HIGH POWER PULSED GENERATOR TRIGGERED BY A PULSE OF IONIZING RADIATION.

Abstract

The invention relates to a device for characterizing a force sensor (12), comprising: - magnetic means (8) for generating a magnetic field along at least one axis (XX'); - means (2, 4, 6) for adjusting and then maintaining a relative position, along the axis (XX'), between a force sensor (12) to be tested and the magnetic means (8); - means (22-24) for measuring a signal representative of a force, in traction or compression, applied to a force sensor directly using said magnetic means. Figure for the abstract: Figure 1A

Description

Title of the invention: HIGH POWER PULSED GENERATOR TRIGGERED BY A PULSE OF IONIZING RADIATION. TECHNICAL FIELD AND PRIOR ART

[0001] The invention relates to the field of high power electrical generators.

[0002] Current pulsed high-power electric generators, of mega-Volt (MV) and mega-Ampere (MA) class, maintain high voltages and then release the electrical energy quickly (i.e. in a few tens of nanoseconds) into a load. This switching is provided by spark gaps, operating like threshold diodes.

[0003] A first problem is linked to the self-priming phenomena which correspond to a transition in passing mode of one of these spark gaps in an unwanted and untimely manner. This results in the loss of electrical energy from the machine and therefore the failure of the experiment.

[0004] Laser-triggered spark gaps are known, which solve self-priming problems; but triggering by pulsed laser poses several problems.

[0005] First of all, the performance of a laser (jitter, intensity, pulse duration) can be significantly degraded by the parasitic electromagnetic radiation produced during the discharge of a generator as well as by the ionizing radiation produced if the generator in question is used for the generation of intense ionizing radiation.

[0006] In addition, laser spark gap triggering requires short wavelengths (in the UV range) to maximize the generation of free electrons by multi-photon ionization. This point makes the beam alignment and transport procedures to the spark gap difficult.

[0007] Another problem lies in the non-linear nature of multi-photon ionization. Consequently, a small change in the performance of the laser can induce a significant change in the performance of the spark gap triggered by this laser, in particular a change in the triggering time and the duration of establishment of the arc regime. This has a strong impact on the performance of a laser-triggered generator.

[0008] Finally, laser-triggered spark gaps are complex to implement: they require specific additional skills, increasing costs. Furthermore, lasers are themselves devices operating in a non-linear regime and are therefore very sensitive to electromagnetic disturbances. encountered in installations generating high pulsed electrical power. Faradization of the installation induces additional costs, and is also limited by space and safety constraints linked to the transport of the laser beam.

[0009] Yet another problem is that of transporting the laser pulse, because the beam must reach the inter-electrode region, which involves additional difficulties during the design phase of the generator. Transport by optical fibers can be considered to reduce this problem. On the other hand, transporting short wavelengths by optical fibers is not efficient and consequently longer wavelengths are implemented, thus reducing the efficiency of the multi-photon ionization process, which affects the control of the spark gap triggering.

[0010] Furthermore, the physical mechanisms induced by laser breakdown are non-linear, poorly understood and therefore poorly controlled. The development of a laser-triggered spark gap therefore requires significant testing and optimization phases, thus impacting the costs and delivery times of a high-power pulsed electrical generator. Presentation of the invention

[0011] The invention aims to solve all or part of the problems set out above or in the remainder of the present application.

[0012] The invention firstly concerns a device which makes it possible to control the triggering of a spark gap of a high-power electrical pulse generator by a pulsed X-ray flux coming from a secondary generator, also called a starting generator in the following.

[0013] The invention relates in particular to a high-power generator, comprising:

[0014] - at least one spark gap, comprising 2 electrodes;

[0015] - means, or a starting generator, for generating an X-ray beam in direction of the inter-electrode space or towards one of the electrodes.

