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. Figure 1

Description

Title of the invention: DETONATION METHOD AND DETONATION DEVICE,

[0001] COMPACT AND WITH AMPLIFIED CURRENT DENSITY

[0002] TECHNICAL FIELD AND PRIOR TECHNOLOGY

[0003] The invention relates to the field of detonators.

[0004] Today, different types of detonators exist on the market and in the scientific literature.

[0005] More specifically, for primary or secondary explosive materials, there are pyrotechnic, hot wire, exploded wire, Nobel type or electrical detonators.

[0006] Opto-pyrotechnical initiators are known in particular, an example of which is shown on page 9 of the document by F. Burlot et al., "State of the art of opto-pyrotechnical technology", 2011, Space Pyrotechnics Working Group.

[0007] This type of device requires the management of several active components (electronic, optical, and optoelectronic), electrical and fiber optic connections, the management and long-term maintenance of alignments and settings, and protection or shielding devices against electromagnetic or radiative threats. Such a device is therefore very complex and its size can prove problematic, particularly for embedded applications.

[0008] One problem that arises, therefore, is 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

[0009] The invention aims to solve all or part of these problems.

[0010] The invention therefore relates firstly to a detonating device, or a pyrotechnic initiating device, for initiating an explosive material, comprising:

[0011] - a cathode;

[0012] - means for concentrating an incoming electron beam generated by the cathode and to generate an outgoing electron beam, having a current density greater than the current density of the incoming electron beam;

[0013] - means for accelerating the outgoing electron flow.

[0014] A device according to the invention comprises elementary components and is therefore robust and inexpensive. Moreover, it requires no special maintenance.

[0015] A device according to the invention meets the requirements of the pyrotechnical field in terms of safety, reliability and performance and is therefore perfectly suited to embedded applications.

[0016] 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.

[0017] 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 pm.

[0018] Such a device implements a current density amplification principle from the emission of secondary electrons from a surface of an insulating or semiconductor material.

[0019] 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.

[0020] In a device according to the invention, the means for accelerating the outgoing electron flow comprise, for example, an acceleration electrode, disposed at the output of the means for concentrating an incoming electron beam.

[0021] A device according to the invention may further comprise:

[0022] - means, for example at least one extraction grid and / or at least one focusing electrode, to direct electrons emitted by the cathode towards the means to concentrate an incoming electron beam;

[0023] - and / or means, for example a voltage source, for applying, between the means to accelerate the flow of electrons out and the cathode, a voltage between 10 V and 500 V.

[0024] 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 ps).

[0025] 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:

[0026] - the generation of electrons or a beam of electrons, called primary electrons, at with the help of a cathode;

[0027] - the concentration of electrons or the electron beam emitted by the cathode, for generate outgoing electrons or electron beam, having a current density greater than the current density of the incoming electrons or electron beam;

[0028] - the acceleration of the electron flow or the electron beam exiting towards the material explosive, to exceed the initiation or ignition threshold of the latter.

[0029] 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 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.

[0030] In a method and device according to the invention:

[0031] - A so-called "primary" cathode generates primary electrons, preferably from very low energies, for example still less than 100 eV, which ensures low power consumption;

[0032] - and / or the cathode is, for example, of the flat cylindrical or concave type or hollow cylindrical;

[0033] - and / or the primary electrons will subsequently interact on, for example, a material, preferably insulating or semiconductor, for example in the shape of a funnel, this shape acting as an amplifier;

[0034] - and / or the secondary electrons at the output of the amplification stage have a density of sufficiently high current (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;

[0035] - and / or the average number of secondary electrons induced per incident electron originating from the cathode is on average equal to 1. Brief description of the drawings

[0036] - Fig. 1 represents an example of a detonator according to the invention;

[0037] - Figures 2A-2C represent cross-sectional views of cathodes that can be used in the context of the invention;

[0038] - Fig. 3 represents an explosive equipped with a detonator according to the invention;

[0039] - Figure 4 represents an example of a detonator according to the invention with means control and command.

[0040] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0041] Aspects of an embodiment of a detonator 1 according to the invention will be explained in connection with [Fig. 1]. The entire device can be encapsulated in a vacuum tube, not shown in the figures.

[0042] It comprises a cathode 2, for example a thermionic cathode, which can be heated by means of 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 a concave cylindrical cathode (as illustrated in Figure 2B), or a hollow cylindrical cathode (the hollow having a diameter Dhop, as illustrated in Figure 2C). In the case of the latter, the cross-section is defined as the difference between Scathode_p (the surface of the cathode as illustrated in Figures 2A-2C) and the Shop surface of the output hole of the amplification stage.

[0043] An extraction grid 4 is disposed at the output of this cathode, allowing an extraction voltage Vgriue 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 make it possible to maintain the electrons on the surface of the cathode in a blocked mode and to extract the primary electrodes in a mode called the "firing phase" or "beam production," which makes it possible to control 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.

[0044] A hollow structure 6, for example with a frustoconical internal shape (for example, funnel-shaped), is positioned opposite the cathode 2, its longer side 8 (or base) facing the cathode, and its axis AA' aligned with the average emission direction of the electrons. The device has rotational symmetry. The center of the cathode 2 is on the same axis as the center of the internal hole 8 and the output of the amplification structure 6.

[0045] 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:

[0046] - capable of emitting a secondary electron for every primary electron at very low energy, less than 100 eV;

[0047] - resistant to electron irradiation, which is the case for insulators such as MgO, SiO2, carbon (C), diamond.

