RU2810648C1 - Method for generating synchronization pulses for high-voltage spark gap with laser triggering and device for its implementation - Google Patents

Abstract

FIELD: pulsed high-voltage technology.

SUBSTANCE: invention is intended to obtain synchronization pulses of laser-controlled spark gaps used as primary switches of high-current pulsed electrophysical devices, in particular in pulsed electron accelerators or high-voltage generators. A method for generating a synchronization pulse for a laser-triggered high-voltage pulse discharger involves using part of the triggering laser radiation to probe the discharge gap. Probing radiation enters the interferometer, the optical axis of the measuring arm of which passes through the discharge gap, and the reference arm is configured to provide destructive interference conditions. This ensures that there is no optical signal in the state of waiting for the arrester to operate. When plasma appears in the discharge gap, this condition is mismatched due to a phase shift of the radiation and/or its absorption in the measuring arm of the interferometer. This results in an optical signal, which is converted into an electrical synchronization signal.

EFFECT: increase in synchronization accuracy no less than tens of picoseconds.

5 cl, 1 dwg

Description

Field of technology

The invention is intended to synchronize the operation of devices with high-current pulsed electrophysical installations, in particular, these can be generators of nanosecond or subnanosecond pulses, as well as electron accelerators. The invention can be used in research electrophysical installations for synchronizing measuring systems and equipment with subnanosecond accuracy.

State of the art

Precise synchronization of external devices with the electron accelerator can be achieved by using the electron beam itself, which generates a signal in the beam current sensor. This signal, in turn, is distributed along cable or optical (when converted) communication lines. To start a synchronized device, as a rule, some so-called dead time is required. This time is important to take into account when synchronizing equipment in the nanosecond and subnanosecond time range [Ivanov S.N., Shpak V.G., Shunailov S.A., Yalandin M.I. Instruments and experimental technology, 2000. No. 5, pp. 51-55]. If the speed of the electron beam is significantly less than the speed of the signal (the speed of signal propagation in the cable and optical communication line), then in principle it is possible to obtain the necessary delay for launching/synchronizing the external device due to the difference in their speeds. However, this approach is difficult to implement for fast, for example, relativistic beams of charged particles. Also, this approach is difficult to use due to the approximate equality of signal propagation speeds if it is necessary to synchronize the device with a high-current pulse generator (i.e., with a current pulse). To solve this problem, a method of precise synchronization was proposed [Method of synchronization of devices in storage electron synchrotrons of synchrotron radiation sources: Pat. 2689297 RF: IPC H04W 56/00, H05H13/04; appl. 05/27/2018], when before a time-accurate synchronization pulse from the electron beam current sensor, a preliminary, but less accurate pulse is supplied. The main disadvantage of this method is the complexity of the synchronization system.

The closest analogue (prototype) of the proposed method is the synchronization method used in the system for synchronized launch of a soft X-ray laser. This method involves the use of a laser controlled spark gap. [Method and apparatus for synchronized starting of soft x-ray lasers: patent. 8792522 B2 USA: IPC H01S 3/30; appl. 07/28/2014]. The system also contains a current transformer, which is used to finally generate the system triggering (synchronization) pulse. The use of a current transformer, due to the fundamentally inductive nature of this element, is the main disadvantage of the method used. Firstly, it limits the rise time (leading edge) of the signal, and therefore reduces the accuracy of switching. The turn-on accuracy of the prototype is +/- 10 ns, which is unsatisfactory when using the method in the nanosecond or subnanosecond time range. Secondly, this leads to a delay in the formation of the synchronization pulse. Thirdly, its presence in conditions of high levels of electromagnetic interference can lead to random operations.

Essence Revealing

The technical result of the present invention is the solution to the technical problem identified above - reducing the uncertainty in determining the moment of operation of high-current pulsed electrophysical devices to a level of no more than tens of picoseconds. It was shown [Lipchak A.I., Barakhvostov S.V. Instruments and experimental technology, 2021, No. 3, p. 40-44], that direct synchronization with the triggering laser pulse leads to instability of switching on the spark gap of the order of 300 ps or more. One of the reasons for this effect is that the transport and optical properties of the substance affected by laser radiation, forming plasma in the spark gap, can undergo strong changes. This leads to “jitter” in the response of the laser-triggered spark gap. [Volkov N.B., Lipchak A.I. Condensed Matter, 2022, vol. 7, No. 4, p. 61-74] To achieve the specified technical result, a method is proposed for generating synchronization pulses of a high-voltage spark gap with laser triggering, which consists in the fact that part of the triggering laser radiation is used to probe the discharge gap. In this case, synchronization must be associated with the overlap of the discharge gap, ensuring the flow of current through it, i.e., the appearance of plasma in it. In addition, this approach makes it possible to generate a synchronization pulse at the initial stage of the formation of a high-voltage pulse or electron pulse, since the high-voltage spark gap is the primary switch for a wide class of high-voltage pulse generators [Mesyats G.A., Yalandin M.I., UFN, 2005, v. 175 , No. 3, pp. 225-246]. This solves the problem of dead time required to start synchronized devices, which, generally speaking, has its own spread and, accordingly, affects the accuracy of synchronization. This eliminates the need to first launch the synchronized devices. It was also shown that the instability associated with the internal processes of the functioning of such generators, excluding this primary switch, does not exceed 25 ps. [Yalandin M., Sharypov K.A., Shpak V.G., Shunailov S.A., Mesyats G.A. IEEE Trans. on Diel and Elec. Ins. 2010. Vol. 17, No. 1. P. 34] In addition, the resistance of devices to accidental operations in conditions of high levels of electromagnetic interference increases due to the use of not electrical, but optical elements in direct contact with high-current pulsed equipment, which also increases the overall synchronization accuracy.

