Forward Calorimeter Shift

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The Forward Calorimeter

The Forward Calorimeter (FCAL) is a 2800 element lead glass detector consisting of 4cm x 4cm x 45cm bars. The light produced in each element is measured using FEU 84-3 PMTs. The PMTs are readout using custom Cockcroft-Walton bases and operate up to 1800 V. The entire detector exists inside an environmentally controlled and light-tight darkroom on the FCAL platform.

Rates Monitoring

Fig. 1. Upstream view of the FCAL with crates colored different colors

The rates will be monitored using the rcm.sh script. There is a tab labeled "FCAL g" which shows the rates for each crate. Figure 1 shows the correspondence with crate and FCAL location where the colors represent the rocfcal number. The bottom of "FCAL g" gives a more detailed view of 12 specific channels symmetric about the beam pipe.

The plot title is formatted like FCAL_X_Y where X and Y are in the coordinates of the hall and the origin is along the beam axis. The coordinates used are:

  • Row 1:
    • FCAL_2_0
    • FCAL_0_2
    • FCAL_-2_0
    • FCAL_0_-2
  • Row 2:
    • FCAL_16_0
    • FCAL_0_16
    • FCAL_-16_0
    • FCAL_0_-16
  • Row 3:
    • FCAL_29_0
    • FCAL_0_29
    • FCAL_-29_0
    • FCAL_0_-29

Turning On The FCAL In Stages

Fig. 2. In red are the bases with a non-zero HV setpoint
Fig. 3. In red are the bases with a non-zero HV setpoint
Fig. 4. In red are the bases with a non-zero HV setpoint

To avoid damaging PMTs from high rates near the center of the beam pipe the FCAL will be turned on in 3 stages. The steps are as follows:

1. Ensure the initial HV setpoint for all channels is 0 by clicking on the "SAVE/RESTORE" button in the FCAL GUI and selecting "Restore FCAL HV Setpoints" and selecting "SetAllTo0Volts.snap" file

2. Ensure the HV is enabled by clicking on the "ALL FCAL HV" button and selecting "Turn On All Bases". This is an expert only operation

3. To turn on the Outer portion of the FCAL select the "Restore FCAL HV Setpoints" option in "SAVE/RESTORE" and select the snap file "OuterToEdgeVoltages.snap". Figure 2 shows the results of selecting tis snap file, the blue blocks have a 0 HV setpoint and the red block have a non-zero HV.

4. To turn on the Middle portion of the FCAL select the "Restore FCAL HV Setpoints" option in "SAVE/RESTORE" and select the snap file "MiddleToEdgeVoltages.snap". Figure 3 shows the results of selecting tis snap file, the blue blocks have a 0 HV setpoint and the red block have a non-zero HV.

5. To turn on the Inner portion of the FCAL select the "Restore FCAL HV Setpoints" option in "SAVE/RESTORE" and select the snap file "InnerToEdgeVoltages.snap". Figure 4 shows the results of selecting tis snap file, the blue blocks have a 0 HV setpoint and the red block have a non-zero HV.


Routine operation

A shift taker will need to monitor the environmental and base sensors through a GUI interface. The darkroom is equipped with 4 sensor boxes, each reads the temperature, humidity, and light conditions inside the darkroom. Each of the 2800 bases are equipped with temperature, high voltage, and current sensors. The following instructions are for non-experts during routine operation. Operations beyond what is specified here shall only be performed by the system expert or under his/her direction. If the expert directs an operation outside the ones described here, a specific note must be entered into the log book.

Control and monitoring of the system is accomplished using the Hall D graphical user interfaces (GUI) to EPICS [1] [2]. A description of how to bring up the GUI screens can be found in Section Slow Controls. We briefly describe the use of these interfaces:

Checking the Darkroom environment

Fig. 5. MyaViewer screen for monitoring the FCAL Darkroom Temperature, Humidity, and Light

Environmental sensors record temperatures and humidity conditions inside the dark room. Automatic alarm systems will be in place in the event an environmental sensor reads a value above what is considered safe or normal operating conditions. In the case an environmental alarm is triggered all power to the bases will be turned off. A non-expert user will call an expert user and do nothing else.

