GB2233076A

GB2233076A - Electrothermally enhanced railgun

Info

Publication number: GB2233076A
Application number: GB9013444A
Authority: GB
Inventors: Volker Wegner; Francis Jamet; Walter Wenning; Hilmar Peter
Original assignee: Institut Franco Allemand de Recherches de Saint Louis ISL
Current assignee: Institut Franco Allemand de Recherches de Saint Louis ISL
Priority date: 1989-06-15
Filing date: 1990-06-15
Publication date: 1991-01-02
Anticipated expiration: 2010-06-15
Also published as: DE3919629A1; GB2233076B; DE3919629C2; FR2648552B1; FR2648552A1; GB9013444D0

Abstract

A railgun 1 for electromagnetic projectile acceleration includes an additional preaccelerator 4 likewise designed as a railgun, which at its rear end, with respect to the direction of projectile movement, is provided with a pressuretight breech 7. This breech prevents the developing plasma from expanding in the direction opposite to the projectile movement, thus using the plasma to enhance the electromagnetic projectile acceleration. A drum or belt including two preaccelerators 4, 14 may be provided between a stationary railgun 1 and breech 7. The preaccelerator may include an additional coil (Figure 2) to intensify the magnetic field acting on the projectile 10. <IMAGE>

Description

__Cl -Y;3 3 Q _ kS Electrothermally Enhanced Railgun

SPECIFICATION

The present invention concerns a railgun for electromagnetic projectile acceleration including an additional preaccelerator.

Railguns for electromagnetic projectile acceleration have been known for a long time, for example from DE-PS 376 391J In such railguns the projectile is subjected to an inductive force (i.e. the Lorentz force) and to an electric current flowing directly through the projectile-With railguns of this kind, however, accelerating the projectile from its initial static position causes problems, as the current flowing through the armature is restricted to one spot on the rails for a relatively long time, thus leading to severe melting and abrasion of material at this spot. - For this reason it had already been proposed to add a preaccelerator to the electromagnetic railgun.

Accordingly, "IEEE Transaction on Magnetics11, vol. MAG-22, No. 6, pp. 1 410-15 (1986) contains a description of an electrothermal preaccelerator from which the projectiles are fired into the electromagnetic railgun. For this purpose, the electromagnetic railgun is built in a modular design; in the first module following the electrothermal preaccelerator the gas exhausting from the electrothermal preaccelerator can be used to create a plasma arc for the electromagnetic railgun.

_Z_ The plasma arc, however, may also be produced in an electrothermal plasma arc source designed specifically for this purpose and located at the module entry; the plasma arc, thus created, will then be injected into the module- Moreover, electrothermal projectile accelerators have been proposed, for example, by N.K. Windsor et. al., "Operation of an Electrothermal Gun", Aeroballistic Range Association, 37th meeting, Quebec, Canada (1986). This publication discusses the difference between electromagnetic railguns and electrothermal accelerators. In an electrothermal accelerator a power supply unit strikes a plasma jet which heats up the propellant and thus causes the projectile to be accelerated due to the pressure buildup at its base. In an electromagnetic railgun, however, the power supply system generates high currents flowing through the rails and inducing a strong magnetic field in the railgun barrel. The resulting force acting on the armature at the projectile base accelerates it together with the projectile out of the barrel. In an electrothermal gun the plasma is generated at the breech end, whereas in an electromagnetic railgun the plasma arc moves along the rails, ideally remaining immediately behind the projectile over the entire rail length.

Finally, it is known that, in addition to the aforementioned accelerator or preaccelerator designs solid propellant guns can be employed as preacceleration devices for electromagnetic railguns.

The underlying purpose of the present invention is to provide an efficient preacceleration device and procedure for an electromagnetic railgun with as little effort as possible.

Concerning the device, the present invention suggests a railgun for the electromagnetic projectile acceleration including an additional preaccelerator which is likewise designed as an electromagnetic railgun and provided with a pressure tight breech at its rear end (with respect to the direction of projectile movement).

--Concerning the procedure, the invention, as a solution to the problem stated, proposes the employment of a procedure for the preacceleration and subsequent electromagnetic acceleration of a projectile where the preacceleration is essentially performed electromagnetically and enhanced in the initial stage of projectile movement by plasma generated which, for this purpose, is prevented 2 -S- to expand in the direction opposite to the projectile movement. This leads to an additional acceleration of the projectile along its path by the plasma generated.

Accordingly the invention is based on the fact that, in a short electromagnetic preaccelerator, the acceleration of the projectile caused by the developing plasma arc is relatively small, and the projectile velocity is relatively low. The plasma developing behind the projectile, however, has a high expansion velocity. Due to the relatively slow movement of the projectile and reasonable current rise times the plasma front moves faster than the projectile and part of the plasma is vented at the rear of the rail gun. According to the present invention, this effect is utilized by providing the electromagnetic railgun of.the preaccelerator with a pressure tight breech at its rear end such as to use'the developing gas pressure, in addition to the Lorentz force, for the acceleration of the projectile. In the final analysis, the present invention thus makes use of an electrothermal effect occurring only at low projectile velocities to enhance the preacceleration of a projectile in an electromagnetic preaccelerator.

A considerable advantage of the present invention is the short overall length of the proposed preaccelerator design. Whereas a state-of-the-art preacceleration system requires a relatively great length to achieve the necessary velocity for the projectile to be injected into the actual accelerator, the combination of the electromagnetic acceleration due to the Lorentz force and the electrothermal effect according to the invention reduces the acceleration phase to such an extent that the very short overall length of the preaccelerator thus possible does not differ substantially from that of the cartridge cases used in conventional chemical propellant guns.

