1. Timepix+GEM project Field cage simulations
M. Alfonsi, G. Croci

2. Preliminary studies - outline
TOOLS
Ansys or Garfield/neBEM for the field map calculation
Garfield for the plots and the results
METHOD TO EVALUATE FIELD DISTORSION
Definition of the geometries to study
No field cages as reference case
Benchmark graphs
Definition of a benchmark quantity
23/03/2010
M. Alfonsi (CERN)

3. Geometry under study Ansys Garfield Active region: ± 0.7 cm 23/03/2010
M. Alfonsi (CERN)

4. Geometry under study (II)
5 cm field cage
Alternate ceramic walls and metallic rings
The reference case is the 5 cm drift region without any metallic ring
Geometrical parameters are:
Number of rings
Ceramic wall thickness
Metal thickness, i.e. how far are field electrodes from the active area
23/03/2010
M. Alfonsi (CERN)

5. Reference case
23/03/2010
M. Alfonsi (CERN)

6. Rings = 3 metal 0.8 mm far
23/03/2010
M. Alfonsi (CERN)

7. Benchmark parameter definition
Evaluation of: √ (Ex2 + Ey2) / Ez over a grid of ~ points in the volume of interest: ± 1 cm (x-y direction) 0 ÷ 5 cm (z direction)
Region of interest Grid of ~10000 benchmark points
Active region: ± 0.7 cm
23/03/2010
M. Alfonsi (CERN)

8. Preliminary results Geometry Average distorsion
Maximum distorsion (place)
No field electrodes
Ansys (refined 1, 0)
8.60%
26.4% at (1.0, -1.0, 0.8)
neBEM
2.22%
12.26% at (-1.0, 0.4, 3.4)
3 rings, 0.8 mm far
ANSYS
0.998%
5.51% at (1.0, 1.0, 0.8)
23/03/2010
M. Alfonsi (CERN)

9. Problems & Plans
Increasing the number of field electrodes, neBEM fails and ANSYS generate a too large number of elements for GARFIELD
I will use directly ANSYS for calculations
I will vary the number of field electrodes and the distance of them from active area
I will keep the ceramic wall at the same distance (if computation is faster)
23/03/2010
M. Alfonsi (CERN)