Abstract
There is provided a method of producing a localized concentration of energy. The method includes creating at least one shockwave propagating through a non-gaseous medium so as to be incident upon a pocket of gas suspended within the medium. The pocket of gas is spaced from a surface shaped so as, at least partially, to reflect said shockwave in such a way as to direct it onto said gas pocket.
Claims
1. A method of producing a localised concentration of energy comprising: creating at least one shockwave; propagating the at least one shockwave through a non-gaseous medium; allowing the at least one shockwave to be incident upon a pocket of gas suspended within the medium, wherein the pocket of gas is spaced from a concave surface; and reflecting said at least one shockwave from the concave surface onto said gas pocket.
2. The method as claimed in claim 1, wherein the concave surface comprises a plurality of discrete portions.
3. The method as claimed in claim 2, wherein the discrete portions are piecewise polynomial.
4. The method as claims in claim 1, wherein the concave surface focuses the reflected at least one shockwave onto the gas pocket.
5. The method as claimed in claim 4, wherein the concave surface focuses the reflected shockwave to a point.
6. The method as claimed in claim 1, wherein the gas pocket is placed no more than three times a maximum radius of curvature of the closest section of the concave surface away from the concave surface.
7. The method as claimed in claim 6, wherein the gas pocket's edge closest to the concave surface is spaced from it by a distance of less than five times the dimension of the gas pocket's widest part.
8. The method as claimed in claim 1, comprising using an external device to apply one or more shockwaves to a static volume of the non-gaseous medium to create the at least one shockwave propagating through the non-gaseous medium.
9. The method as claimed in claim 8, comprising using the external device to create the shockwave with a pressure of between 0.1 GPa and 50 GPa.
10. The method as claimed in claim 1, comprising using a lithotripsy device to create the shockwave with a pressure of between 100 MPa and 1 GPa.
11. The method as claimed in claim 1, wherein the gas pocket is formed with the use of a membrane that defines the boundary between the gas pocket and the non-gaseous medium, and wherein the membrane is frangible and breaks upon impact from the shockwave.
12. The method as claimed in claim 11, wherein the membrane includes a line or region of weakness that breaks upon impact from the shockwave.
13. An apparatus for producing a localised concentration of energy comprising: a non-gaseous medium having therein a pocket of gas, wherein the pocket of gas is spaced from a concave surface; and an external device for creating at least one shockwave propagating through said medium so as to be incident upon said pocket of gas, wherein said concave surface is shaped so as at least partially to reflect said shockwave in such a way as to direct it onto said gas pocket and wherein the gas pocket is placed no more than three times a maximum radius of curvature of the closest section of the concave surface away from the concave surface.
14. The apparatus as claimed in claim 13, wherein the non-gaseous medium comprises a static volume of non-gaseous medium and wherein the external device is arranged to apply one or more shockwaves to the static volume of non-gaseous medium to create the at least one shockwave propagating through the non-gaseous medium.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Certain embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
(2) FIGS. 1a and 1b show two variants of a target surface in accordance with one aspect of the invention;
(3) FIGS. 2a, 2b and 2c show three successive stages of an interaction of a shockwave with a pocket of gas in accordance with another aspect of the invention;
(4) FIGS. 3a and 3b show two successive stages of an interaction of a shockwave with a pocket of gas in accordance with another aspect of the invention;
(5) FIG. 4 shows a further embodiment of the invention; and
(6) FIG. 5 shows a variant of the embodiment of FIG. 3a.
DETAILED DESCRIPTION
(7) FIGS. 1a and 1b show schematically arrangements in accordance with two respective embodiments of one aspect of the invention. In each case a solid surface 6, for example made from high strength steel, is placed inside a non-gaseous medium 8 in the form of a hydrogel, for example a mixture of water and gelatine. Defined in the hydrogel medium 8 is a gas pocket 2 filled with vaporous fuel which is potentially suitable for taking part in a nuclear fusion reaction. In both cases the gas pocket 2 is attached to the target surface 6 inside a concave depression. In the case of the first embodiment in FIG. 1a, the depression 4 is parabolic and relatively large such that only one side of the gas pocket 2 is attached to the surface 6. The size of the apparatus is flexible but a typical dimension of this diagram could be between 0.1 and 110.sup.5 m.
(8) In the case of the second embodiment in FIG. 1b, the gas pocket 2 is received in a much smaller, V-shaped tapering depression 5 which could be machined or formed as the result of a naturally occurring crack in the surface 6.
(9) In operation a shockwave 10 is created from an explosion, for instance with a pressure of 5 GPa, within the gel medium 8. This is represented in both FIGS. 1a and 1b as a line propagating in the direction of the arrow towards the pocket of gas 2. First the shockwave 10 strikes the upper parts of the target surface 6, causing the shockwave 10 to change shape as it advances towards the pocket of gas 2. In this manner the shape of the shockwave 10 that advances into the pocket of gas 2 can be explicitly controlled by shaping the surface 6 accordingly. The shaped shockwave 10 will then strike the pocket of gas 2, compressing it against the target surface 6 as the shockwave 10 propagates through the gas pocket 2. Reflections of the shockwave 10 from the surface 6 after it has propagated through the pocket 2 travel back through the pocket, reinforcing those propagating from the original direction and further compressing the gas pocket. The compression of the gaseous fuel inside the pocket causes intense local heating which potentially may be sufficient to generate a nuclear fusion reaction.
