Detonation method and detonation device, compact and with amplified current density

Abstract

The invention relates to a detonating device for initiating an explosive material, comprising: - a cathode (2); - means (4) for concentrating an incoming electron beam (5) generated by the cathode and for generating an outgoing electron beam (20), having a current density greater than the current density of the incoming electron beam; - means (14) for accelerating the outgoing electron flow.

Description

TECHNICAL FIELD AND PRIOR TECHNOLOGY

[0001] The invention relates to the field of detonators.

[0002] Today, different types of detonators exist on the market and in scientific literature.

[0003] More specifically, for primary or secondary explosive materials, there are pyrotechnic detonators, or hot wire detonators, or exploded wire detonators, or Nobel type detonators, or electric detonators.

[0004] Opto-pyrotechnic initiators are well known, one example of which is shown on page 9 of the document by F. Burlot et al., "State of the art of opto-pyrotechnic technology", 2011, Space Pyrotechnics Working Group.

[0005] This type of system requires managing several active components (electronic, optical, and optoelectronic), electrical and fiber optic connections, maintaining and ensuring long-term alignment and adjustments, and providing protection or shielding against electromagnetic or radiative threats. Such a system is therefore very complex and can be quite bulky, particularly for embedded applications.

[0006] One problem that arises is therefore to find a pyrotechnic initiating device that is simpler and does not present all or some of the problems mentioned above. DESCRIPTION OF THE INVENTION

[0007] The invention aims to solve all or part of these problems.

[0008] The invention therefore primarily relates to a detonating device, or a pyrotechnic initiating device, for initiating an explosive material, comprising: a cathode; means for concentrating an incoming electron beam generated by the cathode and for generating an outgoing electron beam, having a current density greater than the current density of the incoming electron beam; means for accelerating the outgoing electron flow.

[0009] A device according to the invention comprises elementary components and is therefore robust and inexpensive. Moreover, it requires no special maintenance.

[0010] A device according to the invention meets the requirements of the pyrotechnic field in terms of safety, reliability and performance and is therefore perfectly suited to embedded applications.

[0011] The invention makes it possible to solve the problems mentioned above, and in particular the problems encountered in embedded systems, where compactness, lightness, hardening and frugality in servicing and peripheral systems play an important role.

[0012] According to one embodiment, a device according to the invention comprises a cavity having an inlet orifice and an outlet orifice, said cavity comprising, for example, a frustoconical surface, said cavity being at least partially provided with a layer of insulating or semiconducting material, for example comprising magnesium oxide or diamond or SiO2 or carbon (C). This layer of insulating material has, for example, a thickness of between 1 nm and 100 µm.

[0013] Such a device implements a principle of current density amplification from the emission of secondary electrons from the surface of an insulating or semiconductor material.

[0014] Preferably, in a device according to the invention, the ratio between the output current density and the input current density is at least greater than 10. This current density ratio depends on the nature of the explosive to be initiated. Consequently, the current density is configurable, and the current density gain can reach a minimum of 10 and a maximum of 1000.

[0015] In a device according to the invention, the means for accelerating the outgoing electron flow include, for example, an acceleration electrode, disposed at the output of the means for concentrating an incoming electron beam.

[0016] A device according to the invention may further include: means, for example at least one extraction grid and / or at least one focusing electrode, for directing electrons emitted by the cathode towards means for concentrating an incoming electron beam; and / or means, for example a voltage source, for applying, between the means for accelerating the outgoing electron flow and the cathode, a voltage of between 10 V and 500 V.

[0017] The invention also relates to an explosive device, comprising an explosive material and a detonating device according to the invention. For example, the explosive material comprises ZPP (zirconium potassium perchlorate); more generally, the explosive may have a primary composition (very sensitive explosives, with an ignition time on the order of a few ms) or a secondary composition (less sensitive explosives, with an ignition time on the order of a few µs).

[0018] The invention also relates to a method for initiating an explosive material, employing, for example, a detonating device or an explosive device according to the invention, as described above and in the remainder of this application, this method comprising: the generation of electrons or an electron beam, called primary electrons, using a cathode; the concentration of the electrons or electron beam emitted by the cathode, to generate outgoing electrons or an electron beam, having a current density greater than the current density of the incoming electrons or electron beam; the acceleration of the outgoing electron flow or electron beam towards the explosive material, to exceed the initiation or ignition threshold of the latter.

[0019] A method and device according to the invention make it possible to generate a high-current-density electron beam with very low power consumption and while guaranteeing total immunity to electromagnetic interference in the absence of a power supply. The invention is therefore highly advantageous compared to existing solutions, particularly opto-pyrotechnical solutions, due to its compact size.

