The OPAL Discussion Forum

["Snuverink Jochem (PSI)" <jochem.snuverink AT psi.ch>]

Dear Philippe Piot,

 

I believe this is due to the fact that OPAL tracks the particles per time step and consequently records the properties for a given time (and not for a given z-position) in the output ‘stat’ file. The s-position in the output is the distance the bunch travelled at a given time, and mean_x is also the mean x-position at a given time (not a given position).

 

As you have a finite beam size in x,y and z, at a given time, the particles will not have the same longitudinal position and they don’t enter the bend at the same time, leading to the (still smooth) curve you see. If I track with a zero beam size, the trajectory is as you might expect:

 

 

 

To record the particles at a given position, one can use the MONITOR element (in OPAL-T).

 

Hope that helps,

Jochem

 

From: opal-request AT lists.psi.ch <opal-request AT lists.psi.ch> On Behalf Of Philippe Piot
Sent: Freitag, 3. Januar 2020 12:40
To: opal AT lists.psi.ch
Subject: [Opal] trajectory through a simple two-rbend dogleg

 

All,

  I have set up a simple dogleg (see input attached) and cannot understand the trajectory (display below as s versus mean_x. It has kinks at the entrance and exit for both dipoles (at s~0.25, 0.5, 0.75 and 1 m) which seem to coincide with the fringe field region. Is this an artifact due to the way the statistical parameters are computed? or something wrong with my model. Thank you,  -- 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