T-618: A project of E320 and LUXE (DESY) probing the LUXE Cherenkov detector concept at FACET-II

Description of the Experiment

The planned experiment aims to measure Compton electrons from the electron laser interactions arriving at the dump table of FACET-II. The prototype is an in-air system consisting of two complementary subsystems: a scintillating screen and camera system in the front and a Cherenkov detector in the back. The screen consists of terbium-doped gadolinium oxysulfide and the sensitive part of the Cherenkov detector includes 32 thin stainless-steel straws and optical fibers which are placed in air on top of Silicon-Photomultipliers.

The goal is to measure the Compton electron energy spectrum in various modes of the detector setup and determine its performance and accuracy under real physics conditions.

Mechanical Setup

In order to probe various detector configurations the Cherenkov detector part is mounted on a three dimensional stage, placed near the beam dump on the dump table, allowing movements into and out of the beam axis, up and down the Compton electron energy spectrum and a rotation around the vertical axis. These modes enable different sensitivities for different parts of the expected electron intensity range. Since 80/20 frames are used the detector can be easily adjusted to geometrical requirements.

The whole detector shown in the picture above (80/20 frames, screws, threaded rods, patch panels, motors, straw setups, cables, etc.) has a maximal dimension of (100 x 60 x 55) mm³ and a weight of 28 kg.

The Active Detector

The sensitive part of the detector consists two identical setups with several components:

1. Frame
2. Straws
3. Electronics Box
4. Darkening Shutter
5. Fibers
6. LED Box

In the following the quantities of only one of the two setups are given. 

NOTE: For the June experiment only one setup ("Box0") is mounted. It is placed such that the rotational axis of the straws is in between the two rows of straws.

1) Frame

All components in the setup are mounted on aluminium 80/20 frames and are supported by cable ties, velcro, screws and custom aluminium frames like

• 4 rods with max. 10 mm and min. 5 mm diameter
• 2 plates with (~135 x ~40 x ~8) mm³ each
• 1 electronics box

2) Straws

• Stainless-steel of type
• Produced via piercing method
• Cleaned but unpolished inside
• 3 mm inner diameter
• 0.1 mm wall thickness
• 200 mm long
• 16 straws
  • 8 in one row with 1 mm separation
  • 2 rows with 15.5 mm spacing
• The Cherenkov light produced inside the straws is reflected to the electronics box at one end of the straws
• Optical fibers are mounted on the opposite side

3) Electronics Box

The electronics box contains a custom PCB with Silicon-Photomultipliers and passive electronics components. The aluminium box is coated in a black, isolating paint and has the dimensions of  (~110 x ~60 x ~55) mm³.

Its lid has a specific cutout for allowing the straws and the darkening shutter to be mounted on top of the PCB. Inside the box the PCB is connected to 1 4-pin and 17 1-pin LEMO connectors.

4) Darkening Shutter

The darkening shutter is a 1 mm thick carbon plate which is placed between the PCB and the straws to mechanically cut of any created Cherenkov light. This allows for a background measurement of the detector.

5) Fibers

Optical fibers are mounted on the opposite side of the straws for the LED calibration system.

• The 0.6 mm fibers are coated in a rubber isolation which results in a outer diameter of 2 mm
• One end of the fibers is set in a brass cylinder with 3.6 mm diameter and mounted in the aluminium plate above the straws
• 2 times 9 fibers are bundled together (8 to the straw rows & 1 for reference)
• These two bundles and the two reference fibers are connected to the LED box

6) LED Box

THe LED box mechanically connects the two fiber bundles to one pulsed LED each. The LEDs are connected via two 5 m long, 2-core coaxial cables to the microcontroller box.

Microcontroller Box

The microcontroller box controlles the LEDs for calibration (4 LEDs in total) and a temperature readout from the electronics box. It contains an arduino and several passive components. It is connected via a +24V_DC power supply to the power switch at the dump table. Details are described in the Electronics Setup section.

Scintillating Screen

The used screen is of the type DRZ and consists of terbium-doped gadolinium oxysulfide (<Datasheet> ) and has a dimension of 100 x 100 mm² with a thickness of 0.5 mm.

