Beam Line Detectors Shift

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Collimator and Radiators

Move Collimator

  1. Open Hall-D CSS EPICS Control, if not already available, following instructions.
Figure 1. CSS GUI for changing the primary collimator position.
  1. From Main Action Bar, click Motors in BEAM section. This will open the motor main GUI (Figure 4).
  2. Click Collimator to bring up the Collimator Control GUI.
  3. Click the button corresponding to the desired location to move the collimator. Wait until the Motor is Done.
  4. If the communication to the motor is broken, e.g. pink fields showing, refer to instructions to reboot the IOC.
  5. Make a log entry to HDLOG.

Move Radiator on Amorphous Radiator Stick Assembly

Figure 2. CSS GUI for changing the radiator on the amorphous radiator assembly.
  1. Open Hall-D CSS EPICS Control, if not already available, following instructions.
  2. From Main Action Bar, click Motors in BEAM section. This will open the motor main GUI (Figure 4).
  3. Click 'Amorphous' radiator to bring up the radiator Control GUI (Figure 2).
  4. Click the button corresponding to the desired location to move the radiator. Wait until the Motor is Done.
  5. If the communication to the motor is broken, e.g. pink fields showing, refer to instructions to reboot the IOC.
  6. If you just put a radiator or a wire into the beam, make sure that the GONIOMETER is either in RETRACTED or BLANK position.
  7. Make a log entry to HDLOG.


Move Radiators on the Goniometer

Figure 3. CSS GUI for changing the radiator on the goniometer.
  1. From Main Action Bar, click Motors in BEAM section. This will open the motor main GUI (Figure 4).
  2. Click Goniometer to bring up the Goniometer Motor Control GUI (Figure 3).
  3. Click on the position that is needed. There will be a confirmation window asking if the beam is off. The goniometer will start moving and you should be able to see it in the camera view on the same GUI.
  4. Wait until the goniometer motion is complete and the desired radiator button is highlighted in green. The green cross-hair should be pointing to the radiator that you just inserted into the beam. If it points to some other target, please contact the beamline/goni expert.
  5. If you just put in a radiator into the beam, make sure that the amorphous radiator is in RETRACTED position.
  6. Make a log entry to HDLOG.

Halo Counters

Halo counters are PMT-based counters arranged around the beam-pipe to measure the beam halo intensity at various positions along the beam-pipe. the main goal of the halo counters to check the stability of the beam in time and to be used as detectors in beam scanning procedures. If the voltages of the halo counters trip, they need to be restored using the Beamline Voltages GUI that can be opened from the BEAM section of the Main Action Bar .

Radiator Harp Scan

Figure 4. GUI for opening various beamline-related controls screens.
Figure 5. Radiator wire scan control screen.

The radiator harp scan is performed to determine the electron beam profile in X- and Y-directions using two wires mounted on the same insertion device that holds the three amorphous radiator. The wires are mounted at ninety degrees to each other and are inserted into a beam by a stepper motor at 45 degrees with respect to the horizontal plane.

Open Radiator Wire Scan GUI

  1. On the Main Action Bar click on Motors button. A new screen will pop up showing various buttons for beamline related screens.
  2. On the newly open GUI (Fig. 4) click on Radiator Scan GUI button. This will open the radiator scan GUI (see Fig.5 ) that will be used for the radiator scan.


Preparing for Scan

  1. Ask MCC to take the beam away for a few minutes and let them now that we will remove all radiators from the beamline and that we will do harp scan at the radiator position.
  2. When the beam goes away, retract the amorphous radiator or the diamond radiator from the beam line. There should be no radiator in the electron beamline during the radiator wire scan. The goniometer can be put in BLANK position instead of RETRACTED.
  3. Request 100nA beam from MCC and ask them to mask the Ion Chamber and Hall D amorphous radiator motor from the Fast-Shutdown (FSD). Wait for the beam to come back and stabilize at the nominal positions on 5C11B BPM and start the scan.

Performing the Scan

  1. Push the blue SCAN button on the radiator scan GUI. The motor will move to the starting position for the scan and start going through the points and acquiring scaler data. The scan automatically pauses when beam goes away and resumes when the beam is detected again. The scan takes about 7 minutes without beam interruptions.
  2. Periodically check for the messages at the top of the radiator scan GUI. When the last point is acquired, a message Scan Complete will be shown and the motor will stop at that last position. Note that the motor for the radiator scan (and amorphous radiator) will not retract on his own, it will need to be retracted after we are happy with the scan results. If Scan Complete message does not appear on the top of the scan GUI but you are absolutely sure that both wires scanned the whole beam, you need to push ABORT button on the scan GUI. This will abort the rest of the scan and perform some necessary restoration steps. If you are not sure if the wires went through the beam, either wait for the Scan Complete message or call EPICS expert.

