IL24246A - Plasma gun - Google Patents

Description

24246/2 nor a COMMISSARIAT A L'EKBRGIB ATOMIQUB C .23213 This invention relates to plasma guns for the production of plasmas of high density and high ion intensity, in view of the increasingly widespread interest being shown in the field of plasma formation hy reason of its constantly extending range of applications.

As is in fact already known, such applications include research on controlled thermonuclear fusion, space propulsion, re-entry of satellites into the earth's atmosphere, and so forth.

One plasma gun of known type is the Marshall gun shown in Fig. 1 of the accompanying drawings. A high-speed valve injects a burst of gas into the gun 2 at the moment when the charge voltage of a capacitor bank 8 (not shown) is applied between the coaxial electrodes 10 and 12 by means of a ring 6 of coaxial cables (only two of which are shown in the figure). A discharge is then established between said electrodes. If the term J is employed to designate the plasma current and the term B is employed to designate the magnetic field which is produced by said current , the plasma 15 is subjected to a force * which is represented by the product J/V¾* , with the result that said plasma is driven towards the ends of the coaxial conductors (towards the right in the case of the figure).

In these plasma guns as in those of the so-called spiral type, gas must be introduced therein and the operating pressure of these plasma guns corresponds to the minimum of the Paschen curve (approximately 1.33 Pa) by reason of the fact that the gas must be ionized. It is therefore impossible to make use of plasma guns of this type for the purpose of triggering a vacuum spark-gap since the requisite pressure is too high for the triggering value . In the plasma gun referred-to , the quantity of gas introduced is calibrated by means of a quick-opening valve 4-, thus resulting in low precision in the instant of initial emission of the burst of gas.

A plasma gun which serves to overcome the disadvantages of the type referred-to above is illustrated in Fig. 2, and is essentially made up of a stack of washers 16 of hydrogenated titanium and insulating washers 18 arranged in alternate sequence. During operation, discharges takes place between the successive titanium washers „ A capacitor bank 20, the discharge of which is triggered by a spark-gap 22 serves to apply between the electrodes 24—26 a voltage pulse of fairly long duration. The plasma gun is triggered when a short voltage pulse is applied between the electrodes 28 and 24·. It should be noted that the operation of the spark-gap is determined by the application to its starting electrode 30 of a pulse produced by the modulator 32. Said modulator controls the modulator 34- which produces the pulses for triggering the plasma gun through the intermediary of a phase shifter 36. In order to obtain satisfactory operation of the plasma gun, it is necessary to ensure accurate regulation of the pulses applied to the tube and consequently entails the use of a circuit which proves difficult to develop.

This source, known as the Bostick source, as well as other sources which have been designed and developed by the same inventor make use of the property of titanium in which hydrogen is retained in the occluded state. However, is difficult the hydrogenation process which is necessary/ to carry into practice if it is desired to hydrogenate the titanium right hydrogenation . In such a case, the titanium is converted to powdered titanium hydride which no longer has sufficient mechanical strength u Moreover, the occluded hydrogen in parts formed of titanium becomes rapidly depleted when the plasma gun is in operation. The construction of a titanium-wsftier gun is therefore difficult since it proves necessary to divide the conductive metal in such a manner as to produce a discharge which contacts the titanium. The stack of alternately arranged titanium washers and insulating washers provides a partial solution to the problem but it is not possible to maintain the geometrical dimensions of the plasma gun components during hydrogenation. Finally, it has already been explained that the operation of the plasma gun calls for the use of three electrodes and that the application of two triggering pulses to said electrodes entails the use of a complicated electrode which constitutes an obstacle to the practical utilization of this gun.

The plasma gun in accordance with the invention also turns to profitable account the chemical properties of titanium and is not subject to the disadvantages of the known devices which have been discussed in the foregoing.

A plasma gun in accordance with the invention is characterized in that it makes use of a hydrogen reservoir constituted by powdered titanium hydride which is agglomerated by means of an insulating binder, the quantity of binder employed being determined according to the particle size distribution of the hydride.

According to a preferred form of embodiment, the insulating binder consists of araldite.

Finally, the. powdered titanium hydride can be of a ceramic material, the aggregate being then subjected to a sintering process „ According to a first alternative form of the invention, the member which performs the function of hydrogen reservoir has the shape of a cylindrical sleeve, thus permitting the possibility of providing a gun of the axial ejection type.

Finally, according to another alternative form, the hydrogen reservoir is made up of two coaxial cylindrical sleeves placed one above the other at a small distance apart, the two opposite faces of said sleeves being outwardly divergent. This arrangement is favorable to the construction of a plasma gun of the lateral ejection type.

Aside from the main arrangements which have just been outlined, reference will be made in the description which follows to secondary arrangements relating essentially to the design of plasma guns.