[0048] Semiconductors can also be used, for example certain compositions of doped silicon, for example Si-Ge or Csi.

[0049] This layer has, for example, a thickness between 1 nm and 100 pm, this thickness being able to be chosen according to the desired electronic emission properties of the material.

[0050] The hollow structure has an inlet orifice 8 of diameter D and an outlet orifice 18 of diameter d.

[0051] An output electrode 14 is located at the outlet of the hollow structure. It generates a potential difference ("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 so-called 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.

[0052] 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 ([Fig.3]).

[0053] 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., to secondary electron emission 20. The latter can be characterized by an efficiency y (=average number of secondary electrons induced per incident electron). A steady state of transport on the insulating surface is reached if, on average <y>= 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 to be maintained <y>= 1 and not to create an electrical charge on the surface of layer 12.

[0054] 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.

[0055] Consider the electronic emission curve, which gives y as a function of the energy E. Siy>louy <là proximité du premier croisement de cette courbe d’émission electronic with the value y = 1, then the process regulates itself and tends towards a stationary state.

[0056] It is thus possible to generate a secondary electron beam 20, which can be used to trigger an explosive material 22, as illustrated in [Fig.3].

[0057] Given the convergent shape (the apex angle a 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”) at the outlet of the funnel 6 can be determined by the following formula: t — ^cath t Eq. (1) out sout J cath

[0058] where Scath is the surface area of ​​the cathode, Sout the surface area of ​​the output hole 18 and Jcath the current density emitted by the cathode.

[0059] For example, for a cathode with a radius of 0.5 mm with a current density of 1 A / cm2 and a radius of 25 pm for the outlet hole 18 of the funnel, a current density gain of 400 can be obtained.

[0060] For example, we consider a zirconium potassium perchlorate (“ZPP”) explosive 22, 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.

[0061] By fixing a funnel outlet diameter 18 of 100 pm, we deduce the Sout section of outlet 18:

[0062] Sout = jr r2 = jr (0.01 / 2)2 = 7.85.105 cm2

[0063] Taking a cathode with a current density of 1 A / cm2 and an electron energy secondary outputs of a 100 eV device determine the current density required to initiate a "ZPP" composition at the funnel output for a firing time t (t is chosen in this example to be equal to 3 ms): Er j , = 100 « 3 œ = 52.5 4 / cm2 Equation 3

[0064] where E is the ignition energy density.

[0065] Secondly, the surface area, then the diameter Dcathode p of the primary cathode 2, is deduced: / aupAïvr . , , , Equation 4 cathode.^ ......f............. *0 «..m J CiUfi. 7^7 Equation 5 ■^CSillûdi^p ~ ; w ~ pm N

[0066] Based on these sizing calculations, an example of a device according to the invention has a cathode diameter of 720 pm, an output hole diameter of 100 pm and an amplification gain of 52.5. More generally, a device according to the invention may have a cathode diameter between 100 pm and 10 cm, an output hole diameter between 10 pm and 1 cm, and an amplification gain between 10 and 1000.

[0067] The funnel-shaped part has a specific angle, denoted "a", ranging from 10° to 178°. This angle, which can be adjusted according to the nature of the explosive 22 used, can be determined or estimated through simulations performed using the CST® software. Optimizing this angle makes it possible to influence the current density obtained directly at the device's output and therefore, consequently, the efficiency.

[0068] The angle α can be estimated or determined using a theoretical formula (tan(α / 2) = [(4.Eo) / (Er2.Eo)]1 / 2). 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 taken into account, for example, the homogeneity of the beam 20 at the output of the amplification structure and the number of jumps of the secondary electrons on the insulating material 12.

[0069] By applying, using means 9 (voltage source), a strong 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 ([Fig. 3]). The post-acceleration electrode 16 provides the necessary energy to the secondary electrons depending on the explosive material to be initiated.

[0070] As illustrated in [Fig. 4], a detonator 1 according to the invention can further be 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, 9, and the amplification. As can be seen from this figure, all of these means can be located as close as possible to the device, thus allowing for increased safety in embedded systems and a minimization of electrical connections between the control section and the detonator.

[0071] 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.

[0072] The device described has the advantage of not having a direct link between the cathode and the explosive.

[0073] It is also understood that a detonator according to the invention offers resistance to severe environments (ionizing radiation, electromagnetic radiation, stray currents, etc.) inherent in its structure, without the need for specific protection.

[0074] 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.

[0075] Furthermore, there is an intrinsic barrier to the physics of the phenomenon which is the equilibrium condition for electron transport on the insulating surface ( <y>= 1). These three conditions combined allow the explosive charge to be initiated. This constitutes a very strong advantage compared to 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).

[0076] One field of application of the invention is that of pyrotechnic devices, whether on-board or not.

[0077] A device and a method according to the invention is reliable, insensitive and offers operational safety.

[0078] By construction and thanks to the physical principles on which its operation is based, it is "self-safe", and it is not necessary to add specific protections or specific devices.< / y> < / y> < / y>

Claims

Demands

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, 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).

5. Device according to any one of claims 2 to 4, said layer of insulating material (12) having a thickness between 1 nm and 100 pm.

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

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

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

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

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

11. Detonating device according to any one of claims 1 to 10, 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.

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

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

14. 14. A method for initiating an explosive material (22), employing, for example, a detonating device (1) according to any one of claims 1 to 11, 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.

15. 15. Method according to claim 14, 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.

16. Method according to claim 14 or 15, 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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