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Forum: Event and Track Management
Re: None How can I Restart a Stopped Track? (Tom Roberts)
Re: None Re: How can I Restart a Stopped Track? (Vladimir IVANTCHENKO )
Re: None Re: How can I Restart a Stopped Track? (Tom Roberts)
Date: 10 Feb, 2006
From: Vladimir IVANTCHENKO <vnivanch@mail.cern.ch>

On Thu, 9 Feb 2006, Tom Roberts wrote:

> *** Discussion title: Event and Track Management
> Email replies to PublicHyperNews@slac.stanford.edu must include:
>   In-Reply-To: <"/eventtrackmanage/440/1/1"@geant4-hn.slac.stanford.edu>
>   Subject: ...change this to be about your reply.
> 
> Yes,indeed, the electric field is dynamic: it is zero until most of the
> mu+ stop (or are quite low energy). Then after ~1/4 decay time the E
> field is rapidly ramped up to accelerate them out of the material.
> 
> I really want the full Geant4 tracking, energy loss, multiple
> scattering, etc. for tracking these, as I want the simulation to be as
> realistic as possible.
> 
> I'm thinking that my new Process should replace G4StepLimiter on this
> particle, and never actually stop it. My new Process should ensure the
> particle always has ~1/40 eV KE, so it can specify a step length of a
> micron or so, keeping the time interval of each step ~1 ns while waiting
> for the E field to come on. Whenever the particle's KE is too low, it
> would kick it in a random direction.
> 
> For my purposes, errors of a few eV and a few dozen microns are not
> important. That 1/40 eV is of course not arbitrary, and perhaps these
> random kicks are not really "errors" anyway. So I'm not terribly
> concerned how accurate the other physics processes are at such a low
> energy, just that they behave reasonably.
> 
> This way the particles never actually stop.
> 

Hello Tom,

In that case I would propose to try following:

1) make you field time dependent 
2) create a new you own AtRest process for mu+ and include it into 
PhysicsList 

this process should have a method
      
AtRestGetPhysicalInteractionLength

which should return t = delay_time_of_field, as a result, you will sample 
a competition between mu+ decay and this process.

in the AtRestDoIt method the process need to do following:

 - change mu+ status from fStopButAlive to fKilled
 - create a new track of mu+ with the time and point in space exactly as 
   the previous one
 - give to this new mu+ a very small kinetic energy (for example, 10 eV)
  
Please, try and report if any problem.

VI

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