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Such a system is used for chambers constructed from wires and planes unless one of the following conditions is met:
Polar coordinates are internally dealt with by the conformal mapping:
(x,y) = exp(rho,phi) z = zetathanks to which the potential functions and drift line integration procedures for Cartesian coordinates can be used. Most of the commands accept polar coordinates for input and translate the the output to polar coordinates. Procedures as a rule don't do this. A set of procedures is therefore provided for these transformations: CARTESIAN_TO_POLAR, CARTESIAN_TO_INTERNAL, INTERNAL_TO_CARTESIAN, INTERNAL_TO_POLAR, POLAR_TO_CARTESIAN and POLAR_TO_INTERNAL.
The tube coordinates are special in the sense that the wire locations are listed in Cartesian coordinates, while the tube is an object with a polar shape.
Garfield internally uses Cartesian coordinates for cells of this type. Potentials in round tubes are computed using the conformal mapping:
z - z0 z = ----------- 1 - z0bar zwhich maps z0 to 0 and which maps the unit circle onto itself.
Potentials in polygonal tubes are computed by mapping the centre of the tube to a round tube, while the edges are mapped with a local Schwarz-Christoffel expansion.
Formatted on 09/03/10 at 00:22.