Secondary Arc Formation Research Articles

Is the Ibero-Armorican Arc primary or secondary? An analysis of the contraction required to form it by rotation around a vertical axis

Various models have been proposed to explain the formation of the Ibero-Armorican Arc (IAA) as either primary or secondary (rotational). Models for secondary arc formation require significant rotation around a vertical axis at the end of the Variscan orogeny. Estimates for the amount of north–south (present coordinates) contraction (horizontal shortening) required for these rotations range from 54 at the core to 91% at the SE tip of the arc, near to the present day Mediterranean coast. These estimates are compared with coeval deformational structures developed in three areas of the orogen: (1) in the autochthonous hinterland in the southern branch of the arc; (2) in the Cantabrian Zone foreland fold–thrust belt in the core of the arc; and (3) in the SE continuation of the southern branch of the IAA in the present day Iberian Chain. From this analysis it follows that the contraction associated with late Variscan deformation is much less than that needed to explain the formation of the IAA from a formerly linear orogen via rotation around a vertical axis. We therefore propose that the geometry of the arc should be re-evaluated. We discuss the palaeomagnetic data purported to support the secondary origin, as well as the role of late Variscan regional strike-slip faults in modifying the geometry of the Iberian and Armorican massifs. Our analysis suggests that the IAA formed mainly from a primary non-rotational margin-controlled curvature, slightly modified by c. 5–20% of superposed contraction during late Carboniferous and/or Alpine times.

The characteristics of primary and secondary arcs on a solar array in low earth orbit

In this paper, the characteristics of the primary arc and secondary arc on a solar array in low earth orbit (LEO) are investigated. The vacuum plasma environment in LEO has been used to study the primary arc and secondary arc of a high-voltage solar array. Silicon solar cells with rigid substrate specimens are used for the experiment. The series-parallel spacing of the silicon solar cells is 1 mm. The string currents of the solar cells are 0.7 A, 1.5 A and 2 A. The primary arc and secondary arc are photographed by high-speed cameras. The differences between the primary arc and secondary arc are observed. The secondary arc can be observed before the primary arc is extinguished. The primary arc is a single arc when the string current is 0.7 A. Multiple arc columns are accompanied by higher arc current. Two arc columns of the primary arc can be observed at 1.5 A string current and 2 A string current. The multiple primary arc columns are related to higher bias voltage. The threshold for sustained arcing is near 145 V/0.7 A, 105 V/1.5 A and 100 V/2 A at 1 mm string gap. Moreover, the transition time of secondary arc formation is analyzed, and found to be about 10–13 μs. The string currents, string voltages and primary arc have no effect on the transition time of the secondary arc formation.

Characterization Experiments of Secondary Arcs on Solar Arrays: Secondary Arc Physical Parameters

Secondary arcs on solar arrays are a serious threat to the safety of spacecraft operation. Experiments to characterize secondary arcs are currently being conducted. In this study, the effect of external capacitance in the test circuit on the transition from a primary discharge to secondary is investigated. In addition, the effect of flashover current with a long duration of the order of is also investigated. The time delay from the inception of the primary discharge to secondary arc formation and the resistance of secondary arc plasma are investigated by analyzing the experimental waveforms. The transition to secondary arc occurs within from the inception of the primary discharge. The flashover duration does not affect secondary arc occurrence. To maintain a temporary sustained arc, a gap voltage of 30 V can be regarded as the physical threshold for multijunction solar cells. The occurrence of a permanent sustained arc depends on the string current rather than on the energy of the primary arc or gap voltage.

Theoretical and Experimental Analysis of Breech Fed and 40-Distributed Energy Stage Plasma Arc Railguns

The design and experimental results of a 40-stage distributed energy store (DES) plasma arc railgun are presented. The railgun drives a free running hypervelocity plasma arc, one that is not pushing a payload, to velocities in excess of 10 km/s. These high velocities are of interest as they are required to successfully launch payloads into low earth orbit (LEO). The ability to launch payloads into LEO using a hypervelocity electromagnetic launcher has many financial benefits over the more conventional chemical combustion launchers. In collaboration with an Air Force Office of Scientific Research funded Multidisciplinary University Research Initiative project, the Center for Pulsed Power and Power Electronics at Texas Tech University in Lubbock, Texas has been responsible for developing and investigating a functional scale model of a multistage DES railgun to determine its effectiveness to suppress restrike phenomenon and increase plasma armature railgun performance. The distributed energy scheme is theorized to suppress restrike arc formation because the back emf voltage is localized to active stage regions where high gas density and low temperature inhibits breakdown. B-dot sensors positioned along the length of the launcher provide data to measure the plasma arc velocity and detect restrike, arc splitting, or additional secondary arc formation phenomena.

A 40-Stage Synchronous Distributed Energy Railgun

The development process pertaining to the design, fabrication, and testing of a 40-stage free-running arc synchronous distributed energy railgun is presented. Research efforts are still ongoing to suppress the restrike phenomenon that is responsible for causing a velocity ceiling around 6 km/s to exist on plasma armature breech-fed railguns. Numerous solutions have been theorized as viable methods of restrike prevention but lack experimental verification. In collaboration on an AFOSR Multidisciplinary University Research Initiative project, the team at Texas Tech University is responsible for characterizing a functional scale model of a synchronous distributed energy railgun to investigate the effectiveness of a distributed energy scheme to suppress the plasma restrike phenomenon and increase plasma armature railgun performance. The distributed energy scheme is theorized to suppress restrike arc formation because the back-EMF voltage is localized to active stage regions. Synchronous operation refers to the speed of an electromagnetic wave in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> transmission line formed by the rails and capacitors being matched to the velocity of the armature. The railgun drives a hypervelocity (8 km/s) plasma armature, with no payload, to emulate the conditions of a high-altitude microsatellite launch while relieving the financial burden of a large stored energy facility. Experimental data collected from a seven-stage prototype distributed energy system are discussed which will mimic the design and operation of the first seven stages associated with the final 40-stage system, which is currently under construction. The data collected from this prototype as well as the final 40-stage system will be analyzed for secondary arc formation in an attempt to verify the distributed energy scheme's success in suppressing restrike formation.