(10) FIGS. 2a, 2b and 2c show three successive stages of a shockwave interacting with a pocket of gas 12 spaced from a surface 16 in accordance with another aspect of the invention. In this embodiment the pocket of gas 12 is immobilized in the gel 18 in a concave depression 14 in the surface 16.
(11) FIG. 2a shows a shockwave 20 propagating through the gel medium 18, in the direction of the arrow, approaching the gas pocket 12. FIG. 2b shows the shockwave 20 as it is incident for the first time upon the gas pocket 12. The shockwave acts on the volume of gas 12 to compress it, in a similar manner to the embodiments shown in FIGS. 1a and 1 b. At the same time the shockwave 20 is reflected from the upper sides of the concave depression 14 in the surface 16.
(12) FIG. 2c shows the third snapshot in the sequence, by which time the shockwave 20 has passed through the volume of gas 12, compressing it significantly. Also by this time, the shockwave 20 has been reflected from the surface 16 and is travelling back towards the pocket of gas 12 in the direction indicated by the arrow. The reflected shockwave 20 now has a shape resembling the shape of the concave depression 14 and is focused towards the pocket of gas 12 upon which it is incident for a second time, compressing it further and therefore further increasing the temperature and pressure within it.
(13) FIGS. 3a and 3b show, in accordance with yet another aspect of the invention, two successive stages of a shockwave interaction with a pocket of gas 22 attached to a surface 26 so as to cover and fill a V-shaped tapering depression 24. Although the tapering depression 24 is of a similar shape to that in FIG. 1b, relative to the size of the tapering depression, the volume of gas in the pocket 22 is much greater than it is in FIG. 1b. For example the width of the bubble could be of the order of 1 cm.
(14) FIG. 3a shows the shockwave 30 propagating through the medium 28 (which could be the same material as in previous embodiments or a different material could be used), in the direction of the arrow, towards the gas pocket 22. FIG. 3b shows a later stage in the interaction, after the shockwave 30 has struck the gas pocket 22. The portion 27 of the shockwave 30 that has struck the edge of the pocket of gas 22 is reflected as a result of the large change in density from the medium 28 to the gas 22. This reflected portion 27 forms a rarefaction fan which propagates away from the gas pocket 22 and therefore creates a low pressure region between the reflected portion 27 and the gas pocket 22. The medium 28 flows into this low pressure region as a jet 29 which then traverses the gas pocket 22, trapping a fraction of the gas therein between the tip of the jet 29 and the tapering depression 24 in the surface 26, thereby causing compression and heating of the gas in the manner previously described.
(15) FIG. 1b shows a further configuration which is also suitable as an embodiment of this aspect of the invention.
(16) FIG. 4 shows a further embodiment of the previous aspect of the invention in which a pocket of gas 32 is attached to a target surface 36 in a tapering depression 34. This embodiment is different from those previously described in that the pocket of gas 32 is separated from the medium 38 by a prefabricated membrane 33. The prefabricated membrane 33 is frangible i.e. it is designed to break on the impact of the shockwave 40. Once the prefabricated membrane 33 has been broken by the impact of the shockwave 40, the shockwave 40 continues to propagate into the depression 34 compressing the pocket of gas 32 in the same manner as for the previous embodiments.
(17) FIG. 5 is a variant of the embodiment shown in FIG. 3a. In this embodiment there are multiple smaller depressions 42 at the bottom on a large depression 44. The pocket of gas 46 is partially received both by the large depression 44 and by the multiple smaller depressions 42. In operation of this embodiment the jet formed when the shockwave (not shown) hits the pocket of gas 46 will highly compress multiple small volumes of the gas by trapping them in the small depressions 42, in a similar manner to that described above with reference to FIGS. 3a and 3b.
(18) Although specific examples have been given, it will be appreciated that there are a large number of parameters that influence the actual results achieved, for example liquid or gel medium density, ambient pressure and temperature, composition of the gas and of the liquid or gel, impact angle of the shockwave, target surface shape and micro-structure of the target surface.
(19) In each of the embodiments described above, the diagrams shown are a vertical cross-section through a three-dimensional volume of gas and target surface and hence they depict embodiments that are rotationally symmetric. However, this is not essential to the invention. In particular the surface could comprise discrete surface portions in the rotational direction either instead of, or as well as in the vertical cross-section shown. In the latter case the target surface would be multi-facetted. Each facet could give rise to separate but converging shockwaves.
(20) In all of the embodiments described, the apparatus can be used by creating a shockwave in the medium which is incident upon a volume of gas containing deuterated water vapor.
(21) In numerical modeling of the experiment, the techniques described herein give rise to a peak pressure of 20 GPa which is sufficient to cause temperatures inside the collapsed volume of gas in excess of 110.sup.6 Kelvin which potentially may be sufficient for a nuclear fusion reaction of the deuterium atoms. In some non-limiting examples the resulting neutrons could be used in other processes, or could be absorbed by a neutron absorber for conversion of the kinetic energy of the neutrons to thermal energy and thus conventional thermodynamic energy generation.
