Dr. Roland Beyer

Beam line scientist, radiation protection officer FWK
Nuclear Physics
Phone: +49 351 260 3281

The nELBE beam scanner

At nELBE a beam scanner is available to scan the spacial profile of the neutron beam. It consists of two plastic scintillator strips that are 1 m long/42 mm thick/11 mm wide. Each strip is equiped with two Hamamatsu R2059-01 photomultiplier tubes (PMT), one at each end. Both detectors can be moved by means of Berger-Lahr stepping motors. One detector moves in vertical the other one in horizontal direction.

How to move the detectors

The movement of the scanners is controled by means of a LabView program installed on PC FWK374.

The following steps have to be done to get the program started:

  Scanner H (horizontal) Scanner V (vertical)
  • connect to FWK055
rdesktop -z -x 0x80 -u ntofdaq -d FZR -g 1240x900 -k de fwk374
user name: ntofdaq
password: *******
  • open program folder (1)*
C:\Documents and Settings\ntofdaq\Desktop\Motorcontrol_nELBE
  • open program window (2)*
double click Motorcontrol_nELBE.exe
double click Motorcontrol_nELBE_2.exe
  • enter proper COM port and motor address (see Table 1 below) (3)*
COM4, Motor 1 COM3, Motor 1
  • start program (4)*
click "Ausführen" button
  • confirm error messages (5)*
click "OK" button
  • switch motor on (6)*
click "power on motor" button
  • reference motor (7)*
click "Ref" buttom
wait until scanner has reached zero position
* numbers in parenthesis corespond to the arrows shown in Figures 1 and 2

Figure 1: Illustration of the sequence to start the motor control

nELBE Motor Control Screenshot

Figure 2: Illustration of the sequence to start the motor control - Confirm error message

nELBE Motor Control Screenshot 2

Table 1: Assignment of the PMTs of the two scanner detectors

PMT H-up H-down V-left* V-right*
material EJ-230 EJ-200
size 1000x42x11 mm3 1000x42x11 mm3
movement direction horizontal vertical
COM port 4 3
motor address 1 1
zero position right* down
maximum position 865 mm 865 mm
beam position 435 mm 439 mm
voltage divider no. 55 10 1 26
HV channel 03/0 03/1 03/2 03/3
HV cable T1 T2 T3 T4
patch field channel 19 20 29 30
patch cable (12 m) 1 2 3 4
* in beam direction

Table 2: Recommended voltage combinations

PMT H-up H-down V-left V-right
HV channel 03/0 03/1 03/2 03/3
voltage / V 3000 2630 3000 2650
  2800 2480 2800 2500
  2600 2330 2600 2350
  2400 2150 2400 2200
  2200 2000 2200 2050
  2000 1700 2000 1800
  1800 1500 1800 1600

The different buttons and text fields have the following meanings:

Button Meaning Comment
  • Port
COM port of the USB to RS485 Converter Should be changed only before starting the program
  • motor adress
Address of the motor Can be changed by an internal rotary switch
  • desired speed
Velocity of the scanner used for the next movement

Can be choosen in multiples of 12.5 mm/min
Default value is 125 mm/min
Maximum value is 400 mm/min

  • distance
Distance to go during the next movement  
  • position (absolute)
Final position of the next movement  
  • power on/off motor
Button to switch on the motor Has to be pressed before any movement can be done
  •  <--
Move motor over user defined distance into positiv direction  
  •  Pos
Move motor to user defined position  
  • -->
Move motor over user defined distance into negative direction  
  • List
Load a list of position to be reached sequentially The list is an ASCII file containing one comment line and then a list of number pairs separated by a space corresponing to the position in mm to be reached and the time in seconds to wait at this position. Examples can be found in the program directory C:\Documents and Settings\ntofdaq\Desktop\Motorcontrol_nELBE
  •  Ref
Find absolute zero position The motor will move the detector until the limit switch is triggered and slowly move back about 3.5 mm.
  •  Lim+
Move 5 mm in negative direction This button has to be used, when the limit switch was triggered before the program was started.
  •  Lim-

Move 5 mm in positive direction

This button has to be used, when the limit switch was triggered before the program was started.
  • stop motor
Immediately stop current movement If the List option is in use and the detector is waiting at a certain position this button will come into effect not before the waiting time has passed.
  • quit program
Stop the program regularly  
  • kill
Stop the program irregularly  
  • current speed/position
Current velocity and absolute position of the detector  
  • reference/initalized
Displays that lights up green if the motor is inialized and/or referenced  

How to run a beam scan

To perform a beam scan the transmission DAQ has to be used and the following preparations have to be done (if not yet done):

  • tell the operators that you will do some test measurement, so that they should not change the beam settings and call you in case of a beam failure
  • do every thing mentioned above
  • replace Transmission Plastic by Scanner H/V on DAQ channel 00 and 01
move cables in room 250 from patch field 9/10 to 19/20 / 29/30
  • move to the "thickest" absorber
see Pb loop control and Absorber
  • start MBS and LEA
perform step 1-9 from "DAQ manual"
  • set scaler period to 5 s
in setup.ini: "sis3820_LNEtime = 5"
  • adjust supply voltage for both scanner
move scanner to beam position given in Tab.1 (velocity = 250 mm/min)
and adjust voltage (cf. Tab. 2) to get count rate of about 10-20 kHz
  • move both scanner to zero position
position = 0 mm, velocity = 250 mm/min

Two different kinds of beam scans are usually performed. A wide range scan with moderate velocity over the the complete distance the detector can move or a narrow range scan with lowest velosity over a distance just covering the beam. The former takes 34 minutes the latter 28 minuntes.

The following steps have to be done to perform the scan:

    wide range narrow range
  • move scanner to start position
set velocity to 250 mm/min    
set position 0 mm 335 mm
move to position (click "Pos")    
  • set scan velocity
set scan velocity 50 mm/min 12,5 mm/min
  • start DAQ
perform step 1-3 from "Running the DAQ" (DAQ manual)    
  • load position list
click "List" button wide_scan_v=50_start=0.txt narrow_scan_v=12.5_start=335.txt
  • wait until start position is reached again
  • stop DAQ
perform step 5-6 from "Running the DAQ" (DAQ manual)    
  • move scanner back to zero position
position = 0 mm, velocity = 250 mm/min    

Using the position list forces the scanner to move to the final position and immediately back to start position. This helps to determine the absolute position of the beam center.

The content of the position lists is as follows:


insert: [position in mm]spacebar[time of measurment in s]
850 0
0 0


insert: [position in mm]spacebar[time of measurment in s]
510 0
335 0