US3562530A

US3562530A - Method and apparatus of production of noncontaminated plasmoids

Info

Publication number: US3562530A
Application number: US699584A
Authority: US
Inventors: Terenzio Consoli; Lacelle Saint Cloud; Lucien Slama
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 1967-02-02
Filing date: 1968-01-22
Publication date: 1971-02-09
Anticipated expiration: 1988-02-09
Also published as: LU55363A1; DE1300183B; ES349998A1; NL6801494A; FR1518806A; CH488371A; GB1195602A; BE709351A

Abstract

A method for producing and/or heating a plasmoid, consisting in disposing a target at a first conjugate focal point of a closed chamber which constitutes a mirror system and in producing at least at a second focal point which is conjugate with said first focal point a substantial release of electromagnetic energy in the form of a pulse of very short duration, said energy being focused on said target which is thus heated to a high temperature.

Description

I United States Patent llll 3,562,530

[72] inventors Terenzio Consoli [51] Int. Cl G21g 3/00 LaCelle Saint Cloud: [50] Field of Search .l 250/845 21 A l N gg ggj Maggy France Primary Examiner-Archie R. Borchelt i Janzz 1968 Assistant Examiner-Mort0n J. Frome E gf 9 1 Attorney-Craig, Antonelli, Stewart & Hill [73] Assignee Commissariat A LEnergie Atomique Paris, France [32] Priority Feb. 2, 1967 France ABSTRACT: A method for producing and/or heating a 93498 plasmoid, consisting in disposing a target at a first conjugate focal point of a closed chamber which constitutes a mirror system and in producing at least at a second focal point which [54] METHOD AND APPARATUS 0F PRODUCTION OF is conjugate with said first focal point a substantial release of NONCONTAMINATED PLASMOIDS l7 Claims, 8 Drawing Figs.

US. Cl 250/845 electromagnetic energy in the form ofa pulse of very short duration, said energy being focused on said target which is thus heated to a high temperature.

'PATENTED FEB 9m SHEET 1. [1F 4 v 1NVENTOR$ TERI/V210 CU/VSOL/ LUf/E/V SLAHH ATTORNEYS PATENTEI] FEB 9m 3552 530 sum 2 [IF a AAAAAA Ys PA-TENTEn FEB 9mm 3 562 530 SHEET 3 BF 4 BY a ATTORNEY METHOD AND APPARATUS OF PRODUCTION OF NONCONTAMINATED PLASMOIDS This invention is concerned with a method of production and/or of heating of noncontaminated plasmoids and a device for the practical application of said method or a like method.

Many methods have already been proposed or employed for producing dense and hot plasma bursts, or so-called plasmoids. Among these methods can be mentioned the formation of convergent shock waves which are generated from explosion cylinders, in which an explosion permits ultrarapid compression of an intense magnetic field and produces bursts of plasma, or plasmoids, of very high density. Unfortunately, as soon as such a plasma is formed. it is contaminated by the impurities contained in the explosive charge or in the conduc- 7 tive metallic jacket which is enclosed by the explosive.

For the purpose of generating plasrn oids, use has also been made of a laser beam focused on a gaseous target or on a mechanically supported solid target which is maintained in levitation or which falls in a free drop. However, when only a single laser is employed, the energy which is available at the focal point of the focusing dioptric system is relatively small (less than one kilojoule) and it would have very costly increase in this energy by at least one order of magnitude.

An alternative method which appears to be very attractive consists of replacing the limited energy source formed by a parallel beam of a pulsed laser with a noncoherent source which generates higher energy level pulses in other words, the operation of the non coherent source is carried out with free" flashes of very substantial power. It is also an advantage to prevent any variation in the focal distance of a dioptric focusing system as a function of the wavelength ofthe incident radiation.

On the basis of the well-known fact that kinetic energy can be converted to radiant energy with a high degree of efficiency (of the order of 90 percent), the present invention is directed to a method of producing plasma burst and to devices of composite structure wherein a mirror system, is employed so as to dispense with the need for preventing variation of the focal distance as a function of incident radiation the wavelength.

With this object in view, the invention proposes a method which comprises disposing a target at a first of the conjugate point of a closed chamber which constitutes a mirror system and in producing at least at one point which is conjugate with said first point a substantial release of electromagnetic energy in the form ofa pulse of very short duration, this energy being focused on said target which is thus heated to a high temperature,

A better understanding of the invention will be gained from the following description in which various nonlimitive applications of the invention are illustrated by way of example taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagrammatic view of a device according to the invention as shown in cross section along a plane of symmetry which passes through the foci;

FIGS. 2 to 8, which are similar to F107 1, show alternative forms of construction of the device of FIG. 1.