The electrothermal effect can be enhanced advantageously by a substance which, by vaporization, yields dissociation products of low molecular weight. Thus, the pressure exerted on the projectile will be considerably enhanced. This can be utilized to reduce the acceleratio.n phase or to increase the acceleration respectively.

This effect can be further enhanced by employing substances which, after the ignition of the plasma arc, initially show a chemical reaction in the form of a combustion.

3 According to an especially advantageous design of the present invention, the short overall length of the preaccelerator, according to the invenLion, is used to further enhance preacceleration by an additional magnetic field. For this purpose, an additional acceleration coil arrangement is provided by one or more additional turns wound around the preacceleration system and having the same sense of winding as the coils on the rai Is of the preaccelerator system; the current flow through these additional turns further intensifies the magnetic field producing the Lorentz force.

The subject of the invention is further detailed by the following illustrations of design versions showing further advantages and features.

Fig. 1 shows an electromagnetic railgun with an additional electromagnetic preaccelerator according to the present invention.

shows an electromagnetic preaccelerator according to the present invention, with an additional acceleration coil arrangement for magnetic field enhancement.

Figure 1 shows a longitudinal section of an electromagnetic r-ailgun (1) with the accel-eration rails (3) and the power leads (2) to the acceleration rails (3). For clarity purposes the power supply system has been omitted- At its rear end the electromagnetic railgun (1) is provided with an electromagnetic preaccelerator (4) whose acceleration rails (6) are in line with the acceleration rails (3) of the main accelerator. The power leads (8) and (9) are used to supply current to the acceleration rails (6) of the preaccelerator (4).

At its rear end the preaccelerator (4) is sealed by a pressure tight breech (7).

The preaccelerator (4) holds a projectile (10) which has a metal foil (11) attached to its base that is used for ignitfng a plasma. On the back side of the metal foil (11) there is a substance (12), serving as working substance, which vaporizes after plasma ignition, preferably in such a way, that dis sociation products of low molecular weight are generated and/or a combustion process is initiated.

4 The main accelerator (rail gun (1)) and the pressure tight breech (7) remain stationary. The preaccelerator (4) and an additional preaccelerator (14), shown in figure 1, constitute a constructional unit designed either as a drum or as a belt. If the preaccelerators (4) and (14) are designed as a drum, the preaccelerator (4), after firing the projectile (10), is turned around an axis in such a way that the preaccelerator (14) together with the projectile (13), shown in figure 1, is rotated into the position between the main accelerator (1) and the pressure tight breech (7). The preaccelerator (4), now empty, is ready to receive another projectile (15) (Figure 1); this process is repetitive.

If, however, the preaccelerator is designed as a belt, the preaccelerator (4), after firing the projectile (10) is replaced in such a way that the preaccelerator (14) together with the projectile (13) is shifted into the position between the main accelerator (1) and the pressure tight breech (7). The preaccelerator (4), now empty, is ready to be reloaded; this process is repetitive.

Figure 2 shows a longitudinal section of another electromagnetic preaccelerator (4a) which, in contrast to the electromagnetic preaccelerator shown in figure 1, has an additional acceleration coil arrangement to intensify the magnetic field acting on the projectile (10). Like the preaccelerator of the design version shown in figure 1 the preaccelerator (4a) is also provided with a pressure tight breech (7) at the rear.

Apart from the following differences, preaccelerator (4a) functions basically in the same way as that of the design version shown in figure 1_ To avoid repetitions of functional aspects, the reader is thus referred to the description above.

The current flow, however, differs in the arrangement shown in figure 2. Current I enters the preaccelerator (4a) at connection point A and is then conducted from point 8 to a point C via a metal ring M at the front end of the preaccelerator (4a). Current I subsequently flows from point 0 to point E of the acceleration rail (6a), then through the developing plasma current arc at the base of the projectile (10), and back along the other acceleration rail (6b) to point F. In contrast to the design version shown in figure 1, the preaccelerator (4a) shown in figure 2 has an additional coil winding formed by the loop A-B-C-D.

Claims

CLAIMS:

1. A railgun for the electromagnetic acceleration of a projectile which includes a preaccelerator, characterised by the preaccelerator (4, 4a) being likewise designed as an electromagnetic gun and being provided with a pressure tight breech (7) at its rear end, as viewed with respect to the direction of movement of the projectile (10).

2. A railgun as claimed in claim 1, characterised by the preaccelerator including a device to produce a substance (12) which, upon vaporization, yields dissociation products of low molecular weight.

3. A railgun as claimed in claim 2, characterised by the substance undergoing a chemical reaction in the form of a combustion after the ignition of a plasma arc.

4. A railgun as claimed in any one of claims 1 to 3, characterised by the preaccelerator (4a) being provided with an additional acceleration coil arrangement (A-B-C-D) for intensification of the magnetic field.

5. A process for the preacceleration and subsequent electromagnetic acceleration of a projectile, characterised by the preacceleration being mainly induced by electromagnetic means and, in the initial stage of projectile movement being enhanced by the plasma generated, which plasma is prevented from expansion in the direction opposite to the direction of projectile movement.

6. A process as claimed in claim 5, characterised by a substance being vaporised at the rear of the projectile, as viewed with respect to its direction of movement, which upon vaporisation, yields dissociation products of low molecular weight.

7. A process as claimed in claim 6, characterised by the substance undergoing a chemical reaction in the form of combustion.

8. A process as claimed in any one of claims 5 to 7, characterised by the magnetic field of the preaccelerator being enhanced by means of an additional acceleration coil arrangement.

9. An electromagnetic railgun constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

10. A process for the preacceleration and subsequent electromagnetic acceleration of a projectile, the process being substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

Published 19W - at The Patent Office- St,,t. Igni, T4i^