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None Electron multiplication in Electric field : maximum acceptable step 

Forum: Fields: Magnetic and Otherwise
Date: 02 Dec, 2016
From: David Sarria <David Sarria>

Dear all,

I am testing electron multiplication with applied electric fields.

My simulation set-up is the following :

 - An applied electric field (80 MV/km) in a air density of 3.059E-04 g/cm3.
 - Box size is very large
 - Initial 1 MeV electrons
 - using the "UserSteppingAction" I check what is the number of electrons with energy >= 1 MeV at given times of the simulation (1 us, 2 us, ..., 9 us)
 - After hundreds of initial particles shot, I get a multiplication factor, that is the number of electron >= 1 MeV at 6 us divided by the number of electrons shot initially.

I think one of the key points is how the trajectory of the particles are integrated (as they gain energy from the electric field).

I tried to play on three parameters : the range cut and the energy threshold (=production cuts), and the maximum acceptable step of the integrator.

My problem is the following :

when this maximum acceptable step is too low, then the multiplication factor decreases, and goes to ~0 for a step of < 10^-4 meters. I would expect this multiplication to stay constant (i.e. to converge) when the chosen maximum acceptable step reaches a given value that is small enough to integrate the field accurately. But this is clearly not the case here. See the attached figure.

What is the problem ?

Thanks in advance, -David

   Attachment:
      http://hypernews.slac.stanford.edu/HyperNews/geant4/get/AUX/2016/12/02/02.23-40093-multfact_vs_acceStep.png

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1 None: Re: Electron multiplication in Electric field : maximum acceptable step   (David Sarria - 07 Jan, 2017)
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