In one embodiment which is illustrated in FIG. 1, the closed chamber 10 has the shape of an ellipsoid of revolution. Said chamber is confined by a mass 12 of concrete which is buried underground and is endowed with sufficient mechanical strength to withstand the shock waves generated during operation. The concrete structure 12 is fitted with an internal lining 14 formed of a material which has a high coefficient of reflection. Said lining 14 may consist ofa burnished metallic skin or of a coating of silica which is vitrified by means ofa preliminary series of explosions generated within the chamber 10. Said chamber 10 is equipped with means 15 for producing therein a high vacuum (of the order of 10- Torr), as well as with means for measuring pressure or temperature, and with viewing windows.

There is suspended at a first focus or focal point of the chamber a spherical charge 16 of a high explosive (such as TNT, for example) which is intended to constitute a radiation source and which is associated with an electric circuit 18 for initiating an explosion. as illustrated. electric circuit 18 may comprise a capacitor-source circuit. The spherical charge may also be suspended from triggering wiresv A cryogenic device not shown and which may comprise a lock-chamber, serves to introduce and maintain a target at the second focal point of a chamber 10 for a short predetermined time interval. The target may comprise a fragment of solid deuterium or of a solid deuterium tritium mixture.

During operation, the device shown in FIG. 1 is triggered by closing the capacitor 19 of the circuit 18 The spherical charge 16 of high explosive constitutes a spherical source of radiant energy which produces a spherical shock wave and an associated radiation which is reflected from the lining element 14 and focused at the target 20, thereby producing intense ionization and forming a neutron burst as a result of the fusion process which takes place at the target. Since the time of transport of impurities from the first focal point to the second is longer than the time of transfer of the radiation energy. the effect of the radiation (ionization and heating) is more rapid than the effect of contamination by the impurities. The time interval or delay T which elapses between the arrival of radiation and the arrival of material impurities at the second focal point can be estimated; in this connection, with a focal distance of a few meters, an eccentricity of less than one-half and contaminating ions having an energy of 10 keV, time intervals of the order of one-tenth of a microsecond are obtained.

The method is obviously of real practical interest only if two conditions are complied with: on the one hand. the radiation produced by the explosion must be such that it is reflected from the wall so that losses prior to focusing on the second focal point are not excessive; and on the other hand, it is necessary to ensure that an energy which has a high gradient in the vicinity of the second focal point can be focused thereon.

Insofar as the first condition is concerned, it is known that a plasma which is created by an explosion in a gas behaves practically as a black body. In consequence, the total radiant energy is given by the relation:

Z w=f oo()t,'l')dlt=o"l' (1) wherein 0' 5.679 X l0-w/cm. (C. The radiation has a maximum intensity at the wavelength A A,,.T=2.898 IOA.K (2) In point of fact, the plasmas created by explosives in compressed gases can easily attain a temperature above 100 eV. Thus, approximately percent of the energy of the radiation corresponding to short wavelengths (in the visible range and beyond the visible range) are propagated in the ionized medium which is created around the explosion zone at the velocity of light and are subjected to reflection from the walls of the ellipsoidal chamber.

So far as concerns the second condition mentioned above, the characteristics of the plasma which is produced at the second focal point by an energy source IE placed at the first focal point are given by the relation:

2: 2E1 N2T2=-3-K-5 m)4 t wherein N is the total number of charges at the second focal point;

T is the energy of the ions, in K;

0' is the radiation constant; (o'=5.679 X 10- w./cm. (degree);

It is the Bolzmann constant, 1.38 X 10- N is the total charge number in the region of the first focal point;

S, is the surface area of the radiant spherical volume at the origin of the time coordinates (namely that of the spherical explosive charge);

a is a coefficient of transfer efficiency which is variable between 0 and 1, depending on the state of the surfaces.

It is apparent that N T has no theoretical limitation and is solely dependent on the energy E,.

For example, in the case of an efficiency of 40 percent, when a spherical charge of TNT having a radius of 3 cm. is exploded at the first focal point of a chamber having a vacuum of IO Torr and a spherical pellet of solid D having a radius of 2 cm. is provided at the second focal point of said chamber, a burst of 10 neutrons is produced. The burst would be l neutrons with a deuterium-tritium mixture.

