The investigation of electromagnetic processes in electromagnetic launchers using colossal magnetoresistance sensors

Oliver Liebfried

Doctoral dissertation

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The development of rails and armatures which ensure a sliding solid-to-solid contact during the whole projectile acceleration is a great challenge in the field of railgun technology. Multifaceted physics exists at the sliding contact interface: The current concentrates at the rear of the interface due to magnetic diffusion processes and the fast armature movement. Consequently, Joule heating leads to enhanced wear in this region. In this dissertation, magnetic diffusion in railguns is investigated by means of measuring magnetic fields with CMR-B-scalar sensors at static and dynamic experimental conditions. These novel sensors, based on La0.83Sr0.17MnO3 thin films exhibiting colossal magnetoresistance were adapted for the use at railguns.

It was found that these sensors are effective tools to measure the magnitude of high pulsed magnetic fields independent of the field orientation. Magnetic field distributions influenced by proximity and velocity skin effect could be measured in the harsh railgun environment. The obtained results allowed to estimate the skin depth in the rails at the sliding interface of a fast moving armature (>1500 m/s). Furthermore experiments with fixed multiple brush armatures showed that front brushes can have contact problems in case of missing contact pressure.

The dissertation consists of an Abstract, an Introduction, 6 chapters, General Conclusions, References, a List of Publications and 2 Appendices.

The introduction reveals the investigated problem, the importance of the thesis and describes the purpose and tasks of the work. Furthermore, it presents the research methodology, the scientific novelty, the practical significance of results, the defended statements and the acknowledgement.

Chapter 1 gives a literature review and introduces the field of railgun research and the idea behind this dissertation. Chapter 2 describes the experimental setups and main equipment. Chapter 3 deals with the CMR-B-scalar sensor and related metrological questions. The use of the sensor in static and dynamic coilgun experiments is presented in chapter 4. Chapter 5 deals with the investigation of magnetic diffusion and the current distribution in the rails of a railgun. Chapter 6 is about the current distribution in brush armatures.

Seven articles focusing on the subject of the discussed dissertation have been published so far: Six articles in Journals listed in the Thomson ISI Web of Science and one article in the proceedings of an international conference. Seven presentations of the subject have been given at 5 international conferences.

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124 p.
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