Railgun Plasma Research Articles

Plasma Railgun with Capillary–Porous Electrodes

Plasma Railgun with Capillary–Porous Electrodes

Electromagnetic plasma rail accelerator for surface analysis and modification in solids

In this study we investigate the possibility of using plasma rail accelerator as a dense plasma jet generator for scientific and technological purposes. It was found that plasma railgun can generate supersonic plasma jets, both pure and saturated with solid and liquid microparticles. Such jets can cause thermal and mechanical erosion of the target surface, sputtering material of the railgun channel and transferring it to the surface being treated. We studied working regimes of the plasma railgun. SEM and optical micrographs of the treated samples were obtained.

Prospects of use of electromagnetic railgun as plasma thruster for spacecrafts

Estimation of a possibility to use an electromagnetic plasma railgun as a safe and reliable plasma thruster based on calculations of the thrust force and specific impulse of a plasma jet flowing from an accelerator channel is presented. Theoretical and experimental investigations of acceleration of a plasma armature in railguns filled with inert gases (argon, xenon) carried out at Ioffe Institute are described.

Three-dimensional MHD modeling of railgun plasma armature with the CE/SE method

Three-dimensional (3-D) numerical simulations have been carried out taking into account the magnetohydrodynam- ics (MHD) effect of the railgun plasma armature. The 3-D space-time conservation element and solution element (CE/SE) method is derived for solving the coupled Navier-Stokes equations and Maxwell equations. The results show that a steeper gradient of the magnetic field and pressure that appears along the direction of the rail can be observed. The temperature dis- tribution is affected by the boundary conditions for the radiative heat flux, with the maximum temperature appearing in the center near the base of the projectile. Circulation patterns of velocity that are evident in both the rail-to-rail plane and the insulator-to-insulator plane result from the convection and unbalanced force between the Lorentz force and pressure gradient. The periodical variation of the temperature and acceleration is obvious until a new steady state is achieved. This model can efficiently evaluate the dynamics of the plasma motion, and provide a basis on understanding the much more complex physical phenomena.

An Investigation of Internal Gas Dynamics for an Electrothermal Launcher

The Institute for Advanced Technology has been conducting experiments on plasma-armature railguns for the past several years. To control the damage mechanisms associated with this class of railgun, an electrothermal (ET) launcher preinjects the projectile into the plasma railgun bore milliseconds before the arc is energized. During the initial testing of the ET launcher, it was found that injection velocities were significantly lower than expected for a given input energy. Subsequent experiments using photonic Doppler velocimetry to resolve velocity as a function of time confirmed this finding. Using an ablative capillary discharge code written by Powell and Zielinski in 1991, the velocity discrepancy is analyzed, and the properties of the propellant gas-such as ionization fractions, the mass of the propellant gas, and the magnitude and decay of the pressure pulse seen by the projectile-are determined.

Profiling Line-Averaged Compact Toroid Electron Density on CTIX With Arrayed Laser Deflectometry

The compact toroid (CT) injection experiment (CTIX) is a coaxial plasma rail gun originally designed for tokamak refueling. CTIX can form and accelerate CT plasmas of controllable densities and velocities. For a given chord through a plasma, changes in line-integrated transverse electron density gradient can be resolved by measuring the angle of deflection of a laser beam traversing the plasma. A vertical array of four temperature-controlled laser deflectometers was installed in the viewing section of CTIX and used to profile the line-averaged density of an unconstrained CT drifting at high velocity.

Spatial and temporal characteristics of a vacuum-arc rail-gun plasma

The dynamics of a vacuum-arc operated rail-gun plasma were numerically simulated for the undercritically damped regime and confirmed in experiments. Analytical solutions of arc current, its velocity, and position also showed good agreement with the results. The spatial development of the arc is shown here to follow a linear behavior, even though the propulsion velocity followed an exponential-step function due to the sinusoidal nature of the arc current. Peak arc current ∼100 kA, 15 μs period was propelled to ∼106 cm/s as indicated in time-of-flight measurements and simulations. The voltage signal induced on a B-dot probe by the dynamic sinusoidal arc was simulated, which compared well with the measured probe signal. A Gaussian current distribution inside the measured arc length ∼1–2 cm, was established by unfolding the B-dot probe signal. A peak magnetic field of the order 1–5 kG was also interpreted inside the arc. The emerging plasma contained ion current over tens of amperes in the pulse duration encompassing the arc envelope.

