Two-stage Gun Research Articles

Control of discharge time using physical contact in a two-stage coil gun

In this study, a coil gun was designed using a trigger that can discharge a capacitor using physical contact. Controlling the discharge time of the capacitor in a multi-stage coil gun is an important factor for the final velocity of the projectile. To control the discharge time, we used the physical contact of the projectile and the trigger and controlled the point in time when discharge occurs by sensing the projectile location using a sensor. Controlling the discharge using sensors allows for more accurate timing control than physical discharge systems, but the circuit is more complex, and the high current results in a higher risk of malfunction and higher costs. In contrast, systems that use physical contact are simple, have low risk of malfunction, and have low cost. The velocity of the projectile was predicted using the electromagnetic analysis simulation program MAXWELL, and the final velocity of the projectile was compared to the results of a prototype.

Remote control of a high-speed pellet injector and data synchronization & sharing tools

The four-barrel, two-stage gun Ignitor Pellet Injector (IPI) was developed in collaboration between ENEA and ORNL. The prototype injector is presently located at Oak Ridge (TN, USA), and is normally operated locally through a control and data acquisition system developed in LabVIEW. More recently, a remote-control system has been set up, based on RealVNC®, which allows to operate the IPI from a control room in Italy. Tools for data transfer and storage into ENEA ICT area have also been provided. A Staging, Storage and Sharing system, named E3S, developed using OwnCloud as architectural component, is used for file synchronization and sharing of the data acquired by the diagnostic systems. It provides a homogeneous platform able to store and share heterogeneous data produced by many data acquisition systems in large nuclear fusion experiments. This paper reports about the implementation of the IPI remote control, and presents the application of E3S to this specific case, allowing easy storage and sharing of experimental data onto a wide-area distributed file-system, as well as remote data access via web-services based on MDS+ tool, integrated with MySQL metadata. A performance analysis of the architectural components is also introduced.

State of the art and perspective of high-speed pellet injection technology

The injection of cryogenic pellets from the low field side (LFS) has long been in use for core fuelling of fusion devices, but injection from the high field side (HFS) has proved to provide a more effective core particle deposition, despite the severe limitations imposed to the pellet speed (≤300m/s) by inboard accessibility. In the future, an alternative approach may be that of injecting high-speed pellets from the HFS, through suitable “free-flight” paths, eliminating curved transfer systems. Furthermore, the expected length of the plasma discharges will require steady-state repetitive systems. ORNL and ENEA have been collaborating on high-speed injectors since 1990; they successfully realized a high-speed repeating pellet injector (2.55km/s at 1Hz). Since then, good progress has been achieved on both fronts of steady-state extruders, and operation and reliability of two-stage guns. A comprehensive R&D program is therefore proposed to investigate how far speed limits and repetition rates of combined two-stage guns and steady-state extruders technologies can be extended. Simulations results are presented showing pellet penetration for several injection locations on a tokamak under construction such as JT60-SA, on the basis of one set of design plasma parameters.

Design and experiments of multi-stage coil gun system

An electromagnetic launcher (EML) is a device used to propel and accelerate a projectile by converting electrical energy into kinetic energy. A coil gun, which is a type of EML, can propel a projectile without any mechanical friction so that there is no theoretical limit to the velocity. A multi-stage system is a way to raise the effectiveness of the coil gun. It accelerates the projectile by controlling the relations between each stage of the solenoid and projectile. Since a multi-stage system controls the time needed to apply electric current to the coil depending on the position of the projectile, the switching time is extremely important. We performed a finite element analysis using MAXWELL to determine the extent to which the velocity of a multi-stage coil gun improved compared to a single-stage coil gun. In addition, we verified the two-stage performance through timing control by designing and producing a two-stage coil gun based on our research results for a single-stage coil gun. The velocity was increased by 34 % compared to the single-stage coil gun, and the error compared to the analysis result was 16.4 %.