[0020] In a method and device according to the invention: A so-called "primary" cathode generates primary electrons, preferably of very low energies, for example still less than 100 eV, which ensures low power consumption; and / or the cathode is for example of a flat cylindrical or concave or hollow cylindrical type; and / or the primary electrons will subsequently interact with, for example, a material, preferably insulating or semiconducting, for example in the shape of a funnel, this shape acting as an amplifier; and / or the secondary electrons at the output of the amplification stage have a sufficiently high current density (for example, a ratio of 10 to 1000 between the current density at the output of the stage and the current density of the incoming primary electron beam) to detonate the explosive material located at the output of the device;and / or the average number of secondary electrons induced per incident electron from the cathode is on average equal to 1. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] There figure 1 represents an example of a detonator according to the invention; The figures 2A-2C represent cross-sectional views of cathodes that can be used in the context of the invention; The figure 3 represents an explosive device equipped with a detonator according to the invention; The figure 4 represents an example of a detonator according to the invention with control and command means. DETAILED DESCRIPTION OF SPECIFIC IMPLEMENTATION METHODS

[0022] Aspects of an embodiment of a detonator 1 according to the invention will be explained in connection with the figure 1 The entire device can be encapsulated in a vacuum tube, not shown in the figures.

[0023] It includes a cathode 2, for example a thermionic cathode, which can be heated using a filament located at the rear of the cathode; the surface of the cathode can therefore emit electrons. It is, for example, a flat cylindrical cathode (as illustrated in figure 2A ) or concave (as illustrated in figure 2B ), or a hollow cylindrical cathode (the hollow having a diameter D hop, as illustrated in figure 2C ). In the case of the latter, the section is defined as the difference between S cathode_p (cathode surface as illustrated in figures 2A-2C ) and the S hop surface of the output hole of the amplification stage.

[0024] An extraction grid 4 is located at the output of this cathode, allowing an extraction voltage Vgrid to be applied to the electrons emitted by the latter. Alternatively, focusing electrodes, also known as the "Wehnelt" system, can be used. These various means allow the electrons to be held at the surface of the cathode in a blocked mode, and the primary electrodes to be extracted in a mode called the "firing phase" or "beam production," thus allowing control over the timing of the electron beam's activation. Reference numeral 7 designates means (voltage source) for establishing a voltage between the cathode 2 and the extraction grid 14.

[0025] A hollow structure 6, for example with a frustoconical interior (or funnel shape), is positioned opposite the cathode 2, its longer side 8 (or base) facing the cathode, and its axis AA' aligned with the average electron emission direction. The device is rotationally symmetric. The center of the cathode 2 lies on the same axis as the center of the internal hole 8 and the output of the amplification structure 6.

[0026] The inner wall 10 of the hollow structure is covered with a layer 12 of a material that can emit secondary electrons under the impact of incident electrons (emitted by the cathode 2) with energies on the order of a few tens of eV, for example less than 100 eV. This is, for example, a layer of magnesium oxide (MgO) or silicon dioxide (SiO2), more generally insulators, or materials such as: capable of emitting a secondary electron for a primary electron at very low energy, less than 100 eV; resistant to electron irradiation, which is the case for insulators such as MgO, SiO2, carbon (C), diamond.

[0027] Semiconductors can also be used, for example certain doped silicon compositions, such as Si-Ge or Csi.

[0028] This layer, for example, has a thickness between 1 nm and 100 µm, this thickness being able to be chosen according to the desired electronic emission properties of the material.

[0029] The hollow structure has an inlet orifice 8 of diameter D and an outlet orifice 18 of diameter d.

[0030] An output electrode 14 is located at the outlet of the hollow structure. It generates a potential difference (an "amplification voltage") between the extraction grid 4 or the cathode 2 and the output of the amplification device. The latter may also be equipped with a post-acceleration electrode 16, separated from the output electrode 14 by an insulating layer. By applying a potential difference, using means 17 (a voltage source), between electrodes 16 and 14, the secondary electrons are accelerated. A second acceleration can therefore be present at the device output via this electrode 16.

[0031] Thus, the electrons 5 emitted towards the hollow structure will generate, in the layer 12, secondary electrons 20 which will be accelerated towards the exit 18 of the hollow structure. Secondary electrons with an energy, for example, of 100 eV to 5 keV (thus enabling the initiation of primary and secondary explosives) can be obtained at the interface between a detonating device 1 according to the invention and an explosive material 22 ( figure 3 ).

