SOURCE: Simulation and Design of Electron and Ion Sources

This package computes the properties of electron and ion sources, including thermionic guns (e.g. LaB6), cold and thermal field emission (TFE) sources, liquid metal ion sources, and sources with magnetic focusing.  The program can handle rotationally symmetric or planar electrode structures with large changes in geometrical scale factor, includes dielectric materials and space charge effects.  Theprogram computes the apparent position and size of the crossover, the cathode current density

distribution, the total beam current and the beam brightness as a function of the beam half-angle.

The basic method used in the software is the second-order finite element method (SOFEM).  Curved electrodes are easily handled, and pointed cathodes with sub-micron radius spherical tips can be modeled accurately, even when the extraction electrode is several millimeters away from the tip.

In regions where the emission is temperature-limited, the Richardson-Dushman equation is used, with Schottky's correction.  If the emission is in the field-emission regime, the Fowler-Nordheim

equation is used.  In the extended Schottky region, a set of numerical formulae are used to compute the emission current density.  Child's law is used in regions where the emission is space-charge limited.  A special equation relating cathode field and emission current density is used in the case of ion sources.

The optical properties of the gun are output in tabular form, and facilities are provided for computing and plotting any specified equipotentials and electron trajectories, and for plotting graphs of the beam brightness as a function of the beam half-angle. 

Software packages for post-processing the results in a graphical form and transferring the ray data into subsequent lenses of the column are available.  After analyzing an electron or ion source with the standard SOURCE software, many (tens of thousands) of rays are computed in the source region with the initial rays conditions randomly generated, taking into account the current density distribution over the cathode surface and the Maxwell-Boltzmann initial velocity distribution.  These rays are used to plot spot diagrams, current density and current histograms, current distributions through knife-edge, and emittance diagrams.

If you are interested in the SOURCE package, please contact us at info@electronoptica.com.

TFE gun - Enlarged view of tip region       TFE gun with a magnetic lens 

Spot diagrams, current density and current histograms at                                    Emittance diagram

five planes around the virtual crossover (right).

LaB6 gun -- Enlarged view of tip region