Experiments on simple railgun with the compacted plasma armature

Abstract

Our objective was to elucidate the physical reasons of the velocity limitation in the plasma armature (PA) railgun at the 6 k d s level. To do this, we have designeda simple system having no vacuum and no preaccelerator. The 1-2 g mass projectile is launched at the maximum possible constant acceleration4he limit of the projectile strength or the electrothermal explosion of rail surfaces, while making use of the effects of the material strengthening under the great confining pressure and rail current redistribution due to the presence of conducting shields. Such an approach provides the maximum possible energy efficiency of the launcher at its minimum conceivable length (as short as 50-80 cm). This greatly simplifies the design and fabrication but leads inevitably to the idea of the "fixed round"-"one assemblyone shot". Our experiments have confirmed the known hypothesis that the cause of the velocity saturation at the 6 k d s level is drag and decay of PA o'Wing to the increase of the inductive counter-emf with velocity and overload of PA with the ablated matter. The use of a compacted PA allowed us to overcome the "6 km/s limit" and to launch a 1 g projectile to 7.1 k d s in a bore length of 56 cm at a total efficiency of 10%. We believe that the simplest way to furtber velocity increase, while taking advantage of the compacted PA, is to increase the barrel length along with a corresponding increase of the energy stored. discussed below in a comp'uison with our experimental results which shed some light on the reasons for the "6-km/s limit". This will be followed by experiments carried out with acomp'xt PA which demonstrate the possibility of overcoming this limit.Our dztzz suggest that the velocity saturation is un'mbiguously due to the PA sprmding along the b'mel, so that to force the plasma to function properly, one should maintain the PA in the compact sme.In the ideal case of neglecting the losses for heating, wall ablation, friction etc. EM speed-up of a body in a railgun at a constant current I ('and, accordingly, constant acceleration a) is described by simple relations [4] Here V is the final projectile velocity, L' = const is the electrode unit length inductance, At is the acceleration time, 'and Q = IAt is the total electric charge consumed in At. This velocity is rtxzched at the lengthI . THE "G-KM/S LIMIT" IN PLASMA ARMATURE S = V A t / 2 = L'Q2/4m (2) RAILCUN LAUNCHING which paradoxically does not depend on acceleration time 'and ( h l y limited progress in EM 'acceleration of solid bodies has been reported in the fifteen years after the pioneering work of Rashleigh and Marshall [l] who accelerated a lexan projectile of 3 g in mass to 5.9 km/s in a 4 m-long railgun by means of a plasma armature (PA). Despite a comprehensive thwretical development of the EM launch problems 'and somewhat contradictory 'announcements of a velocity 8.5 km/s rexhed with m = 2 g [2], the published results obtained by other researchers remain at the 1978 level. An increase of the energy input and variation of the launc...

Development of a plasma railgun for affordable and rapid access to space

“…However, several decades of railgun research showed a persistent velocity ceiling of about 5-6 km/s for plasma-armature launchers. Railgun researchers working in the early 1970s had assumed that plasma armature railguns should be able to achieve exit velocities of tens of kilometers per second; however, they were only able to achieve velocities of 4-5 km/s for medium-bore (25-50 mm) railguns operating at typical accelerations of 400-600 kG [2], [3], and 6-7 km/s in smaller-bore guns operating at 1 MG or greater [4], [5]. These fast accelerations enabled researchers to outrun most of the problems that contribute to the velocity ceiling.…”

Electromagnetic Launch to Space

“…Researchers involved in that research were met with a great deal of challenge and difficulty, especially in getting plasma armatures to accelerate payloads to muzzle velocities in excess of 6 km/s at acceleration levels under 1 MG [1]. In those experiments, velocities of only 4-5 km/s were achieved for medium--bore (25-50 mm) railguns operating at typical accelerations of 400-600 kG [2,3], and velocities of 6-7 km/s were achieved in smaller bore guns operating at 1 MG or greater [4,5]. The researchers involved proposed a * corresponding author; e-mail: david wetz@iat.utexas.edu number of theories to account for the velocity ceiling and even proposed a number of solutions that could be used to overcome the obstacles, but no significant effort was put into implementing them.…”

Possibility of self-sustaining bombardment of inner planets

“…The problem is mainly the low efficiency of shock heating as the shock wave carries greater part of the impact energy into the target. On the other hand, Shoemaker (1977) and O' Keefe and Ahrens (1977) (Kondo and Ahrens, 1983;Drobyshevski et al, 1990) indicating the presence of overheated gas in such regimes when, by calculations, liquid phase would just appear. The averaged hydrodynamic description obviously fails in such conditions.…”