The OPAL Discussion Forum

[Wei Hou Tan <tanweihou AT outlook.com>]

Dear Nicole,

Thanks for your suggestion.

Unfortunately, it did not help much.

For my example, I did not turn on space charge calculation.

From the plot below, it seems like there is a mismatch in RF phase, as seen by the reference particle.

Is there a way to check which reference particle that OPAL uses for its calculation ? (For ASTRA, it is the bunch centroid)

Thanks.

Regards

Wei Hou

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From: Nicole R Neveu <nneveu AT stanford.edu>
Sent: Saturday, January 23, 2021 6:25 AM
To: Wei Hou Tan <tanweihou AT outlook.com>; opal <opal AT lists.psi.ch>
Subject: Re: [Opal] Reference particle in OPAL

 

Have you tried more emission steps?

I think the default is only ‘1’, and this value was too low for my case.

Here’s my standard distribution:

 

Dist:DISTRIBUTION, TYPE = FROMFILE,

                   FNAME = "opal_emitted.txt",

                   EMITTED = TRUE,

                   EMISSIONMODEL = NONE,

                   EMISSIONSTEPS = 100,

                   EKIN=0;

 

Other things that I needed to adjust were:

• Grid size / # particles ratio (maybe you’ve already done a convergence study?)
• Number of Fourier samples in the field maps (originally I had this number too high)

 

Thanks,

 

Nicole

 

From: Wei Hou Tan <tanweihou AT outlook.com>
Date: Friday, January 22, 2021 at 2:16 PM
To: Nicole R Neveu <nneveu AT stanford.edu>, opal <opal AT lists.psi.ch>
Subject: Re: [Opal] Reference particle in OPAL

 

Dear Nicole,

 

The distribution was generated by external scripts, which then converted into ASTRA and OPAL inputs.

The distribution comes with initial momentum pz, I did not add extra Ekin as shown in the code below.

 

Here's the distribution command look like

 

Dist: DISTRIBUTION, TYPE = FROMFILE,

        FNAME = "opal.ini",

        EMISSIONMODEL = NONE,

        EKIN=0,

        EMITTED = True,

        WRITETOFILE=True,

        NBIN = 100;

 

Thanks.

 

Regards

Wei Hou

---

From: Nicole R Neveu <nneveu AT stanford.edu>
Sent: Saturday, January 23, 2021 6:07 AM
To: Wei Hou Tan <tanweihou AT outlook.com>; opal <opal AT lists.psi.ch>
Subject: Re: [Opal] Reference particle in OPAL

 

Hi Wei Hou,

 

When I did a similar exercise for the LCLS-II injector, one cause of discrepancy for me was the definition of Ekin.

Are you suppling the same particles distribution to ASTRA and OPAL?

Or letting the codes generate the distribution?

What does your distribution command look like?

 

Thanks,

 

Nicole

 

 

From: <opal-request AT lists.psi.ch> on behalf of Wei Hou Tan <tanweihou AT outlook.com>
Reply-To: Wei Hou Tan <tanweihou AT outlook.com>
Date: Friday, January 22, 2021 at 1:59 PM
To: opal <opal AT lists.psi.ch>
Subject: [Opal] Reference particle in OPAL

 

Dear OPAL developers,

 

This is Wei Hou TAN, graduate student working with Prof. Philippe Piot in the Northern Illinois University.

 

I would like to learn OPAL, starting by cross-checking its results with ASTRA.

 

In my toy example, I simulated a rf gun with both ASTRA and OPAL.

However, I am having problems getting same results in OPAL.

I have checked that both ASTRA and OPAL have the same distributions, same RF phase.

 

I suspected that OPAL has a different definition of reference particle but I could not find any documentations on it.

 

What is OPAL convention of reference particle ?

 

Thank you.

 

Regards

Wei Hou