Milliqan logo.png

Get access to the MilliQan cavern (USC55 dranaige gallery)


Following the dosimetry service instructions:

Self-rescue mask training


Access should then be requested through Adams (it could also be good to ask for the access to P5 surface building)

1. Trigger Board

The Run 3 MilliQan detector is triggered using a trigger board documented here Trigger Board Documentation. The trigger board takes LVDS inputs from each group (pair of two channels) in a CAEN V1743. The CAEN boards send out triggers for these 8 groups that are the or between two channels (0&1, 2&3, ..., 14&15). In the trigger board the LVDS inputs are then used to determine if a global trigger should be sent to the CAEN boards. The trigger is sent out of the SMA output connectors on the trigger board, with each SMA connector outputting the trigger signal for one CAEN board. This trigger is sent into the trigger input on the face of the CAEN board.

Trigger Board

Trigger Board Inputs/Outputs

The trigger board has 64 LVDS inputs, 16 SMA outputs, 16 SMA inputs, 4 pairs of central I/O pins, and space for an extra 16 SMA outputs. In the center of the board there is a connector for a usb blaster next to the FPGA that is used to program the firmware. Finally, there is a usb connector which can provide power to the boards as well as interact with the board over serial (VME connector can also provide power).

Bar Detector

The bar detector has 5 CAEN boards (80 input channels) to accommodate the 78 needed channels.

Channels needed:

  • 64 PMTs for the bars
  • 12 PMTs for the veto slabs (2 PMTs each for 2 top, 2 left, and 2 right slabs)
    • 4 PMTs for 2 top slabs
    • 4 PMTs for 2 right slabs
    • 4 PMTs for 2 left slabs
  • 2 PMTs for the front and back slabs.

CAEN Board Channels.png
PMT to CAEN channel mapping for the bar detector. Diagram shows 4x4 PMTs of each layer and the CAEN channel that each is plugged into. CAEN channels are labeled as the digitizer, group, and channel that each PMT is plugged into. Ex. The top left bar in layer 0 of the bar detector is plugged into CAEN digitizer 0, channel 0 (part of group 0).

The trigger board takes CAEN group triggers as LVDS inputs. The trigger groups are mapped to the LVDS pins in the below image.

Trigger board LVDS to CAEN group trigger LVDS wiring map.

Each CAEN board has 8 group triggers sent out of the top 8 LVDS pairs. The bottom 8 CAEN LVDS pairs output the BUSY, VETO, TRG, and RUN signals. Only the BUSY, VETO, and RUN signals are propagated from board to board in a daisy chain. The BUSY and RUN signals are also propagated to the trigger board. The BUSY signal prevents the trigger board from firing when the CAEN digitizers are busy, and the RUN signal allows timing synchronization between the trigger board and the CAEN digitizers.

Trigger Board LVDS Inputs:

  • 40 trigger inputs (8 each from 5 CAEN digitizers)
  • BUSY signal from final CAEN digitizer
  • RUN signal from final CAEN digitizer

The trigger board is also used to propagate a 50MHz clock to all of the CAEN digitizers. The first pair of central I/O pins on the trigger board outputs a 50MHz clock. This is then plugged into the CLK IN of the first CAEN digitizer and daisy chained between digitizers using clock cables between CLK IN and CLK OUT. Any delay from propagating the CAEN signal between boards can be accommodated by changing the firmware on the CAEN boards. There is firmware to introduce 5ns and 7.5ns delays on the CAEN digitizers allowing synchronization to within 2.5ns.

The CAEN digitizers are triggered by the SMA outputs from the trigger board plugged into the TRG IN of the CAEN digitizers. There are 16 primary SMA outputs on the trigger board and each CAEN digitizer gets its TRG IN from one of these outputs. The CAEN TRG IN and TRG OUT are limo connectors.

Wiring map between CAEN digitizers, trigger board, and computer.

The CAEN digitizers send/receive signals from the computer over optical link. The optical cable is sent out of the DAQ computer and daisy chained between digitizers and then sent back to the computer. There is also a serial link between the trigger board and the DAQ computer that allows us to send/receive data from the trigger board. The serial USB is plugged into a USB port on the DAQ computer and a USB extender is used to connect to the trigger board. This link is used to:

  • Set coincidence time
  • Toggle output enable
  • Reset the trigger board clock
  • Set triggers
  • Get list of triggers fired and time of firing
  • Set dead time
  • Set prescales
  • Set trigger mask

The final connection on the trigger board is the JTAG connector which is used to reprogram the firmware on the FPGA. This JTAG connector plugs into a USB port on the DAQ computer.

Trigger Logic

Within the trigger board there are 8 triggers hard coded into the firmware. These 8 triggers are checked every clock cycle of the trigger board's 50MHz clock. If any trigger is fired this will fire all 16 SMA outputs. The trigger that is fired will also be recorded in a bitstring along with the time that it was fired. The bitstring records the triggers fired within a 100ns coincidence window started when the first trigger fired.

