Particle dynamics applications
CST Studio Suite
CST Studio Suite contains a wide range of solvers, enabling the simulation of complex devices and the development of new technologies.
Often these complex devices are difficult to understand and it’s not easy to have analytic estimations, especially when they involve particles and the behavior is transient. Simulation is able to mimic the complex electron/wave interaction, responsible for a power generation/amplification process. The prediction of performance by means of simulation is a key task throughout the design.
CST Studio Suite includes several tools for designing charged particle devices, including the Particle Tracking Solver, the Particle-in-Cell (PIC) Solver and the Wakefield Solver. These can be used to design beamline components from particle sources, to magnets, to cavities, to absorbers.
Particle dynamics simulation is also crucial in the design of vacuum electronics devices. Magnetrons, gyrotrons, klystrons and traveling wave tube amplifiers are among the components that can be designed with CST Studio Suite. Breakdown effects such as multipaction and corona effects can be simulated and, with multiphysics simulation, the thermal and mechanical effects of high-power microwaves can also be taken into account.
There are several types of accelerators around the world such as Linear Accelerators, so-called LINACs, Synchrotrons to provide an energetic source of photons for material characterization, irradiation, biology and colliders constituted of rings where particles collapse and generate new energetic particles usually present in space and synthesized in laboratory for fundamental research and Universe understanding.
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 inclusion of the beam, the Wakefield solver is an incredibly versatile tool (read more about CST Studio Suite solvers here).
If you consider the 9-Tesla cavity accelerator shown here, the goal is to maintain the electron beam accelerated during the whole propagation along the accelerator axis. The induced EM-Field established in the Tesla cavities when the electrons are passing through needs to keep the right phase to maintain the particle acceleration. Therefore, one can see that the cavity oscillations and the generation of higher order modes could limit or interrupt the acceleration process. The simulation and the use of the Wakefield solver allows accurate design of the accelerator components.
Thermal effects can be included in a coupled simulation where low frequency (LF) losses are imported into the thermal solver.
If the LF solver is used, the eddy currents can be found (diagram on the left). With the losses of the material, these eddy currents represent a loss density evaluated automatically by the LF solver. This can be loaded into the thermal solver, which then shows the weak temperature behavior in the diagram on the right. This loop can be automized with our System Assembly and Modelling Approach, which allows a parametric coupling of the different physics.
Particle beams in the accelerator have to be guided and focused. That is possible via potentially complex magnet designs. Opera 2D or 3D is a market-leading software for this application. Depending on the user preference, this can also be simulated within CST Studio Suite.
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.
Plasma for Fusion
Plasmas for fusion are very hot plasmas are created in tokamaks and provide a new source of energy production. This is one of the sustainable energy under investigation nowadays to answer the energetic problems the world is facing with. 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 proper frequencies. The waves transfer their energy to the plasma leading to the heating process.
A very special feature in SIMULIA is RF-Breakdown analysis such as Multipactor and Corona effects.
For instance, let’s think about a rocket launch, where you of course need to have some electronics active to communicate with the vehicle and safely get the payload into orbit.
The question is what happens to the RF-components that are used for the onboard communication as it goes through the different levels of pressure during the launching process. This is important because you do NOT want to lose such mission due to possible RF-breakdown on critical RF-components.
Two ways of investigation can be performed here. When working at relatively low pressures, The Corona effect is dominant whereas for components embedded in space (which means very close to vacuum), the Multipactor effect is dominant. The multipactor is governed by the material properties and the so-called Secondary Emission Yield which controls the probability of emitting more than one electron from the impact of a primary electron on the RF-component surface. When the power of the RF-device is strong enough so that the local EM-Field can accelerate some electrons leading to a multiplication of secondary electron emission, creating an avalanche of electrons, multipactor occurs.
Multipactor and Corona effects are strong constraints which have to be taken into account during the design phase of the RF-components and the qualification tests.