Spectroscopic measurements of railgun plasma armatures in an augmented railgun using a permanent magnet

Measurements of electron density using Stark broadening of the H/sub /spl alpha// line are performed to investigate the behavior of plasma armatures in rail guns with and without an augmenting magnetic field. A permanent magnet with a magnetic flux density of 1.25 T was used to augment the magnetic field of one railgun. Driving currents of 20 and 25 kA are supplied to the railguns with and without the augmenting magnetic field, respectively, in order to maintain the same peak Lorentz force on the projectile. Also a gradual temporal increase in electron density and length of the plasma armature is observed in the augmented railgun.

レールガン動作の駆動電流立ち上がり依存性

Railguns are facilities to accelerate projectiles up to several km/s by the electromagnetic force due to a driving current. A variety of current waveforms are used for railguns developed in the world This paper describes the dependence of a railgun operation on a rising rate of the driving current. The use of the exploding wire as an opening switch enables to change the rise time of the driving current. A secondary arc is likely to appear and the erosion on a rail surface is more severe when the current with a short rise time is used. According to the non-dimensional railgun plasma simulation, the current with a short rise time heats up the plasma so fast that plenty of particles ablated from the bore surface, which seem to be the cause of the secondary arc, increase rapidly in the early phase of acceleration.

3-D MHD simulation of a railgun hybrid armature

A 3-D plasma MHD code MAP3 was developed to simulate the flow in railgun plasma armatures. MAP3 has now been used to simulate qualitatively the plasma flow around a hybrid armature. The first simulation considered an aluminum hybrid armature in a 1-cm square bore, similar to the conditions for hybrid armature experiments performed earlier at UTSL. Simulation results agree with flow paths observed visually on the recovered experimental armatures at UTSL. The second simulation considered a hybrid armature in a 2-cm square bore. The fraction of the current carried in the solid armature increases with the bore dimension, which is consistent with experimental observations.

Spatial effects in a railgun plasma armature

The results of mathematical simulation of thermal, mechanical and electromagnetic interaction of railgun plasma armature and channel walls are presented. A generalized 2D-approach taking into account turbulent friction, radiative and turbulent heat transfer and spatial inhomogeneity of the magnetic field was used. The heat regime of electrodes was considered in the 2D-approach. The momentum and energy transfer from the flow core to the electrodes and the process of involving the erosion mass into acceleration were investigated in detail. It has been shown that magnetic field inhomogeneity causing the appearance of spatial induction currents influences essentially the momentum, energy and mass balance in the near-electrode region and the armature characteristics as a whole. It leads to an additional drag force and the release of Joule heat near the rail surface and to the increase in erosion. Under some conditions this can cause instability of plasma armature and its sharp extension. Calculations have shown that the electrode melting, destruction of the liquid film, involving of drops into acceleration and their vaporization in the flow seem to be the most probable mechanism of plasma mass increase for typical regimes of railgun operation.

3-D numerical simulation of plasma armature railguns

In this paper an equivalent network model for the three-dimensional analysis of a railgun plasma armature is presented. The plasma armature is decomposed in volume elements in which a uniform distribution of the current, momentum and heat flux densities is assumed. Then, three equivalent networks are derived. A first electric network is obtained for the determination of the current density and magnetic field distribution in the plasma arc; a second equivalent network allows the determination of the pressure and the mass density distribution and the internal motions in the plasma arc. The model was used in a previous work for the analysis of an isothermal plasma. In this paper the third equivalent network that is derived from the energy conservation and Saha equations has been used for the determination of the temperature distribution in the railgun plasma armature. Numerical simulations have been carried out assuming different boundary conditions for the radiative heat flux.

Numerical comparison between a differential and an integral approach in MHD simulations of electromagnetic railgun plasma armatures

In this paper an integral approach for the analysis and the numerical simulation of the plasma armatures operating in rail launchers is tested by comparison with a differential approach. After a brief recall of the main theoretical and numerical aspects of the two approaches, a benchmark problem is presented and analyzed. The comparison between the results obtained confirms the validity and the effectiveness of both methods. Moreover, possible advantages or drawbacks of the computer codes implementing the two approaches are discussed.