When a solid deuterium-tritium target is employed as has just been indicated, a high degree of vacuum is maintained throughout the chamber. However, when it is desired to employ two different atmospheres around the spherical charge of explosive 16 and around the target 20 respectively, it is merely necessary to provide a radiation transparent wall 21 between the charge 16 and the target 20. As shown in chain-dotted lines in FIG. 1 such a wall 21 divides the chamber into two compartments. By employing such a wall it is possible, for example, to produce a high vacuum solely within the compartment which surrounds the explosive sphere while maintaining a deuterium atmosphere within the compartment which contains the target. It is also possible to place the explosive sphere in a rare-gas atmosphere (xenon or xenon-krypton mixture) and to place the target in a deuterium atmosphere.

The presence of the wall 21 makes it possible not only to maintain two atmospheres within the chamber but also to prevent contamination of the target 16 by the ions which are derived from the explosive sphere 16. In the case in which only the second result is sought, it is possible to employ a magnetic field having lines of force which are transverse to the major axis of the ellipsoid so as to constitute a barrier which prevents the passage of charged particles derived from the explosive sphere. Said magnetic field could also confined the plasma which is created by the point, thereby initiating the explosion of the spherical charge 16,,: The heat energy and light energy emitted by the explosive charge are reflected from the wall 14,, and focused onto the already preionized target 20,, so as to produce a burst of plasma and of neutrons.

FIG. 3 shows another alternative form in which the explosive sphere 16,, is replaced by a spark-gap 16,, which is brought to a potential very slightly below the disruptive potential by a capacitor bank. In this case also, triggering is effected by means of a pulsed laser.

When it is found desirable to divide the chamber into two compartments by means of a material wall, all of the foregoing arrangements make it necessary to provide a wall of substantial diameter. However, it is somewhat difficult to provide a wall having both a substantial diameter and a sufficient strength to withstand an explosion. In order to solve this problem, the arrangement shown in FIG. 4 can be adopted. Thus, the central portion of the chamber is narrowed by means of an internal portion 26 of increased thickness which is delimited by a segment of ellipsoid 28 and two segments of

hyperboloids

30 and 32 which are homofocal with the wall 14 in this manner the wall 21, has a small diameter the focusing thereof remains total by virtue of the well-known properties of homofocal conics. There is shown by way of example in FIG. 4 a light beam which has been reflected a number of times before being focusedon the target 20,.

Since the extreme case of a hyperboloid is constituted by the midplane between the two foci, one of the terminal faces (such as the face 30, for example) can be flat and located at a point midway between the sphere 116, and the target 20, (the face 30 being indicated in chain target. Furthermore, in the case in which the magnetic field is of sufficient amplitude to ensure that the charged particles having the highest energies are capable of passing through it, it could be made possible to recover the energy by Hall effect.

Among the alternative embodiments of the invention which can be contemplated, a few variants are illustrated very diagrammatically in FIGS. 2 to 8, in which the walls limiting the chamber are merely shown in outline.

In the device shown in FIG. 2, an explosive sphere I6, is again suspended at the first focal point of the chamber 14 In this embodiment, the explosive is not triggered by an electric circuit, but by a concentration of energy from a laser beam. To this end, the chamber is fitted with a dioptric system 22 which serves to focus the beam of a laser 24 onto the second focal point at which the target 20,, is located. Said target can again be either suspended from a wire (not shown) or released in free fall, or maintained in levitation by means of electrodes (not shown). The target can be formed by a fragment of deuterium or a mixture of deuterium and tritium in the solid state in order a vacuum is maintained within the entire chamber.

During operation of the device shown in FIG. 2: the laser 24 is triggered and the resulting flash is focused on the point 20,, by the dioptric system, whereupon a preionization of the target takes place. The image of the laser beam or of the burst produced by the laser (with a vacuum of the order of one mil limeter of mercury) is then reflected along the walls 14,, of the chamber and focused on the first dotted lines in FIG. 4).

In the case in which it proves unnecessary to establish a material separation between the target and the spherical explosive charge (that is to say when the atmosphere can be the same, but when it is desired to avoid any direct path between the spherical charge and the target), it is possible to employ the device illustrated in FIG. 5, which can be considered in some degree as being symmetrical with that of FIG. 4. Thus, the device comprises a central obstacle 34 delimited by reflecting walls having the shape of segments of an ellipse 28,, and of

hyperboloids

30,, and 32,, which are homofocal with the wall 14,,. It should be noted that, especially in the case of an elongated ellipsoid, it is possible by means of this arrangement to delimit a chamber of substantial volume around the spherical charge 16,, and a chamber of small size around the target 20,,.