[0032] Inelastic interactions occur between the incident electrons 5 (emitted by the cathode 2) and the electrons of the atoms constituting the material of the layer 12. During its deceleration within the material, an incident electron transfers some of its kinetic energy to the electrons of the target material. This energy transfer leads to the emission of some electrons through the surface of the layer, i.e., secondary electron emission 20. This can be characterized by an efficiency γ (= average number of secondary electrons induced per incident electron). A steady state of transport on the insulating surface is reached if, on average, <γ> = 1.An accelerating voltage threshold (which depends on the voltage source 9), for example between 10 V and 500 V (between electrode 14 and electrode 4 or cathode 2) between the two ends of the surface allows the state <γ> = 1 to be maintained and not to create an electrical charge on the surface of layer 12.

[0033] We seek to maintain a stationary state around y = 1; indeed, if y > 1 or y < 1 then, on average, at each interaction, an electrical charge is created on the surface of the insulator (positive if y > 1, negative y < 1), which is detrimental to maintaining a stationary state.

[0034] Consider the electronic emission curve, which gives y as a function of the energy E. If y > 1 or y < 1 near the first crossing of this electronic emission curve with the value y = 1, then the process regulates itself and tends towards a stationary state.

[0035] This allows us to generate a secondary electron beam 20, which can then be used to trigger an explosive material 22, as illustrated in figure 3 .

[0036] Given the convergent shape (the apex angle α of the cone can be between 10° and 178°) of the hollow structure, the secondary electrons 20 are compressed in the exit hole 18. If the current density of the cathode, the cross-sections D (of the cathode or the inlet 8) and d (of the exit hole 18) are known, the current density (“ J out " at the outlet of funnel 6 can be determined by the following formula: J out = S cath S out ∗ J cath where S cathode is the surface area of ​​the cathode, S out the surface area of ​​the output hole 18 and J cathode the current density emitted by the cathode.

[0037] For example, for a cathode with a radius of 0.5 mm with a current density of 1 A / cm 2< and a radius of 25 µm for the outlet hole 18 of the funnel, a current density gain of 400 can be obtained.

[0038] For example, we consider a zirconium potassium perchlorate explosive (“ZPP”), whose ignition threshold is 1.24 mJ, which corresponds to an energy density of 15.75 J / cm² for an ignition delay between 0.39 and 3 ms.

[0039] By setting a funnel outlet diameter 18 of 100 µm, we can deduce the cross-sectional area S out of outlet 18: S out = π r 2 = π 0 , 01 / 2 2 = 7,85 . 10 − 5 cm 2

[0040] By taking a cathode with a current density of 1 A / cm² and a secondary electron energy at the device output of 100 eV, the current density required to initiate a "ZPP" composition at the funnel outlet for an ignition time t (t is chosen in this example to be equal to 3 ms) is determined: E J cm 2 = 100 ∗ J out ∗ 3 ms → J out = 52,5 A / c m 2 where E is the ignition energy density.

[0041] Secondly, the surface area and then the diameter D cathode p of the primary cathode 2 are deduced: S cathode _ p = J out ∗ S out J cath = 4,12 . 10 − 3 cm 2 D cathode _ p = 4 ∗ S cathode _ p π = 720 μ m

[0042] Based on these sizing calculations, an example of a device according to the invention has a cathode diameter of 720 µm, an output hole diameter of 100 µm and an amplification gain of 52.5. More generally, a device according to the invention may have a cathode diameter between 100 µm and 10 cm, an output hole diameter between 10 µm and 1 cm, and an amplification gain between 10 and 1000.

[0043] The funnel-shaped part has a specific angle, denoted "α", ranging from 10° to 178°. This angle, which can be adjusted depending on the type of explosive used, can be determined or estimated through simulations performed using the CST® software. Optimizing this angle influences the current density obtained directly at the device's output and, consequently, the efficiency.

[0044] The angle α can be estimated or determined using a theoretical formula (tan(α / 2) = [(4E₀) / (E₁ - 2E₀)]). Optimization can be performed using a simulation tool (e.g., CST software) to determine the amplification gain as a function of the angle α. Other parameters can be considered, such as the homogeneity of the beam 20 at the output of the amplification structure and the number of jumps of secondary electrons on the insulating material 12.

[0045] By applying, using means 9 (voltage source), a significant electric field (~< kV) called "V_amplification" between the funnel outlet 18 and the grid 4, the generated secondary electrons are directed towards the device outlet 18. The secondary electron beam 20 has a high current density at the device outlet, thus enabling the initiation of the explosive material 22 ( figure 3 ). The post-acceleration electrode 16 provides the necessary energy to the secondary electrons depending on the explosive material to be initiated.