[0016] The means for generating an X-ray beam (the starting generator) are preferably of the kilo-Volt and kilo-Ampere class, generating a flux of X-rays, the performance of which is known and fixed by the operating current and voltage. These means have, for example, an operating voltage of the order of a few hundred kV (for example between 100 kV and 500 kV or even 1 MV), and a current of accelerated electrons of the order of kA (for example between 0.5 kA and 1 kA or 5 kA).

[0017] The high electrical power pulse which can be generated by a high power generator according to the invention can have a peak voltage of between 1 and 20 MV, to which current pulses of between 100 kA and 1 MA can be associated (depending on the resistivity of the load subjected to this pulse).

[0018] The ignition generator makes it possible to initiate the start of an electric arc in a spark gap, under vacuum or containing a gas, of a high-power electric generator.

[0019] The invention allows:

[0020] - to control the triggering of the pulsed high voltage electrical pulse;

[0021] - to control the electrical conductivity of the inter-electrode medium of the spark gap.

[0022] The invention also allows:

[0023] - to overcome the experimental difficulties linked to the synchronization of pulses of laser radiation and high pulsed power. In fact, the high-power electrical pulse is triggered by the initiating generator(s) and not by the self-initiating mechanism;

[0024] - to control the ionization of the inter-electrode medium and consequently the phase of spark gap triggering;

[0025] - to control the radio-induced conductivity of the inter-electrode medium of the spark gap, and consequently the operating phase of the spark gap;

[0026] - to better control the priming delay compared to self-triggering or a laser trigger;

[0027] - to limit the scope of skills required for the operation of installation (no need for a team of laser technicians).

[0028] Finally, the experimental implementation of the priming generator(s) is less complicated than that of lasers because the ionizing radiation, unlike the laser, can pass through the different mechanical parts of the pulsed high power generator. Thus, the design of the machine is simpler and faster, and therefore the costs are reduced.

[0029] In a generator according to the invention:

[0030] - each X-ray generator can for example deliver pulses of duration between 1 ns and 50 ns.

[0031] - and / or the means for generating an X-ray beam comprise at least one target and means for generating an electron beam and directing this beam towards said target.

[0032] A generator according to the invention may comprise, or a method according to the invention may implement:

[0033] - a plurality of spark gaps, and an X-ray generator for each spark gap;

[0034] - or a plurality of spark gaps, and an X-ray generator (20) common to several of said spark gaps;

[0035] - or a plurality of spark gaps, and an X-ray generator arranged to send a cascaded X-ray beam to several of said spark gaps.

[0036] In a generator according to the invention, or in a method according to the invention, the electrodes of each spark gap may be in a gas which comprises SF6 or air or other gas with similar voltage withstand performance, such as NOVEC (C6Fi2O) or HFO (C3H2F4). Alternatively, each spark gap is under or under vacuum. A generator with multiple spark gaps may have some spark gaps in a gas atmosphere, and some others under vacuum.

[0037] A generator according to the invention may for example be of the Marx generator type.

[0038] The invention also relates to a method for generating high-power pulses, for example implementing a device according to the invention, as described above or in the remainder of the present application.

[0039] The invention also relates to a method for generating high-power pulses, for example implemented with a device according to the invention (as described above or in the remainder of the present application), this method comprising the triggering of at least one spark gap, comprising 2 electrodes, using at least one X-ray beam directed towards the inter-electrode space or towards one of said electrodes.

[0040] The high electrical power pulse is for example produced as soon as the spark gap(s) are irradiated by the beam(s) of ionizing radiation (X or electrons). BRIEF DESCRIPTION OF THE FIGURES

[0041] [Fig.1A] represents an example of a gas discharger, equipped with an initiation generator according to the invention;

[0042] [Fig. 1B] represents another example of a vacuum spark gap equipped with an initiation generator according to the invention;

[0043] [Fig.2] represents a spark gap structure to which the invention is applied, using a starting generator;

[0044] [Fig. 3] represents a generator equipped with several sources of ionizing radiation;

[0045] [Fig.4] represents a generator provided with a source of ionizing radiation which irradiates a plurality of generators in cascade; DETAILED DESCRIPTION OF THE INVENTION

[0046] [Fig.1A] schematically represents the 2 electrodes 12, 14 of a spark gap 10 under a gaseous atmosphere and an ignition generator 20. The latter generates a pulsed X-ray flux, directed towards the inter-electrode space. The gas constituting the spark gaps can be SF6, or dry air (which has the best performance in this application and is the least polluting) or another gas, such as NOVEC (C6F12O) or HFO (C3H2F4).

