The OPAL Discussion Forum

[Philippe Piot <piot AT nicadd.niu.edu>]

Hi Andreas, 

  The nominal (free-space Green's function approach) space-charge algorithm should not care about the location where the cathode seats. In fact, it is already possible to locate it anywhere in x,y. My understanding is that it is just OPAL's convention to use the z=0 as the emitting plane. Am I missing something? Thanks,  -- Philippe. 

Philippe Piot,
https://www.niu.edu/advanced-accelerator-randd/
Northern Illinois University, Dept of Physics and
Northern Illinois Center for Accelerator & Detector Development
DeKalb, IL 60115, USA
Tel: 815 753 6473, Web:  http://www.physics.niu.edu/physics/

Argonne National Laboratory, Advanced Photon Source
Accelerator System Division

Lemont, IL 60439, USA

Tel: 630 252 2415, Web:  https://www.aps.anl.gov/Accelerator-Systems-Division 

On Mon, Feb 10, 2020 at 11:28 AM Adelmann Andreas (PSI) <andreas.adelmann AT psi.ch> wrote:

Hello Phillipe thanks for the replay. Yes your assessment about the emission model seams correct. 

This also has to do with the boundary conditions for the field solver what has to be fulfilled, which is 

of course easy in case of a plane emission surface at z=0. However with the SAAMG-PCG solver the 

boundary conditions can be arbitrary i.e. read in from a processed gmsh file for example. This capability

was implemented in V 1.6 but not maintained, however the code is available and in case this is important

for you we could bing this back. The OPAL retreat at SLAC would be the ideal place to do so. Are you planing to 

join?

Cheers A

------
Dr. sc. math. Andreas (Andy) Adelmann
Head a.i. Labor for Scientific Computing and Modelling 
Paul Scherrer Institut OHSA/ CH-5232 Villigen PSI
Phone Office: xx41 56 310 42 33 Fax: xx41 56 310 31 91
Phone Home: xx41 62 891 91 44
-------------------------------------------------------
Friday: ETH HPK G 28   +41 44 633 3076
============================================
The more exotic, the more abstract the knowledge, 
the more profound will be its consequences.
Leon Lederman 
============================================

On 10 Feb 2020, at 12:26, Philippe Piot <piot AT nicadd.niu.edu> wrote:

Hi Andreas,

  I did not get an answer for item 3 but it seems to me that OPAL defacto assumes the emitting surface (injected particles) is at z=0. It allows only for transverse and time offset right now. Best, -- Philippe.

On Sun, Feb 9, 2020, 7:06 PM Adelmann Andreas (PSI) <andreas.adelmann AT psi.ch> wrote:

Dear Philippe did you get an answer ?

Cheers A

------
Dr. sc. math. Andreas (Andy) Adelmann
Head a.i. Labor for Scientific Computing and Modelling 
Paul Scherrer Institut OHSA/ CH-5232 Villigen PSI
Phone Office: xx41 56 310 42 33 Fax: xx41 56 310 31 91
Phone Home: xx41 62 891 91 44
-------------------------------------------------------
Friday: ETH HPK G 28   +41 44 633 3076
============================================
The more exotic, the more abstract the knowledge, 
the more profound will be its consequences.
Leon Lederman 
============================================

On 22 Jan 2020, at 13:35, Philippe Piot <piot AT nicadd.niu.edu> wrote:

Dear All,

  Thank for the answer to my items 2, and 4 below. 

  - Regarding 1, I noticed that my simulation works if I turn off AUTOPHASE (set AUTOPHASE=0 instead of =4) and phase the cavity manually so the hanging seems to be due to the auto-phasing routine somehow.

  - Regarding 3, I would appreciate if somebody has good advice on how to emit a particle from an arbitrary location. It seems the emission mode is only for z=0 (so the cathode by convention is always located at z=0?). Related to this item, I also find in the manual there is a SOURCE element (sec. 6.4) but I am confused about its use or relevance and I could not find any mention of this element anywhere else (I try adding it in my simulation but it did not change anything as far as I can tell). 

  All the best,  -- Philippe. 

 

On Mon, Jan 20, 2020 at 5:56 AM Philippe Piot <piot AT nicadd.niu.edu> wrote:

Dear All,

  I would like to track the dark current (field-)emitted from the wall of an RF gun. As a first simplified approach, I would like to emit a few particles from different sites (on the cavity wall) and follow their trajectories.

  I have a few issues and I hope somebody can make some suggestions:

-1  I prepared a SuperFISH field-map that contains the field inside the cavity (instead of just the paraxial region as usually done) -- the header of the map is:

"

2DDynamic XZ
0.0 66.5  1330
199.6043527245878
0.0 30.0  620

"

OPAL starts and hangs on the map it stops after displaying 

Ippl{0}> * ************* G U N *********   

it does not terminate but just hands and I decided to ctrl+C after 15 mins...  Is there a limit on the map size? The same map dumped over the paraxial region  (header of the map is 

"

2DDynamic XZ
0. 30. 600
199.6043527245878
0. 5. 50
")

works fine (so my fields are OK) and it takes only a few seconds to run OPAL on my laptop (CentOS 8.1).

-2 how do I turn off space charge? I would have thought that just setting the bunch charge to zero would do the trick. But if set the charge to zero and reduce the number of particles to a few 100s, OPAL still cares about the fact that the space-charge mesh size is not set properly (so presumably it is still trying to call the space-charge solver for some reason) 

-3 is the best approach to emitted electron from the cavity wall to set the coordinate/momentum of the particle in the "FROMFILE' type fine? Or can I use another type of distribution?

Finally, I saw OPAL has been used for dark current and multipacting studies https://arxiv.org/abs/1208.6577 .  Are these capabilities still in Opal 2.2? Is there an example file that could be shared?

Thank you very much, -- Philippe.

Philippe Piot,
https://www.niu.edu/advanced-accelerator-randd/
Northern Illinois University, Dept of Physics and
Northern Illinois Center for Accelerator & Detector Development
DeKalb, IL 60115, USA
Tel: 815 753 6473, Web:  http://www.physics.niu.edu/physics/

Argonne National Laboratory, Advanced Photon Source
Accelerator System Division

Lemont, IL 60439, USA

Tel: 630 252 2415, Web:  https://www.aps.anl.gov/Accelerator-Systems-Division