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AllPixSimulation.md

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How to simulate in AllPix^2

Setup

In the folder allpixconf is a basic configuration for simulating 1000 events with CLICPix2.

[AllPix]
log_level = "WARNING"
log_format = "DEFAULT"
number_of_events = 1000
detectors_file = "placement.conf"

[GeometryBuilderGeant4]
world_material = "air"

[DepositionPointCharge]
model = "scan"
number_of_charges = 100
source_type = "point"

[ElectricFieldReader]
model="linear"
bias_voltage=-30V
depletion_voltage=-50V

[GenericPropagation]
temperature = 293K
charge_per_step = 10

[SimpleTransfer]
max_depth_distance = 5um

[ROOTObjectWriter]
include = "DepositedCharge", "PropagatedCharge", "PixelCharge"

The important variables are number_of_events which is how many points you are going to scan. This should preferably be a number N such that N = n^3 where n is a natural number, otherwise AllPix^2 will automatically adjust to the nearest number of such type (so better be explicit then implicit). The second important variable is number_of_charges which is how many "test" charges you place in one volume (in allpix^2 terminology voxel) and trace them over the volume.

Execution

To run AllPix^2 with such a configuration runs

$ allpix -c basic.conf
|17:52:02.364|  (STATUS) Welcome to Allpix^2 v1.5.0
|17:52:02.365|  (STATUS) Initialized PRNG with system entropy seed 9336901550865671610
|17:53:23.691|  (STATUS) Loaded 6 modules                     
|17:53:26.358|  (STATUS) Initialized 6 module instantiations  
|17:53:27.728|  (STATUS) Finished run of 1000 events
|17:53:27.789|  (STATUS) [F:ROOTObjectWriter] Wrote 13439 objects to 3 branches in file:
                                              /home/mpetric/AllpixDigi/allpixconf/output/data.root
|17:53:27.793|  (STATUS) Finalization completed
|17:53:27.793|  (STATUS) Executed 6 instantiations in 4 seconds, spending 65% of time in slowest instantiation GeometryBuilderGeant4
|17:53:27.794|  (STATUS) Average processing time is 4 ms/event, event generation at 244 Hz

The execution has produces output/data.root when the information on the movement of charges is stored

Extraction of map

the script scripts/extractMap.C extract from the allpix simulation the map that connect the position of the deposited charge to which pixel has fired. It's output in a file where an object of type vector<vector<short>>. The vector size is equal to the size of all voxels (N=n^3). Please take note that the scanning order is X,Y,Z. Each vector entry is a vector of dynamic size, representing to how many pixels the charge has drifted e.g.:

[100, 0, 0]
[[20, -1, 0], [80, 0, 0]]

The first line represents a case where all the charge has drifted to the same pixel, and the second line represents a case where 20% has drifted to neighboring pixel that is moved for (-1,0) relative to the center of the original pixel and 80% remained in the same pixel.

This information is then used in the AllpixDigiProcessor to calculate hit possitions.