### Development of a Multirate Method for Adjoint Sensitivity Analysis in Nonlinear Networks

2022

### Modeling and Simulation of Insulation Layers in Superconducting Magnets

2021

### Architecture Optimization in Physics-Informed Neural Networks

2021

### Transient Finite-Element Simulations of Fast-Ramping Muon-Collider Magnets

2023

Bachelor thesis, Master thesis, HiWi Position

Currently, an international consortium develops a concept for a muon collider [1].

Because of the short lifetime of a muon, fast-ramping magnets are needed for bending and focusing the beam. For their design, efficient and reliable transient finite-element (FE) simulations are needed. In this student project, 2D transient FE models will be set up for two already proposed magnet designs. Moreover, models will be selected to consider the relevant losses in the yoke and the coils.

A field-circuit coupling will be developed for considering the excitation by a resonant power-electronic circuit. Options for operating the magnets under high saturation, and possibly with a bias current, will be studied.

**Supervisor**: Prof. Dr.-Ing. Herbert De Gersem### Geometry/Topology Optimization in High End Lithography

2023

Master thesis

This research project is planned in cooperation with Carl Zeiss SMT GmbH, the Semiconductor Manufacturing Technology business group of ZEISS. Nowadays, most high-end microchips are produced using EUV-Lithography, where a design from a photomask is repeatedly printed on a wafer. Due to the electrodynamic light matter interaction, the photomask design and the corresponding image on the wafer may differ significantly. The goal of this thesis is the formulation, development, and benchmarking of a top-notch topology optimization solution solving inverse problems.

**Supervisors**: Armin Galetzka , M.Sc., Prof. Dr.-Ing. Herbert De Gersem### Enabling Quasi-3D Simulations in Pyrit - a finite-element solver in Python

2023

### Simulation of HVDC Cable Joints

2023

Bachelor thesis, HiWi Position

In the context of the green energy transition, the interest in high voltage direct current

(HVDC) cable systems is growing. Cable joints (see Fig. 1) are known to be

the most vulnerable part of these systems and must be designed carefully. In this

project, a HVDC cable joint is simulated and analyzed using commercial simulation

software (COMSOL) as well as the in-house simulation tool Pyrit. The main

focus of the project is a clear and appealing visualization of the results.

**Supervisors**: Maren Greta Ruppert-Schmidt, M.Sc., Dr.-Ing. Yvonne Späck-Leigsnering### Surface Impedance Boundary Conditions for a Scattered Field Formulation

2023

Master thesis, HiWi Position

To improve the simulation of particle dynamics, we couple two types of solvers using a scattered field formulation to solve Maxwell's wave equations in the time domain. Herein, the total electric field E is decomposed into a prescribed incident field E_i and a scattered field E_s. The two are coupled by the PEC-boundary condition which the sum of the two fields (but not each individually) have to fulfill.

The aim of this thesis is to generalize the concept of a scattered field approach to non-perfectly conducting materials at the boundary. When using a single field formulation, one can use surface impedance boundary conditions (SIBC). We want to apply this concept also to the scattered field formulation and implement it into our current simulation code.

The student will gain a broad background in the modeling workflow: How to start from physical equations, how to transfer them to a discrete representation and how to finally implement an effective realization in an existing code framework.

Prerequisites: Strong interest in numerical methods for electromagnetic field computations (PDEs, FIT) and their application. Interest in working with C++.

Feel free to pass by Jonas Christ for more details.

**Supervisors**: Jonas Christ, M.Sc., PD Dr. rer. nat. Erion Gjonaj### Implementation of a Graphical User Interface for the PBCI Code

2022

### Electrodynamic Model of a Pyrotechnical Switch for High Voltage Battery Systems

2022

Master thesis

**Introduction:**Soon the electromotive market will rapidly grow up. One aspect for this growth is the increase of the energy density of high voltage battery systems. This systems are built up with Li-Ion cells with a module voltage up to 850V. To increase the performance of such systems, the inner resistance of the module has to be as small as possible. As a result, the short circuit current of such High Voltage Batteries reaches up to 20kA. To interrupt such a high short circuit current within 2ms the Pyrotechnical Battery Disconnector was developed by Joyson Safety Systems Aschaffenburg GmbH.**Task:**Development of an electrodynamic model of a pyrotechnical battery disconnector. Transient nonlinear electrodynamic FE simulations to improve the design of the Pyrotechnical Battery Disconnector.**Supervisor**: Prof. Dr.-Ing. Herbert De Gersem### Software development and maintenance for Pyrit - a finite element solver in Python