In the embodiment illustrated in FIG. 6, use is made of the caps located next to the apices of two paraboloids which have a common axis and which are joined to each other by a cylindrical portion so as to form a closed chamber. The spherical charge 16,. and the target 20, are located at the focal points of the chamber embodiment. This makes it possible to reduce the maximum diameter of the device at the price of a loss of energy, inasmuch as that portion of the energy which is emitted outside the solid angle limited by the paraboloid cap is evidently not focused on the second point. Similarly, instead of an ellipsoidal chamber, if an energy loss resulting from inadequate focusing can be accepted, it is possible to make use of two ellipsoid segments surrounding the focal points and joined to each other by a cylindrical portion.

It is also apparent that a plurality of mirror systems can be associated either in series or in parallel. By way of example, FIG. 7 shows a chamber in which the wall 14, is constituted by four segments of ellipsoids having a common focal point. In the embodiment which is illustrated, the ellipsoids are identical and of revolution and the four other focal points are disposed at right angles to each other about the common point. Four spherical explosive charges 16, which are located at the four separate points are triggered simultaneously. Triggering can be performed by focusing a laser beam on the common focal point, said beam being directed along a plane at right angles to that of FIG. 7. As thus designed, this arrangement would produce a loss of energy as a result of the absence of a cap on each ellipsoid, this loss being of correspondingly smaller magnitude as the ellipsoids are of greater length. This loss is avoided by providing screens 30fconstituted by caps or segments of hyperboloids which are homofocal with the ellipsoids and which extend through thesolid angle having a vertex 16f. Said segments are applied against the line of intersection of the ellipsoid considered with the adjacent ellipsoids. Without producing any appreciable loss of energy, the screens can be supported by full members, provided that said members do not project beyond the cones which are applied against the edges of the screens 30f, the vertices of said cones each being constituted by the corresponding focal point 16f.

FIG. 8 gives one example of an association in series of a plurality of ellipsoids which constitute a chamber 14g; in this case also,

screens

30g, 30g, 30"g in the form of caps of hyperboloids which are homofocal with the ellipsoids are provided for the purpose of preventing energy losses.

Generally speaking, it can be noted that any portion which is removed from an ellipsoid of revolution can be replaced by any one of an infinite number of segments of surface cut from a hyperboloid. The hyperboloid segments must be homofocal with the ellipsoid by a cone which is applied against the contour of the removed portion, the vertex of said cone being constituted by the focal point at which the emission takes place; by way of illustration, hyperboloids of this type are shown in chain-dotted lines in FIG. 5.

It is readily understood that the invention is not limited solely to the embodiments which have been illustrated and described by way of example and 'that the scope of this patent extends to alternative forms of all or part of the arrangements herein described which remain within the definition of equivalent means as well as to any application of such arrangements such as, for example, the generation of energy by Hall effect by producing a periodic magnetic field having an amplitude such that the paths of the charged particles which have the highest energies are simply deflected but not stopped between the target and the energy source.

We claim: 1. A method for producing an outburst of nonpolluted plasma which comprises:

providing at a first focal point of a mirror system in a closed chamber a target comprising a substance which will form a plasma under the influence of intense heat; and

liberating at a second focal point of said mirror system a pulse of electromagnetic energy of short duration, said second focal point being the conjugate of said first focal point so that the energy liberated at said second focal point is reflected by said mirror system and focused on said target to heat said target and form a plasma therefrom which is free from the impurities associated with the energy pulse.

2. The method of claim 1, wherein said pulse of electromagnetic energy is produced by an explosive charge.

3. The method ofclaim 1, wherein said pulse of electromagnetic energy is produced by an electric arc.

4. The method of claim 2, wherein a laser beam is impinged on said target and then reflected by said mirror system and focused on said second focal point to initiate the explosion of said explosive charge, said target thus undergoing a preionization immediately prior to said explosion.

5. The method of claim 3, wherein a laser beam is impinged on said target and then reflected by said mirror system and focused on said second focal point to initiate said electric arc, said target thus undergoing a preionization immediately prior to said explosion.

6. The method of claim 1, wherein a magnetic field is established between said first and second focal points to oppose the passage toward said target of charged particles originating at said second focal point.

