The OPAL Discussion Forum

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

All,

  Regarding my question #1 below. I realize there is no way to locate the cathode at an arbitrary location for an "emitted" distribution and the reason my run was hanging on the gun is due to particle not moving in my simulations... Thanks, -- 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