2022

HiWi Position

Pyrit is a Finite Element Method Based numerical field simulation software written in Python to solve coupled systems of partial differential equations. Currently, the modular solver covers static and quasistatic electric and magnetic fields, stationary current problems, stationary, and transient heat conduction problems. The different modules can be coupled to analyze multiphysical engineering applications, such as e.g. foil windings, cable joints, and surge arresters. The software is under continuous development. Thus, developing further parts and maintaining existing parts of Pyrit are the main tasks.

**Supervisor**: Jonas Bundschuh, M.Sc.### Optimization of a 320kV Cable Joint Specimen During Steady State Operation

2022

Bachelor thesis, Master thesis, HiWi Position

In the context of the green energy transition, efficient long-distance power transmission becomes increasingly important. The losses of extruded high voltage direct current (HVDC) systems are lower than those of high voltage alternating current systems and, hence, more and more HVDC systems are being deployed.

Cable joints connect cable segments, which are limited in length due to transport limitations. Cable joints are known to be the weakest part of HVDC systems as they are exposed to high internal field stresses. These stresses can be reduced by inserting a layer of so called field grading material (FGM), that features a strongly nonlinear conductivity. The FGM balances the electric field stress by becoming highly conductive in areas with high field strengths and, thus, shifting the voltage drop to less stressed areas. The aim of this work is to optimize the nonlinear conductivity of a 320kV HVDC cable joint specimen during steady state operation.

**Supervisor**: Maren Greta Ruppert-Schmidt, M.Sc.### Numerical Simulation of a Plasmonic Niobium Photocathode for SRF Gun Applications

2022

Bachelor thesis, Master thesis, HiWi Position

Currently available linear accelerators are operated in pulsed mode to prevent a thermal overload of the entire system. Upcoming planned CW operations are possible using SRF photoinjectors with either warm or cold photocathodes. The use of warm cathodes in an otherwise cold cavity, which initially appears advantageous, unfortunately leads to a variety of difficulties. On the other side, a cold photocathode cannot be made from the efficient semiconducting materials such that metals with intrinsically lower quantum efficiencies have to be applied instead. Nanostructured surfaces can be used to increase the effective quantum efficiency by surface plasmon resonance enhancement. Optimized nanostructures enable the efficient application of a given laser with a specified wavelength and allow a promising operating regime for future photoinjectors.

**Supervisor**: Dr.-Ing. Wolfgang Ackermann### Numerical Simulation of SRF Gun Coupler Kicks

2022

Bachelor thesis, Master thesis, HiWi Position

At DESY the currently available electron gun is based on a normal conductive copper cavity operated in pulsed mode. It will be replaced by a superconducting variant to enable also CW operation. The required electromagnetic field in the cavity is then excited by a dedicated input-coupler system originating from the well-known TESLA input power coupler. Additional HOM couplers are not considered in the current design phase but may be added if required. Due to the asymmetric coupling of the resonator fields to the external sources the extracted electron beam will observe a parasitic coupler kick which has to be minimized.

**Supervisor**: Dr.-Ing. Wolfgang Ackermann### Finite-Element Simulation of Eddy-Current Effects in Orbit Corrector Magnets

2022

Bachelor thesis, Master thesis, HiWi Position

The orbit corrector magnets of the PETRA IV will be excited at elevated frequencies. This causes eddy-current effects in the magnet’s yoke and in the beam pipe. The eddy currents may deteriorate the aperture field. Moreover, they cause losses, which need to be cooled away. Accurate predictions thereof are necessary already during early design stages. In this student project, 2D and 3D finite-element magnet models will be set up. Appropriate model parts for the laminated yoke parts, the windings and the thin beam pipe will be inserted. They should allow to accurately simulate the particular eddy-current effects in these parts. A parameter study of the eddy-current effects for different design choices will be carried out.