7. The method of claim 6, wherein the intensity of said magnetic field is such that the most energetic of the charged particles of the source of electromagnetic energy can pass through said magnetic field and that a portion of the kinetic energy thereof is converted into electric energy by the Hall effect.

8. A device for producing a plasma outburst which con prises:

a closed chamber including: a catadiotric system having a first focal point and at least one second conjugated focal point;

a plasma forming target disposed at said first focal point.

and

means for liberating a short burst ofelectromagnetic energy at said second focal point.

9. The device of claim 8, wherein said chamber has an ellipsoidal confi uration.

10. The evice of claim 8, wherein said chamber comprises two paraboloidal sections having a common axis and being interconnected by means ofa substantially tubular member.

11. The device of claim 9, wherein said chamber is constricted in the central portion thereof by an annular enlarge ment of the chamber wall, said annular enlargement being defined by portions of surfaces of revolution whose generatrices are homofocal cones of said wall.

12. The device of claim 10, wherein said chamber is constricted in the central portion thereof by an annular enlargement of the chamber wall, said annular enlargement being defined by portions of surfaces of revolution whose generatrices are homofocal cones of said wall.

13. The device of claim 9, wherein said chamber is separated into two compartments occupied by different atmospheres by a material wall which is transparent to electromagnetic radiation.

14. The device of claim 10, wherein said chamber is separated into two compartments occupied by different atmospheres by a material wall which is transparent to electromagnetic radiation.

15. The device of claim 8, wherein said chamber is comprised of a plurality of ellipsoids each having one common focal point.

16. The device of claim 15, wherein each of said ellipsoids is provided with a hyperboloidal reflecting surface screen which is homofocal with the noncommon focal point of each respective ellipsoid.

17. The device of claim 8, wherein said chamber is under a high vacuum, and wherein said target is a solid mass selected from the group of deuterium, tritium and mixtures of deuterium and tritium.

Claims

2. The method of claim 1, wherein said pulse of electromagnetic energy is produced by an explosive charge.
3. The method of claim 1, wherein said pulse of electromagnetic energy is produced by an electric arc.
4. The method of claim 2, wherein a laser beam is impinged on said target and then reflected by said mirror system and focused on said second focal point to initiate the explosion of said explosive charge, said target thus undergoing a preionization immediately prior to said explosion.
5. The method of claim 3, wherein a laser beam is impinged on said target and then reflected by said mirror system and focused on said second focal point to initiate said electric arc, said target thus undergoing a preionization immediately prior to said explosion.
6. The method of claim 1, wherein a magnetic field is established between said first and second focal points to oppose the passage toward said target of charged particles originating at said second focal point.
7. The method of claim 6, wherein the intensity of said magnetic field is such that the most energetic of the charged particles of the source of electromagnetic energy can pass through said magnetic field and that a portion of the kinetic energy thereof is converted into electric energy by the Hall effect.
8. A device for producing a plasma outburst which comprises: a closed chamber including: a catadiotric system having a first focal point and at least one second conjugated focal point; a plasma forming target disposed at said first focal point; and means for liberating a short burst of electromagnetic energy at said second focal point.
9. The device of claim 8, wherein said chamber has an ellipsoidal configuration.
10. The device of claim 8, wherein said chamber comprises two paraboloidal sections having a common axis and being interconnected by means of a substantially tubular member.
11. The device of claim 9, wherein said chamber is constricted in the central portion thereof by an annular enlargement of the chamber wall, said annular enlargement being defined by portions of surfaces of revolution whose generatrices are homofocal cones of said wall.
12. The device of claim 10, wherein said chamber is constricted in the central portion thereof by an annular enlargement of the chamber wall, said annular enlargement being defined by portions of surfaces of revolution whose generatrices are homofocal cones of said wall.
13. The device of claim 9, wherein said chamber is separated into two compartments occupied by different atmospheres by a material wall which is transparent to electromagnetic radiation.
14. The device of claim 10, wherein said chamber is separated into two compartments occupied by different atmospheres by a material wall which is transparent to electromagnetic radiation.
15. The device of claim 8, wherein said chamber is comprised of a plurality of ellipsoids each having one common focal point.
16. The device of claim 15, wherein each of said ellipsoids is provided with a hyperboloidal reflecting surface screen which is homofocal with the noncommon focal point of each respective ellipsoid.
17. The device of claim 8, wherein said chamber is under a high vacuum, and wherein said target is a solid mass selected from the group of deuterium, tritium and mixtures of deuterium and tritium.