The OPAL Discussion Forum

[Chris Hall <chall AT radiasoft.net>]

Hi Christof,

It's good to see that OPAL 2.0 does give the expected result for the chicane.

Is 2.0 sufficiently stable that it is worth trying to install and use for my chicane simulations right now?

Thanks for all your help looking into this issue.

Chris

On Sat, Nov 4, 2017 at 2:32 PM, Christof Metzger-Kraus <christof.j.kraus AT gmail.com> wrote:

ps: I got this result with the upcoming version of OPAL, *not* version 1.6.0.

On Sat, Nov 4, 2017 at 9:31 PM, Christof Metzger-Kraus <christof.j.kraus AT gmail.com> wrote:

Hi Chris,

if found the reason why the particle with x,px,y,py,z,pdz=0 didn't stay perfectly on the reference trajectory: I assumed that the momentum is exactly 85 (\beta\gamma) but instead it's 85.0000057697 (\beta\gamma). Now the trajectory stays much better on the reference trajectory, see attachement.

christof

On Sat, Nov 4, 2017 at 11:40 AM, Christof Metzger-Kraus <christof.j.kraus AT gmail.com> wrote:

Hi Chris,

the results for the upcoming version of OPAL (v. 2.0, release date not yet fixed) seem to be much better. However a particle with x,px,y,py,z,dz=0 doesn't stay perfectly on the reference trajectory, see attachement. I'll have to investigate more into this to find out why this is so.

My suspicion is that OPAL 1.6.0 can't handle this case correctly. The way how OPAL 1.6.0 places elements and tracks the bunch is in many ways inadequate for lattices with several dipoles. When simulating bERLinPro we ran into several issues which finally led to the development of "OPAL-T3D" (see http://accelconf.web.cern.ch/AccelConf/ipac2016/papers/wepoy034.pdf).

christof

On Fri, Nov 3, 2017 at 3:30 PM, Chris Hall <chall AT radiasoft.net> wrote:

Hi John,

The higher-order terms are also a good point. I have tried to make sure this is not what I am running into by constructing an identical chicane in elegant (using CSBEND, so higher-order effects should be included) and importing my initial distribution from my OPAL tests. In this elegant test I saw negligible emittance growth.

Once I have a working file I'll definitely pass it along to the list.

Best,

 Chris

On Fri, Nov 3, 2017 at 6:20 AM, Power, John <JP AT anl.gov> wrote:

Hi Chris,

Just to add what Bettina said, any non first-order or collective terms (2nd order or higher, Space-charge, or CSR) will make emittance growth so i thought maybe this is what you are seeing.  However, it now sounds like you are down to the simplest possible case and should not be seeing emittance growth.  

I am also interested in building a chicane in OPAL so if you and Christof figure this out would you please share your input file to the list?

thanks,

John Power

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From: opal-request AT lists.psi.ch <opal-request AT lists.psi.ch> on behalf of Chris Hall <chall AT radiasoft.net>
Sent: Thursday, November 2, 2017 10:56 PM
To: Kuske, Bettina
Cc: opal AT lists.psi.ch
Subject: Re: [Opal] Example of a chicane?

 

Hi Bettina,

Sorry, I should have mentioned that I been seeing this emittance growth in the absence of space charge (fieldsolver turned off). 

Originally, I was trying to simulate an asymmetric chicane with quads used to restore achromaticity. However, I was seeing unexplained emittance growth.

Trying to make sure I can correctly set up the lattice, I have now reduced all the way down to just a simple, symmetric chicane, running without space charge. That I see emittance growth still in this case led me to believe I am making a mistake somewhere in my setup.

Christof offered to take a look at my input file so hopefully he will be able to find where I am going astray.

Thanks,

 Chris

On Tue, Oct 31, 2017 at 3:23 AM, Kuske, Bettina <bettina.kuske AT helmholtz-berlin.de> wrote:

Hi Chris, 

Try to turn the space charge off.

If it is achromatic then, your have a problem with what we call space charge dispersion. Due to the nonlinear, defocussing effect of space charge the chicane is not closed anymore. You can only try to minimize it, and you will find emittance growth. 

What do you need the chicane for? 

Bettina

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-------- Ursprüngliche Nachricht --------

Von: Chris Hall

Datum:31.10.2017 00:00 (GMT+01:00)

An: opal AT lists.psi.ch

Betreff: [Opal] Example of a chicane?

Hello,

I was wondering if anyone has an example of standard 4 dipole bunch compression chicane implemented in OPAL 1.6?

There is a chicane in regression-tests but it is currently listed as broken. I have tried several implementations of my own but the result never appears to be achromatic and I see emittance growth if my bunch has any energy spread.

Thank you,

  Chris

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