• Which Products are you interested in ?

    CST offers a wide range of EM simulation software to address design challenges across the electromagnetic spectrum, from static and low frequency to microwave and RF, for a range of applications, including EDA & electronics, EMC & EMI and charged particle dynamics.

  • Antenna Magus
  • IdEM
  • FEST3D
  • Optenni Lab
  • Looking for a Training, Workshop or eSeminar ?

    CST STUDIO SUITE® is being demonstrated at trade shows and workshops all over the world. Take a look at the list of conferences and exhibitions CST will be attending and get further information regarding CST workshops, eSeminars and training days.

  • TrainingsRegular training courses are held in CST's offices in Asia, Europe, and North America. Please check our trainings section for detail of trainings in all over the globe. Advance registration is normally required.

  • WorkshopsCST hosts workshops in multiple languages and in countries around the world. Workshops provide an opportunity to learn about specific applications and refresh your skills with experienced CST support staff. Make sure you visit our workshop section.

  • eSeminarsThroughout the year, CST simulation experts present eSeminars on the applications, features and usage of our software. You can also view past eSeminars by searching our archive and filtering for the markets or industries that interest you most.

  • Check our latest Events
  • Why create a MyCST Account ?

    A MyCST account may facilitate your access to many of the offerings on the CST website, for example the registration for eSeminars and the watching of eSeminars recordings, setting email preferences, and there is more functionality to come. It is required to participate in workshops and trainings.

  • Personal PreferencesAllows you to update your email preferences and areas of interest. It helps us to personalize your experience.

  • EventsSearch for events by location, industry and application. Once you are registered, you will be able to manage your registrations and check important details about your events. This section also provides you with a repository for Workshop & Training material.

  • LibraryYou can collect articles you find on the CST website to reference or read later by clicking on the “Add this article” button at the bottom of the article page.

  • Create Your Own Account
  • Need technical Support ?

    Customers can customize their accounts once they have completed the account creation process. This platform acts as vivid interface between CST and our customers.

    We therefore offer access to the latest Service Packs (including an automatic notification that a new Service Pack is available), a steadily growing database of Frequently Asked Questions (FAQs), Application Notes and Training Videos, as well as an individual FTP section for easy exchange of large files with our support team.

  • Do I need an Account?To access the Support Site a valid maintenance contract and a one-time registration is required.

    Please note that your Support login does not work for the MyCST account.

  • Get Support
  • How to request a Trial License ?

    Get your license in only three steps:

    1. Fill in the required fields in the contact form on the right and click "Send Us Your Request".

    2. Lean back and wait until one of our CST Experts contacts you.

    3. Enjoy a our trial license.

  • Student Edition

    Student Edition The CST STUDIO SUITE® Student Edition has been developed with the aim of introducing you to the world of electromagnetic simulation, making Maxwell’s equations easier to understand than ever. With this edition you have, bar some restrictions, access to our powerful visualization engine and some of the most advanced solvers of CST STUDIO SUITE.

    Student Edition

CST – Computer Simulation Technology

Ku-Band Traveling Wave Tube

The simulation of a traveling wave tube includes many aspects of physics and therefore a broad spectrum of the solvers available in CST Studio Suite® is needed. The structure of the tube is shown in figure 1. The particle beam is created in an electron gun and enters an adjacent slow wave structure. There, the beam interacts with the helical circuit to amplify the signal fed in at the RF input coupler. At the RF output the amplified signal is obtained. Since the particles would deflect each other due to an equal sign of charge, a magnetic field is used to keep the beam focused. In order to provide such a focusing magnetic field, a periodic permanent magnet (PPM) stackup is employed. Finally, when passing the RF output coupler the particles end in a collector, where their energy is recovered....

Figure 1: Traveling Wave Tube Structure

The simulation of an electron gun, where the particle beam is created, involves the evaluation of an electrostatic field in combination with particle tracking. A more detailed structure of the electron gun is shown in figure 2. The particles are emitted from the cathode towards the anode. A second electrode is used for focusing the generated electron beam.

Figure 2: Structure of the electron gun

Electric potentials are applied to generate an accelerating and simultaneously focusing electrostatic field. The electric potentials are applied in CST PARTICLE STUDIO® (CST PS), where also later on the particles are included. The corresponding routines of CST EM STUDIO® (CST EMS) to evaluate the electrostatic field are called internally by the software. The resulting electrostatic potential is shown in figure 3.