Motors

The motors are used to move the straw detector on three axes (x, y, r). The motors are Permanent Magnet Stepper Motors (StepperMotorRS535-0489.pdf) in NEMA17 formfactor.

The motors move self-made stages of 1.5 mm threaded rods (x,y) and a toothed belt with translation gear (r).

Wiring

Motor phases and limit switches are connected as the following (might be in inverted order depending on rotation direction).

Alignement

• Stage has 230 mm length in x and y
• Angle range is -27° to +33° for r
• Center of straws is on rotational axis
• Limit switches are placed
  • at maximum for x and y
  • such that no mechanical obstacles (e.g. darkening shutter) move into beam axis (aka rotational axis) .

Controller

• The used motor controller is Newport XPS-D Motion Controller
• The used drivers are three Newport XPS-DRV01 Stepper Motor Drivers

• The motors are connected to the motor controller MC17 (FKG20-27)
• The IP address of the controller is 172.27.76.58
• For programming the controller:
  • Open web interface http://<ip address> and log in
  • Go to Stages → Add, remove or edit stages and create new file by duplicating and modifying old ones
  • Go to System → Quick configuration and assign the new driver file to the driver channel
  • Reboot and wait for Happy Sound 
• The following firmware is used:
  • LUXE_CherenkovDetector_X
  • LUXE_CherenkovDetector_Y
  • LUXE_CherenkovDetector_R

• XPS:LI20:MC17:M1 → x direction (transversal, into the beam (+x) and out (-x))
• XPS:LI20:MC17:M2 → y direction (vertical, up (+y) and down (-y))
• XPS:LI20:MC17:M3 → r direction (rotation around y, counter-clockwise (+r) and clockwise (-r))

Calibration

• x direction ranges from 0 mm → +229.541 mm ± 0.002 mm* (software range limit ± 232 mm)
• y direction ranges from 0 mm → +231.362 mm ± 0.034 mm* (software range limit ± 232 mm)
• r direction ranges from 0° → +59.388° ± 0.024°* (software range limit ± 60°)
• Straws perpendicular at r = 27° ± 0.2°**

*Standard deviation over 5 measurements

**Measurement accuracy with a ruler, (114.0 ± 0.5) mm distance from upstream side profile, 180 mm in -x from the rotation axis. This corresponds to an angle of arctan(±0.5 mm / 180 mm) =  ±0.16°

Placement 

It is planned to install the detector system on the dump table of FACET-II as shown in the CAD drawing below. The rotational axis of the straws will be placed on the beam axis when in operation.

• Straw carrier backwards edge to end of dump table: 25.10 cm
• Detector frame overlaps dump table: 23.45 cm
• Straw carrier frontwards edge to straw frame aluminium rod: 13.7 cm

Important motor positions (from 0 position):

• x = 194.0 mm→ Rotational axis in beam
• y = 114.0 mm → First straw center height (ch8) in gamma beam (according to mark on dump table → 6.35 mm under global 0 mm)
• r = 27.0° → Straws at 0° 
• For FACET coordinates (0, 0, 2017.2525) m (z is global position of rotational axis, which is in between the two straw rows) → (x,y,r) = (194.0, 120.35, 27.0) 

Fibers in parking position x = -66mm, diag 140mm from photon axis

outer edge (top) of straw frame in parking position x = -90mm, diag = 100 mm from photon axis

The exact placement on the dump table in FACET coordinates is (top right corner):

• x = -0.5969 m
• y = -0.3060 m
• z = 2017.5895 m

Upper Al rod to first straw → ~6.5 cm

Lower Al rod to first straw → ~7 cm

Electron 10 GeV beam 61.3 mm below gamma axis at LFOV.

→ At EDS rotational axis → 61.3 mm * ( (2017.2525 - z_Dipole) / (2015.59 - z_Dipole) ) = 71.86 mm

→ Default y position is 14 mm → when gamma beam above AL rods and electron 10 GeV below:

• y = 114 mm → gamma beam on first straw
• y -= 70 mm → e- beam on first straw
• y -= 30 mm → y = 14 mm default position!