The novel nature of the active portion of the hydrogen reservoir from which the ions are extracted readily permits of numerous geometries, thereby considerably increasing the potential uses of a source of this type.

Lastly, as each burst of plasma is ejected, the' discharge comes into contact with the hydride which is incorporated in the binder. Surface erosion and automatic regeneration of the ion carriers take place. It is the mass as a whole which contains the ion carriers whereas in the case of. plasma guns of known type (washer-type guns) hydrogenation was superficial.

The characteristic features of this invention description of two forms of embodiment which, as will be understood, are not intended to set any limitation either on the mode of operation of the invention or on the potential applications thereof,, - Fig. 1 illustrates a plasma gun of the Marshall type „ - Fig. 2 illustrates a plasma gun of the titanium washer type .

- Figs. 3 and 4 illustrate plasma guns of the axial ejection and lateral ejection type.

The body of the gun of Fig. 3 comprises a tubular member 40 of generally cylindrical configuration and formed of an insulating material such as araldite . A metal plate 42 closes off the gun at the rear end. A conducting member 43 having the shape of a cylindrical sleeve is secured to the insulating member 40 and adapted thereto. Said member is provided with a lateral annular flange 45 which serves to secure the gun in position. A meta] cylinder 44 is disposed within the central opening of the gun and fitted with a base 46 which is pierced by a central opening. An assembly of a number of coaxially arranged members is applied against said base 46 and consists of electrodes 48 and 50 having the shape of a cylindrical sleeve. Between said electrodes are fitted a mica washer 52 and a block 54 which performs the function of a hydrogen reservoir. Said block, which has the shape of a sleeve, is formed of powdered titanium hydride which is agglomerated by means of araldite, the quantity of this insulating material being determined according to the particle size distribution of the hydride. Central openings formed in the members 48, 50, 52, 54 define the that the external diameter of the block 5 is smaller than the external diameter of the electrodes since an 56 araldite sleeve/is fitted over said member 4.

Said plasma gun operates without any need for a third triggering electrode. The voltage of a capacitor bank is directly applied between the two electrodes 48 and 50, the discharge comes into contact with the inner face of the araldite-agglomerated hydride block . The outer face of said block is bonded to the araldite sleeve 56 in such a manner as to ensure that the discharge path is well defined . The function of the mica washer 52 is similar to that of the sleeve 56. The voltage between the two electrodes 48 and 58 is withstood by the insulator 40.

The elimination of the triggering electrode results in a simplification of the associated electronic circuitry.

Apparatus for providing synchronization between the triggering pulse of the plasma gun and the triggering pulse of the spark-gap which supplies the main discharge accordingly serves no further purpose.

Fig. 5 which has just been described illustrates a gun for axial plasma ejection whilst Pig. 4 relates to a plasma gun 57 of the lateral ejection type. In this latter case a burst of plasma is formed when the discharge which is established between the concentric electrodes 8 and 60 comes into contact with the hydride blocks 62, 64 which are agglomerated by araldite. and which constitute identical coaxial rings centered on the electrode 60. The coaxial rings or sleeves 62, 64 are placed at a small distance from each other, the two opposite faces thereof being outwardly divergent. ί It should be noted that the invention also applies to the design of a plasma gun in which the ejector tube has an intermediate opening between 0° (axial ejection) and 180° (lateral ejection),,

Claims (6)

SAVWQ HOW particularly described and ascertained · + the ature of our said iaventlon and in what manne the asano^ is to be performed, tfe declare that what we claim is 9

1. O Plasma gun which utilizes the chemical properties of titanium to advantage, characterized in that said plasma gun entails the use of a hydrogen reservoir made up of powdered titanium hydride agglomerated "by means of an insulating binder in a quantity which is determined according to the particle size distribution of the hydride employed.

2. Plasma gun in accordance with Claim 1, characterized in that the insulating binder is araldite.

3. Plasma gun in accordance with Claim 1, characterized in that the titanium hydride is mixed. so as to be agglomerated with powders which constitute the starting products of a ceramic material, the aggregate being then subjected to a sintering process.

4. . Plasma gun in accordance with Claim 1, characterized in that the hydrogen reservoir has the shape of a cylindrical sleeve.

5. Plasma gun in accordance with Claim 1, characterized in that the hydrogen reservoir is made up of two coaxial cylindrical sleeves placed at a short distance from each other, the two opposite faces of said sleeves being outwardly divergent.

6. Plasma gun comprising a hydrogen reservoir formed of powdered titanium hydride agglomerated by means of an insulating binder, substantially as hereinbefore described with reference to. and as illustrated in the accompanying drawings. Dated this 29th day of Augus , 1965