Reflection of rays in planes of reflection symmetry in the absence of a magnetic field.
Rays should usually be started only in the minimum sector -for example if x=0 and y=0 are reflection planes, the starting points should be confined to the region of positive x and y.
The user can choose which planes the rays are to reflected in -see note on specification of ray reflection- except that no reflections are allowed if the voltages are time-dependent. If there are space-charges the rays will automatically be reflected (see general note on space-charge).
The user would usually only want to reflect rays in planes that pass through the axis of the beam (that is, transversely to the direction of the beam).
A plane through which rays are reflected must also have been declared at the beginning of the program as a plane of positive voltage reflection symmetry.
In CPO2D the z axis is an axis of symmetry, and so any straight-line ray that appears on the screen is in fact a cylindrical or conical sheet of current. If the ray crosses the axis then there are two conical sheets, the end points of which meet on the axis at the crossing point. There is then a choice of representing the ray as (1) a line that crosses the axis, which is the representation used in CPO2D and CPO2DS or (2) as a line that is reflected at the axis. We have chosen the first option because this is what happens physically (for a meridional ray). See also further notes on space-charge in CPO2DS.
The reflected rays appear on the screen in all the 2D and 3D pictures, but are not entered in the output data file.
The beam section also contains the crossing points of the reflected rays (unless the beam section plane is inclined in such a way that these reflections are not appropriate for the beam section).
Possible imperfections: If a symmetric electrode geometry is set up without the use of planes of symmetry then the segments might not have exactly the same symmetry, because of the way in which the electrodes are subdivided. Then the rays might not have exactly the expected symmetry. This happens for example in xmpl3d41. See also the note on electrode reflection symmetries.
Return to general note on symmetries.