28th example file, carbon nano-tube, for field emission source
The tube has inner and outer diameters of 6 and 10nm respectively, and has a semi-circular end. To create a field a plate is placed arbitrarily 100nm away, with a potential
of 20V.
The semi-circular end is taken as the cathode. It is subdivided into 10 segments, and the program starts a ray from the centre of each of these segments.
Including the line:
'field emission cathode xa 3.'
has the effect of adding 3eV to each initial kinetic energy. See the comments at the end of xmpl2d28.dat for an explanation.
The 5 rays coming from the lower half of the semi-circle carry currents that are much smaller than those carried by the rays in the top half.
The maximum field at the surface of the nano-tube is approximately 2.8E6 V/mm. Compared with the nominal field of 20V over 0.0001mm, this is approximately 14 times larger, which is therefore the 'enhancement factor'.