Figure 3: Electrostatic potential

The particle beam is then emitted from the cathode according to Child's Law. This represents an emission limited due to the space charge in front of the cathode. The emitted current and the particle trajectory (see figure 4) are obtained in CST PS. The color of the particle trajectories can indicate different values, as for example energy, velocity or charge of the particles. In figure 4 the color indicates the energy of the particles. This illustrates nicely that the particles start slowly (blue color), are accelerated by the electrostatic field to a final energy (red) and finally are only focused.

Figure 4: Particle Trajectories

The particles will leave the electron gun and enter the slow wave structure, where they are focused by a magnetostatic field. This field is generated by means of PPM stackup, which consists of several cylindrically shaped permanent magnets. The magnets show a varying remanent magnetization along longitudinal (z) direction. They can be easily included as source in a magnetostatic simulation. The resulting z-component of the magetic field along the z-axis can be seen in figure 5 (right).

Figure 5: Periodic Permanent Magnet (PPM) structure (left) and resulting longitudinal magnetostatic field along longitudinal axis (right)

After having analyzed the electron gun and the magnetostatic field of the PPM, the next step is the design of the slow wave structure. Here a helical slow wave structure supported by dielectric rods is used (see figure 6). The dispersion diagram of the structure can be obtained by a parameter sweep in CST MWS (see also Periodic Eigenmode Simulation of a Traveling Wave Tube). Besides the dispersion diagram shown in figure 6, the parameter sweep directly gives interaction impedance and phase velocity vs. frequency. The intersection point of beam line and ω-β diagram gives then either the operating frequency or the necessary beam voltage (see [1], Chapter 8, Figure 8.9 or 8.10).

Figure 6: Dispersion diagram for forward mode (red), backward mode (green) and third mode (blue). The x-axis shows phase shift for one helix length. The y-axis is angular frequency

In order to suppress the backward wave, the support rods are often coated with lossy material. This coating shows usually a longitudinal variation. To apply this spatial variation in the simulation, several parts of the support rods with spatially varying material properties are created with a customized VBA macro (see figure 7).

Figure 7: Spatially varying loss inside the helical circuit (varying color indicates varying loss)

After having performed the aforementioned cold test the RF amplification is simulated with the Particle-In-Cell (PIC) solver of CST PS. The resulting signals are shown in figure 8. In red is the low power RF input signal depicted. The blue curve represents the amplified RF output signals. The signals are obtained by waveguide ports embedded also in CST MWS. Their amplitude is sqr(Power) such that the power amplification can be evaluated by the signal amplitudes. The oscillation and the amplitude of the input signal (red) can hardly be seen in figure 8, since an amplification of 46.5 dB is gained.

Figure 8: PIC simulation time signals: RF input (red), reflection (green), RF output (blue)

This article shows the different physical aspects of a traveling wave tube design and their usage of the broad spectrum of the CST STUDIO SUITE. It involves the evaluation of electrostatic and magnetostatic fields (CST EMS). Particles need to be tracked through according to Lorentz Force equation to compute the DC current of the electron gun (CST PS). Possible RF interaction between the slow wave structure and beam needs to be carefully analyzed without particles in a so called cold test (CST MWS). And finally, a Particle-In-Cell (PIC) simulation with mutual coupling between fields and particles is perfomed to obtain the gain in a true transient process (CST PS).


[1] J. Benford, J. A. Swegle, E. Schamiloglu, "High Power Microwaves", 2nd Edition, Taylor & Francis Group, 2007

Rate this Article

0 of 5 Stars
5 Stars
4 Stars
3 Stars
2 Stars
1 Stars
contact support

Your session has expired. Redirecting you to the login page...

We use cookie to operate this website, improve its usability, personalize your experience, and track visits. By continuing to use this site, you are consenting to use of cookies. You have the possibility to manage the parameters and choose whether to accept certain cookies while on the site. For more information, please read our updated privacy policy

Cookie Management

When you browse our website, cookies are enabled by default and data may be read or stored locally on your device. You can set your preferences below:

Functional cookies

These cookies enable additional functionality like saving preferences, allowing social interactions and analyzing usage for site optimization.

Advertising cookies

These cookies enable us and third parties to serve ads that are relevant to your interests.