[0047] Thus the priming generator 20 produces, between the electrodes 12, 14, a plasma 15 out of thermodynamic equilibrium whose degree of ionization depends on the dose rate. produced by generator 20. This dependence is close to linearity, particularly for X-ray doses between 1 Gy and 7000 Gy (and even outside these limits), which induce a degree of plasma ionization much lower than unity.

[0048] The articles by M. Ribière et al. cited below present measurements of plasma parameters (electronic density and electrical conductivity) for different dose rates in air. These results show the control of these plasma parameters when the latter is produced with a source of ionizing radiation.

[0049] [Fig.lB] schematically represents the same 2 electrodes 12, 14 of a spark gap 10', but which operates under vacuum, and the ignition generator 20. The latter still generates a pulsed X-ray flux, but directed towards the cathode 14.

[0050] Generators 20 (or 20i, 202, .. .20n) which can be used in any embodiment of the invention are for example marketed by the company Europulse.

[0051] In both cases (gaseous medium spark gap and vacuum spark gap), the generator is preferably of kilo-Volt and kilo-Ampere class. For example, it has an operating voltage of the order of a few hundred kV (for example between 100 kV and 500 kV or 1 MV), and an accelerated electron current of the order of kA (for example between 0.5 kA and 1 kA or 5 kA).

[0052] The durations of the pulses of this priming generator are of the order of ten nanoseconds (for example between 10 ns and 100 ns).

[0053] During the charging phase of the spark gap 10, the ignition generator(s) do(es) not operate. The discharge phase of the spark gap 10 is ensured by irradiating the spark gap (or spark gaps in the examples which follow) by means of one or more ignition generator(s) 20 (or 20i, 202, ...20n: see [Fig.4] described below)

[0054] Each spark gap can be triggered either directly by the X-ray flux produced by the priming generator, or indirectly by converting electrons into X-ray radiation, for example broad spectrum (between 0 and a few tens of keV) by braking the electrons on a target, preferably made of a material with a high atomic number.

[0055] The control of the parameters (current and voltage) of the electrical pulse of the priming generator 20, which results from the fact that the electrical components constituting this type of generator are simple and robust, makes it possible to manage and / or control the dose rate produced and the energy deposited in the spark gap, and therefore the ionization and the electrical conductivity of the inter-electrode medium.

[0056] The invention makes it possible to control the triggering of a pulsed high voltage electrical pulse. Control of the chemical kinetics of the irradiated gas in the gap 15 of the spark gap, or control of the flow of photoelectrons emitted by the irradiation of the electrodes 14 of the spark gap, makes it possible to control the spark gap in its phase of triggering as well as in its operating phase. On the contrary, the known laser pulse triggering technique is based on the generation of electrons by multi-photon processes, which are highly non-linear mechanisms and therefore difficult to control.

[0057] The invention also makes it possible to control the electrical conductivity of the inter-electrode medium 15 of the spark gap. Indeed, by controlling the parameters (the voltage and the current) of the ignition generator, the flow rate of energy deposited in the spark gap, the conductivity of the plasma in the latter, as well as the triggering and operation of the spark gap are controlled.

[0058] As explained above, during the charging phase of the spark gap 10, the ignition generator(s) 20 (20i, 202, ...20n) do(es) not operate. The discharge phase of the Marx generator is ensured by the irradiation of the spark gaps by means of one or more of said ignition generators.