The current trigger bits are:

  1. 4LayersHit - at least one hit group in all four layers
  2. threeInRow - at least one hit group, in line, in each of three layers
  3. twoSeparatedLayers - at least one hit group in each of two non-adjacent layers
  4. twoAdjacentLayers - at least one hit group in each of two adjacent layers
  5. NLayersHit - at least one hit group in each of N layers, where N can be changed in a config file
  6. External - an external trigger signal from a pulse generator, the slab detector, or the LED flashing system
  7. gtNHits - at least N hit groups anywhere in the detector, where N can be changed in a config file
  8. internalTrigger - any of the digitizers provides a trigger signal using their own internal logic

These triggers bits can then be turned on/off individually by the global trigger which is a bitstring. The bits in the global trigger bitstring correspond with the numbering of the above list.


  • 4Layers Hit -> '00000001'
  • threeInRow or gtNHits -> '01000010'

Output of Triggers Over Serial

The trigger board keeps a list of the last 8 triggers fired along with the time they were fired. This is encoded into a 64 bit number where the first 56 bits is the clock counter and the last 8 bits are the trigger bits.

Ex. If triggers 0, and 4 both fire within the coincidence window starting at 300000000 clock cycles the output bitstring would be 0b10110010110100000101111000000000 | 00010001

2. DAQ Software

Synchronizing CAEN Digitizers

The CAEN digitizers are synchronized using a 50MHz clock created by the trigger board and propagated by clock cables daisy chained from CLK IN to CLK OUT. The delay between digitizers is accounted for by changing the firmware on the digitizer. The process to synchronize the digitizers is detailed below.

  1. Run the synchronize script ./Synchronize. This will open links with the digitizers and display the following options:

[s]: start run

[c]: check clock alignment

[q]: quit

  1. Press c to check clock alignment. The 50MHz clock is now output from TrigOut on the face of the digitizers.
  2. Plug TrigOut from the boards into an oscilloscope and trigger on digitizer 0.
  3. Look at the time difference between clocks for digitizer 0 and 1. A PLL delay on digitizer 0 will affect the clock out (ie. delay the clock for digitizer 1).
  4. Quit Synchronize and open the CAENUpgraderGUI (caen/new/CAENUpgrader-1.7.1/CAENUpgraderGUI/)
  5. Select Upgrade PLL and the type of board (V1743)
  6. Select the upgrade file desired from the directory "caen/firmware/PLL/". There are delays of 0, 5, and 7.5ns. Reminder that the delay will be on the output of the selected board.
  7. Select OPTLINK as the connection type. The link number is the port in the optical link card (should be 0). The "bd number" is the number of the board in the chain. Leave the base address blank.
  8. Click upgrade and run Synchronize script again to check synchronization. Note: you may see the below error because the PLL files are .rbf files, click OK.
  9. Repeat successively with all boards until they are synchronized.

Example of matched digitizer clocks (left). The CAEN Upgrader GUI (right).

3. Run 3 Construction Instructions

Slab PMT Attachment and Testing Procedure

Overview: Follow PMT attaching procedure for first PMT. Then follow testing procedure for first PMT. If the rates are below 10kHz continue by attaching the next PMT. After each PMT is attached check the rates using the first PMT. Once all PMTs are attached, connect the base to each PMT and check the rates and if below 10kHZ record the rates. Otherwise check for light leaks until each PMT shows rates under 10kHz.


  • 2 people
  • 2 inch electrical tape
  • 1/2 inch electrical tape
  • Scissors
  • Aluminum foil
    • 2 strips 2x4 inches
  • PMT mount
  • Oscilloscope (or Haascope, DRS, etc)
  • HV cable
  • BNC cable
  • PMT base

Attaching PMTs to Slabs:

  1. Inspect the PMT and slab:
    1. Look for any scratches or defects in the tape of slab/PMT
    2. Check to make sure the PMT has a mu metal shield that is close to the edge of the PMT
    3. Make sure no pins on the PMT are bent
  2. Write down the number of the PMT and slab in the google sheet
  3. Place the slab on its side between the supports on the table
  4. Remove the tape/tyvek covering PMT hole on slab
  5. Clean the opening on the slab and PMT face with paper towel and alcohol (don't rip tinfoil)
  6. Line up PMT on hole, notch on base should be facing towards face with slab label
  7. One person should hold the PMT firmly against the slab
  8. Second person folds foil strip and places it on top of PMT and in seam between PMT and bar
    1. Make sure the foil is pushed into the edges, this is where most light leaks are
    2. Tape foil to slab
  9. Repeat step 7 with second foil strip on bottom of PMT
  10. Use smaller tape to wrap around the PMT until foil is covered
  11. Use larger tape to cover slab to PMT on all sides
  12. Add the PMT mount and wrap small tape around the holder base
    1. One person should squeeze the mount together while the other wraps
    2. Be careful not to rip the foil with the mount
  13. Tape along mount to slab with tension to hold together
    1. Make sure to do this on both faces
  14. Wrap small tape around mount again to secure the tape from step 12
  15. Add more tape to slab to secure the tape from step 12
    1. Add enough tape to cover the rest of the mount
  16. Check size of PMT mount with calipers
    1. Size must be below 66mm
    2. If size exceeds 66mm unwrap and redo
    3. Can try using another PMT incase PMT is problematic


