Level-0 Trigger


The BGV trigger consists of scintillator plates with dimensions 30x30cm2, arranged in 3 stations. A pair of scintillators is located before the gas target and is used to veto interactions occurring upstream of the target chamber. A second trigger plane is placed downstream of the scintillating fiber (SciFi) stations and provides the trigger signal. A third trigger plane has recently been installed and will be commissioned during the LHC 2017 run. It will be used in coincidence with the second plane to reject background from the other beam and confirm a crossing particle produced in the gas volume by the correct beam.

Position of the L0 trigger scintillators around the BGV experiement :

full_sketch.png bgv_overview_4.jpg

Drawings of the scintillator plate and the light guide:

The PMT used is one from Hamamatsu : http://www.hamamatsu.com/us/en/product/category/3100/3002/H1949-51/index.html

Photos of a scintillator in the test lab:

IMAG0022.jpg IMAG0020.jpg
With this setup, it is possible to measure signal from cosmic particles, from the LED and to test the cards (high voltage and acquisition).

Measurement of the length of the cables in the tunnel :

Tunnel installation

Network devices information in the tunnel :

  • cfv-ua43-bgv : The control card of the vme crate
  • cfvm-ua43-bgv : The vme crate
  • Information on the configuration of the fan tray of the crate can be found here
  • More general information on front-ends can be found here, also mentioning the process for remote reset.
  • To login to these devices one needs to be a member of dscdev unix group

Cables connections :

Cable Id Channel Scintillator (2016 Run) Scintillator (2017 Run)
1425 362 Channel 3 Signal Bot Confirm Top
1425 363 Channel 4 Signal Top Signal Top
1425 431 Channel 1 Veto Bot Veto Bot
1425 432 Channel 2 Veto Top Veto Top
1425 355 Channel 3 HV Signal Bot Confirm Top
1425 356 Channel 4 HV Signal Top Signal Top
1425 358 Channel 1 HV Veto Bot Veto Bot
1425 359 Channel 2 HV Veto Top Veto Top
1425 434 LED Veto Top ?
1425 435 LED Veto Bot ?
1425 365 LED Signal Top ?
1425 366 LED Signal Bot ?

The length of each cable path can be seen below. Based on the 2016 setup we have a delay of 26ns, therefore L0 Latency setting of 115 on ODIN should be OK (to be verified).


VME Crate organisation :

  • Slot 1 : CPU/control card : cfv-ua43-bgv
  • Slot 7 : BRAN-B card (acquisition)
  • Slot 9 : High-Voltage card
  • Slot 12 : BOBR card

CAEN Modules

Two VME modules from CAEN were purchased in order to better control the trigger. These were the V812 constant fraction discriminator (CFD) and the V2495 programmable logic board.

Information on the firmware of the V2495

  • The documentation can be found here.
  • In order to install the firmware to the board a Windows/Linux machine is needed and a USB-miniUSB cable to connect to the front panel of the V2495
  • [Linux] - Install CAENVMELib, CAENComm
    • for an ubuntu14 machine also openjdk-8-jre [jdk] and a 64bit version of fdt2xx was also needed)
  • Then install CAENUpgrader utility
    • Then from the CAENUpdater select the following:
      • Action->Upgrade Firmware, Model->V2495, choose appropriate .rpd file / Connection type-> leave this as is - no VME Base address / Flash Memory-> Application 5, Skip Verify ticked
      • Upgrade - wait few minutes - should be OK !

Setting up the boards

For these examples we are assuming base addresses for V812 as 0xeeff0000, and for V2495 as 0x32100000 - as it is currently the case.

Setting up V812

Register Address Value Comment
Threshold Ch.0 0xEEFF0000 0xC8 Set threshold of ch0 (-5->-255 mV)
... ... ... ...
Threshold Ch.15 0xEEFF001E 0xC8 Set threshold of ch15 (-5->-255 mV)
Output pulse width 0xEEFF0040 0x64 Pulse width for ch0-7 (~20ns)
Output pulse width 0xEEFF0042 0x64 Pulse width for ch8-15 (~20ns)
Dead Time 0xEEFF0044 0x0 Dead time for ch0-7 (150ns)
Dead Time 0xEEFF0046 0x0 Dead time for ch8-15 (150ns)
Pattern Inhibit register 0xEEFF004A 0xFFFF Enable (all) channels

Setting up V2495

Register Address Value Comment
Input configuration Ch.0 0x32101800 0x0 Set threshold of ch0 (Enabled - not inverted)
... ... ... ...
Input configuration Ch.5 0x32101814 0x0 Set threshold of ch5 (Enabled - not inverted)
Control Register 0x3210181C 0x0 External LHC clock / Mon7=Coincidence / NIM

