This thesis derives working expressions from electromagnetic physical laws to gain a deeper understanding of the nature of railguns. The expressions are refined for ease of use and then compared to electromagnetic simulators that solve complex equations that arise from different rail geometry. Further simplifications lead to an expression for the final velocity of the projectile and showcase the importance of the system resistance to projectile flux gain ratio. A Simulink simulation then incorporates the resulting non-linear differential equations and approximates the projectile velocity over time based on physical dimensions and material properties. Some equations derived can be found in literature regarding the subject but often lack explanation. This work is intended to provide a thorough derivation of all the relative constituent relations between the critical characteristics of the gun such as the strength of the forces acting on the rail and projectile, rail current, and initial velocity of the projectile. This makes it easier to identify what influences acceleration of the projectile, how much bracing each rail needs, how much initial velocity to give the projectile, etc. Design options discussed besides the standard design include the augmented rail system, a magnetic shell design, and a “wrap around” design. The tradeoffs encountered in each design are discussed in length. Due to the lack of a sufficient power source during testing the projectile was unable to travel down the length of the rails due to metal binding, insufficient pulse duration, and too much circuit resistance. It was found that using copper tungsten for the rails ensures that the rails can withstand the arcing inflicted by the kilo-Ampere current along the rails very well compared to other materials. Also, the copper in the tungsten alloy ensures high conductivity while the tungsten provides structural integrity to the rails during arcing between them and the projectile. Frequency response of conductive projectiles is characterized and improvements such as laminated projectiles are suggested as solutions to mitigate eddy currents induced in the projectile and improve performance.

This thesis provides insight into the different aspects of compulsator design for use with railgun systems. Specifically, the design space is explored for passively compensated, permanent magnet iron-core compulsators. Seven design parameters are varied within a compulsator model developed for the Cal Poly Compulsator (CPCPA). The Matlab code for this model is included within the appendix. Efforts were made to compare and validate this compulsator model to published data from existing systems. The compulsator model was found to match closely with discharge pulse length, but resulted in lower values for peak current and projectile velocity by 50% and 30% respectively when compared to published data.

Railguns undergo excessive wear between the projectile and the electromagnetic launcher rails due to the hypersonic relative motion and very large current density involved. The wear effects at the small-scale on the rail-armature interface are not well known but need to be examined in order to support the development of a multishot launcher. Proposed contact regimes in the surface asperity interactions include solidsolid contact, liquid-metal lubricated contact, and arcing. In the present work, a modified Mesoscale Friction Tester (MFT) equipped with a probe and substrate was used to investigate experimentally the arcing and friction conditions that the rail-armature interface would experience. Copper probes with a range of radii of curvature were electrochemically etched and polished to submicrometer roughness. The minimum electrode distances for arcing to occur was found in air at atmospheric pressure and led to a modified Paschen curve where field emission of electrons was the dominant physical mechanism as opposed to Townsend avalanche of ionized gas. Arcing erosion was studied by varying the current, number of strikes, dwell time, and nearest electrode positions horizontally and vertically. Copper-copper friction with a constant normal force resulted in reduced wear when applying a constant current between the electrodes. / text

The study of shock-waves in supersonic plasma jets is essential to understanding the complex dynamics involved in many physical systems. Specifically, ion-species separation caused by a shock wave propagating through a plasma is an important but not yet well understood phenomenon. In inertial confinement fusion implosions, a shock wave precedes the rapid compression of a fuel pellet to ignition conditions that theory and computational studies suggest may be separating the fuel and reducing the neutron yield. In astrophysics, the shock wave produced when a supernovae explodes has been shown to have an effect on nucleosynthesis as a result of shock heating. In both these cases the time and length scales make them difficult to study experimentally, but experiments on more reasonable scales can shed light on these phenomena. This body of work provides the basis for doing just that. The work begins by describing the development of a small, linear, plasma-armature railgun designed to accelerate plasma jets in vacuum to high-Mach-number. This is followed by discussion of an experimental campaign to establish a plasma parameter space for the jets, in order to predict how effectively the accelerator can be used to study centimeter-scale shock structures in jet collisions. The final section presents an experimental campaign in which jet collisions are induced, and the resultant structures that appear during the collision are diagnosed to assess how conducive the experiment is to the future study of shock-wave induced species separation in laboratory plasmas. This work is a foundation for future experimental studies of ion-separation mechanisms in a multi-ion-species plasma. This research was supported in part by the National Science Foundation under grant number PHY-1903442. / Doctor of Philosophy / Plasma, the so-called fourth state of matter, is an ionized gas that often behaves like a fluid but can also become magnetized and carry an electric current. This combination leads to a lot of interesting yet often un-intuitive physics, the study of which is very important for understanding a wide array of topics. One subset of this field is the study of shock-wave induced species separation. Just like the shock-wave a jet aircraft produces when it moves through the air at a speed greater than the speed of sound, a plasma shock is characterized by a large change in parameters like density, temperature, and pressure across a very small region. A shock-wave propagating through a plasma can cause different ion species present to separate out, a phenomenon that is driven by the gradients that are present across a shock front. Understanding how these mechanisms work is important to a number of applications, including fusion energy research and astrophysical events. The first section of this work discusses the design and development of a plasma-armature railgun, a device that can produce and accelerate jets of plasma to high-Mach-number within a vacuum chamber. The next and most substantive section of the work presents results from experimental campaigns to characterize the accelerated plasma jets and then to induce plasma-jet collisions with the hope of producing shock-waves that exist on time and spatial scales that can be readily measured in a laboratory setting. This work is a foundation for future experimental attempts to measure separation induced by a shock-wave in order to better understand these complex phenomena.

