US3094474A - Apparatus for carrying on nuclear reactions - Google Patents

Description

June 18, 1963 A. J. GALE- APPARATUS FOR CARRYING ON NUCLEAR REACTIONS Filed Nov. 22. 1960 Fatente'd June 18, 1963 3,094,474 APPARATUS FOR CARRYlNG on NUCLEAR nEAerroNs 7 Alfred J. Gale, Lexington, Mass, assigpor to High Volt- This application is a continuation-in-part of my copending application Serial No. 625,679, filed December 3, 1956, now abandoned.

This invention relates to the production of nuclear reactions by the bombardment of materials with high energy ions. One of the goals of modern science has been the fusion of nuclei. This invention relates to apparatus for research with a goal of obtaining fusion.

In accordance with the invention, a sequence of pellets of material is bombarded with a high energy ion beam for a very short interval of time with an extremely high current. The pellets are in liquid or solid form, and the bombardment is very intense and very short, so that evaporation and resultant expansion of the pellets are minimized, while the temperature thereof is raised extremely rapidly. Moreover, the size of the pellets is so chosen with respect to the energy of the ions that most of the ion energy is delivered to the interior of the pellets, thereby minimizing losses by causing the high-temperature part of the mass to be surrounded by a cold outer shell.

The invention may best be understood from the following detailed description thereof, having reference to the accompanying drawings, in which:

FIG. 1 is a somewhat diagrammatic view, mainly in vertical section, of one embodiment of the invention, wherein a sequence of pellets of material is bombarded with a plurality of high energy ion beams;

FIG. 2 is a diagrammatic view in vertical section of a modification of a portion of the apparatus shown in FIG. 1, and shows another type of pellet-feeding mechanism; and

FIG. 3 is a diagram of a single pellet.

Referring to the drawings and first to FIG. 1 thereof, material is formed into pellets 1 by a suitable pelletforming mechanism 2, and the resultant pellets 1 are fed in any convenient manner, as by gravity, into a reaction chamber 3. Within the reaction chamber 3 the the pellets are bombarded by ions which have been accelerated to high energy by one or more particle accelerators 4. In order to obtain maximum ion current, it is desirable to bombard each pellet simultaneously with the ion output of a plurality of ion accelerators 4-, and the ion output of each accelerator 41 is preferably pulsed so that ion pulses are delivered to the reaction chamber 3 in synchronism with the delivery of pellets thereto.

If in the solid state, the material may be in wire form, as shown at 5, and the pellet-forming mechanism 2 may comprise a simple cutting device into which the wire 5 is fed continuously by a suitable feeding mechanism. The repetition rate of the cutting device determines the spacing between pellets 1, which are allowed to fall freely into the reaction chamber 3, and the rate of feed of the feeding mechanism determines the size of each pellet 1. The construction of such a cutting device and feeding mechanism will be obvious to those skilled in the mechanical arts, and is therefore not shown in the drawing nor described herein in detail. Within the reaction chamber 3 each pellet 1 is bombarded by an ion pulse 6 from each accelerator 4.

If the material is in liquid form, the pellet-forming mechanism 2 may be modified as shown in FIG. 2. The liquid material 7 is fed into the chamber 3 through a suitable capillary tube 3, by which the liquid 7 is formed into drops or pellets 1. The vapor pressure above the liquid material 7 may be varied by an appropriate mechanism, such as the piston 9, and in this manner the rate of flow of the liquid through the capillary tube 8 may be controlled. The size of each pellet 1 is determined by the diameter and shape of the opening 10 at the bottom of the capillary tube 8.

Referring now to FIG. 3, let it be assumed that the radius of each pellet 1 is l millimeter. In order that the high-temperature part of the pellet 1 may be surrounded by a cold shell, the diameter of the ion beam or beams must be substantially less than the diameter of the pellets 1, and in FIG. 3 the ion beam diameter is shown as .2 millimeter. If the acceleration due to gravity be taken as approximately 10 cm./sec. and if it be assumed that the pellet-forming mechanism 2 is spaced no more than 5 meters from the target zone of the reaction chamber 3, then the velocity of the pellet at the target zone will not exceed 10 cm./sec. If the duration of each ion pulse 6 is 10' seconds, then the displacement of each pellet 1 during bombardment will not exceed 10* cm. Since the ion beam diameter is .2 millimeter, the pellets 1 are virtually stationary during bombardment thereof.

Representative nuclear reactions are the T-D reaction, the Li reaction, and the D-D reaction. The reactions available for thermonuclear purposes are well-known in the art and need not be discussed herein in any detail. Merely for illustrative purposes, and without limiting the invention thereto, the operation of the invention will now be described in terms of the T-D reaction.

