Dipl.-Phys. Franziska Reimann

Fakultät für Informatik und Elektrotechnik
Albert-Einstein-Straße 2 
18059 Rostock
Haus 5, Ex 137
Tel.: 0381-498-7075
Fax: 0381-498-7081
Email: franziska.reimann(at)uni-rostock.de



The overall aim of the BMBF-funded project „WAKOMP“ is the development of concepts to manipulate the longitudinal phase-space distribution of electron beams, specifically their energy widths.

To achieve this, passive wakefield dechirping methods are studied, which rely solely on the use of a simple waveguide structure, the so-called “dechirper”. Possible dechirping structures encompass cylindrical and rectangular waveguides of comparatively small dimensions, where the generation of a wakefield is assisted by either a corrugated surface or the insertion of dielectric coatings or slabs.

Figure 1: A dielectrically lined rectangular waveguide. Indicated in green is the electron beam.

For ELBE, it was decided to use a dielectrically coated rectangular waveguide. This type of structures, due to its geometric simplicity (c.f. figure 1), provides several advantages: On the one hand, the structure can be built in a way that allows for a tuning of the desired dechirping by adjusting the gap width between the dielectric slabs, which can be fitted in a movable way. On the other hand, the obvious similarities to the standard textbook problem of a rectangular waveguide, the dechirper can be considered in an analytical way that allows for a calculation of a Green’s function wakefield. The Green’s function wakefield, in turn, provides the most fundamental component to understand the effect of the dechirper on a variety of possible electron beams.

Figure 2: Electric field strength of the LSM_101 mode inside a dielectrically lined rectangular waveguide.

Figure 3: Electric field strength of the LSE_011 mode inside a dielectrically lined rectangular waveguide.


  • Semi-analytical mode analysis of the dielectrically lined rectangular waveguide
    (c.f. figure 2 and 3)
  • Analytic calculation of the electric and magnetic field of a single point charge inside the dielectrically lined rectangular waveguide using an eigenmode  expansion
  • Deriving the longitudinal point-charge wakefield (i.e. the Green’s function) from the calculated electric field
  • Convolution of the Green’s function with arbitrary shapes of electron bunches and determination of the subsequent change in the phase-space distribution (c.f. figure 4)

Figure 4: Effect of a rectangular dechirper with different gap widths on a Gaussian beam with an energy chirp.


The Green’s function wakefield calculation is carried out by a Python programme developed in 2014 in the course of this project.

R E S E A R C H   I N T E R E S T

Numerical simulation and analytic description of electromagnetic fields

  • Wakefields and passive wakefield dechirping; especially in rectangular waveguides with dielectric slabs
  • Phase space analyses of electron beams exposed to wakefields
T E A C H I N G   A C T I V I T I E S
  • Seminar: Advanced Computational Electromagnetics and Multiphysics (SS 2015)

  • Exercise: Numerical Simulation of Electromagnetic Fields/ Computational Electromagnetism (WS 2015/2016)

F. Reimann, U. van Rienen, U. Lehnert, P. Michel, Wakefield-based Dechirper Structures for ELBE, Proceedings of the International Particle Accelerator Conference 2014, Dresden, Germany (2014).


F. Reimann; U. van Rienen, P. Michel, U. Lehnert: A dielectrically lined rectangular waveguide as a wakefield dechirper for ELBE. 2015 Intl. Conf. on Electromagnetics in Advanced Applications (ICEAA 2015), 7-11 Sept. 2015, Torino, Italy.