The OPAL Discussion Forum

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

Hoi Philippe,

I think the reason is that all particles are deleted when they exit on the side of an element. Simon had a similar problem (alpha magnet). I’ve implemented an option to switch this behavior off a few weeks ago (

https://gitlab.psi.ch/OPAL/src/-/issues/673). This should help. However this feature didn’t make it into release 2021.1. You could reorder the field sampling, wait for the next release or build the executable.

I could help you reorder the field sampling.

Christof

Philippe Piot <philippe.piot AT gmail.com> schrieb am Mi. 15. Sept. 2021 um 12:57:

Thank you, Andreas, Simon, and Christof. Unfortunately, none of the suggestions worked:

- adding the ELEMEDGE to the drifts did not change anything

- I had looked at the particle trajectories; see below and they seem like following the trajectory I would expect in a deflecting cavity with a vertical deflection kick.

- I set my field to very low values and try to remove my -Pi/2 rotation and the simulation runs all the way. So I suspect something to do with the rotation.

The fields I was given were dumped on an (x,y,z) with x being the cavity axis hence my rotation by -Pi/2 around the y axis (by the way in orientation the {Theta, Phi, Psi} Theta is the rotation along the y-axis) I use the L=0.032 corresponding to the length of the cavity (which corresponds to the direction in the original CST file).

In case somebody wants to check I made a tar-ziped file attached. Thank you very much. All the best, -- Philippe.

On Tue, Sep 14, 2021 at 7:18 AM Christof Metzger-Kraus <christof.j.kraus AT gmail.com> wrote:

Hi Philippe,

could you create the outline of the beamline (python data/deflector_ElementPositions.py --project-to-plane), plot it with gnuplot and check that everything looks fine? If it does look fine then you could also plot the path of the reference particle (in data/deflector_DesignPath.dat columns 4 and 2).

I've tried a similar scenario with the Slit-2 regression test (https://gitlab.psi.ch/OPAL/regression-tests/-/tree/master/RegressionTests/Slit-2) by replacing ELEMEDGE with ORIGIN. It worked fine.

Christof

On Tue, Sep 14, 2021 at 12:58 PM Philippe Piot <philippe.piot AT gmail.com> wrote:

Dear All,

  I have a very simple beamline as follows:

TDC:   RFCavity, L = 0.032, VOLT = 1*Vtdc, ORIGIN = {0,0,0.016},
       ORIENTATION = {-Pi/2.,0.0, 0.0}, TYPE = "STANDING",
       FMAPFN = "./xBandDeflector.T7", FREQ = 11700.0, LAG = tdcPhi;
DR1: DRIFT, L = 1.0, ORIGIN = {0., 0., 0.0};
MyLine: Line = (TDC, DR1);

combined with the track command

TRACK, LINE = MyLine, BEAM = BEAM1, MAXSTEPS = 1900000, DT = 1.0e-13, ZSTOP=0.15;

  Somehow OPAL always end at 0.032 (which appears to coincide with the end of the RFCavity element) and the output ends with

OPAL {0}[2]> * Wrote beam phase space.
ParallelTTracker {0}[2]> Dump phase space of last step
Ippl{0}[3]> DR1 gone off
Ippl{0}[3]> DR2 gone off
Ippl{0}[3]>
Ippl{0}[3]> * ************ I N F O *********************************************************
Ippl{0}[3]> * freed fieldmap './xBandDeflector.T7'                                         *
Ippl{0}[3]> * ******************************************************************************
Ippl{0}[3]>
Ippl{0}[3]>
Ippl{0}[3]> TDC gone off
OPAL{0}> done executing ParallelTTracker at 05:54:44
OPAL{0}> * End of input stream "deflector.in".

  Somehow it claims (I think the "gone off" meaning) there is no more element after the RFCavity?

    I also tried different combinations with drift but it did not help. Thank you, -- Philippe.