Referring to FIGS. 1 and 3, it will be observed that by far the greatest concentration of ions occurs Within a sphere 11 whose radius is .1 millimeter. It can be shown that, in order to maintain a thermonuclear chain reaction in a pellet of deuterium having a radius of .1 millimeter (i.e. a pellet the size of the core 11 of the pellet of FIG. 3), it must be held at 7.5 million degrees centigrade; or, in other words, each particle in the pellet must have an energy of about 750 electron volts. This energy or temperature represents a very rapid evaporation. The pellet must therefore acquire this temperature very rapidly, before significant evaporation takes place. The velocity of particles at several million degrees approximates 10 cm./sec., so that the delivery of energy to the pellet in order to raise its temperature should preferably be delivered in 10' seconds or less. Therefore, in accordance with the invention, each ion pulse should have a duration of 10' seconds or less.

Assuming that the number of atoms N in said .l-millimeter-radius sphere is 1.8 lt) the energy which must be supplied to this sphere to raise its temperature to the necessary 7.5 million degrees, at 750 electron volts per particle, is 1.3 10 e.v. If this energy is supplied by a stream of particles with an energy loss approximating 10 m.e.v. in passing through the .1-mm.-radius sphere, which corresponds roughly to alpha particles, the number 3 of bombarding particles required is 1.3x 10 Since these particles should be delivered in 10" seconds or less, the ion current required is at least 200 amperes, and the current density is 2 million amperes per square centimeter. Space charge limitations therefore point to the need for using high energy particles.

Under the foregoing circumstances, in which liquid pellets of a suitable mixture of tritium and deuterium and having a radius of .1 millimeter are bombarded with l-m.e.v. alpha particles, it might be expected that, if the reaction rate were extremely fast, a large proportion of the available fusion energy would be gained. The Q of the T-D reaction is about 17 m.e.v., so that the total energy available is 2.4 10 joules. Thus from an input of 20 joules (200 amperes at mev. for 10 sec.) a gain in excess of 10 might be obtained. 7 Each particle accelerator 4 should be designed so 'as to provide maximum current output. Thus, for example, each particle accelerator 4 may comprise an electrostatic accelerator adapted to provide a high-current pulsed output in accordance with the teachings of a copending application assigned to the assignee of the present invention, Serial Number 431,439, filed May 21, 1954, now Patent No. 2,847,611, dated August 12, 1958. In any event, the high-energy ion beam from each particle accelerator is deflected in the plane of the drawing by an ion deflector 12, which may comprise, for example, a pair of deflector plate-s perpendicular to the plane of the drawing across which a radio-firequency electric field is impressed and between which the high-energy ions travel. The ion deflector 12 is thus adapted to subject the ion beam to a deflecting field which varies cyclically in time; and if the deflecting field is adapted to increase lineally in time and decrease virtually instantaneously, as in the case in the horizontal sweep of the electron beam of a conventional television receiver, the ion beam will be broken up into segments 6 as shown in FIG. 1. If now these segments 6 are caused to traverse a magnetic field, such as. that produced by the magnet 13, all the ions in each segment 6 will follow a circular path while in the magnetic field. The pole faces of the magnet 13 are so shaped, however, that the outermost ions remain in the magnetic field for a longer period than the innermost ions, so that all ions tend to converge laterally towards the same place. Moreover, the outermost ions are also ahead of the innermost ions in the same segment; and, since the outermost ions follow a longer path than the innermost ions, the innermost ions catch up to the outermost ions, so that all ions in each segment 6 tend to converge longitudinally (i.e. along the beam axis). As a result, each segment 6 is compressed into a compact ion pulse. This method of form-ing ion pulses is fully described by R. C. Mobley in an article entitled Proposed Method for Producing Short Intense Monoenergetic Ion Pulses, Physical Review, volume 88, page 360 (1952) and need not be described herein in any further detail.

The construction of a particle accelerator 4 having a pulsed output providing 10 -second pulses of 2 amperes is feasible :at the present time, and the combination of the ion deflector 12 and the magnet 13 can convert each Z-ampere 1O second pulse into a ZOO-ampere 10 -sec- 0nd pulse. In order to achieve a current density of 2 millon amperes per square centimeter, each ZOO-ampere pulse must be compressed laterally into an area of 10- square centimeters. In accordance With the invention, this is accomplished by means of the so-called pinch effect, which is produced by subjecting the ion pulses 6 to the action of a very intense magnetic field, of the order of 10 gauss. Such a magnetic field is produced by :a coil 14 which surrounds the ion trajectory and through which a very high current is driven by a suitable pulse generator 15.

Of course, the ions must travel in vacuo, and so the evacuated region of each particle accelerator 4 is connected to the reaction chamber 3 by a suitable evacuated structure 16. The pellet-forming mechanism 2, the pulse generators 15, the ion-deflectors 12, and any pulsing system in each particle accelerator 4 must, 0:6 course, be synchronized so that the ion pulses 6 and the pellets l collide. The literature citations of Physical Methods in Chemical Analysis, volume III, by Taylor and Havens, pages 470- 473, and Annual Review of Nuclear Science, volume 4, 'by Berkerley, pages 101-109, describe time-of-fligh-t velocity selectors for pulsed accelerators and nuclear particle coincidence techniques which, in combination illustrate the nature of the components and circuitry required for such synchronization. However, such synchronization may be achieved by means well within the capabilities of those skilled in the electronic arts and such means are therefore not described herein. For example, each pellet 1 could be caused to fall between a light source (not shown) and a photocell (not shown) so as to generate a signal which could be used to trigger the pelletforming mechanism.