[0046] As illustrated in figure 4A detonator 1 according to the invention can be further equipped with a set of electronic control means 30, preferably reliable and compact, for controlling the cathode power supply means 3, the grid power supply means 7 and 9, and the amplification means. As can be seen from this figure, all of these means can be located as close as possible to the device, thus improving the safety of embedded systems and minimizing the electrical connections between the control section and the detonator.

[0047] In general, a detonator according to the invention offers ease of integration due to its extreme compactness but also to the elimination of optical fibers which require that the angles of curvature do not exceed a certain value.

[0048] The device described has the advantage of not having a direct link between the cathode and the explosive.

[0049] It is also understood that a detonator according to the invention offers resistance to harsh environments (ionizing radiation, electromagnetic radiation, stray currents, etc.) inherent in its structure, without the need for specific protection.

[0050] In a detonator according to the present invention, 3 parameters allow the ignition threshold of an explosive to be reached: the current intensity of the cathode, the geometry (which defines the emissive surface of the cathode 2 and the amplification ratio) and the total acceleration voltage established between the potential of the cathode 2 and the surface of the explosive 22.

[0051] Furthermore, there is an intrinsic barrier to the physics of the phenomenon: the equilibrium condition for electron transport on the insulating surface (γ = 1). These three conditions, when met, allow the explosive charge to be initiated. This constitutes a significant advantage over other existing solutions on the market and allows this firing device to be classified among the most insensitive according to the DRAM standard (Damage due to electromagnetic radiation on weapons and ammunition).

[0052] One area of ​​application for the invention is that of pyrotechnic devices, whether on-board or not.

[0053] A device and a method according to the invention is reliable, insensitive and offers operational safety.

[0054] By design and thanks to the physical principles on which its operation is based, it is "self-safe", and there is no need to add specific protections or specific devices.

Claims

1. Detonating device for initiating an explosive material, comprising: - a cathode (2); - means (4) for concentrating an incoming electron beam (5) generated by the cathode and for generating an outgoing electron beam (20) having a current density greater than the current density of the incoming electron beam; - means (14) for accelerating the outgoing electron flow.

2. Device according to claim 1, the means (4) for concentrating an incoming electron beam generated by the cathode and for generating an outgoing electron beam comprising a cavity having a frustoconical surface (6) provided with a layer (12) of insulating or semiconducting material.

3. Device according to claim 2, said frustoconical surface having an angle between 10° and 178°.

4. Device according to claim 2 or 3, said layer of material comprising magnesium oxide, or diamond or SiO2, or carbon (C) and / or said layer of insulating material (12) having a thickness between 1 nm and 100 µm.

5. Device according to any one of claims 1 to 4, the ratio between the input current density (5) and the output current density (20) being between 10 and 1000.

6. Device according to any one of claims 1 to 5, the means for accelerating the outgoing electron flow comprising an accelerating electrode (16), disposed at the outlet of the means for concentrating an incoming electron beam.

7. Device according to any one of claims 1 to 6, further comprising means (4) for directing electrons emitted by the cathode towards means for concentrating an incoming electron beam.

8. Device according to claim 7, the means (4) for directing electrons emitted by the cathode towards the means for concentrating an incoming electron beam comprising at least one extraction grid and / or at least one focusing electrode.

9. Detonating device according to any one of claims 1 to 8, the cathode (2) being of the flat cylindrical or concave or hollow cylindrical type.

10. Detonating device according to any one of claims 1 to 9, further comprising means (9) for applying, between the means (14) for accelerating the outgoing electron flow and the cathode (2), a voltage of between 10 V and 500 V.

11. Explosive device, comprising an explosive material (22) and a detonating device according to any one of claims 1 to 10.

12. Explosive device according to claim 11, the explosive having a primary or secondary composition.

13. A method for initiating an explosive material (22), employing for example a detonating device (1) according to any one of claims 1 to 10, said method comprising: - the generation of electrons or an electron beam (5), referred to as primary electrons, using a cathode (2); - the concentration of the electrons or electron beam (5) emitted by the cathode (2), to generate secondary electrons or an outgoing electron beam (20), having a current density greater than the current density of the incoming electrons or electron beam (5); - the acceleration of the outgoing electron flow or electron beam (20) towards the explosive material, to exceed the initiation or ignition threshold of the latter.

14. Method according to claim 13, the ratio between the current density of the outgoing electron flow or electron beam (20) and the current density of the primary electron beam (5) being between 10 and 1000.

15. Method according to claim 13 or 14, the average number of secondary electrons (20) induced per incident electron from the cathode (2) being on average equal to 1.

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