CEA Codes forum

Dear Didier,
I still want to figure out how the reference trajectory is determined in “Field map with curved reference trajectory”. Is it an arc linking the entrance point and the exit point, and meets the tangent angle requirement of the entrance ?
In the instruction, it tells that “If your ouptut frame is not correctly defined in SUPERPOSE_MAP_OUT, positions and angles shifts are applied at the end of the calculation in the superposed field_map.” Cound you please illustrate why the shifts happen?
BTW, if I want to know the particle coordinates in field map with curved reference trajectory, what shoud I do?
Thank you so much.
Kind regards,
Jie Li

Dear Jie Li,

In field maps, the reference trajectory is calculated by transportation with time of the reference particle* in the field map (in X, Y, Z, pX, pY, pZ).

The beam particles are also transported in time in the field map (in X, Y, Z, pX, pY, pZ) and they position (x, x', y, y', phase, Energy) are plotted with respect to the reference particle position and direction (x, y is the plan orthogonal to the reference particle direction).

The transport is stopped when each particle (reference and beam) cross the exit plan (defined by SUPERPOSE_MAP_OUT). The exit plane is defined by construction as the position and direction of the downstream linac. Then :
- the reference particle longitudinal position are conserved but its transverse coordinates are set to 0, defining the downstream linac.
- the longitudinal and transverse coordinates of beam particles are defined with respect to the new reference particle. That is why one can observe a "jump" when the reference particle does not exit the fied map at the expected position. This is not a bug, but this informs us that the field is not well matched to allow the beam to enter centered in the downstream linac.

I hope it is clearer to you.

Regards.

Nicolas.

Dear Sir,
Thank you so much for your kind help. I have another question to ask.

The particle bunch with some energy spread goes through the element "SOLENOID". The particles with different energy have different focus length. It is called chromatic aberration. Some scientists exploit chromatic aberration to achieve chromatic energy filter.

When particles go throught a "SOLENOID", the results of "Part" in "Charts" shows chromatic aberration phenomenon. I want to know what kind of magnetic field the element "SOLENOID" supply behind the code. I guess it has some formulas of solenoid magnetic field.

By the way, could you please tell me the relationship of tracewin and zgoubi ? I use these two to benchmark my study. I hope they are different.

Looking forward to your reply.

Kind regards,
Jie Li