Electronics Setup

Electronics Details

The setup makes use of several custom and self-designed electronics components including

1. Silicon-Photomultiplier electronics
2. Darkening shutter
3. Microcontroller
4. Readout electronics
5. Scintillating screen

1) Silicon-Photomultiplier Electronics

• Hamamatsu S14160-3015PS s14160-1315ps.pdf
  • ~40k pixel with 15 µm pixel size
  • 3x3 mm² sensor size
  • ~5*10⁵ gain
  • Breakdown voltage ~38 V
• SiPMs sit on a self-designed PCB (PCBSchematics.pdf)
  • Temperature sensor of type PT1000 (FST08-B-1K0E.pdf)
  • Contains passive bias and signal filters 
  • The PCB is mounted inside the electronics box ("Box0" & "Box1")
  • All signal and bias channels are fed out via LEMO00 connectors
  • Temperature is connected to a 4-pole LEMO connector

2) Darkening Shutter

In order to move the darkening shutter (see Mechanical Setup) a magnetic switch is attached to the carbon plate. When +12 V_DC are applied the shutter is being pulled and the straws are optically disconnected from the SiPMs. The datasheet can be found here DatasheetMagneticSwitch.pdf.

3) Microcontroller

The microcrontroller box contains a self-made PCB holding an Arduino Micro and various analog components (MicrocontrollerSchematics.pdf). It has two purposes:

1. SiPM calibration system
   1. Generating a pulse to control the 4 LEDs inside the 2 LED boxes
   2. LEDs are blue LEDs (DatasheetBlueLED.pdf) which are mechanically modified to have a flat lens
2. Temperature sensor
   1. Reading the voltage variation over the temperature sensor
   2. 50 times every 5 s → Mean and standard deviation returned

In order to communicate with the microcontroller over long distances a half-duplex serial communication using TTL is being used. Furthermore, a TTL trigger signal is being generated for a timed readout of pulsed LED signals.

A second microcontroller board is sitting close to a PC to establish a Serial-to-USB interface. It is configured as the following:

• Baudrate: 9600
• Bytesize: 8
• Parity: None
• stopbits: 1
• Commands:
  • "T" : Reads back temperature value
    • Returns: "T=0.00 0.00 0.00 0.00 "
    • With temperature1 std1 temperature2 std2 (left to right)
    • If no temperature sensor connected → "T=NaN NaN NaN NaN " returned
  • "R=0" : Sets pulser frequency (int value)
  • "L=1111" : Binary mask for LED channels → "L=0001" enables LED0 only 
  • "U=13000" : Sets LED voltage (int value in mV) of LED0 and LED1
  • "V=13000" : Sets LED voltage (int value in mV) of LED2 and LED3

4) Readout Electronics

For the SiPM signal readout the CAEN VX1742 sampling digitizer (located in FKG20-24) is used. 

• 12 bit resolution
• Up to 5 GS/s
• 1024 bit buffer size
• 32 channels
• 2 trigger channels
• TTL or NIM trigger input
• DatasheetCAENVX1742.pdf

The DAQ software is self-programmed in C++ based on this example: https://github.com/samdejong86/CAEN-v1730-DAQ.

5) Scintillating screen

The camera setup includes a scintillating screen (Type ) and camera (Basler ) which is placed before the Cherenkov detector.

• Placement:
  • (x,y,z) = (-0.02, 0.669, 2016.6595) m (mounting screw location in facet coordinates, uncertainty of +/- 0.02 m) 
  • tilting angle of 36°
  • Camera focused at center of screen at motor position y = 55 mm
• Networking
  • POE adapter in AC power strip channel 16 (ACSW:LI20:NW06:16XXX
  • IP address 192.168.100.5
  • Ethernet at dump table to FKG20_2434 back channel 1
  • LAN2 port of DAQ PC configured with 192.168.100.2
• Trigger splitted from camera trigger pm03-01

SiPM Power Supply

The SiPMs are powered via the Keysight E36234 from the electronics rack (FKG20-24) via a long BNC cable to the dump table.

• 2 channels
• 0 to 60V_DC
• ~5mV_PP ripple noise
• Usage here: 1 channel with 36V_DC to 45V_DC

Signal Cables

*E320 patch panel has common ground!

**Gallery patch panel (FKG20-24) has common ground!

***Cables ch07&15 are 48cm longer!

Trigger Logic

The NIM pulse width of discriminator outputs is set to 20 ns by default.

