DCOPS Readout Hardware
Each DCOPS sensor has an adapter board which handles data manipulation
Several adapter boards are connected to a single interface to an RS422 cable, which via an adapter connects to a terminal server
One terminal server handles all the DCOPS for one side
Commands and data travel along the RS422 line, one DCOPS at a time (with slight exceptions)

12. DCOPS Readout
The existing system runs on Linux and uses two program streams.
There is a DIM server that creates sentinel files to control the operation of the main readout system. It could in principle be used to monitor the status of the main readout system.
The main readout system is a bash script which reads a configuration file and from it generates and executes auxiliary scripts to control the lasers, read the DCOPS, and write the information to the database.

13. grandloop.sh Uses a text file describing the system
Polls the DCOPS periodically to read laser-off background levels which are subtracted on-board
Turns on one laser at a time, polls the DCOPS, and requests a background-subtracted hex dump of the spectrum
Preprocesses the spectrum and uses root to run a fitting routine
Collects fit information and stores it in the development database

14. Results
The DCOPS readout runs continuously in a loop taking a little over an hour, so if the magnetic field changes during that time the results are likely to be inconsistent.
We have data from several magnet ramp-ups, and are able to look at displacement vs time and displacement vs current.
We are able to estimate disk bending angles using Transfer Line 5

15. Laser Beam Slope vs Magnet Current

16. DCOPS ME+3/1-14 (SLM2) Laser PT5

17. Stability
As you can see from the previous slide, the center of the laser peak does not return to quite the same place once the magnetic field turns off. We can easily see the magnetic deflections.
We also see some long-term drifts, which may be relaxation of the iron.
We also see some discontinuities not associated with the magnetic field, which are not understood at the moment.
If I try to minimize laser bumping effects by asking for deviations from a fit, I get plots like the following:

20. Stability Within Time Interval
As you can see, the laser beam position is fairly stable, with a .05 mm sigma, provided we restrict ourselves to one of the stable time intervals.

21. Transfer lines

22. In the following slide, the laser (at ME+4) is nearest the upper left
In the following slide, the laser (at ME+4) is nearest the upper left. As you go from left to right or down a row you get farther from the laser.
These plots are for stations ME+4/ME+3,ME+2, then ME+1/YE+1/YE+0, then YE-0 and YE-1
The TP2 stations are less constrained than the TP5 stations
The horizontal axis is magnet current in amps
Positions for CCD2 and CCD4 are plotted

24. Behavior of Transfer Line 5
The DCOPS next to the laser shows hardly any variation, of course, but the next two stations show a good deal more. They are both fixed to the same disk, one cantilevered forward and the other backward, which provides a lever arm to enhance the displacement of the first and reduce that of the second.
It is plain from the bottom two MAB DCOPS that the angle through which the beam bends as field is applied will result in a shift that exceeds the aperture of the DCOPS at the far end of a Transfer line.

25. Transfer line
Using the data for ME+1 on Transfer Line 5, I estimate that the laser's mount was bent backward by about 1.1 milli-radian
Using the data for ME+3 ME+1 I estimate a change in the laser direction of .9 milli-radian.
Since the distance between the two ends is about mm, the change in beam position at the far end would be of order 21 mm, although the deflection at YE-0 and YE-1 (at less than full field) suggests that the deflection might be substantially greater.

26. ME+2/SLM2 : PT5 Laser

27. ME+2/SLM2 : PT5Laser
There are 10 DCOPS in this laser line. The one nearest the laser is the lower left, and they lie farther from the laser the higher the row is and the farther to the left.
The laser goes offscale on the upper left DCOPS before the magnet reaches full current.
The near side of the disk does not bend much relative to the laser line: there's a jump as the laser reaches the other side.
The deflection at the center must be

28. HSLM1

29. HSLM1
The laser is nearest the upper left DCOPS, and the DCOPS are farther from the laser as you go right and down.
The deviation is only .5 mm in the farthest DCOPS at 3.7 Tesla. The disk must be bending roughly in the shape of a cone.

30. More plots
See for references and plots.

31. Near Term Plans (week)
Try to understand the stability issues. I miss quite a bit of the high field data because of this.
Fold the shimming into a fit, using the complete calibration.

32. Medium Term Plans (1 -2 months)
Incorporate suggestions from Vladimir to speed up the readout.
Tinker with the fitting algorithm and fold several of the processing programs into a single executable. This should make the program substantially faster and give us better statistics.