Several methods of increasing railgun barrel performance and lifetime are investigated. These include two different barrel-projectile interface coatings: a solid graphite coating and a liquid eutectic indium-gallium alloy coating. These coatings are characterized and their usability in a railgun application is evaluated. A new type of projectile, in which the electrical conductivity varies as a function of position in order to condition current flow, is proposed and simulated with FEA software. The graphite coating was found to measurably reduce the forces of friction inside the bore but was so thin that it did not improve contact. The added contact resistance of the graphite was measured and gauged to not be problematic on larger scale railguns. The liquid metal was found to greatly improve contact and not introduce extra resistance but its hazardous nature and tremendous cost detracted from its usability. The simulated resistivity augmented projectiles were able to mitigate harmful current build-up on the back of a projectile using different conductivity gradients. Within the range of conductivity of aluminum alloys no simulated gradient was able to fully level the current density, however, once the range was expanded to include the lower conductivity of titanium, nearly uniform current density was achieved.

Electromagnetic launchers are currently being developed for their use as military weapons. These devices launch a projectile to extremely high speeds using very large electric currents. One obstacle facing the development of electromagnetic launchers is damage to the rails and armature during launch. The damage occurs due to current arcing in the armature-rail interface and is denoted as a transition. One solution is to use a lubricant injection system contained inside the armature to provide a conductive lubricant to the interface. The lubricant will ensure good electrical contact, prevent solid-solid contact, and cool the interface to prevent a launch from transitioning. Various different armature designs are currently under development. Each design must be analyzed through armature-rail interface modeling in order to predict the physical behavior and identify causes of transitions. There have been many studies on the physical behavior of sliding contacts. Some of which are directly applied to electromagnetic launch. In particular the magneto-elastothermohydrodynamic model is the most comprehensive model found for use in simulating electromagnetic launch. It includes calculation of the electromagnetic field, elastic deformation of the armature, calculation of the armature temperature history, and a hydrodynamic study of the lubricant both in the injection system and the armature-rail interface. The magneto-elastothermohydrodynamic model has been applied to only one armature design with limited success due to the assumptions used. The magneto-elastothermohydrodynamic model is applied to six different armature designs each requiring modifications to be made in order to predict the distinct behavior of each launcher. Modifications to the model include consideration of turbulent flow in the injection conduit, unique injection configurations, dry-out of the armature-rail interface, two dimensional pressure fields, and analyses of cylindrical bore launcher designs. The results show the model is effective in predicting when a transition will occur and what physical event leads to a transition when compared to experimental launch data. Additionally, experimental observations are used to affirm the simulation of other physical characteristics. It is found by the simulation that the base case armature is successful in preventing a transition of the shot, which is consistent with the experimental results. The simulation of NRL shot 223 reveals that such a small amount of lubricant is supplied by the reservoirs that the armature-rail interface partially dries out making a transition likely at a time of 4.7 ms; agreeing with the experimentally observed transition at a time of 4.5 ms. It is determined that the transition of NRL shot 406 is not due to a lack of lubricant inside the interface and that the amount of lubricant which leaks from the joint is negligible. IAP shot 7 did not transition in the experiment, however, after a time of about 3.5 ms the muzzle voltage began to rise. The simulation presents a possible explanation, showing that the armature-rail interface is beginning to empty out after 4.2 ms. The simulation of the GTL-2-4C armature shows that the experimentally observed transition is caused by the reservoirs emptying out at about 2.1 ms. The exploratory simulation of a modified GTL-2-4C armature determines that the absence of the slit in the armature trailing edges will not prevent the transition nor extend the successful portion of the shot.

