The OPAL Discussion Forum

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

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