**Supervisor**: Prof. Dr.-Ing. Herbert De Gersem### Finite-Element Electric-Machine Simulations Accelerated by Cheap Surrogates

2022

Bachelor thesis, Master thesis, HiWi Position

The scientific question is whether a surrogate (low-fidelity) machine model can be employed to accelerate a computationally expensive (high-fidelity) finite-element machine simulation. The research hypothesis is that a well-constructed surrogate may perform better than a pure algebraic surrogate for standard machine types. It is expected that an established machine model can be trusted in a region which is substantially larger than a standard quadratic surrogate of the high-fidelity model. In order to preserve accuracy, the surrogate model will be adapted algebraically such that it locally has at least a linear consistency with the finite-elmeent model. This will be achieved by additive or multiplication defect corrections. In particular, an additive correction with quasi-second-order consistency will be set up using Broyden-Fletcher-Goldfarb-Shanno updates for the Hessian of the high- and low-fidelity models.

**Supervisor**: Prof. Dr.-Ing. Herbert De Gersem### Circuit simulation with a discontinous Galerkin based data-driven modified nodal analysis solver

2022

Master thesis, HiWi Position

An electrical circuit can be fully described through Kirchhoff's circuit laws and the employed lumped elements. Kirchhoff's circuit laws are directly derived from Maxwell's equations and thus considered to be exactly known. Contrarily, the behaviour of the lumped elements is at first only known through measurements. In conventional approaches, a model that fits best to the available measurement data must be derived. This is typically accomplished by means of empirical modeling approaches, which however cannot represent the elements' behaviour exactly, introduce epistemic uncertainties, and can be difficult to apply for sophisticated elements.

Data-driven solvers dispense with empirical models by solving the underlying problem directly on the measurement data instead.

Therefore, errors arising from the modelling process as well as epistemic uncertainties are avoided and the data-driven solutions can be considered as assumption-free.

The aim of this work is to develop a data-driven modified nodal analysis solver that employs a discontinuous Galerkin formulation to solve along the time scale.

**Supervisors**: Armin Galetzka , M.Sc., Dr.-Ing. Dimitrios Loukrezis### Simulation of the electromagnetic properties of accelerator cavities

2022

Master thesis

At DESY in Hamburg the particle accelerator PETRA will be equipped with new rf resonators for the acceleration of the particles. For this reason the electromagnetic properties of these cavities have to be investigated. The 3D electric and magnetic fields can be simulated with numeric tools. And these fields need to be evaluated by post processing to calculate the accelerating and deflecting effects on the charged particle beam.

**Supervisor**: Dr. phil. nat. Wolfgang F.O. Müller### Modeling and Simulation of Foil Windings

2022

Bachelor thesis, Master thesis, Projectseminar, HiWi Position

In many applications, foil windings are preferred over wire windings or Litz-wire windings because of their better thermal properties, higher fill factor, lower resistance and easier construction. Foil windings are used in inductors, magnet systems and transformers. Contemporary developments are focusing on increasing frequencies, lower weight and production cost and shorter time-to-market. Further research on foil windings is driven by applications such as, e.g., foil-winding transformers for DC-DC converters and foil windings used in filters or for wireless power transfer.

The skin effect which becomes increasingly important at higher frequencies, is counteracted by using thinner foils. For a skin depth below the foil’s thickness, the skin effect is assumed to be only relevant at the foil tips. There, however, high current densities may lead to hot spots, even when the tips are well cooled. Additionally, fringing flux impinging perpendicularly on the foils causes eddy currents, possibly leading to unacceptably high local losses.

**Supervisors**: Jonas Bundschuh, M.Sc., Dr.-Ing. Yvonne Späck-Leigsnering

### Development of a Multirate Method for Adjoint Sensitivity Analysis in Nonlinear Networks

2022

### Modeling and Simulation of Insulation Layers in Superconducting Magnets

2021

### Architecture Optimization in Physics-Informed Neural Networks

2021