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Forum: Fields: Magnetic and Otherwise
Re: Question discripancy between firing a particle with a given energy and using electric field to accelerate it to the same energy (Robert Nnaemeka)
Re: Feedback Re: discripancy between firing a particle with a given energy and using electric field to accelerate it to the same ener (Gumplinger Peter)
Re: Feedback Re: discripancy between firing a particle with a given energy and using electric field to accelerate it to the same ener (Robert Nnaemeka)
Re: Feedback Re: discripancy between firing a particle with a given energy and using electric field to accelerate it to the same ener (Michael H. Kelsey)
Date: 30 Apr, 2015
From: Robert Nnaemeka <Robert Nnaemeka>

Thanks very much for the explanations. I launched the proton with energy of 1 eV. They are all accelerated, although the kinetic energy they acquire a the opposite end of the box is less than the energy the field is expected to give them. I guess it might be due to energy loss from collision. This quession: does decreasing the step length gives a better tracking? CPU power is not a problem as my code isn't big and my computer has a generous processing power.

 On Thu, 30 Apr 2015 16:56:59 GMT, Michael H. Kelsey wrote:
> On Wed, 29 Apr 2015 22:57:04 GMT, Robert Nnaemeka wrote:
> 
> > I have a box filed with nitrogen gas at very low pressure. I Then
> > created a uniform magnetic field and associated it with the box logical
> > volume. The electric field strength is such that when a proton is
> > released from one end it will accelerate to a kinetic energy of 120 keV
> > when it reaches the opposite end. The purpose is to study electron
> > production via ionization at low pressure. However, there is no
> > ionization. But if I deactivate the field and fire a proton with 120 keV
> > kinetic energy I get some electrons as should be expected.
> 
> I have a few observations. When you "release" the proton in your job, do
> you give it exactly zero energy, or do you give it a small but finite
> energy (e.g. 0.1 eV)? Geant4 does not have a mechanism to "restart" a
> particle which is Stopped; a stopped proton will simply be killed. If
> you give it a small energy, then G4Transportation will be able to apply
> the E field during the step and accelerate it.
> 
> Second, from your description, the two tests are different. When you
> launch a very slow proton at one end, it is probably too low energy to
> ionize until it gets partway through the box. The 120 keV at the far end
> is the _maximum_ energy, not the average.
> 
> Finally, as you know, ionization energy loss is a steeply rising
> function as you go down to zero energy. I'm not sure that protons will
> behave the way you think they will: the slowest protons should lose
> their energy all in one step, with no opportunity to be accelerated very
> much. Your tests above will tell you for sure, but you may need to be
> launching your protons with energy above the "single step" limit, so
> that they can both lose energy and be accelerated by the field, without
> being stopped.
> 
>   -- Michael Kelsey
> 

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1 None: Re: discripancy between firing a particle with a given energy and using electric field to accelerate it to the same ener   (Mike Kelsey - 30 Apr, 2015)
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