The E166 Spectrometer.

  Positron tracks visualization under MERMAID field map μ=4  "using Wired3".

  • WIRED3 is a Java program that was developed to let physicsts visualize single event data on any platform. It has evolved into a browser for data from any source that either provides HepRep XML files or a HepRep-enabled HepEventServer. This data may be particle physics events, Geant4 detector geometries or some other hierarchical graphics data.

  • When E166_G4_SIM is coupled to wired3 via a HepRep files, one can have a very instructive positron/charged particle track visualisation in the vaccum chamber under the MERMAID magnetic field map (μ=4).

  • The spectrometer current for this simulation study is : 100 A.

  • The Lens current is : 0 A (Off)


    Animated top and perspective views are under    (click on the links below)

Top View (Anim) Perspective View (Anim)

    Track visualisation ( click on the below)

500 events 1000 events 2000 events 4000 events 8000 events 16000 events.


Relevant Parameters for the present simulation study (E166_G4_SIM)

Material and values

Positron energy

Uniform distribution [0 , 8.3] MeV.

positron beam shape at the conversion target

Disk 3 mm radius.

Positron (angular distribution)

Uniform in cos(ө) [0.99, 1] and Uniform in phi [0, 2π].

Reconversion target Material

Tungsten (W).

Reconversion target Thickness

0.5 X0.

Reconversion target radius.

Radius = 25 mm

Vacuum (vacuum chamber)

3E-18 Pascal

Vacuum chamber inner space

(H, L, W) 54 , 156, 132 mm fort the  small chamber

(H, L, W) 54, 334, 188 mm  for the big chamber

Entrance of the spectrometer.

Radius = 18.255 mm

Exit of spectrometer.

Radius = 23 mm

Jaws (momentum slit)

Maximum Opening at 30 mm

Distance (exit of spectrometer-reconversion target)

182.4 mm

Spectrometer magnetic field.

Alexander’s MERMAID calculation ( μ =4 ).

3D linear interpolation

Unitary cube method (3D local linear interpolation)

G4 tracking in a magnetic field “step length “

100 μm


Table 1: The most relevant parameters for the present Geant4 simulation study.


Karim Laihem, DESY Zeuthen, June 20th 2006.