A field emitter tip is usually one part of a so-called field emitter array. Such an array consists of lots of field emitters that are typically located on a 2D plane. For example, they are used to build displays, diodes, lasers and phosphor-lamps.
As the name suggests, the emission of a field emitter is depended on the electric field. Thus we use the field-induced emission model of the Particle Tracking Solver that is based on the Fowler-Nordheim equation. Additional information about this type of emission model can be obtained from the online help.
As the top of the cone is very small, the electric field is very high in this region - in our case the electric field is about 3e9 V/m. Without such a high field, the field-induced emission would not work properly.
The field emitter tip's cathode consists of a PEC cone and sphere, that is placed on the cone's top. A particle source is defined on the sphere's surface and emits particles depending on the chosen field emission model parameters.
Two PEC plates are used to accelerate the particles. The lower has a potential of 54.5 V whereas the upper plate has a potential of 1000 V. As the tip has a potential of 0 V and the particles emit with a low momentum, the particles hits the upper plate with an energy of 1000 eV.
To obtain a finer mesh in the emission region, a vacuum "dummy" body is set up. A change of the local mesh properties of this dummy results in a better local mesh refinement.
To simulate the behavior of the field emitter tip, two solvers have to be used - the E-Static Solver and the Particle Tracking Solver. As the gun iteration modus is enabled, the solution is calculated iteratively. That means the tracking solver calculates a charge density, which is used as source for the tracking solver. The particle solver uses the electric field to calculate emission and movement of the particles.
E-Static solver run.
Particle Tracking Solver run. The electric field is used the calculate the particles' emission and their movement.
E-Static solver run. The charge density of the tracking solver is used as source the E-Static solver.
... and so on ...
The solution process is finished when the accuracy of the user defined value -20 dB is reached.
After the particle tracking solver has finished, the tracking results can be found in the navigation tree. To get an overview what happened to the electrons, it is always interesting to have a look at the trajectories like in the picture above: "2D/3D Results\Trajectory". Additionally, you can compare the electric field before and after the gun iteration. Both fields are listed in the "2D/3D Results" folder of the navigation tree.
Information about the solver convergence and the development of the emitted current are available in the "1D Results" folder and can be already get during the solver run.
Some so-called solver notes (text files) are also a part of the navigation tree. For example, you can get data about the particle-solid interaction in the "Collision Information" solver note.