CEA Codes forum

Dear Didier,
I am trying to simulate the transport of a long bunch. I encounter some problems with periodic boundary conditions.

According to the TraceWin instructions: “When the bunch is not short compared to the intra-bunches distance, effect of neighbor bunches are taken into account and particles out of +/- 180° are temporary “moved” into the bunch (with 360° jumps) by the SC routine to estimate their contribution to the SC and calculate the SC they fill.”

So when the particle goes beyond the period, it will enter again from the other end of the period . But the instructions don't mention about the interactions between neighbor bunches. For a long bunch, if a particle is near +/- 180°, will it be effected by the space charge forces from its neighbor bunches? As far as I known, Tracewin uses PICNIC as its inner field solver，but classical PICNIC just calcuates interforce between marco-particles in the bunch.
does Tracewin consider the interaction between neighbor bunches? For example, when I calculate the transport of a long bunch, or a more extreme example, when I calculate the transport of a DC beam, can Tracewin handle periodic boundary effects?

Best regards

Dear QiXinimp,

When the beam bunch is longer than 180° (based on a RMS calculation), PICNIC does 2 things:
- It puts temporary (just for the SC calculation) each particle that is out of +/-180° main window by -/+360° until it comes back to the main window,
- It adds neighboor bunchs on each side (+/- 360°) of the main window with the same distribution.
- It calculates the SC force in the main windows produced by main windows and in neighboor windows.
- it applies the force on each particle according to its position in the main windows.
In these conditions, when the beam is continuous, the longitudinal field at the frontier of the main window is also zero as it is produced by the charge in the main window and in the neighboor window, which compensate each others.

I hope it is clear.

Best regards.

Nicolas.

Thank you. I fully understand! It is so kind of you, Nicolas.

My pleasure.
Have fun with beam dynamics !