[0059] Initially, in the case of a spark gap 10 in a gaseous atmosphere, the ionizing radiation pulse from the ignition generator 20 produces a pre-plasma 15 out of thermodynamic equilibrium in the gas constituting the spark gap, then, under the effect of the high charging voltage V, the electronic avalanche occurs (triggering phase of the spark gap 10) to then reach an established arc regime (operation phase of the spark gap 10).

[0060] In the case of a vacuum spark gap, the triggering is produced by the pulse of ionizing radiation which produces a flow of photoelectrons emitted by the surfaces of the irradiated electrodes. The flow of photoelectrons emitted by the cathode 14 is accelerated towards the anode 12 by facilitating the generation of a micro protrusion 17 on the cathode 14 ([Fig.lB]), thus generating a precursor of an electric arc.

[0061] In this vacuum configuration, the priming generator 20 is oriented towards the cathode and makes it possible to irradiate the latter so as to amplify the electronic emission from a micro protrusion 17 of the cathode 14.

[0062] [Fig. 2] represents an exemplary embodiment of another device 30 to which the invention can be applied. It is a Marx generator, represented here in the charging phase. A Marx generator comprises capacitors 32 (C), spark gaps 34 and resistors 36 (Rb R2). Such a generator is for example described in the document DE 455933, or in the work High Voltage Engineering - Fundamentals, E.Kuffel et al., Newnes, Second edition 2000, published by Butterworth-Heinemann, ISBN 0 7506 3634 3, p. 61-64. In this type of generator, capacitors 32 (C) initially in parallel are connected in series through the spark gaps 34. Note that, as a variant of a Marx generator, the device can implement any device containing spark gaps whose triggering is controlled according to the present invention.

[0063] Here again, according to the present invention, the discharge phase of the Marx generator is ensured by the irradiation of the spark gaps 34 by means of one (this is the case in [Fig.2]) or several (see [Fig.4]) ignition generator(s) 20 (or 20i, 202, ...20n), of the type mentioned above.

[0064] Each ignition generator is arranged so as to be able to irradiate a spark gap 34, or several spark gaps 34 simultaneously, making it possible to initiate the start of an electric arc in a spark gap under vacuum or containing a gas.

[0065] [Fig.3] represents a Marx generator whose triggering is ensured by the cascade irradiation of all the spark gaps. There may be a delay between the triggering of the spark gaps which are located upstream, and which first see the X-ray beam, and the triggering of those which are located downstream; but, in practice it is small compared to the duration of the high voltage pulse. A possible attenuation of the flux seems to have little influence on the overall operation of the generator because as soon as the first spark gaps are triggered, the downstream spark gaps will be easily triggered by the voltage pulse.

[0066] [Fig.4] shows another embodiment and mode of operation in which each spark gap is triggered by a trigger generator 20i, 202, .. .20n. A specific synchronization of the latter with each other is implemented by means of a generator capable of producing voltage pulses having controlled delays between them. The latter are therefore operated in parallel. An example of such a generator can be found at the following address:

[0067] https: / / fc-equipments.com / products / dg535-digital-pulse-delay-generator-stanfordresearch-systems /

[0068] In order to produce high voltage pulses, we seek to maintain the high voltage at the terminals of each spark gap for the entire duration of the charging of the Marx generator. To do this, we seek to avoid self-priming phenomena, for example by increasing the trigger threshold of the spark gap, which can be done:

[0069] - either by increasing the distance between the electrodes; the inter-electrode distance is for example between 1 cm and 10 cm;

[0070] - either is by increasing the pressure of the gas; the pressure is for example included between 1 and 5 bars. ;

[0071] In this way, self-priming phenomena are avoided, because the high electrical power pulse is produced as soon as the spark gap(s) are irradiated by the pulsed X-ray priming generator(s).

[0072] Generally, the spark gap trigger threshold increases as the pressure and the distance between the electrodes increase. Irradiation of the spark gap decreases the trigger threshold.

[0073] The invention, which implements a radiative pulse trigger, allows better control of the physical mechanisms leading to the pre-ionization of the inter-electrode space (or "gap") of the spark gap, the "gap" being able to contain a gas or be in a vacuum.