The effect of serrated bore surfaces on plasma armatures

The use of serrated bore surface has the potential to overcome the velocity performance limitations of railgun plasma armatures. The authors evaluated several serrated bore configurations to determine their effect on plasma armature length, stability and velocity performance. They found that plasma armature length and stability are significantly influenced by bore serrations. Plasma armatures in serrated rail-serrated insulator bores are very compact and stable. Many small serrations in the rail also cause compact armatures. These micro serrations gave extremely stable armatures that were highly repeatable. The authors were unable to demonstrate the effect of serrated bores on plasma armature velocity performance. >

3-D plasma armature railgun simulations

A three-dimensional Navier-Stokes code has been extended to provide a simulation for the railgun plasma armature. This code was previously used with an approximate electromagnetic model to provide a two-dimensional simulation of a railgun plasma armature flow in the plane containing the insulators. A new three-dimensional electromagnetic solver has been incorporated into the code to permit full 3-D nonsteady MHD simulations of the plasma armature flow in a railgun. The finite-difference equations for magnetic vector potential and electric potential are solved using the ICCG method. The new electromagnetic solver was validated using 3-D solutions obtained from the finite element electromagnetic code MEGA. A full bore, 3-D simulation of a plasma armature reveals flow patterns significantly different than those of rail or insulator plane 2-D simulations. In particular, the maximum J/spl times/B force occurs off-axis and results in a plasma flow away from the projectile along the axis of symmetry. A zone of high shear flow forms near the rail surfaces which increases the viscous losses. Zones of low current, nearly stagnant flow form near the base of the projectile, consistent with experimental observations of a buffer between the armature and the projectile. >

Temporally resolved visible and UV spectroscopy of exploding wires

This paper presents experimental spectra resulting from simple exploding wires used in railgun plasma production and shows initial comparisons with basic theory. Exploding wire spectra have been obtained by discharging a 1200 /spl mu/F capacitor bank at a voltage in excess of 1 kV through both metal wires and carbon fibres. The spectrometer used has enabled spectra to be recorded in the visible and ultraviolet wavelength regimes. Furthermore, the use of a charge coupled device (CCD) as the recording medium allows the time resolution of the spectral emission. A maximum of 512 spectra per discharge is possible, with a minimum acquisition time of less than 10 /spl mu/s per spectrum. The transient current in the exploding win was monitored by a Rogowski coil. Analysis of the experimental data has enabled the fluctuations in the spectral intensity to be related to the development of the electrical discharge.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurement of temperatures in optically thick railgun plasma armatures

In this paper, the authors present Bartels' method for estimating temperatures from the spectra of optically thick plasma armatures. They have applied this method to the analysis of spectra from the Thunderbolt and UTSI railguns and the results of the analysis are presented. Temperatures estimated from Bartels' method are on average 45% lower compared to temperatures estimated by the solution of the radiation transfer equation. The authors have also estimated temperatures via black body approximation conductivity measurements, and the application of Stefan-Boltzmann law. They have found the temperatures estimated from these methods to be lower than the values estimated by the solution of the radiation transfer equation. This has led them to believe that the temperatures in the plasma armatures are lower than previously estimated by the solution of the radiation transfer equations. >

Full-bore simulation for plasma-driven railguns

The authors have embarked on a program to develop a full-bore simulation of the railgun plasma armature. The simulation extends from the back of the projectile to the breech of the railgun, thereby treating explicitly the entire bore. The extent of the armature is unrestricted, and the armature is allowed to grow into the background gas as dictated by physical interactions. This paper documents their progress to date in achieving this full-bore simulation. Most of the activities have focused on formulating the defining equations and boundary conditions, and implementing (and then validating) a numerical technique capable of resolving the steep gradients that they expect to encounter in the simulation. >

The effects of hyper velocity impact phenomena on radiation induced defects

Effects of high speed impacts on radiation-induced defects were investigated with a plasma rail-gun. Vitreous quartz targets irradiated by γ-ray were shocked with polycarbonate projectiles at a speed of 7 km/s, then the remaining destroyed pieces were examined by ESR spectroscopy to investigate the degree of “impact-annealing”. The white substance from the impact point showed a trace of melting and no ESR signal, while the rest of the scattered pieces showed a decrease of E' center density to 50 ± 10% of the initial density. The defect production efficiency for the impacted silica was almost two-third of the original material.

The analysis and modeling of the ARDEC 2.5 km/s 20-mm plasma railgun shot

The 20-mm round-bore plasma railgun was successfully fired at the ARDEC electric gun facility. The 4-m gun with copper rails and alumina composite insulators was operated using a light-gas gun injector to start the projectile, already located in the gun, moving prior to the introduction of current. Current from the EMACK homopolar generator was commutated into the gun by an explosively actuated opening switch. The muzzle velocity was recorded by breakwires and flash X-rays at 2.5 km/s. B-dot sensors, rail current Rogowski coils, and breech and muzzle voltage measurements provided data on the in-bore dynamics of the armature. Postshot analysis using the ARMRAIL code successfully provided calculations reproducing all the main features of the data. Models account for the observed secondary arcs present throughout the shot, and the basis for the code and physics modeling is given. >