CEA Codes forum

In my project, I have a 3D magnetic map that corresponds to a quadrupole magnet. This map is placed within the transmission line using the SUPERPOSE_MAP command. I have tried rotating the quadrupole map around the z-axis, by setting θ_Z0 (4th) parameter to various values. My expectation was to see the focusing direction change correspondingly, for example, flipping x- and y- focusing if the rotation angle is 90 degrees. However, it appears that changing θ_Z0 has no effect, specifically:

• The beam envelope plot is unaffected by θ_Z0 angle changes

• The [Superposed] magnetic map field plots are also unaffected by θ_Z0 angle changes

Not sure what I am doing wrong.

Dear Vlad,

As specified in the manual, this optionnal parameter is only used in a very specific context.

The optionnals parameter, X0 Y0 θ Z0 θ X0 θ Y0 are required when the following field map curves the reference trajectory (See Field map with curved reference trajectory). Another command is also needed to inform code to output frame.

I would suggest 2 other possibilities that are probably easier to implement
utiliser la commande BEAM_ROT Or use the error command : ERROR_QUAD_NCPL_STAT, in this case have a look about chapter "Error study"

Regards,

Didier

Thank you very much for the explanation. I have tried, and it looks like adding SUPERPOSE_MAP_OUT statement does result in the maps being properly rotated around z-axis. From the manual it did seem to me that the SUPERPOSE_MAP command is functional including optional parameters, even without the SUPERPOSE_MAP_OUT statement, presumably how it was implemented prior to 2.8.0.0. I now understand now that it's incorrect, and optional parameters are only valid if SUPERPOSE_MAP_OUT statement is present. This time around I also noticed that the manual is clear that the field plot ignores the optional parameters as well.

I am not sure how to use BEAM_ROT statement in may case, as I have multiple overlapping field maps, and it seems to interfere with the SUPERPOSE_MAP statement. I will check the ERROR_QUAD_NCPL_STAT.

As a little follow up, I see that the curved trajectory disables the space charge effect calculations. Is it possible to enable this functionality? I do not think the curvature is ever so significant as to meaningfully impact the space charge effects, so I assume the reason it's not available must be technical in nature. In principle, the z-coordinate along the trajectory is being used in the plots, so hypothetically the PICNIC meshing should be possible.

Dear Vlad,

Indeed, BEAM_ROT is not really usable if you only want to apply rotations on only some element of a set of overlapping field map.
Concerning the space-charge in curved trajectories, I will have a discussion with our specialist and see if this option could be proposed with the reserves which is necessary in these conditions taking into account the current algorithm not adapted. I will keep you posted, but probably not until September because of the holidays.

Regards,

Didier

Thank you Didier. I am glad to hear that enabling the space charge in curved maps could be possible. Looking forward to hearing the outcome of your inquiry into this.

Dear Vlab,

As promised in my previous post, the space charge is now effective in the trajectory curving field maps. Of course code upgrading is mandatory to get this new feature.

Regards,

Didier

Wow, great news! Thank you very much.