xmpl3d81, 81st 'example' data file for CPO3DS

Multichannel electron multiplier.

(See xmpl3d82 for tilted channels.)

One channel is simulated. It has diameter 0.1mm, length 5mm. The 2 ends are shielded with small field-free boxes. The voltage difference between the ends is 1500V.

20 electrons are injected with an energy of 100eV.

The ray tracing inaccuracy is put at 1e-5, to stop any secondary rays penetrating the wall of the tube (which they might do if their initial energy is very small and the ray tracing inaccuracy is not small enough).

When an electron hits the side of the channel it produces secondaries. The energy, direction and current of the primary ray are measured when the primary hits a side and these parameters are used to determine the energy, direction and current of the secondary ray. Each ray represents a set of electrons. In principle there should usually be more than one secondary electron per primary electron, but CPO3DS cannot generate more than one secondary electron, so the currents of the rays carry the information about the number of electrons that are represented by the ray.

3 options are triggered in this example:

A Maxwellian distribution of the energies of the secondaries.

A Lambertian (cosine) distribution of directions.

A Poisson distribution of the currents.

Information on all of these can be found in the note on secondaries.

A further 2 options are triggered:

1. The voltages V1 and V2 are applied to the ends of the channel at z = 0 and 5. Therefore the oints of application of V1 and V2 do not coincide with the

ends of the individual segments, which would cause a warning message to appear. We avoid this by checking \databuilder\segments\advanced options\allow 2 different voltages to be applied at points outside electrodes\.

2. We have allowed for a large number of collisions at which secondaries are produced (up to 30), but do not want secondaries to be produced at the anode or its surroundings. So the option \databuilder\tracing rays\advanced options\restrict range of active segments\ has been checked and the value 680 entered for the number of active segments. This is the number of segments that make up the channel (and is deduced by temporarily using the highest print level for segment information).

The simple choice of a constant mean multiplication factor of 3 is used, but another possibility is the formula for the mean multiplication factor per collision taken from A. V. Raspereza et al, Submicrochannel plate multipliers, Applied Surface Science 111 (1997) 295-301.

In the present example, the mean multiplication factor n-mean (see the note on secondaries) is used for each collision (that is, the 'mean-poisson' option is used). This might represent an approximation to the real process but is the only viable choice here.

The 'minimum incident energy' for collisions is given the value 5eV, so if a primary ray has an energy smaller than this the ray is stopped. This is the main cause of rays not reaching the anode.

Here 16 rays reach the anode at the end of the channel, carrying a final total current of 0.250 mA (before reflections), so 1.00 mA after reflections. The initial total current of the 20 rays is 1.00E-6 mA. Therefore the multiplication factor is 1.00E6 in this example.

To investigate the effects of space-charge, which can affect the field alomg the channel, space-charge iterations should be used.