Stopping rays when they hit an electrode.
In both CPO2D and CPO3D there is an option to stop rays when they hit an electrode (that is, attempt to cross the electrode). This involves a slight increase in computing time for CPO3D.
For some simulations the rays should be allowed to pass through all the electrodes, for example when an electrode is simulating a partially transparent grid or mesh.
In other simulations the rays are allowed to pass through (n-1) electrodes and are then stopped at the n'th crossing -this option is also available.
Crossing electrodes presents no difficulty in the BEM because the physical electrodes are replaced by sheets of charge, through which rays can pass.
There is also an option to stop rays at a selected test plane.
Stopping rays at electrodes:
The final point of a ray that hits an electrode is the hitting point (which is obtained by interpolation in the same way that crossing points of the test planes are obtained). If the ray step length is large and the electrodes are closely spaced then it can happen that more than one crossing occurs inside a step, but the programs looks for only two such crossings.
Disabling the 'hit electrode' option:
For some simulations the rays should be allowed to pass through the electrodes, for example when an electrode is simulating a partially transparent grid or mesh. There is no problem in the BEM method about rays passing through electrodes, because the electrodes are effectively replaced by sheets of charge, which particles can easily pass through.
Disabling the option gives a small decrease in the computing time.
One further comment about particles hitting electrodes:
When a ray has a high curvature and is in the vicinity of an angle between two electrodes it might occasionally appear to hit the wrong electrode. This happens because the program takes a straight line between the end points of a ray step to decide which segment has been crossed (but of course interpolates more exactly to establish the coordinates at the crossing point, even if this then lies outside the segment). The problem is easily obviated by using a smaller step length or time for the ray tracing.
Backward tracing, time markers
It is possible to choose the active range of electrodes, that is, to allow some electrodes to be transparent while other electrodes are not.
Go to general note on fields of view and ray limits.
For users who are editing or constructing an 'input data file' without the use of the data-builder -that is, pre-processor:
But Manual editing is certainly not recommended -it is a relic from the time when the databuilder was not available All users are strongly encouraged to use the databuilder, which always gives the correct formats and which has many options for which the formats are not described or easily deduced.
CPO2D: Put 'y' or 'n' at the start of the relevant line (for 'yes, stop' or 'no, do not stop').
CPO3D: Put 'y' or 'n' in the third space of the line that starts with + or -.
CPO2D and CPO3D: For stopping at the n'th crossing, use 'Y' instead of 'y' and follow on the same line with the number of crossings.