Data Acquisition

The data is stored on EOS, in the folder : /eos/bgv/data/L0Trigger

Two types of files are created : TriggerData _(unixTime).dat and BunchData _(unixTime).dat

The unixTime stamp tells from when the data starts in this file. The files are text files and are organised like this :

In order to monitor the data, the following script is present in the folder /afs/cern.ch/project/lhcbgv/L0Trig/scripts :

The script needs to be run from lxplus, there are 3 different ways to use it :

The arguments <start time> and <stop time> can be either unix : 1436190224

or UTC time in the format : "16/07/15 15:25"

Results example :

Here I show the results of a fill of 298 bunchs at 6.5 TeV. The high voltage of the PMT are all 1400V, the thresholds of the downstream scintillators are 200, for the upstreams it is 50. The logic is such that we create trigger signal only when signal is detected in both downstreams and nothing in the upstreams. This should correspond to interactions happening only in the gas tank.

To get the next plot, I used the command : python FullAnalysis_EOS.py -b "15/07/15 23:00" -l 30000

rate_16_07_15.png rate_16_07_15_zoom.png
On the left plot, we see that the higher rate for the the Downstream scintillitor, which agree with the fact that they have the smallest thresholds. The difference between the two can be due to slightly different gain. The "Veto" rate corresponds to the upstream scintillators in coincidence.

Next are the two Downstream scintillators which have bigger threshold and then "Hit" rate corresponds the downstreams in coincidence.

Finallly, the trigger rate is the one defined by the logic. It is around 400 Hz but without gas injected. With gas injected, the pressure should increase by a factor 10^3, so we can expect the rate to be around 400 kHz.

The script gives also as results the settings of the trigger system during the selected period of time.

All the plots and the trigger settings for all files can be found in the folder /afs/cern.ch/project/lhcbgv/L0Trig/Plots

The control panel :

This panel gives a live view of the results and control the acquisition card and the High-Voltage card.


One can access this panel with the following procedure:

  • ssh -X <username>@cs-ccr-dev1
  • /afs/cern.ch/project/l/lhcbgv/L0Trigger/Control_Panel

Other info

Notes from meetings:

LHCb Documents:

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf 2014_06_26--L0_Trigger1.pdf r1 manage 65.3 K 2015-03-24 - 11:26 PlamenHopchev  
PDFpdf Drawing1_Light_guide.pdf r1 manage 42.7 K 2015-04-20 - 11:30 QuentinVeyrat  
PDFpdf Drawing2_scintillator.pdf r1 manage 48.5 K 2015-04-20 - 11:30 QuentinVeyrat  
JPEGjpg IMAG0020.jpg r1 manage 2215.0 K 2015-04-20 - 11:30 QuentinVeyrat  
JPEGjpg IMAG0022.jpg r1 manage 1289.0 K 2015-04-20 - 11:30 QuentinVeyrat  
Unknown file formatxlsx L0CableLength.xlsx r1 manage 7.8 K 2015-04-20 - 12:10 QuentinVeyrat Excel file of the long cable length for the L0 Trigger
PNGpng L0_control_panel.png r1 manage 141.2 K 2015-08-14 - 11:45 QuentinVeyrat  
PDFpdf L0link_edms478756_2.pdf r1 manage 162.1 K 2015-03-24 - 11:26 PlamenHopchev  
PDFpdf V2495_BMS_firmware_description.pdf r1 manage 185.8 K 2017-05-23 - 12:10 UnknownUser caen_v2495_firmware
PDFpdf WienerFanTrayConfigInstructions.pdf r1 manage 162.9 K 2016-04-27 - 19:03 UnknownUser Wiener Fan Tray Configuration Instructions
JPEGjpg bgv_overview_4.jpg r1 manage 70.1 K 2017-05-23 - 10:27 UnknownUser BGV L0 Trigger Layout and naming
PNGpng bunch_16_07_15.png r1 manage 98.4 K 2015-07-17 - 09:42 QuentinVeyrat  
JPEGjpg cables_trigger.jpg r1 manage 29.7 K 2017-05-24 - 10:33 UnknownUser  
PNGpng data_format.png r1 manage 33.6 K 2015-07-06 - 16:10 QuentinVeyrat Data format
PNGpng full_sketch.png r1 manage 60.9 K 2015-03-24 - 11:26 PlamenHopchev  
PNGpng l0_sketch.png r1 manage 30.1 K 2015-03-24 - 11:26 PlamenHopchev  
PNGpng rate_16_07_15.png r1 manage 110.1 K 2015-07-17 - 09:42 QuentinVeyrat  
PNGpng rate_16_07_15_zoom.png r1 manage 104.7 K 2015-07-17 - 09:42 QuentinVeyrat  
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