The FCAL Darkroom environmental variables can be viewed using MyaViewer and selecting the group 'HD_FCAL_ROOM'

HV Alarms

The FCAL will alarm when a base reads back a current greater than 14.9 mA for 30 consecutive minutes. In the case an alarm is tripped a shift taker can disable the HV to that bases from the alarm handler.


Voltage control

Fig. 6. User screen for the FCAL. This is the primary screen used for a non-expert shift taker. With this GUI a shift taker can save/restore HV setpoints for the 2800 bases, turn off/on the bases, or select 25 bases to display in a table (by selecting a quadrant then the strand on that quadrant, and finally the quarter to display)

The bases generate their own high voltage which can be set through the GUI interface. A non-expert user will only be able to do the following from the non-expert shift taker GUI shown in Figure 2:

  • Restore HV setpoints
    • Click 'SAVE/RESTORE' and select 'Restore FCAL HV Setpoints'
  • Select 25 bases to display in a table
    • This is done by first selecting a quadrant, then selecting a particular strand in that quadrant, and finally choosing which quarter of that strand to display
    • For convenience you can type the column and row number then use the right area of the FCAL GUI. Then press "Submit" and the chain starting with quadrant then strand and position in that strand is output.

Below is a brief explanation of the other functionality capable on the non-expert GUI, but a shift taker must be directed by an expert to use any of the following:

  • Enable HV on all bases
    • Click 'All FCAL HV' and select 'Turn On All Bases'
  • Disable the HV on all bases
    • Can be done in 2 ways: 1) At the top of the screen there is a red outline area with 'Turn OFF ALL' written, click the 'HV' button to power off all bases, 2) click 'All FCAL HV' and select 'Turn Off All Bases'
  • Save HV setpoints
    • Click 'SAVE/RESTORE' and select 'Save FCAL HV Setpoints'

Correlating strands with FCAL coordinates

Below is slow control map where each color represents a different strand. Each strand is daisy chained to 100 bases. This view is looking upstream at the FCAL and the strands are numbered from 1 to 28. Strand 1 to 14 is only the left half of the FCAL and starts in the upper left corner and ends at the lower left corner. Strand 15 to 28 starts in the upper right corner and ends at the lower right corner.

FCAL Slow Control Map Strands.png

FCAL features a shift taker should be aware of

It is known that some bases are either not setting their HV properly or have other unwanted behavior so there will be holes in FCAL occupancy plots. Below is an explanation of some of the reasons a hole may appear:

1. After an IOC reboots a few bases will disable it HV, ~ 4 bases per reboot. It is unknown why this happens but an expert will re-enable the HV for those bases every morning.

2. Recently a few bases have been observed to read back a HV around 2200 Volts. It was verified that this is a real read back and the reason is still unknown. If a base reads over 2200 Volts that base will automatically have its HV disabled. The current solution is to recycle the power to that strand, this is an expert operation and only experts can will resolve these issue.

It's good to also be aware of the voltage setpoints in the EPICS GUI. It is known that the FCAL EPICS IOC crashes about every 4 hours. The IOC is setup to automatically reboot but when it does the HV setpoints will all be set to 0. Do not try to fix the issue or call an expert, this is a know problem but the setpoint seen in EPICS is not a real reading of the base. The base is essentially unaware of the IOC reboot and will continue enabling its HV with no interruption.

Interlocks

Power supplies for the bases are interlocked and will be turned off when a) both doors to the dark room are open simultaneously, b) environmental sensors (light, temperature or humidity) in the dark room exceed preset limits or c) there is a loss of power. Should the interlock system trip, an expert should be called to reset the condition. Changes to the interlock settings are only allowed by an expert, or under his/her guidance.

Expert personnel

The individuals responsible for checking that the FCAL is ready to take data and setting its operating parameters are shown in following table. Problems with normal operation of the FCAL 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 FCAL system
Name Number Date of qualification
Manuel Lara (956) 622-8216
Adesh (757) 816-3649