The OPAL Discussion Forum

[wangchuan02513 <wangchuan02513 AT 163.com>]

Hi, Frederic

First I'm happy someone other than Andreas and myself are interested in FE model in OPAL:-)

 

First I have a question about the  .oxxx file, because as far as I know, I didn't write any .oxxx file during the FE based simulation. Do you add this new feature in OPAL? If so, please give me more information about the .oxxx file.

 

W.r.t you question, I would first introduce what the FE model in OPAL exactly do, which may help you to find out what the problem is. In the FE model in OPAL,

1. we traverse all the surface triangles in each time step, read and compute the Efields normal to the triangles, compare the Efields with a threshold defined by user in input file.

2. If Ffield<threshold, skip following algorithms and see the next triangle.

3. If Ffield>=threshold, compute the emission current density J according to Fowler-Nordheim formular. Then compute the nominal emitted particle number Nn. As the field emission process is a quantum process which may generate so many particles that beyond the memory limit of a cluster, so we scale the real emission particle number Nr with a larger charge Qreal = Qinitial*Nn/M, if Nn>M, where M is the allowed maximum number of emitted particles per triangle per time step. And in this case Nr=M.

So probably, first you can try to set the threshold=0, which will make OPAL go through the full algorithms of FE model, then you should use tot charge/Qinitial instead of the number of simulation particle number in each time step. Hopefully these can help you, if not, please let me know.

Best regards

Chuan

At 2011-08-29 23:59:36,"frederic.le.pimpec" <frederic.le.pimpec AT psi.ch> wrote:
>Dear Chuan,
>
>I am wondering about the particle emission depending of the RF phase of 
>the accelerating structure, case of an RF gun, 2 and a 1/2 cell, S band, 
>meaning 1ps=1deg of rf phase. Pure Field emission (FE)
>
>I have set in the ini file, 1000 steps. 1 ps = 1 step for every ps.
>
>The .oxxx file give the number of particle emitted per step.
>let say for at least the first 25 steps, the emission is constant and 
>correspond to 27 particles.
> From the Field emission model and the RF phase , the number should 
>either increase or decrease over 25 deg of RF phase.
>
>Sometimes during the emission the number of particle emitted is 
>identical to 22 and then jump at 400, then it decreases.
>
>So I am not really understanding the behaviour of the emission !
>
>Bests
>Frederic
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