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Forum: Fields: Magnetic and Otherwise
Re: Question Low energy electron drift processes (Zach Kohley)
Date: 08 Nov, 2010
From: Gumplinger Peter <Gumplinger Peter>

Hi Zach,

Good question. I don't have the answer but I use this opportunity to summarize what I know at present.

There is an effort to merge and code an interface between Garfield and Geant4 (part of CERN project RD51 led by Alain Bellerive / Carleton). My understanding is that the G4 collaboration never considered rewriting Garfield's Magbolz functionality under its framework and only Alain's prototype interface exists

This solution is based on G4FastSimulationModel whereby HEED (like shower parameterization in calorimeters) takes over from G4 when a track enters a drift volume. HEED tracks the particle in the gaseous volume, then returning the exiting tracks back to G4 for continued tracking elsewhere. This is certainly one viable solution but leaves the physics with HEED and reduces G4 to the geometry model only.

Geant4 includes a so called Photo Absorption Ionization Model (PAI) model - G4PAIModel class (Geant4 et al, NIM A, vol. 453, pp. 579-605,2000). It is possible to define different EM physics models for each G4Region. The PAI provides for a detailed simulation of ionization but is very time consuming and hence only practical if it is restricted to specific detector regions (TestEm8). See also Section 7.11 in the Geant4 PhysicsReferenceManual:

My understanding is that this model (PAI) is similar to how HEED calculates single ionization clusters along the particle path and is applicable for thin and/or gaseous detectors.

HEED and PAI are models which are using similar approach. Vladimir Ivantchenko told me that simulation of ionisation clusters is not necessary property of such model only; e.g. that G4 is capable to do this even with standard ionisation, fluctuation and extra helper class. Inside PAI at each step a sampling of each ionisation collision is performed. For the time being this is used only to sample fluctuation and not returned to user, so PAI is working equivalently to the standard model. Standard EM is competative and is used for production of real experiments with TPC.

As an aside, FYI, I also came across an interesting article about interfacing TRIM to GARFIELD (TRIMCAT 2009):

According to these authors, HEED - the program interfaced to GARFIELD by default - generating the ionization clusters from which electrons drift, is more appropriate for the simulation of particles types and energies relevant to particle physics experiments rather than nuclear physics.

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1 None: Re: Low energy electron drift processes   (Zach Kohley - 08 Nov, 2010)
(_ Idea: Re: Low energy electron drift processes   (Vladimir Ivanchenko - 14 Nov, 2010)
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