Secondary Arc Formation Within a Distributed Energy Railgun

Experimental results comparing a breech-fed scheme and two distributed energy schemes for a free-running arc are presented. Analysis and observations of the issues associated with distributed energy switching of a plasma arc in the railgun are explored. The use of a free-running arc allows experiments to emulate the ablation and restrike phenomenon of a plasma armature railgun at high speeds (> 5 km/s) without the requirement of a large amount of stored energy. Numerous experimental tests were conducted to investigate the dynamics of plasma arcs within a distributed energy source railgun. Variations of switch timing, bore pressure, bore material, current amplitude, and current pulse length within each stage have been tested. These data reveal important design parameters for distributed energy railguns. The arc length, stage length, and stage trigger timing play a crucial role in distributed energy railgun performance. Failure to take these parameters into consideration will result in velocity reduction through plasma arc restrike and/or splitting.

A Plasma Railgun Experiment Addressing Launch-to-Space Issues

The Institute for Advanced Technology has recently been awarded a grant by the U.S. Air Force Office of Scientific Research to undertake research in the area of hypervelocity, plasma-driven electromagnetic launch. This paper describes our technical approach to achieving 7 km/s at accelerations that are lower than typical for plasma launchers. Our approach to managing plasma restrike and secondary arc formation is to reduce the emission of ablated materials into the gun bore through the use of augmentation and ceramic sidewalls. In addition, preinjection to 1 km/s is used to provide an initial velocity for the launch package while introducing minimal dense cold gas, since such gas can also contribute to restrike. This paper describes the hardware that is being put in place for this experiment

低地球軌道プラズマ環境下での二次アーク発生条件

Arcing on satellite solar array due to interaction with space plasma may cause permanent loss of satellite power, once the arc becomes permanent sustained arc. An arc on solar array becomes a secondary arc when solar array circuit is short-circuited and provides energy to the arc plasma. The permanent sustained arc, the final stage of the secondary arc, destroys a solar array string or the complete power circuits at the worst case. To investigate the threshold conditions for the secondary arc formation, laboratory tests are carried out in a xenon plasma chamber simulating LEO plasma environment with an external circuit simulating a spacecraft power system. Solar array coupon panels simulating the hot and return ends of a string circuit are tested for various combinations of string voltage and string current. Experimental results show that formation of secondary arc strongly depends on the string voltage and duration of secondary arc depends on the string current.

External magnetic field influence on the behaviour of arc-driven railguns

An analysis of the effects of the application of an external magnetic field on the behavior of plasma-driven railguns is carried out. An evaluation of the quantity of material ablated from the rail and insulator walls and of the mass leakage from the rear of the arc and an estimate of secondary arc formation are carried out, modeling the characteristic quantities of the plasma arc by means of an adimensional model that was suitably adapted in order to reproduce some experimental data. The calculated data can reproduce the experimental data if a plasma mass leakage from the rear of the arc is assumed. The analysis of the application of the external field for the same propulsive force of a conventional railgun has shown that reduction of ablated mass, increase of final velocities, and a smaller probability of secondary arc formation can be reached. >

An experimental investigation of plasma armature railgun performance in the 3.2 to 4.2 km/s regime

The authors describe a set of experiments in which velocities up to 4.2 km/s were achieved in a midsize gun (51 mm) without discrete secondary arc formation. A figure of merit is described which relates the muzzle velocity to the electrical action applied to the barrel during acceleration. This figure of merit declines from the lower to the higher velocity firings. An efficiency roll-off in a mid-sized railgun as the launch velocity increased from 3 to 4.2 km/s was observed. The momentum efficiency in the velocity regime was measured at approximately 75%. Armature behavior was monitored closely in each shot of the eight shot high velocity test series. No armature bifurcation was observed but data from the induction probes strongly suggest that the armature current distributed included a long tail that increased in length throughout the launch time. Finally, it is noted that the changes made to the bore configuration to perform the high velocity test series also appear to have had a beneficial effect on bore lifetime.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Review of armature research (railguns)

Plasma and hybrid armature research are reviewed. The role of secondary arcs in limiting the velocity in hypervelocity experiments is discussed. Possible mechanisms for secondary arc formation are outlined and techniques for controlling the behavior of secondaries, such as the use of confined plasmas, are described. The physical picture of the hybrid armature that has evolved from small-bore, hybrid-armature tests is also reviewed. Finally, recommendations for future work are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Armature formation in a railgun using a two-stage light-gas gun injector

The authors summarize the problems encountered in attempts to achieve hypervelocities with a railgun. Included is a description of the phenomenology and details of joint Sandia National Laboratories, Albuquerque/Lawrence Livermore National Laboratory (SNLA/LNLL) work at SNLA on a method for forming the needed plasma armature. Attention is given to such problem areas as secondary arc formation through growth and separation of the propulsive plasma armature and arc restrike. Potential solutions to the problems are being incorporated in the STARFIRE railgun project. The primary improvement is to provide a high-injection velocity with a 2SLGG (two-stage light gas gun), which offers the additional benefit of filling the barrel behind the projectile with electrically insulating hydrogen. The resulting additional challenge of forming a propulsive armature behind the projectile has been met with an injected metal vapor and a projectile-mounted fuse which are used to initiate rail commutation and begin the formation of a hydrogen plasma armature.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>