Electric Launcher Research Articles

Options for an Electric Launcher System

Railguns are current-driven guns that allow reaching large muzzle velocities and energies. In the military context, the long-range artillery scenario makes use of these two capabilities to enable the launch of hypervelocity projectiles to target distances above 100 km. As of today, the most advanced railgun project is conducted by the Office of Naval Research, Arlington, VA, USA, and features railguns with a muzzle energy of 32 MJ. Such large artillery railgun systems with efficiencies above 30% are fed by a pulsed power system with a nominal energy content of about 100 MJ. In contrast to this, experiments with French-German Research Institute’s (ISL) most powerful railgun, PEGASUS, have reached muzzle energies of 2 MJ, only. The nearer future ISL has to answer two questions: 1) is the railgun technology adequate for a long-range artillery scenario? 2) can the railgun launch a hypervelocity projectile which is being developed by other groups in ISL? To do so and to support the development of the hypervelocity projectile, a larger railgun installation with a significant increase of the energy and free flight capability is required. In this paper, three different railgun systems were investigated using an electric circuit simulation code. The systems are referred to by the energy being stored in the capacitors as 25, 50, and 100 MJ. The aim of this paper is to investigate what masses can be accelerated to the relevant velocity range for the long-range artillery scenario by these different primary energies. The results of this paper can be used to aid the decision about the required size, with respect to the military scenario, of a potential future railgun system.

Hybrid waveguide/coaxial feeder for dual‐pol Fabry‐Perot cavity antennas radiating omnidirectional TM/TE waves

A hybrid waveguide/coaxial transverse magnetic (TM)/transverse electric (TE) launcher is proposed as a feeder for planar Fabry-Perot (FP) cavity antennas radiating omnidirectional beams. The structure is based on a pair of nested coaxial cables. The inner coax (TM launcher) operates on the standard TEM mode and feeds a vertical probe protruding into the antenna cavity through the ground plane. The outer coax (TE launcher) operates on the TE01 mode excited by an aperture-coupled rectangular-waveguide feeding network. Geometrical symmetry ensures high isolation between the TM and TE input ports, which can be alternatively excited to achieve dual-pol operation with either horizontal or vertical linearly-polarised far field. Good impedance matching and omnidirectional dual-pol radiative features are demonstrated for an FP cavity antenna operating at 16 GHz and based on a thin periodic metal partially-reflecting surface.

Frequency Characteristics of Helical Electromagnetic Launchers

As a kind of future weapon, an electric launcher uses high current to drive projectiles reaching velocities on the order of several kilometers per second. As is known, high and rapidly changing currents through electric launcher can lead to strong radiation. A PSPICE model is used to analyze the frequency content of currents in the helical electromagnetic launcher (HEML) by nonuniform fast Fourier transform. The frequency spectrum is mainly determined by conducting duration and intensity of entering current. The main frequency of HEML is low, but high-frequency components can produce more radiation. The total radiation can be considerable.

Velocity-Induced Current Profiles Inside the Rails of an Electric Launcher

Previous investigations have shown that an array of novel CMR-B-scalar sensors based on the colossal magnetoresistance effect can be used to measure the magnetic field distribution in the vicinity of the rails of a railgun. However, the data obtained suffered from electromagnetic interference. Therefore, the measurement system was considerably improved to obtain better signal quality. In this paper, the results obtained during the dynamic operation of the ISL railgun RAFIRA are presented. The magnetic field distribution in the vicinity of the rails was measured at different armature velocities. Additional information was obtained using high-speed camera snapshots. The experimental results are compared with simulations performed with the finite element code COMSOL Multiphysics. In particular, the influence of the armature current on the measurements is discussed. It is concluded that the magnetic field distribution in the vicinity of the rails clearly indicates an increased current concentration in the rear part of the armature–rail contact interface. Moreover, the current concentration depends on the speed of the armature. Velocity-dependent skin depths at the surface of aluminum (Dural) rails for projectile velocities ranging between 750 and 1500 m/s are investigated.

A pulsed magnetohydrodynamic generator for electric launcher

An invention scheme of pulsed magnetohydrodynamic generator (PMHDG) in milliseconds order of magnitude that can be used directly in electric launchers is presented for the first time. It is either different from ordinary small power dc MHD generators for power plants, or different from explosive MHD generators where its pulsed current width is in the microseconds order of magnitude. Operating principle of the PMHDG is as follows: fuels or oxidizing agents within two storage vessels are injected into a combustion chamber to combust by a pump and a valve, after waiting for the pressure (or density) of generated conductive electric MHD ascends some threshold value, a self-controlled valve in combustion chamber throat is opened automatically. As a result, conductive electric MHD passes into a generating channel in pulse to generate electric current. Obviously, by controlling the amount of the working substance entering into the combustion chamber with the injector valve, and adapting the spring pressure of the self-controlled valve, we can control the pulsewidth and obtain different values of high power to be used directly by the electric launcher. Besides, this paper gives a theory-mathematical model in which some characteristics of the generator were expressed. This helps us to understand the relationship between various physical quantities about the generator, and provides a basis to research their mutual influences. In addition, in physical design of the circuit, we adopted a proper high energy density capacitor as auxiliary energy storage. On one hand, the generator can realize the self-excited generation by using the capacitor; on the other hand, the high energy capacitor is charged directly by the generator and energy stored within the capacitor is realized, so as to form a generator-capacitor combined high power pulsed power supply that can be used by high energy electric launchers.

