The OPAL Discussion Forum

[Christof Metzger-Kraus <christof.j.kraus AT gmail.com>]

Dear Philippe,

the shifted Green's function is used for all emission models to ensure that the tangential components of the space charge field vanish at the cathode. I thought that NONEQUIL also takes the longitudinal component into consideration in order to determine if a particle is emitted. However it always emits particles but uses the external field (field map) to determine the momentum distribution.

Opal had a feature to create a more realistic particle distribution taking the Schottky effect into account. There is a feature request pending to reintroduce it (https://gitlab.psi.ch/OPAL/src/-/issues/261). Is this what you need?

Cheers,

Christof

On Tue, Jun 1, 2021 at 1:39 PM Philippe Piot <philippe.piot AT gmail.com> wrote:

Dear Christof,

   Thank you for your help. Apparently, I misunderstood the manual and thought that the ASTRA vs NONEQUIL was simply related to the momentum distribution at emission but you are saying it also affects the shifted Green's function algorithm for image-charge calculation? I thought this was only controlled via the "EMITTED" parameter (though it is not absolutely clear to me). 

   I just played a bit with the NONEQUIL and it essentially reproduces the EMISSIONMODEL=ASTRA so far. So more puzzle on my side... Thank you! -- Philippe. 

On Tue, Jun 1, 2021 at 5:51 AM Christof Metzger-Kraus <christof.j.kraus AT gmail.com> wrote:

Dear Philippe,

with EMISSIONMODEL=ASTRA all particles are emitted, it doesn't take into consideration any space charge induced fields at the cathode. The model NONEQUIL does this but I don't know how well it works.

The warning about rebinning can be ignored, as Nicole wrote, Opal doesn't rebin (i.e. put all particles into a single energy bin) while particles are still being emitted. You can delay the moment when the energy bins are deleted with e.g.

OPTION, MINSTEPFORREBIN = 1000;

However from the extract of the input I would assume that you don't use any energy bins at all (NBIN is commented out).

Cheers,

Christof

On Mon, May 31, 2021 at 2:13 PM 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.