Particle dynamics applications

Accelerator components

Accelerator components such as cavities or beam position monitors are typically designed with the Eigenmode, Transient or Frequency Domain solvers. However, when it comes to the interaction with the beam, the Wakefield solver is an incredibly versatile tool (read more about CST Studio Suite solvers here).

We consider the 9-cell cavity of the TESLA accelerator shown here. The goal is to maintain the electron beam acceleration during the whole propagation of the beam along the accelerator. RF-power is generated and coupled in to the TESLA cavities to establish these EM-Field in the cavities. The electrons passing through the cavities need to keep the right phase relation to the field in order to maintain acceleration. The electron beam, a strong current by itself, however induces high frequency fields and excites modes, the so-called wakefields, while traveling through the cavities that could limit or interrupt the acceleration process. The Wakefield solver computes these fields and helps to improve the design of the accelerator components.   

Vacuum Electron Devices such as Traveling Wave Tubes (TWT) are used mainly for satellite communication because of their reliability, but also thanks to their performances. For instance, in the frequency range between 1-60 GHz, the amplified signal can reach an output power up to 500W with an efficiency over 50% (for space TWTs).

In contrast to their solid state counterparts, they show higher efficiency, higher reliability, better thermal performance and a slightly better linearity. However, they are more expensive to build. Thus, TWTs are used when reliability is a must, such as for high powers and on satellites. Simulation is very attractive in these design processes as it reduces the need for multiple costly prototypes.

The design of a TWT can be completely performed using the PIC solver to characterize the Slow Wave Structure (SWS) which corresponds to the interaction region between the electron beam and the RF-signal sustained by the helical structure.

An RF-signal is introduced from an input coupler. During the propagation of the electrons along the SWS, the kinetic energy of the electrons is transferred to the traveling wave. Along the tube, the electron beam starts to be bunched and the electrons lose their kinetic energy which is globally transferred to the traveling wave. The traveling wave is then amplified with a maximum power extracted in the output coupler.  

Plasma applications typically have large time scales and the plasma can be described by its space charge interaction between the electrons and the ions. The Electrostatic Particle-In-Cell (ES-PIC) technology computes space charge versus time, taking into account the electrostatic effect only. This means that compared to a pure PIC approach, there is no current and H-Field induced but it is very well suited for these plasma applications. It also stays valid for plasma applications where the phenomenon can be described by the space charge dynamics and collisions at relatively low pressure, neglecting the temperature gradients of the ions and the convection effects which would require another numerical approach.

Power Sources for Fusion Plasma

Plasmas for fusion are very hot plasmas. They are created in tokamaks and provide a new source of energy production. This is one of the sustainable energy under investigation today to answer the energetic problems the world is facing. The energy of the future must come from clean, safe and controlled fusion.

In the main operating principle, the plasma needs to be maintained confined. This is the role of the very complex magnetic coils design surrounding the tokamak. Then, the plasma needs to be sufficiently hot to maintain the thermonuclear reactions. This is the role of the Gyrotron Devices which can be fully designed and simulated with the PIC solver.

Gyrotrons are high power vacuum electron devices capable of generating output powers in the order of hundreds of kW with operating frequencies up to several hundreds of GHz. Gyrotrons are very well suited for plasma heating process because the microwave frequency generated can excite one of the plasma frequencies. The waves transfer their energy to the plasma leading to the heating process.