OS1919 斜め衝突におけるクレータ形状とイジェクタサイズ

The effects of oblique impact angle on ejecta fragment size were investigated by striking aluminum alloy 6061-T6 targets with 3.2-mm-diameter aluminum alloy 2017-T4 spheres at velocities 4 km/s. The two-stage lighet-gas gun at the Institute of Space and Aeronautical Science (ISAS)/ Japan Aerospace Exploration Agency (JAXA), was used for the experiments. The cumulative number of ejecta was proportional to the square of the vertical-direction component of the impact velocity. The experimental formula for the cumulative number distribution of ejecta size was created using bilinear exponential distribution.

Experimental and numerical evaluation of the performance of supersonic two-stage high-velocity oxy-fuel thermal spray (Warm Spray) gun

The water-cooled supersonic two-stage high-velocity oxy-fuel (HVOF) thermal spray gun was developed to make a coating of temperature-sensitive material, such as titanium, on a substrate. The gun has a combustion chamber (CC) followed by a mixing chamber (MC), in which the combustion gas is mixed with the nitrogen gas at room temperature. The mixed gas is accelerated to supersonic speed through a converging-diverging (C-D) nozzle followed by a straight passage called the barrel. This paper proposes an experimental procedure to estimate the cooling rate of CC, MC and barrel separately. Then, the mathematical model is presented to predict the pressure and temperature in the MC for the specific mass flow rates of fuel, oxygen and nitrogen by assuming chemical equilibrium with water-cooling in the CC and MC, and frozen flow with constant specific heat from stagnant condition to the throat in the CC and MC. Finally, the present mathematical model was validated by comparing the calculated and measured stagnant pressures of the CC of the two-stage HVOF gun.

Theoretical Calculation of Pressure Characteristics in Two-Stage High-Velocity Oxy-Fuel Thermal Spray Gun Employing Supersonic Flow (Validation by Cold Flow and Actual Spray Gun Tests)

The theoretical calculation of a two-stage high-velocity oxy-fuel thermal spray gun was conducted for the purpose of predicting the stagnant pressure in the mixing chamber (MC). The theoretical results were compared with the experimental ones obtained by the cold flow and actual spray gun tests. The effect of the diffuser shape installed between the combustion chamber (CC) and the MC was also investigated in the cold flow test. It was clarified in this study that 1) the theoretical calculation shows that in order to obtain a larger pressure in the MC the diameter rations of d3t/d1t and d1e/d1t should be chosen to satisfy Eq.(11), to keep the diffuser throat unchoked, 2) the theoretical results of p03/p01 agree with the results of cold flow test within an accuracy of 6%, 3) the theoretical results of p01 agree with the results of actual two-stage HVOF gun test within an accuracy of 4%, demonstrating the validity of the present theoretical calculation.

Effect of projectile hardness on deformation and fracture behavior in the Taylor impact test

The ballistic perforation performance of a kinetic energy projectile would be much more influenced by the projectile’s deformation during the impact process. A projectile may suffer from large deformation and even fracture as more and more advanced materials are used as resistant components. A comparison investigation was presented in this study concerning the deformation and fracture behavior of kinetic energy projectiles manufactured from 38CrSi steel of two different hardness values. Flat-nosed projectiles were fired in a two-stage compressed gun test facility against hard steel plates within the velocity range of 200–600 m/s. The impact process was monitored by a high-speed camera. Experimental results showed that, for the soft projectiles there are three deformation and fracture modes, i.e., mushrooming, shear cracking and petalling, and that for the hard projectiles there are also three modes, mushrooming, shearing cracking and fragmentation.

Two-stage plasma gun based on a gas discharge with a self-heating hollow emitter

The paper presents the results of tests of a new compact two-stage bulk gas plasma gun. The plasma gun is based on a nonself-sustained gas discharge with an electron emitter based on a discharge with a self-heating hollow cathode. The operating characteristics of the plasma gun are investigated. The discharge system makes it possible to produce uniform and stable gas plasma in the dc mode with a plasma density up to 3x10(9) cm(-3) at an operating gas pressure in the vacuum chamber of less than 2x10(-2) Pa. The device features high power efficiency, design simplicity, and compactness.

