The OPAL Discussion Forum

[Christof Metzger-Kraus <christof.j.kraus AT gmail.com>]

Hi Anastasia,

the variable "LAG" determines the phase relative to the on-crest phase (see also here: 1.14.1. OPAL-t mode in https://gitlab.psi.ch/OPAL/Manual-2.2/blob/master/elements.asciidoc). The auto-phasing algorithm determines for which phase the reference particle is most strongly accelerated. You can switch off the auto-phasing algorithm for each cavity individually by using APVETO. Then you should be able to see the behavior that you expected. However you'll also have to find the on-crest phase manually.

 I hope this helps.

christof

On Fri, Jan 10, 2020 at 6:16 PM Anastasia <anastasia.ierides AT varian.com> wrote:

Hi Opal team,

I am trying to understand what effect the variable “LAG” in the RFCAVITY
definition has on the field/particles.

For example, if I have several consecutive cavities that I want to implement,
each with its own field map. Suppose I know that the field values change sign
from positive to negative with each consecutive cavity, I would assume that
switching “LAG” from 0 in one cavity and to Pi in the next would show that the
electric field seen by the reference particle would show similar behavior,
shifting from positive to negative.

Are there more nuances to this?

Should all cavities start out with LAG = 0, and assume that the program will
figure it out?

Thanks,

A.I.