Consistent Charged Particle Simulation of a Pierce Gun

The pierce type gun example demonstrates the analysis of an electrically  large gun configuration. The acceleration of the electrons takes place in only a small part of the computational domain, nearly 90% of the gun consists of a drift-tube. 

The electric field is established by the cathode, which acts at the same time as particle source, a guiding electrode and the anode, which incorporates the drift-tube. The magnetic field is produced by a large current-driven coil and guided by a highly  permeable cylinder which encloses the whole configuration.

Figure 1 shows the geometry of the gun which consists of hollow cylinders forming the guide for the magnetic field, the drift tube, the emitting cathode and the focussing cathode. typical construction features used to create the model include lofting, chamfering and blending operations. The geometric properties of the coils were created with the aid of two curves, one for the coil cross-section, the other for the coil sweep path.

Three solvers have to be applied to perform this gun-analysis: First the E-static and M-static solver calculates the Electromagnetic fields which accelerate and focussing the particles. For the electrostatic calculation, the cathode was assigned a potential value of 0V, while the anode carries a potential of 90 KV. The magnetic coil is driven by a current of 1000 Ampere-Turns. The particle source, shown in Figure 2, covers the concave face of the cathode and emits the particles. The gun-iteration is then performed : the space-charge limited emission model was applied so that particles are emitted as long as the field in the near of the particle surface is larger than zero.

Figure 3 shows the electric and magnetic fields on a central plane through the cathode.

All electromagnetic field quantities are available. Figure 4 shows a typical trajectory plot of the particle velocities in the pierce gun. Other impulses included are the energy, beta and gamma. These can be visualised in time using the animation plot features in CST PS. Other quantities resulting from the Gun iteration can also be viewed: the magnetic energy, the electric energy, the emitted current and the perveance of the particle source over the iteration cycles.

As in all of CST's products, full parameterisation and optimisation modules are included as default. Full CAD support complements these facilities to ensure rapid model creation and simulation.