Power Supply Options for a Naval Railgun

Large railguns require powerful power supply units. At the French-German Research Institute of Saint-Louis (ISL) most experimental railguns are driven by power supply units based on capacitors. Recent investigations at ISL explore the possibility to use coil based systems to increase the energy density of the power supply. In this study an electrical circuit simulation is used to investigate the difference for railgun operation in between a capacitor and a coil based power supply with respect to current amplitude behavior and projectile velocity. For this a scenario of a 25 MJ muzzle energy railgun is simulated with two different power supply options, replacing capacitors by coils and using a range of circuit resistances. The resistance determines to a large part the losses of the system and defines therefore the efficiency of the launch and the size of the power supply. The interpretation of the results of the performed simulations leads to the conclusion that the capacitor based system "naturally" pro- duces a favorable current pulse trace with respect to launching a mechanical delicate payload. Further simulations show that the disadvantage of the inductor based supply can be mitigated by increasing the power supply unit subdivision into smaller units.Comment: Submitted to IEEE Transactions on Plasma Physic

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

Summary of doctoral dissertationSummary of doctoral dissertatio

Elektromagnetinių procesų tyrimas elektromagnetinėse svaidyklėse naudojant milžiniškos magnetovaržos jutiklius

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.Doctoral dissertatio

On the use of lithium batteries at high power pulses discharge rates

This paper deals with the use of Lithium Batteries at high pulses discharge rate. The use of a commercial nanophosphate-based ultra high power Li-Ion cell discharged by high current pulses is analyzed by means of an ad - hoc experimental setup. Main cell parameters like nominal capacity, internal impedance, discharge efficiency are measured and discussed. An ad - hoc test procedure and a new strategy for defining the 'end of test' condition are presented and discussed in order to specify a stress-relieving condition for the battery during high pulsed power applications

Experimental tests for Lithium batteries discharged by high power pulses

This paper deals with the characterization of Lithium batteries discharged by high power pulses. The experiments were conducted with a commercial ultra high power Li-Ion cell (A123 26650M1-A), which was tested by means of an ad - hoc implemented experimental setup under controlled climatic conditions. Performance reduction of the cell, in terms of capacity and efficiency losses, is analyzed and discussed. Furthermore, this paper investigates the degradation effects and aging of the battery with regard to the frequency behavior of the equivalent impedance using the electrochemical impedance spectroscopy technique

Measurement of the magnetic field distribution in railguns using CMR-B-Scalar sensors

Colossal magnetoresistance effect B-scalar magnetic field sensors with effective areas of 0.05 mm(2) were used very close to the rails for magnetic field measurements. These measurements were performed during static and dynamic railgun experiments. In static experiments three different rail materials were used and the results are compared to a finite element simulation

Thin film manganite-metal interconnection and "Loop Effect" studies in CMR-based high magnetic field sensors

The design, technology and main characteristics of Ag contacts as well as "loop effect" peculiarities of colossal magnetoresistance B-scalar high magnetic field sensor based on La1-x(Ca)SrxMnO3 films used for measuring high magnetic field pulses are presented