A special design condition to increase the performance of two-stage light-gas guns

Abstract This paper reports a theoretical and numerical study aimed at increasing the operating efficiency of two-stage light-gas guns by appropriately changing their working conditions. In particular, a method is presented for increasing the projectile speed without any rise of the maximum breech pressure. The classic design theory of two-stage guns starts from the assumption that the highest velocity is reached in a gun which constantly maintains the maximum acceptable pressure at the base of the projectile during the full launching time. The main drawback of this working condition is that it may require an unfeasible rise of the gun maximum pressure, especially when very high muzzle speed is requested. To overcome this limitation, a new reference case different from the constant-base-pressure one is presented, based on a novel gas-dynamics solution that can be expressed in exact form if losses are not accounted for. According to such an approach, it is theoretically shown that the projectile base-pressure can be appropriately shaped (i) to improve the final speed without increasing the breech pressure or, in other terms, (ii) to achieve a given muzzle velocity with reduced maximum gas pressure. The analytical application of the new gas-dynamics condition showed the capability of obtaining a 1 km/s velocity improvement with no increase of the breech pressure or, alternatively, a pressure reduction up to 30% with no penalty on the model final speed. A numerical verification of the calculations was performed through the CISAS light-gas gun full numerical model, which includes real effects such as friction losses and heat transfer. Finally, an experimental verification of the numerical test case was attempted and a speed augmentation of 0.8 km/s with no increase in the breech pressure was confirmed in laboratory, highlighting the agreement with numerical predictions.

Particle launch to 19 km/s for micro-meteoroid simulation using enhanced three-stage light gas gun hypervelocity launcher techniques

Particle launch experiments were performed to study application of the enhanced hypervelocity launcher (EHVL), i.e. the third-stage addition to the two-stage gun, for launching micron to millimeter sized particulates at velocities unobtainable with a standard two-stage light gas gun launch. Three types of particles or fliers were tested along with several barrel designs. For micron scale particles fine-grain polycrystalline ceramics were impacted and fractured, launching particulate clouds at velocities of 15 km/s. Multiple titanium particles ∼400 μm diameter embedded in plastic were “shotgun” launched to velocities of 10 km/s. Flier plates of 3 mm diameter by 1 mm thick Ti6Al4V were launched to 19 km/s. All experiments used a second-stage projectile with graded density facing impacting a flier in an impact generated acceleration reservoir. This paper describes the modification and adaptation of the Sandia EHVL to provide micrometeoroid simulation capabilities.

Systematics of the metallization of low-Z and alkali fluids

Hydrogen, nitrogen, oxygen, cesium, and rubidium undergo nonmetal–metal (NMM) transitions in the degenerate warm fluid phase. It is quite likely that all these fluids are monatomic or very nearly so. For N, O, and H, these NMM transitions occur under quasi-isentropic compression to ∼100 GPa (1 Mbar) pressures and densities of ∼10 times initial liquid density in the case of H. These conditions were achieved with a two-stage gun. In the cases of Cs and Rb, these transitions occur at only ∼0.01 GPa in the expanded fluid at 2000 K. These NMM transitions are Mott transitions. The values of the minimum metallic conductivities are essentially the same for all five because minimum metallic conductivity depends weakly on density of metallization and number of conduction electrons per atom. In contrast, the density dependences of the semiconductivities are very different. In the spirit of Mott, quantum mechanical wave functions of the free atoms are used to estimate the densities at which semiconductivies are appreciable. The radial extents of the charge-density distributions are well correlated with the Mott-scaled density dependences of the semiconductivities. These radial extents depend on the degree to which the filled-electron core screens the valence electron(s) from the nuclear Coulomb force. This simple picture gives a qualitative explanation for the density dependences of the semiconductivities of all five and for the Herzfeld criterion, which predates quantum mechanics.