The development of high powered electro-magnetic devices has generated interest in the effect of combined electromagnetic and mechanical loading of such structures. Materials used in high-current applications – aluminum alloys and copper – are subjected to heat pulses of short duration (in the range of a few hundred microseconds to a few milliseconds); immediately following or along with such heat pulses, these materials are also subjected to large mechanical forces. In previous work reported in the literature, ejection of material from the vicinity of preexisting defects such as cracks, notches or discontinuities have been observed resulting from short-duration high-intensity current pulses; after a series of pulses, permanent deformation and weakening of intact material has also been reported. But a lack of complete understanding of the effects of short duration current pulses hinders the assessment of the reliability of such conductors in high energy applications. Therefore, an investigation was undertaken to examine the behavior of electromagnetically and mechanically loaded conductors. This work investigates the effects of short-duration, high-current-density pulses in combination with viii mechanical loading. The aim is to develop a theoretical model to describe the resulting mechanical response. The model is to provide a characterization of the possible effects of thermally-induced plastic strains on metals loaded beyond or just below their yield strength or below the critical stress intensity factor. In the experiments reported here, two types of specimens, undamaged and damaged, were subjected to combined electromechanical loads. Undamaged specimens were used to observe thermally-induced plastic strains - strains not caused by an increase in mechanical loading, but rather resulting from the reduction of yield strength and post-yield stiffness due to the increase in temperature. The experiments were conducted such that it would be possible to develop a model that would conclusively account for the observed material behavior. The second sets of specimens were weakened a priori by the introduction of a crack in order to study the influence of such crack-like defects on the electrical and mechanical fields, and to produce a safe design envelope with respect to the loading conditions. Failure was found to occur due to melting triggered by joule heating; a quantitative criterion based on current concentration and heat accumulation near the crack tip has been developed based on these experimental results. / text

The numerical analysis of electromagnetic railgun dynamics under transient load is considered in current PhD thesis. The object of investigation is electro-magnetic accelerator EMA-3 at French-German institute of Sain-Louis (ISL). The aim of work covers the development of the finite element model of the EMA-3 rail gun and its application for investigation of the mechanical behaviour of railgun under differently induced loading regimes. There are several tasks under consideration. The first one is development of the finite element model. The 2D model consisting of four node plane and elastic springs was suggested and examined. The second one is evaluation of influence particular loading to dynamic behaviour and giving of recommendations. This thesis contains introduction, four chapters, the summary of results and conclusions, and the list of cited literature and list of publications of the author. In introductory chapter, the problem is formulated and relevance of the work is discussed. The goals and objectives of the work, research methodology and scientific novelty, practical significance and defended propositions are briefly described. Publications and reports at conferences on the theme of dissertation are presented at the end of introduction. The first chapter covers the review of the references on the electromagnetic railgun. It contains description of the development history, physical principles and decisive factors. Later, the gun structure is considered with the... [to full text] / Disertacijoje baigtinių elementų metodu nagrinėjamas elektromagnetinės šaudyklės (EMŠ) konstrukcinių dalių mechaninis būvis, veikiant dinaminei ap-krovai. Tyrimo objektas yra EMŠ „EMA-3“. Šaudyklės mechaninė dalis sudaryta iš elektrai laidžių bėgių, pritvirtintų prie dielektrinio pagrindo. Tiriama mechani-nio būvio rodiklių priklausomybė nuo apkrovos pobūdžio ir šaudyklės bėgių įtvirtinimo. Šaudyklės mechaninio būvio nustatymas jos darbo metu leistų tiks-liau prognozuoti jos elgseną, pagreitintų projektavimą, tobulinimą ir atpigintų eksploatavimą. Disertacijos tikslas yra skaitiniais metodais aprašyti ir ištirti šau-dyklės mechaninį deformavimą, veikiant dinaminei apkrovai, ištirti mechaninio būvio rodiklių priklausomybes nuo apkrovos parametrų, palyginti skirtingus ap-krovų režimus. Remiantis gautais skaičiavimo rezultatais, siekiama įvertinti šių veiksnių įtaką ir teikti siūlymus režimų patobulinimui. Darbe spręsti keli uždaviniai: sudarytas ir ištirtas „EMA-3“ šaudyklės skaiti-nis baigtinių elementų modelis. Pasiūlytais rodikliais įvertintas šaudyklės mecha-ninis būvis ir palyginta realių apkrovų įtaką bėgių deformavimui. Uždaviniai su-formuluoti atsižvelgiant į esamų modelių ribotumą, į šaudyklės rezonansinę elgseną kritinio greičio aplinkoje ir į tinkamo darbinio režimo parinkimo proble-mą. Disertaciją sudaro įvadas ir keturi skyriai. Įvade apibrėžta tyrimų sritis ir aktualumas, aprašyta mokslo problema, su-formuluotas darbo tikslas ir uždaviniai, paminėti naudoti tyrimo... [toliau žr. visą tekstą]

This master thesis focuses on literature research of problematics linked to power actuators working on electromagnetic principle to accelerate metal projectiles. It’s goal is mathematical analysis and constuction of selected type of electromagntic power actuator – induction coilgun

This master thesis focuses on literature research of problematics linked to power actuators working on electromagnetic principle to accelerate metal projectiles. It’s goal is mathematical analysis and constuction of selected type of electromagntic power actuator – induction coilgun