While each particle accelerator 4 may be of any of several well-known types, I prefer to use electrostatic accelerators, which produce a monoenergetic ion beam. Of course, unless a device such as that disclosed in the aforesaid copending applications is used, a pulsed electrostatic accelerator Will produce pulses in which the energy falls lineally in time during the pulse; however, the ion output is otherwise monoenergetic, and this linear decrease in energy during each pulse may be compensated by appropriate control of the magnet 13. For example, if each pulse-length is equal to the half-cycle of the iondeflector 12, each pulse of the particle accelerator 4 will produce one segment 6 of ions whose energy varies along the length thereof, and such energy variation may be compensated for merely by appropriate shaping and spacing of the pole faces of the magnet 13.

Having thus described the method of the invention, together with illustrative embodiments of apparatus for carrying out the method, it is to be understood that although specific terms are employed they are used in a generic and descriptive sense and not for purposes or" limitation, the scope of the invention being set forth in the following claims.

I claim:

1. Apparatus for carrying on nuclear reactions comprising in combination at least one ion accelerator adapted to produce a beam of high-energy ions; an ion deflector adapted to deflect said ion beam periodically, whereby said ion beam is divided into linear segments each of which is at an angle to the direction of travel of the ions therein; a magnet adapted to subject said segments to the deflecting action of a magnetic field so distributed in space that the ions in each segment converge both laterally and longitudinally so as to form an ion pulse; means for subjecting said ion pulses to the pinching action of an intense magnetic field; a pellet-forming device adapted to form exoergi'c material into pellets; and means for causing said pellets to collide in free space with said pinched ion pulses, wherein the transverse diameter of said pulses is sufliciently small with respect to the diameter of said pellets so that a substantial portion of the energy of the ions in each pulse is absorbed by the central portion of the volume of the pellet which is struck by said pulse.

2. Apparatus for carrying on nuclear reactions comprising in combination at least one ion accelerator adapted to produce a beam, of high-energy ions; an ion deflector adapted to deflect said ion beam periodically, whereby said ion beam is divided into linear segments each of which is at an angle to the direction of travel of the ions therein; a magnet adapted to subject said segments to the deflecting action of a magnetic field so distributed in space that the ions in each segment converge both laterally and longitudinally so as to form an ion pulse; a coil supported so that said ion pulses travel axially therethrough; a pulse generator adapted to generate a large electric current in said coil while ion pulses are traveling therethrough,

whereby said ion pulses are pinched; a pellet-forming device adapted to form exoergic material into pellets; and means for causing said pellets to collide in free space with said pinched ion pulses, wherein the transverse diameter at said pulses is suflicient'ly small with respect to the diameter of said pellets so that a substantial portion of the energy of the ions in each pulse is absonbed by the central portion of the volume of the pellet which is struck by said pulse.

References Cited in the file of this patent UNITED STATES PATENTS Szilard June 13, 1939 Kallman July 29, 1941 Brasch Oct. 21, 1947 Wells et a1 Mar. 14, 1950 Weber Ian. 30, 1953 Berghaus et a1 June 3, 1958 Salsig et a1 Ian. 13, 1959

Claims (1)

1. APPARATUS FOR CARRYING ON NUCLEAR REACTIONS COMPRISING IN COMBINATION AT LEAST ONE ION ACCELERATOR ADAPTED TO PRODUCE A BEAM OF HIGH-ENERGY IONS; AN ION DEFLECTOR ADAPTED TO DEFLECT SAID ION BEAM PERIODICALLY, WHEREBY SAID ION BEAM IS DIVIDED INTO LINEAR SEGMENTS EACH OF WHICH IS AT AN ANGLE TO THE DIRECTION O TRAVEL OF THE IONS THEREIN; A MAGNET ADAPTED TO SUBJECT SAID SEGMENTS TO THE DEFLECTING ACTION OF A MAGNETIC FIELD SO DISTRIBUTED IN SPACE THAT THE IONS IN EACH SEGMENT CONVERGE BOTH LATERALLY AND LONGITUDINALLY SO AS TO FORM AN ION PULSE; MEANS FOR SUBJECTING SAID ION PULSES TO THE PINCHING ACTION OF AN INTENSE MAGNETIC FIELD; A PELLET-FORMING DEVICE ADAPTED TO FORM EXOERGIC MATERIAL INTO PELLETS; AND MEANS FOR CAUSING SAID PELLETS TO COLLIDE IN FREE SPACE WITH SAID PINCHED ION PULSES, WHEREIN THE TRANSVERSE DIAMETER OF SAID PULSES IS SUFFICIENTLY SMALL WITH RESPECT TO THE DIAMETER OF SAID PELLETS SO THAT A SUBSTANTIAL PORTION OF THE ENERGY OF THE IONS IN EACH PULSE IS ABSORBED BY THE CENTRAL PORTION OF THE VOLUME OF THE PELLET WHICH IS STRUCK BY SAID PULSE.

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