Novel PFN with current turn-off capability for electric launchers

In the last years at ISL a lot of work has been performed in order to develop and install highly flexible pulse forming networks (PFN), based on capacitors as the energy source for electric guns (railguns, ETC-guns). In this paper, the principle of the novel pulse forming unit is shown and discussed. Besides this, a first prototype is presented together with its electrical features. A PFN consisting of four units was built and investigated. First experiments with this PFN were performed, while the discharge was made into a dummy load. The high flexibility of this pulse power supply is shown, concerning the shaping of different current pulses and the turn-off capability. Finally results obtained by PSpice simulation with a real railgun load are presented. The results show the feasibility of using the rectifier-based PFN to drive an electric launcher. Due to the current turn-off capability and the highly modular design, an efficiency enhancement could be demonstrated.

Multipulse discharge in the chamber of electric discharge launcher

The investigation results of an electric discharge launcher's (EDL) chamber operation at hydrogen initial pressure 20-40 MPa, discharge current 0.5-1.0 MA, current rise rate (0.5-1.0)/spl times/10/sup 10/ A/s and input energy up to 2.2 MJ are presented. The coaxial electrode system consists of cylindrical anode and conic cathode. The discharge is initiated by copper wire in the interelectrode gap of 0.8-2.5 mm. The conditions of multipulse discharge current appearance, at the pulses number 5-15 (in comparison with usual multipulse regime 2-3 pulses), amplitude 0.5-1.0 MA and single pulse duration 50-200 /spl mu/s, are determined. The speeds of arc movement (1.5-3.0 km/s) and arc channel expansion (0.2-0.4 km/s), were measured by means of high-speed camera. The efficiency of energy transfer from the power supply (capacitor storage) to the arc was about 85% and from the arc to gas-90%. Electrodes erosion was found to be 30-40% less compared with usual multipulse regime. Besides the anode and cathode, total erosion was 30-40 mg/C at passed charge up to 800 C. The results estimation of different mechanisms contribution to heat transfer from the arc to surrounding hydrogen are discussed. It was shown that both repeated dissipation of arc plasma internal energy after arc extinction and the shock waves, appearing at the breakdowns of interelectrode gap, increase the efficiency of gas heating. It was proposed that decreasing of electrodes erosion at the multipulse regime is connected both with the growth of electrode spots movement speed and with the decreasing of current amplitude from 1.5-2.0 MA (usual multipulse regime) to 1.0 MA.

Review of component erosion in electric launcher technology

Component erosion in electric launcher technology (electromagnetic, electrothermal and electrothermal-chemical) plays a major role, which determines the launcher's bore lifetime, launch velocity and operational limits. Erosion studies have been conducted on the electrothermal launcher SIRENS, which simulates expected operational conditions of high heat flux deposition in electric launchers. Various material surfaces have been exposed to SIRENS plasma to test their performance, erosion behavior and lifetime. Tested materials are pure metals, alloys, refractory materials, specially-coated materials, insulators and composites, pure and composite graphites. Results showed that coating reduced erosion. Tungsten-based alloys have no observable erosion. Vapor shield phenomena have been characterized for different materials, and the energy transmission factor through the vapor shielding layer is obtained. >

The use of coupled EM-hydro finite element techniques for the design of railguns

The primary goal of the electric launcher modelling team is to develop techniques to aid our understanding of the physics of railgun launch. This is essential in order to combat the problems which will degrade the performance of railguns from their theoretical limits, especially with the Kirkcudbright facility in mind. In particular, we need to understand die transient material response caused by the launch process. Plasma transitioning and nonideal contact between armature and rail are just two of the problems that analysis codes must be able to address. This paper shows the results of finite element (FE) simulations, at 90 mm scale, of the armature-barrel interaction. Special emphasis is put on the resolution and validation of high temperature hot spots in the armature and in the prediction of transient barrel response. The FE method is based on a soft linking of the 3D FE transient electrical-thermal code MEGA to the dynamic structural code DYNA3D. This version of the MEGA-DYNA3D link has a multi-slide line capability which allows stressing to be calculated by taking into account the hydrodynamic effects of the rail-armature interaction as well as the electromagnetic forces.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Helical rail glider launcher

The electromagnetic acceleration group at MIT has undertaken to build an electric glider launcher. The launcher features a mobile helical rail accelerator and power supply. It will launch a 6 foot radio-controlled glider for an overall range of several miles. This device is a prototype for a larger system that will provide a launch platform for munition and supply loaded gliders and a wide variety of RPV's. A 6 meter helical rail launcher has been constructed and is being tested. It is a twin boom device designed to accelerate a 5 kg glider to 100 m/s at 100 g's acceleration.