Free-electron maser driven by a two-stage ferroelectric electron gun

A two-stage ferroelectric electron gun is employed in a free-electron maser (FEM) oscillator experiment. This gun produces a pulsed electron beam of a 5–15 keV energy, ∼0.5 A current, and ∼3% energy spread. The FEM output microwave pulse train is coupled out with a 66 W peak power. The microwave frequency is tunable in the range of 2.9–3.3 GHz by varying the electron beam energy. The interaction mechanism is identified by a comparison to the known FEM tuning relation. The energy spread of the two-stage ferroelectric electron gun satisfies the FEM acceptance parameter in the microwave regime.

A two-stage pellet injector with a cryogenic piston for plasma fueling of thermonuclear devices

A new two-stage gun was developed for solid-hydrogen-or deuterium-pellet formation and injection into plasma of thermonuclear devices. A cryogenic piston made from solid carbon dioxide was first used to compress and heat the propellant gas in the second gun stage. The piston was produced simultaneously with fuel pellets before each shot. Deuterium pellets with a 1.5-mm diameter and up to 5-mm length were accelerated to a speed of 1.7 km/s. The experimental results of cryogenic-piston formation with a 4-mm diameter and up to 30-mm length are presented.

Acceleration of large size deuterium pellets to high speeds using a small two-stage pneumatic gun

The technology of two-stage pneumatic pellet injectors represents by far the most reliable way to perform deep plasma fueling, with pipe gun devices capable of routinely launching small or medium size (up to 4 mm) D2 pellets at speeds in excess of 3 km/s, using rather small two-stage guns. It is still an open question, however, if scaling of the pellet size to the International Thermonuclear Experimental Reactor relevant values (6–8 mm) will or will not require a somewhat proportional increase in the physical size of the two-stage gun. In order to investigate this question, an extensive study was carried out at ENEA Frascati, using numerical simulation codes. It clearly indicated that a “compact” two-stage gun may have the potential to accelerate large size pellets at speeds up to 5 km/s. A low cost experiment was also scheduled. A spare pipe-gun cryostat of the single-shot two-stage pneumatic injector, previously used for high-speed pellet fueling of the Frascati tokamak upgrade, was modified in order to accommodate larger bore (up to 6 mm) launching barrels. In this article, we will mainly discuss the results of numerical simulations. A very early experimental campaign, carried out in 1996, will also be briefly reported, during which intact 6 mm D2 pellets were launched at speeds up to 2.5 km/s.

Minimum metallic conductivity of fluid hydrogen at 140 GPa (1.4 Mbar)

Electrical conductivity measurements indicate that fluid hydrogen achieves the minimum conductivity of a metal at 140 GPa, ninefold initial liquid-${\mathrm{H}}_{2}$ density, and 2600 K. Metallization density is defined to be that at which the electronic mobility gap ${E}_{g}$ is reduced by pressure to ${E}_{g}\ensuremath{\sim}{k}_{B}T,$ at which point ${E}_{g}$ is filled in by fluid disorder to produce a metallic density of states with a Fermi surface and the minimum conductivity of a metal. High pressures and temperatures were obtained with a two-stage gun, which accelerates an impactor up to 7 km/sec. A strong shock wave is generated on impact with a holder containing liquid hydrogen at 20 K. The impact shock is split into a shock wave reverberating in hydrogen between two stiff ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ anvils. This compression heats hydrogen quasi-isentropically to about twice its melting temperature and lasts \ensuremath{\sim}100 ns, sufficiently long to achieve equilibrium and sufficiently short to preclude loss of hydrogen by diffusion and chemical reactions. The measured conductivity increases four orders of magnitude in the range 93 to 140 GPa and is constant at 2000 (\ensuremath{\Omega} ${\mathrm{c}\mathrm{m})}^{\mathrm{\ensuremath{-}}1}$ from 140 to 180 GPa. This conductivity is that of fluid Cs and Rb undergoing the same transition at 2000 K. This measured value is within a factor of 5 or less of hydrogen conductivities calculated with (i) minimum conductivity of a metal, (ii) Ziman model of a liquid metal, and (iii) tight-binding molecular dynamics. At metallization this fluid is \ensuremath{\sim}90 at. % ${\mathrm{H}}_{2}$ and 10 at. % H with a Fermi energy of \ensuremath{\sim}12 eV. Fluid hydrogen at finite temperature undergoes a Mott transition at ${D}_{m}^{1/3}{a}^{*}=0.30,$ where ${D}_{m}$ is the metallization density and ${a}^{*}$ is the Bohr radius of the molecule. Metallization occurs at a lower pressure in the fluid than predicted for the solid probably because crystalline and orientational phase transitions in the ordered solid do not occur in the fluid and because of many-body and structural effects. Tight-binding molecular dynamics calculations by Lenosky et al. suggest that fluid metallic hydrogen is a novel state of condensed matter. Protons are paired transiently and exchange on a timescale of a few molecular vibrational periods, $\ensuremath{\sim}{10}^{\ensuremath{-}14}\mathrm{sec}.$ Also, the kinetic, vibrational, and rotational energies of the dynamically paired protons are comparable.

