Option for importing charges.

 

 

See also note on electrostatic force and also test3d29 and xmpl3d85, which show the representation of macroscopic charged particles.

 

This option is accessed from the bottom of the sheet /databuilder/segments/advanced options/.

 

This is the procedure for setting up a simple object that has known surface charges (see section g below for more complicated objects):

(1) Use CPO3D to create a data file for the object.

(2) Put the object at V = 1 (or at some known potential) and put the printing level at 'all'.

(3) Disable the 'zero total charge' option.

(4) Run CPO3DS to obtain the surface charges.

(5) Copy the ray output file to tempin.dat

(6) Run program30, which will read tempin.dat and put the charges into tempout.dat.

(7) Go back to the data file and insert further electrodes, placing them before the object.

(8) Go to /databuilder/segments/advanced options/. At the bottom of the sheet click on the option for importing charges and enter the requested numbers, the scale factor and the file name (which is tempout.dat, unless you have changed this).

(9) Be careful about the 2 requested numbers. You should check them by looking at the segment and charge information in the previous ray output file, or by inspecting the graphics pictures.

(10) Disable the 'zero total charge' option.

(11) Run.

 

By zooming and doing a potential contour plot you will see that the contours around the body are modified by the presence of the other electrodes.

 

Miscellaneous notes:

(a) The body could be made of dielectric material, but this does not affect the present simulation, because CPO3D is only aware of the surface charges and so is not aware of how they were produced nor of the type of surface on which they are situated.

(b) If the body is a dielectric then CPO3D/Dielectric can be used to find the surface charges.

(c) The charges on the segments of the body could be calculated externally and then put into tempout.dat. Remember that in CPO3D a symmetrical object such as a sphere does not have segments that all have the same area. So an external calculation might have to take account of the segment areas.

(d) When the segments of the object are moved, using the ‘transform’ option, then the imported charges move with them.

(e) There is an option to scale the imported charges.

(f) There is also an option to find the net electrostatic force on the object.

(g) When the ‘object’ consists of more than one electrode and is a part of a larger system then the procedure changes slightly. For example the object might be an acceleration tube and the larger system might include an electron gun and the user might want to alter the geometry or conditions of the gun without changing the tube. If the user is confident that changes to the gun do not affect the surface charges on the tube then the above procedure would become:

(1) Use CPO3D to create a data file for the gun and tube, specifying the gun electrodes before the tube electrodes.

(2) Put the electrodes at their known potentials and put the printing level at 'all'.

(3) Disable the 'zero total charge' option.

(4) Run CPO3DS to obtain the surface charges.

(5) Copy the ray output file to tempin.dat

(6) Run program30, which will read tempin.dat and put the charges into tempout.dat.

(7) Edit tempout.dat to remove the charges on the gun.

(8) Go to /databuilder/segments/advanced options/. At the bottom of the sheet click on the option for importing charges and enter the requested numbers, the scale factor and the file name (which is tempout.dat, unless you have changed this).

(9) Be careful about the 2 requested numbers. You should check them by looking at the segment and charge information in the previous ray output file, or by inspecting the graphics pictures.

(10) Disable the 'zero total charge' option.

(11) Run.