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Question Re: Need help starting to put together a Physics List for an RFQ linac 

Forum: Physics List
Re: Question Need help starting to put together a Physics List for an RFQ linac (Marlin Mixon)
Re: Idea Re: Need help starting to put together a Physics List for an RFQ linac (Tom Roberts)
Date: 13 Jul, 2010
From: Dragos Constantin <Dragos Constantin>

Hi Tom,

I have to model an electron gun. The space charge interaction, the self-magnetic field interaction and eventually secondary electron generation from beam collisions with the electrodes have to be taken into account.

Can I use G4beamline to model all of the above mentioned processes? Is G4beamline more like Parmela, i.e., it transports the macroparticles and the it applies the space charge routine?

Thank you for your help.

Dragos

On Tue, 13 Jul 2010 05:25:18 GMT, Tom Roberts wrote:

> It's not worth your time to worry about it. Just use QGSP_BERT. Use
> G4PhysListFactory to construct it. Sure it creates a lot of particles,
> but if you want a realistic simulation you'll need them (beam particles
> do hit apertures).
> 
> For an accelerator like this, don't forget to call
> G4FieldManager::SetFieldChangesEnergy(true), and use
> G4EqMagElectricField.
> 
> The challenge, of course, is to get the electric and magnetic fields for
> the complex geometry of the RFQ into your program. Note that the
> geometry of an RFQ depends on the initial KE of the particles, their
> charge/mass, and the RF frequency; the spatial distributions of the
> fields depend on the geometry. So it's not just as simple as applying
> different frequencies, you need different geometry and field maps for
> each frequency. You'll need a good EM modeling program to generate the
> field maps (unless you have a simple enough geometry for an analytical
> solution, which I doubt).
> 
> As for dd fusion, I'm not sure that it is in any physics list. In
> general, particle-particle interactions are not included in Geant4
> physics lists, only particle-material interactions are there. So if it
> is available, it will be for a deuteron beam traversing a flask of
> deuterium, not for particle-particle interactions within the beam. Think
> about how Geant4 tracks particles and this will be obvious. If you are
> interested in modeling particle-particle interactions, I have
> implemented this in my program (G4beamline), but it is non-trivial and
> involves re-writing the RunManager, EventManager, TrackManager, and
> SteppingManager, so they track all of the tracks in parallel; plus
> adding a whole new class of interactions between particles, plus
> modeling particles as macro-particles (it's infeasible to simulate the
> 10^9 particles of a realistic bunch). Also think about what it takes for
> dd fusion to occur; a deuteron accelerator is not going to do it in the
> beam, you'll need to put the beam into a flask of deuterium for it to
> happen, and the beam must be above threshold. If you want to simulate a
> tokamak, plasma physics is extremely important and not present in
> Geant4.
> 
> Finally, you should realize that space charge will probably be important
> in the RFQ, and that Geant4 cannot simulate it. The motivation for
> implementing particle-particle interactions in G4beamline was to be able
> to model space charge (as its name implies, it is a Geant4-based program
> for modeling beam lines). As I said, this is non-trivial. G4beamline is
> open source, and you can look at how I did it and even re-use my code:
> http://g4beamline.muonsinc.com
> 

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1 More: Re: Need help starting to put together a Physics List for an RFQ linac   (Tom Roberts - 16 Jul, 2010)
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