Analyzing Data

Figure 6. TOP GUI for selecting the wire scan file for analysis/fitting.
Figure 7. Overview GUI for selecting detector for analysis/fitting.
Figure 8. ROOT analysis GUI for fitting the x- (left) and y- (right) profiles. The fit results are shown in the fit parameter box. The units are in mm. The mean positions and the widths are in the horizontal and vertical direction, while the x-axis of the plot is the index of the stepper motor in mm-s.
  1. Once the scan is complete, push Analyze button on the bottom of the radiator scan GUI. This will open a xterm window, a small top window (Fig. 6) and an overview window (Fig. 7) that shows the response of various detectors versus the motor position of the scanner. The main feature of each detector plot is that there are two peaks at different position motors, one for x and the other one for y. If the peak is not visible for one detector that means that detector is not sensitive to having a wire through the beam and fitting that signal is pretty much useless. Note that the actual screen that shows up may be different from what is shown in Figure 7 since the number of enabled detectors in the scan can be different.
  2. Select the detector that shows the best signal (usually signal/background ratio is the best indicator) by clicking the corresponding Analyze button. This will open the screen with the fit of the signal. Usually the best once are those from HALO:T:electron:tag detectors. Note that one can open multiple detector views with the fit to compare. The new screen that pops out will show the results of the fit for the x-profile on the left panel and for the y-profile on the right panel. The x-axis of the histograms are the motor position in millimeters, while the fit results are the beam positions and width in the horizontal and vertical positions. The horizontal and vertical positions are related to the motor position by a simple factor of sqrt(2) from the scanner geometry. The vertical axis of the histograms are detected scaler rates from the selected detector.
  3. If the fit is good, make a log entry by clicking Make Log Entry button on the bottom of the screen. A small dialog box will pop-up for a comment, and after the comment is filled and Submit button is clicked a log entry will be made. It is a good idea to check the logbook to make sure that log entry has been submitted successfully.
  4. If the fit is not good, one can improve the fit. The points in the views are ROOT histograms, so one can right-click on the histogram points and bring up the fit-panel and improve the fit by selecting the initial values for the parameters and limits for the fit. Keep in mind that the x-mean and y-mean are not the same as the positions of the peaks on the horizontal axis of the shown histogram. Once the fit is satisfactory, a log entry should be made by clicking Make Log Entry button on the bottom of the screen.

Evaluating Results

We expect to see approximately Gaussian distributions of the beam intensity in both x- and y- directions similar to ones shown in Figure 8. The expected sigmas of the Gaussian distributions are expected to be approximately within 0.6mm to ~1.2mm. Distributions with sigma in either X- and Y- directions greater than 1.5mm is too wide and might cause problems at the diamond radiator. Note that narrow beam profiles do not mean better photon beam since the Hall D beamline was designed to have a wider beam spot at the radiator focusing at position of the primary collimator. An accelerator physicist will evaluate the result of this scan together with other scans upstream of the radiator to determine the conversion quality of the electron beam image at the converter. We also expect to not see any shoulders and halos around the Gaussian distributions above 10^-4 level in this wire scans. Whether the halo or the widths are not satisfactory and what actions need to be taken right after the scan depends on the instructions from the run coordinator.

Backout from scan

  1. From one of the ROOT analysis GUIs select File->Exit to close the ROOT screens if not needed anymore.
  2. Request the beam to be taken away for a minute.
  3. When the beam is off, insert the desired radiator in the beam, and retract the amorphous radiator if not using the amorphous radiator. Remember that the harp and the amorphous radiators are on the same insertion device.



Upstream Beam Profilers

There is a beam profiler installed in the beam line just in front of the primary collimator to measure photon beam profiles. The profiler has two planes scintillator fibers to give X-Y 2D information. Each plane consists of 64 fibers of 2 mm width and they are readout by eight Multi-anode PMTs.

Open Beam Profiler GUI

  1. Open Hall-D CSS EPICS Control if not already available following instructions.
  2. From Main Action Bar, click Beam Upstream Profiler in BEAM section.
  3. In the GUI, one will see the scaler counts plotted as a function of X and Y axes. The updating frequency is controlled by the DWEL parameter. The update interval is DWEL×256.
  4. There are three modes of data presentation and we are currently using two of them: Raw and Accumulative.
    • The Raw mode update the plot with the new counts coming from the most recent interval.
    • The Accumulative mode keeps the sum of all hits until the Reset button is pressed.
Figure 9. Beam profiler GUI.

Adjust BP Voltages

The power used by the Beam Profilers includes both High Voltages and Low Voltages. The HVs are used to power the MaPMTs while the LVs are used to power the pre-amplifiers.

High Voltage
Each MaPMT is powered by its own HV channel. Therefore there are eight channels for each plane. These HVs can be adjusted through HV X/YPVU/D: Show X/Y HV Channels. As the threshold for the discriminator is embeded in hardware, adjusting the HV is the way to effectively change the threshold.
Low Voltage
Readouts from the same plane share two groups of Low Voltages. Each group needs two 5-V and one 1-V inputs. Always make sure that they are ON. No adjustment is allowed.

Expert Personnel

The individuals responsible for checking that the beamlineis ready to take data and setting its operating parameters are shown in following table. Problems with normal operation of the beamline instrumentation should be referred to those individuals and any changes to their settings must be approved by them. Additional experts may be trained by the system owner and their name and date added to this table.

Table: Expert personnel for the beamline instrumentation
Name Component Extension Date of qualification
Alex Barnes Active Collimator (570) 242-1844 June 4, 2014
Hovanes Egiyan BPU & TAC & GONI x5356 March 25, 2016
Alexandre Deur Beamline June 4, 2014