By tuning the first discriminator one can change the pulse timing at the OR input.

The final NIM trigger pulse is 60 ns long.

The delays are tuned such that pulse trigger input and signal are ~300 ns apart (see picture below: pulse trigger in (yellow), dig. trigger in (blue), LED signal ch0 (magenta).

For the beam trigger the delays are tuned such that trigger input and signal are ~ ns apart (see picture below: pulse trigger in (yellow), dig. trigger in (blue), LED signal ch0 (magenta).

The beam trigger is delayed via the gate and 5*20 m BNC cable (~5*100 ns) by ~1700 ns. The trigger signals for TR0/1 is delayed by aditional ~5 ns and is 10 ns long.

The beam trigger is received at the VME crate in FKG20-24:

This trigger can be controlled in facethome:

• Experiment LI20
• FKG20-24 level 35
• Triggers
• Front panel → No 2

Readout and DAQ

EPICS

• to find process variables: $ eget -ts ds -a name ACSW:LI20:NW06:13%
  • eget -ts ds -a name is the command to search
  • ACSW:LI20:NW06:13 is the known part
  • % is the wildcard
• the other (slower) option is $ findpv ACSW:LI20:NW06:13%

•  the data directory is facet-srv20:/nas/nas-li20-pm00/T618/epicsData/ before transferring the EPICS data to our machine

FACET DAQ

• can be started via: facethome → Physics Apps... → FACET DAQ
• scan functions are saved in: /usr/local/facet/tools/matlabTNG/F2_DAQ/scanFunc_XYZ.m
• an example scan for the vertical position scan is: scanFunc_luxe320_Y.m
• darkening of the SiPM can probably not be scanned since it uses two EPICS addresses (POWERON and POWEROFF)

Computer

The network of our machines looks as follows:

• gateway computer flaci@cpu-li20-sp01, accessible from mcclogin, facet-srv*, or thinsrv01
• digitizer computer luxelab@192.168.0.2 (in FKG20-24), accessible only from cpu-li20-sp01 (in FKG20-01)
  
  • ssh flaci@cpu-li-sp01
  • ssh luxelab@192.168.0.2

An example configuration file for the permanent tunnel is here: ssh-config-file

It also includes an example of a proxy jump. This can be applied the same way to go directly into facet-control.

Setup the Tunnel between luxelab and facet-srv20

• set up the SSH tunnel between the luxelab computer and the facet-srv20 we use the following command:
  
  • [fphysics@facet-srv20 ~/ivoschul ]$ ssh -F .ssh/config -N -f luxelab
  • -F defines the config file which is not at the default location, it defines
    • the users, key-pair, IPs, and proxyjump
    • RemoteForward 62882 localhost:62882
    • RemoteForward 62883 localhost:62883
  • -N makes the session non-interactive
  • -f puts the session in the background
• to kill the session we can use the following:

  • [fphysics@facet-srv20 ~/ivoschul ]$ ps aux | grep 'ssh -F .ssh/config'

  • this will output three processes, one is the grep command and two are the ssh connections to the gate and to the luxelab
  • get the process ID of the connection to the gate and kill it with [fphysics@facet-srv20 ~/ivoschul ]$ kill processID

Run the Time Server

• create the tunnel between luxelab and facet-srv20 with the proper port forwarding (see above)
• log in to facet-srv20
• create or reattach the screen session (usually called ivoschul_timeSrv)
• run $ python /home/fphysics/ivoschul/timeServer.py
• log in to luxelab
• run $ /home/luxelab/LUXE320/control/timeClient/build/timeClient
• it should print the server and client times

Port Usage

• 62882 / 62883 → ports between luxelab and facet-srv20
• 62884 → Ivo's jupyter server on facet-srv20
• 62885 → daq server on luxelab
• 62886 → Antonio's jupyter server on luxelab

Data Backup

• data backup is triggered via crontab
  • $ crontab -l → lists all active crontabs
  • $ crontab -e → allows to change the crontabs
  • our crontab entry is
    • 5 * * * * /home/luxelab/LUXE320/dataBackup.sh
    • 5 * * * *  → run every 5 minutes
    • /home/luxelab/LUXE320/dataBackup.sh → shell script that does get executed
• the backup script is dataBackup.sh contains