Slab Testing Procedure

  1. Set up the oscilloscope:
    1. Zero out the voltage offset on scope (or DRS, Haasscope, etc)
    2. Trigger threshold set to 16mV
    3. X-axis 2mus per division, Y-axis 0.1V per division
    4. Gain x10
  2. If this is the first PMT tested on the slab:
    1. Attach PMT base to PMT with HV +1450V
    2. Make sure HV is off while attaching, turn on once attached
  3. If this is not the first PMT tested on the slab, continue testing rate with first PMT
    1. This ensures change in rates is due to attachment of new PMTs
  4. Check the rate on the oscilloscope
    1. Should be between 1-10kHz
  5. If above 10kHz perform checks:
    1. Use dense material, blanket, felt, etc over problematic spots: corners, PMT mounts, holes for PMTs
    2. Light leak tester can be used if rates are low enough (close to 10kHz)
    3. Add foil and tape to problematic areas
    4. If material is added recheck size of mount with calipers (must be 66mm or less)
  6. Add the radioactive sample and check rates again
    1. Should increase by ~100kHz
  7. If rates are under 10kHz continue
  8. Attach next PMT and retest rates
  9. Once all 4 PMTs are attached and tested:
    1. Attach the PMT base to each PMT sequentially
    2. Check the rates of the PMTs themselves, should remain under 10kHz (w/o source)
    3. Record rates w/ and w/o source in google sheet
    4. If above 10kHz perform checks
  10. If all rates of all PMTs are below 10kHz slab is complete

4. Links to Important Documents

Below is a list of important documents for the MilliQanCollaboration Run 3 detector. This list includes google docs and git repositories.

Git Repositories

  1. MilliQanCollaboration DAQ
  2. Trigger Board Firmware
  3. MilliQanCollaboration DAQ GUI
  4. MilliQan Offline

Run 3 Construction Documents

  1. Run 3 Triggers
  2. Construction Schedule and List of Supplies
  3. Bar Assembly Guide
  4. Trigger Board Documentation
  5. Preparation and logistics
  6. Light leak tester info
  7. PMT base info

Other Links

  1. Run 3 MilliQan ELOG
  2. Cavern and demonstrator pictures
  3. Synchronizing CAEN Boards

5. MilliQanCollaboration Papers

  1. MilliQanCollaboration LOI
  2. Looking for milli-charged particles with a new experiment at the LHC
  3. Search for millicharged particles in proton-proton collisions at √s=13TeV
  4. Sensitivity to millicharged particles in future proton-proton collisions at the LHC with the milliQan detector
  5. Technical Proposal for the milliQan sub-detector

6. MilliQanCollaboration Collaborators

-- MichaelWilliamCarrigan - 2022-01-28 -- AntoineLesauvage - 2022-02-28

Topic attachments
I Attachment History Action Size Date Who Comment
PNGpng CAENDigiSync.png r1 manage 3652.1 K 2022-04-18 - 20:32 MichaelWilliamCarrigan  
PNGpng CAENV1743_side.png r1 manage 2545.9 K 2022-04-15 - 20:07 MichaelWilliamCarrigan  
PNGpng CAEN_Board_Channels.png r1 manage 122.4 K 2022-04-18 - 00:42 MichaelWilliamCarrigan  
PNGpng CAEN_LED.png r1 manage 125.0 K 2022-04-15 - 20:07 MichaelWilliamCarrigan  
PNGpng CAEN_LVDS.png r1 manage 98.9 K 2022-04-15 - 20:07 MichaelWilliamCarrigan  
PNGpng CAEN_OpticalLink.png r1 manage 118.7 K 2022-04-15 - 20:07 MichaelWilliamCarrigan  
PNGpng CAEN_V1743.png r1 manage 190.7 K 2022-04-15 - 20:07 MichaelWilliamCarrigan  
PNGpng CAEN_triggerIO.png r1 manage 164.9 K 2022-04-15 - 20:07 MichaelWilliamCarrigan  
PNGpng LVDSWiring.png r1 manage 649.1 K 2022-04-18 - 00:42 MichaelWilliamCarrigan  
PNGpng Milliqan_logo.png r1 manage 140.3 K 2022-02-02 - 20:43 MichaelWilliamCarrigan  
PNGpng PMTAttachment.png r1 manage 1220.6 K 2022-05-18 - 15:05 MichaelWilliamCarrigan  
PNGpng PMTSlabHolder.png r1 manage 1587.8 K 2022-05-18 - 15:03 MichaelWilliamCarrigan  
JPEGjpeg SlabPMT3.jpeg r1 manage 3206.0 K 2022-05-18 - 15:03 MichaelWilliamCarrigan  
JPEGjpeg SlabPMT_1.jpeg r1 manage 2422.7 K 2022-05-18 - 15:03 MichaelWilliamCarrigan  
PNGpng TriggerBoard.png r1 manage 2209.4 K 2022-04-17 - 23:04 MichaelWilliamCarrigan  
PNGpng TriggerBoardCAEN.png r1 manage 1146.1 K 2022-04-17 - 23:03 MichaelWilliamCarrigan  
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