High-speed multishot pellet injector prototype for the Frascati Tokamak Upgrade

The Frascati Tokamak Upgrade (FTU) may require multiple high-speed pellet injection in order to achieve quasi-steady-state conditions. A research and development program was thus being pursued at ENEA Frascati, aimed at developing a multishot two-stage pellet injector (MPI), featuring eight “pipe gun” barrels and eight small two-stage pneumatic guns. According to FTU requirements, the final goal is to simultaneously produce up to eight D2 pellets, and then deliver them during a plasma pulse (1 s) with any time schedule, at speeds in the 1–2.5 km/s range. A prototype was constructed and tested to demonstrate the feasibility of the concept, and optimize pellet formation and firing sequences. This laboratory facility was automatically operated by means of a programmable logic controller (PLC), and had a full eight-shot capability. However, it was equipped as a first approach with only four two-stage guns. In this article we will describe in detail the guidelines of the MPI prototype design, which were strongly influenced by some external constraints. We will also report on the results of the experimental campaign, during which the feasibility of such a two-stage MPI was demonstrated. Sequences of four intact D2 pellets in the 1.2–1.6 mm size range, fired at time intervals of a few tens up to a few hundreds of ms, were routinely delivered in a laboratory experiment at injection speeds above 2.5 km/s, with good reproducibility and satisfactory aiming dispersion. Some preliminary effort to address the problem of propellant gas handling, based on an innovative approach, gave encouraging results, and work is in progress to carry out an experiment to definitely test the feasibility of this concept.

Study of a transaugmented two-stage small circular-bore railgun for injection of hypervelocity hydrogen pellets as a fusion reactor refueling mechanism

Injection of hypervelocity hydrogen pellets has become widely accepted as the most effective means of refueling magnetically confined fusion reactors. Pellet velocities on the order of 10 km/s are desired and hydrogen pellet erosion during acceleration must be minimized. It is important to maintain uniform bore surfaces during repetitive shots, implying that, if a railgun is to be used to accelerate the pellets, damage to the sidewalls and rails of the railgun due to local heating must be limited. In order to reduce the amount of power dissipated within the bore and increase the propulsive force generated by the plasma-arc armature while minimizing losses due to pellet, rail, and sidewall ablation, we have employed a magnetic field transaugmentation mechanism consisting of a two-turn pulsed electromagnet. The two-stage gun consists of a light-gas gun which accelerates a 4- to 5-mg pellet to a speed around 1.2 km/s and injects it into the plasma-arc armature railgun. Currently, we have achieved a final output velocity for a hydrogen pellet of 2.11 km/s with a time-averaged acceleration of 4850 km/s/sup 2/ using a 58-cm railgun pulsed with a peak rail current of 9.2 kA and 28.0 kA of transaugmentation current. This paper will present a description of our hydrogen-pellet-injector railgun system, a discussion of the data on hydrogen pellet acceleration, and projections for future systems.