  • rsync -av --log-file=/home/luxelab/LUXE320/rsync.log /home/luxelab/LUXE320/data/ /media/luxelab/data1/backup_LUXE320/

  • -a → archive (fundamental backup option)
  • -v → verbose
  • --log-file → the verbose output is sent to rsync.log
  • source:  /home/luxelab/LUXE320/data/
  • destination: /media/luxelab/data1/backup_LUXE320/

Synchronization

One issue with the setup is, that the digitizer DAQ is not in the FACET network. Therefore, it has no synchronization of the events. Various options exist to synchronize the data. One option is using timestamps on both systems and synchronization via some protocol. This was not successful so far. The other option is to use the data itself.

Charge/Position Correlation

One idea is to use the charge and/or position dependence of a signal in both systems. This could be a BPM, toroid, or camera data from the EPICS side and signal amplitude in a straw on the LUXE EDS side. The events can be shifted such that the correlation between the two test variables is maximized.

Beam Background

The FACET DAQ provides the option, to perform a beam background measurement before a run/scan. In that case, the beam is blocked by the MPS shutter (Brendan, slack, 06/12) for some events. This gives a clear start signal.

Pockel Cell

The Pockel cell can control the electron beam on an event basis. The corresponding EPICS variable is TRIG:LT10:LS04:TCTL (Spencer, email, 06/16). The idea is that at the beginning of a run, the cell is activated/deactivated in a specific pattern that allows the events to be matched based on that pattern.

Machine/Beam Trigger

1. open facethome (from the control network)
2. navigate to the Experiment - LI20 section
3. select the Triggers... menu in the FKG20-24 section
4. our trigger is channel 2 in the front panel section, called trigger FP2
5. we use the following settings
   
   1. beam trigger (coming from trigger RP2)
   2. normal polarity
   3. 1000 ns width
   4. 10 ns delay

AC Power Switch

• ACSW:LI20:NW06:13XXX
• ACSW:LI20:NW06:14XXX
• ACSW:LI20:NW06:15XXX

DAQ settings

Time schedule and planning

Pre-PAMM

• Fix EPICS motor control
  
• Create power switch (darkening) control
• Ivo Schulthess Create temperature logger control
• Test detector movements
• Test setup with LED
• Remove box1 (and cabling of it)
• Antonios Athanassiadis Documentation of commissioning
• Straw alignment with respect to rotation axis
• Count signal cables 

PAMM 06/04

• Turn of XPS controller
• Bring detector into tunnel
• Align detector on optical table (make notes!!!)
• Connect and test motor controller
• Define detectors parking position
• Connect and test power switches for darkening
• Place, connect, and test the arduino (above table?)
• Connect trigger, communication, and signal cables
• E320 patch panel has common ground?
• Measure motor position for being in the beam
  
• Measure distance beam window to straws/rotational axis 
• Set up trigger delays
• Test setup with LED
  
• Selfie with detector
• Foto Arduino front panel
• One fiber calibration
• LED Voltage/SiPM gain scan
• fight for PP-06 J16 and Spencers channel

Post-PAMM (Pre-Beamtime)

• Write EPICS / CAEN communication
• Create runlist planning
• Test CAEN saving on stop
• Test CAEN saving every N event
• Create main control script
• Extend quickDraw script
• Tidy up computer, put everything in one directory
• ctrl-C proper disconnect
• Update trigger scheme
•  

Measurements

Move-in procedure

1. SiPM bias at 0 V
2. Motor homing (0, 0, 0), out of beam
3. Set dipole to 10 GeV 'LI20:LGPS:3330:BACT'
4. Park beam at TD11
5. Move:
   1. x = 194 → beam in the center of straws
   2. y = 14 → beam axis 30 mm above Al profile, electrons between Al profile and straws
   3. r = 27 → perpendicular to beam
6. De-park beam
7. SiPM bias at 42 V

Move-out procedure

1. SiPM bias at 0 V
2. Park beam at TD11
3. Move home before end switches:
   1. r = 2
   2. y = 5
   3. x = 5
4. De-park beam