The OPAL Discussion Forum

[Nicole R Neveu <nneveu AT stanford.edu>]

Hi Philippe,

 

I’m not sure what’s causing your SC issues, but I think your rebin warning is coming from the rebin default + emission process.

OPAL wont rebin during emission, and your emission steps (500) is larger than the rebin default (200?).

i.e. the warning is saying emission is taking longer than expected, but not that there’s a major problem.

Others can chime in and correct me, if that’s no longer the case.

 

Good luck,

 

Nicole

 

From: <opal-request AT lists.psi.ch> on behalf of Philippe Piot <philippe.piot AT gmail.com>
Reply-To: "philippe.piot AT gmail.com" <philippe.piot AT gmail.com>
Date: Monday, May 31, 2021 at 6:46 PM
To: opal <opal AT lists.psi.ch>
Subject: Re: [Opal] emission from cathode in OPAL

 

Dear All, 

  It seems that adding the SOURCE element fixed one of the problems (removing particles moving backward) and I can see space-charge saturation effects.  However, the current distribution is incorrect so far (it shows modulation one would expect toward the bunch tail from emission turning off due to space charge and on later) but with a much higher peak current. I suspect it may still be related to a binning issue and probably to the warning regarding the rebin() function (I looked at the source code but could not figure it out yet...).  Thank you! -- Philippe.

 

 

On Mon, May 31, 2021 at 7:12 AM Philippe Piot <philippe.piot AT gmail.com> wrote:

Dear All,

  I am trying to understand how does the emission work in OPAL Specifically, in my simulation, I emit a Gaussian beam from a cathode with:

 

    DistFT: DISTRIBUTION, TYPE = GAUSS,
   SIGMAX  = 0.002,
   SIGMAY  = 0.002,
   SIGMAT  = 3.4e-12,
            EMISSIONSTEPS = 500,
   CUTOFFLONG = 3,
   CUTOFFX = 0.5,
   CUTOFFY = 0.5, // CUTOFFR is not implemented/wotking?
            EMITTED = True,        
            EMISSIONMODEL = ASTRA,
            EKIN = 0.55,      
//    NBIN=5,
            WRITETOFILE = True;

 

   What surprises me is that as I increase the charge I should see the onset of space-charge-induced saturation and not all the particle being emitted anymore. But OPAL does emit all the particles -- ultimately the distribution is extremely disrupted (but not as one would expect from space charge). Am I doing anything wrong above?  

  Also, I noticed, independently of charge (or even with FC_solver=None) I get a warning:

OPAL{0}> *****************************************************

OPAL{0}> Warning: attempted to rebin, but not all distribution
OPAL{0}> particles have been emitted. Rebin failed.
OPAL{0}> *****************************************************
OPAL{0}> *****************************************************
OPAL{0}> Warning: attempted to rebin, but not all distribution
OPAL{0}> particles have been emitted. Rebin failed.
OPAL{0}> *****************************************************

 

 

   Thank you,  -- Philippe.