High-speed repeating hydrogen pellet injector for long-pulse magnetic confinement fusion experiments

The projected fueling requirements of future magnetic confinement fusion devices [e.g., the International Thermonuclear Experimental Reactor (ITER)] indicate the need for a flexible plasma fueling capability, including both gas puffing and low- and high-speed pellet injection. Conventional injectors, based on single-stage pneumatic guns or centrifuges, can reliably provide frozen pellets (1- to 6-mm-diam sizes) at speeds up to 1.3 km/s and at suitable repetition rates (1 to 10 Hz or greater). Injectors based on two-stage pneumatic guns and ‘‘in situ’’ condensation of hydrogen pellets can reliably achieve velocities over 3 km/s; however, they are not suitable for long-pulse repetitive operations. An experiment in collaboration between Oak Ridge National Laboratory (ORNL) and ENEA Frascati is under way to demonstrate the feasibility of a high-speed (≳2 km/s) repeating (∼1 Hz) pneumatic pellet injector for long-pulse operation. A test facility has been assembled at ORNL, combining a Frascati repeating two-stage light-gas gun and an ORNL deuterium extruder, equipped with a pellet chambering mechanism/gun barrel assembly. The main issues to be investigated were the strength of extruded deuterium ice as opposed to that produced by in situ condensation in pipe guns (hence the highest acceleration which can be given to the pellet without fracturing it), and the maximum repetition rate at which the system can operate without degradation in performance. Pellet velocities of up to 2.55 km/s have been achieved in joint experiments at ORNL. A new pressure tailoring valve was developed by the Frascati group for this application and proved to be a crucial component for good performance. Tests carried out in repeating mode, at frequencies of 0.2–0.5 Hz and speeds up to 2.2 km/s, indicate no significant degradation in performance with increasing repetition rate. Some preliminary tests using 3.7 mm pellets gave very encouraging results. The equipment and the experimental results are described in this article.

The early years of aerodynamics ranges, light-gas guns, and high-velocity impact

The age of supersonic flight began at the end of the 19th century when the inventions of smokeless powder and high strength steel enabled an increase in gun velocities to supersonic speeds. However, neither theory nor experiment were available at this time for the science of supersonic flight. The approach being taken then was to record the flight of the body and to compute the forces from its motions, but, unfortunately, unsolved problems in instrumentation stood in the way. The author was assigned the task of solving these problems at the Army's Ballistic Research Laboratories in 1940. His success in this endeavor led to the development of an apparatus, called an “Aerodynamic Range”, for recording the projectile's flight and, hence, determining the aerodynamic forces. World War II had started by this time, and the Aerodynamics Range was put to work immediately measuring the aerodynamic characteristics of gun-fired projectiles, bombs, rockets and some guided missiles. The “cold” war started right after the “hot” war and with it came a new challenge in the form of the InterContinental Ballistic Missile armed with an atomic explosive warhead. Aerodynamic Ranges, which had been built in various laboratories by this time, were put to work on impact tests to determine the lethality of kinetic energy weapons in countering the ICBM threat. In addition, the moon landing program had been started and tests were needed to evaluate the effects of meteorite impact on the lunar surface. Implementing these new programs required a gun capable of launching projectiles at the re-entry and meteoroid velocities of 8 to 10 km/s. The development of a new design of a two-stage high-velocity gun had been started at the Colorado School of Mines, a gun called a “light gas gun” because it used hydrogen as the propellant of its second stage. The author and others continued with its development until a design had been evolved capable of firing projectiles at the required velocities. The gun was then put to work in Aerodynamic Ranges on the assigned tasks of kinetic energy weapon lethality and meteoroid impact.The Early Years paper is an account of the trials and errors in the initial developments of Aerodynamic Ranges and High-Velocity Light Guns and the beginnings of research in high-velocity impact. It is not a formal research paper. Rather, it is an anecdotal account of the events taking place at the starts of these new programs to give the reader a feeling for the ambiance of the times with just enough technology thrown in for credibility. In a sense, telling about the successes and failures of The Early Years belongs with Kipling's verse: “To meet with Triurnph and Disaster and treat these two Impostors just alike”.