[0074] In the case of a gas spark gap, the ignition generator produces a thermodynamically non-equilibrium plasma whose degree of ionization depends on the dose rate produced by the generator. This dependence is close to linear, as explained in the articles “Reduced kinetics model for X-ray-generated atmospheric air plasmas fitted by microwave transmission measurements”, by M. Ribière et al., published in J. Appl. Phys. 125, 083303 (2019) and in “Microwave absorption and optical emission spectrometry analyses of ambient air plasmas induced by pulsed electron beams”, by M. Ribière et al., published in J. Appl. Phys. 128, 093304 (2020), which makes it possible to improve the control of the spark gap operation, in comparison with a laser-triggered spark gap.

[0075] In the case of a vacuum spark gap, the triggering is produced by the pulse of ionizing radiation which produces a flux of photoelectrons emitted by the surfaces of the irradiated electrodes 14. In this embodiment, there is also an operating range where the linearity (in particular between 1 Gy and 7000 Gy) between the dose rate and the flux of photoelectrons emitted by the irradiated electrodes is respected. Note however that if the dose rate increases significantly, space charge phenomena induce non-linearities which do not prevent the operation of the generator but can induce a delay between the pulse of the X-ray generator and the triggering of the spark gap. This delay depends on the pressure of the gas in the spark gap and the dose rate of the X-ray generator. These delays are stable when the two previously mentioned parameters are stable and can easily be taken into account for the overall operation of the machine.The invention also makes it possible to overcome issues related to laser safety, by including the ionizing phenomena produced by the ignition generator in the radiological safety study of the complete installation.

[0076] The applications of the invention relate, for example, to the generation of high pulsed electrical powers for various applications, for example, depending on the terminal load, to generate pulses of ionizing radiation, electromagnetic pulses, high pressure pulses, etc.

[0077] Other applications concern inertial nuclear fusion by "Z-pinch" or "dense plasma focus" scheme. Indeed, these devices also use generators of Marx and are therefore subject to the problems of synchronization and self-priming mentioned above.

Claims

Claims

1. Marx type high power generator, comprising: - a plurality of spark gaps (10, 32), each comprising 2 electrodes (12, 14); - a plurality of means (20, 20i, 202, .. .20n) for generating a plurality of X-ray beams, each beam being in the direction of the inter-electrode space (15) or towards one (14) of the electrodes of each spark gap; - a synchronization of the means (20, 20i, 202, ...20n) for generating a plurality of X-ray beams.

2. Generator according to claim 1, the electrodes (12, 14) of each spark gap being in a gas which comprises SF6 or air or C3H 2F4 or C6F12O.

3. Generator according to one of claims 1 or 2, each spark gap being empty.

4. Generator according to one of the preceding claims, each of the means (20, 20i, 202, .. .20n) for generating an X-ray beam delivering pulses of duration between 1 ns and 50 ns.

5. Generator according to one of the preceding claims, each X-ray generator (20, 20i, 202, .. .20n) having an operating voltage of between 100 kV and 500 kV or 1 MV), and an accelerated electron current of between 0.5 kA and 1 kA or 5 kA.

6. Generator according to one of the preceding claims, capable of producing high electrical power pulses having a voltage between 1 and 20 MV.

7. Generator according to one of the preceding claims, the means (20, 20i, 202, .. .20n) for generating an X-ray beam comprising at least one target and means for generating an electron beam and directing this beam towards said target.

8. Method for generating high-power pulses, using a generator according to one of the preceding claims, comprising: - triggering a plurality of spark gaps (10), each comprising 2 electrodes (12, 14), using a plurality of X-ray beams, each beam being directed towards the interelectrode space (15) or towards one (14) of the electrodes of each spark gap; - synchronizing the means (20, 20i) to generate a plurality of X-ray beams.

9. 11 Method according to claim 8, in which the high electrical power pulse is produced as soon as the spark gap(s) (34) are irradiated by the beam(s) of ionizing radiation (X or electrons).

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