Beam Line Detectors Expert

Active Collimator

Control and DAQ

The Active Collimator screens are here:

Main Action Bar -> Under "BEAM" select Monticello -> Select BPM -> Hall D Active Collimator Diagnostics (you may need to move the window to see the correct option as it tends to stretch onto another monitor)

The preamp gains, 1Hz data and averaging/digital gain are on that screen. Go to the Raw Wire Data button for the individual plots and Time Domain Graph HDACI/O for positions.

Changing preamp gains

Once Monticello is opened to the active collimator diagnostics page you'll be able to adjust the preamp gains. On the left side of the screen there should be two sets of 4 buttons labeled IAC5H01I Gains and IAC5H01O Gains. These are typically kept at 10E-10 A/V. To change these, click on one of the buttons and select a new gain setting.

• Note: With increased radiator thickness and/or current, the preamp gains should go from 10E-10 A/V -> 10E-9 A/V and so on.

To determine if the preamps are saturated, look near the bottom left of the screen where it says IAC5H01L ADCs and IAC5H01O ADCs. If these numbers are approaching +/- 32k then the preamps are saturating.

Performing a collimator scan

The basic idea of the collimator scan is to move the collimator in X and Y and monitor counting rates some detectors in the hall behind the collimator to find the position of the collimator that allows largest intensity of the photon beam in the hall. For the collimator position we identify the response of the active collimator in terms of X and Y, assuming the Active Collimator is calibrated. Once these Active Collimator position is found, the collimator will be returned to its original position and request the beam to be placed at the AC position found. Since the Active Colimator is moving in this procedure and we want the beam to stay stable, the photon beam positions need to be locked using the Upstream Beam Profiler (BPU).

1. Make sure that all beamline voltages are on by opening "Beamline Voltages" GUI from the main CSS menu.
2. Insert BPU into the beam.
3. Set the probper gains on AC. For a 2e-5 RL radiator and 50 or 100 nA beam, use the 10E-10 gain setting (current default) for the active collimator. If using a different combination of radiator and current, adjust the preamp gains to prevent saturation. See above for adjusting the gains. If you aren't sure, contact the active collimator expert.
4. Ask MCC to centre the beam on the Upstrem Beam Profiler (BPU) at (x,y)=(0,0) (or whichever at that time is believed to be the best positions) and to turn the slow lock from AC to BPU.
5. On the main CSS overview GUI, select "Motors" under the "Beam" section. This will open a new window.
6. Select "Collimator". This will open the basic collimator motor GUI. Move the active collimator to the current hole position.
7. Select "Collimator Scan GUI". This will open two GUIs.

Optimal transmission scans

• Example logbook entry

1. Move the active collimator to the current hole position
2. For a 2e-5 RL radiator and 50 or 100 nA beam, use the 10E-10 gain setting (current default) for the active collimator. If using a different combination of radiator and current, adjust the preamp gains to prevent saturation. See above for adjusting the gains. If you aren't sure, contact the active collimator expert.
3. Ask MCC to center the beam on the active collimator.
4. Explain to MCC that an active collimator scan is in progress and the position will appear to drift significantly. Tell them not to adjust
5. On the main CSS overview GUI, select "Motors" under the "Beam" section. This will open a new window
6. Select "Collimator Scan GUI" AND "Collimator"
7. In the "Collimator Scan GUI"
   1. Set the start value to be -116.700 and end at -106.700 for the 5.0 mm hole. Use -15.240 to -5.240 for the 3.4 mm hole.
   2. Set 0.5 mm steps
   3. Use a 10 s positioner settling time
8. Once step 3 is complete and the scan GUI has been configured, in the "Collimator" GUI use the expert mode to move the colilmator to the furthest negative position for the scan (-116.7 or -15.240)
9. Start the scan in the "Collimator Scan GUI" by clicking SCAN
10. When the scan finishes use the "Collimator" GUI to move the collimator back to the nominal hole.
11. As HDOPS, go to /home/hdops/active_col_scans and execute the MyaViewer_plotter script.
    1. This script will display the active target rate, the PS and PSC coincidence rates and the inner x position of the active collimator
    2. ./MyaViewer_plotter <begin> <end>, where <begin> and <end> are in YYYY-MM-DD HH:MM:SS format
    3. From the plot, find the maximum of the active target and coincidence rates and compare it to the x position of the active collimator.
    4. This will be the optimal x position for the active collimator
12. To get the optimal y position, as MCC to move the beam vertically to 1 mm, 2mm, -1 mm, and -2 mm and record the active target and coincidence rates at each of these positions
13. From the recorded rates determine the optimal y position.

Calibration scans

• Example logbook entry

1. Move the active collimator to the 5 mm hole
2. For a 2e-5 RL radiator and 50 or 100 nA beam, use the 10E-10 gain setting for the active collimator. If using a different combination of radiator and current, adjust the preamp gains to prevent saturation. See above for adjusting the gains. If you aren't sure, contact the active collimator expert.
3. Ask MCC to center the beam on the active collimator.
4. Explain to MCC that an active collimator scan is in progress and the position will appear to drift significantly. Tell them not to adjust
5. On the main CSS overview GUI, select "Motors" under the "Beam" section. This will open a new window
6. Select "Collimator Scan GUI" AND "Collimator"
7. In the "Collimator Scan GUI"
   1. Set the start value to be -139.999 and the end position to be -80
   2. Set 2 mm step size
   3. Use a 2 s positioner settling time
8. Once step 3 is complete and the scan GUI has been configured, in the "Collimator" GUI use the expert mode to move the colilmator to -139.999
9. Start the scan in the "Collimator Scan GUI" by clicking SCAN
10. When the scan finishes use the "Collimator" GUI to move the collimator back to the 5 mm hole.
11. If performing a 2-d scan
    1. Ask MCC to raise the beam vertically by 0.5 mm to 1 mm, depending on the study. Repeat the process to the positive and negative vertical limit.

MCC will eventually have a hard time to move the beam at the extremes at which point the scan in that direction is done.