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RE: [Opal] trajectory through a simple two-rbend dogleg

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  • From: "Snuverink Jochem (PSI)" <jochem.snuverink AT>
  • To: "'piot AT'" <piot AT>
  • Cc: "opal AT" <opal AT>
  • Subject: RE: [Opal] trajectory through a simple two-rbend dogleg
  • Date: Mon, 6 Jan 2020 11:08:51 +0000
  • Accept-language: en-US, de-CH
  • Authentication-results: localhost; iprev=pass ( smtp.remote-ip=; spf=pass; dmarc=skipped

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,



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



  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,
Northern Illinois University, Dept of Physics and
Northern Illinois Center for Accelerator & Detector Development
DeKalb, IL 60115, USA
Tel: 815 753 6473, Web:

Argonne National Laboratory, Advanced Photon Source
Accelerator System Division

Lemont, IL 60439, USA

Tel: 630 252 2415, Web: 

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