The OPAL Discussion Forum

[Matthias Toggweiler <matthias.toggweiler AT psi.ch>]

Hi John

My colleagues already answered most points, but to summarize and to give a 
little bit more detail:

- Runge-Kutta integrator per se does not use adaptive time steps, but is just 
an integrator of higher order available in OPAL-CYCL in addition to the 
standard Boris-Buneman integrator.

- OPAL-T has only the Boris-Buneman integrator (second order leapfrog-like 
scheme). There is no plan to add a Runge-Kutta integrator here; memory 
requirements of RK are higher.

- The adaptivity in our current work deals with varying the time step 
according to how strong space charge forces are. Simulations where space 
charge effects are important (RF photoinjector is a perfect candidate) can 
profit from this adaptivity a lot. 

- Simulations where space charge is less important do not profit noticeably 
from the variable time stepping. There, another approach makes more sense. 
For example, a multiple-time-stepping integrator in OPAL-CYCL evaluates space 
charge effects less often than external field effects.

- Not everything will be automatic: for example, you will still have to set 
an initial time step. Nevertheless, less manual work will be required to 
achieve better quality solutions.

- In my masterthesis, good results were obtained with a first prototype (see 
scenario EGun-CTF3 in 
http://e-collection.library.ethz.ch/eserv/eth:5175/eth-5175-01.pdf). The 
problem there was that the time step used for space charge effects dictates 
the time step used for external field effects. We are working on an improved 
prototype where the integration of these two effects is less tightly coupled. 
Our understanding how to the time step should be chosen has also improved 
since then.

To conclude, I am happy that you are interested in this work and we are 
working hard to get this going. However, as already noted, it is not magic 
that will do everything automatically, but one step towards more intelligent 
integration.

Best,
Matthias

Am 04.05.2012 um 17:55 schrieb Power, John:

> Dear All,
>  
> I am looking for an alternative to PARMELA so I am lurking on your list. J
>  
> I see in the user’s manual that the Runge-Kutta time integrator is only 
> available in OPAL-CYCL.  Since I work mostly with RF photoinjectors, and I 
> would rather not have to set the time step manually as is done in PARMELA, 
> I wonder if there are any near term plans to add this to OPAL-T since.
>  
> cheers,
> John