It is known that plasma created by laser radiation absorbs this radiation. [Meyerand R.G., Haught A.F. Physical Review Letters, 1964, 13(1), p. 7-9] If the probing radiation enters an interferometer designed so that its measuring arm passes through the region of possible plasma appearance, and the reference arm is configured to provide destructive interference conditions [p. 355, Born M., Wolf E. Fundamentals of optics. M.: Nauka, 1973. 720 pp.], then we can determine the moment of its occurrence. This configuration of the interferometer will ensure that there is no signal in the waiting mode for the discharge gap to overlap with the plasma, i.e. before turning it on. In the case of the appearance of plasma in the discharge gap, i.e., when the high-voltage spark gap is turned on, a mismatch of this condition occurs due to a phase shift of the radiation in very short times up to the femtosecond range [Agranat M.B., Andreev N.E., Ashitkov S.I. et al. Letters to JETP, 85:6, 2007, 328-333] and/or due to partial or complete absorption of radiation (see link Meyerand, above) in the measuring arm of the interferometer. This results in an intense optical signal, which, for example, can be converted into an electrical signal using wideband semiconductor detectors with a bandwidth of up to several tens of gigahertz for subsequent transmission as an electrical signal, which is used for synchronization.

When conducting an analysis of the level of technology, including a search in patent and scientific and technical sources and identifying sources containing information about analogues of the claimed invention, characterized by features identical to all the essential features of this invention, no such analogues were found. Determination from the list of identified analogues of the prototype as the closest analogue in terms of the set of essential features made it possible to identify a set of essential distinctive features from the prototype set out in the claims. Consequently, the claimed invention meets the “novelty” condition.

To verify the compliance of the claimed invention with the “inventive step” condition, the applicant conducted an additional search for known solutions in order to identify features that coincide with the features of the claimed method and the device implementing it that are distinctive from the prototype. As a result of the search, no technical solutions with these characteristics were identified. On this basis, it is possible to draw conclusions about the compliance of the claimed invention with the “inventive step” condition.

A simplified schematic diagram of a device that implements the proposed method is illustrated by the drawing (Fig. 1):

1 - laser,

2 - laser radiation,

3 - laser beam splitter,

4 - system for focusing the triggering beam of laser radiation,

5 - rotating elements (prisms or mirrors),

6 - optical windows of the high-voltage arrester,

7 - divider/combiner, interferometer laser beams,

8 - electrodes,

9 - optical signal sensor,

10 - optical platform.

The device implementing the claimed method contains a window 6' for input of laser radiation and coaxially located electrodes 8, made in the form of bodies of rotation, which are placed in a sealed housing filled with gas with a pressure from 0.1 MPa to 10 MPa. The device also contains a trigger laser 1, a laser radiation splitter 3, which splits the laser radiation beam 2 into two beams. The first serves to create plasma on one of the electrodes of the high-voltage spark gap 8 through the optical window 6' and a coaxial hole in the other electrode. The second beam is used for interferometric probing of the plasma in the discharge gap. For this purpose, the device contains an interferometer assembled on an optical platform 10, which is mounted on one of the flanges of the high-voltage arrester. The interferometer is formed by rotating elements 5, a laser beam splitter 7' and an element 7'' that combines the separated laser beams. The interferometer contains a measuring arm, the optical axis of which passes through the discharge gap through 6'' and 6''' using optical elements 7' and 7''. The arm that forms the reference beam of the interferometer is formed by elements 7', 5', 5'', 7'' (Fig. 1).

The method is carried out as follows.

Initially, the interferometer is adjusted so that the phase difference between the reference and measuring beams is π, in other words, the radiation of the two beams arrives at the optical signal sensor 9 in opposite phases, due to which destructive interference is realized. The laser pulse is focused using a focusing system 4 on the surface of the electrode 8''. As a result of this, plasma appears; due to its occurrence, the condition of destructive interference is violated due to a change in the refractive index of the medium in the discharge gap and/or complete or partial absorption of the radiation of the measuring beam due to the appearance of plasma in the discharge gap. This provides an optical signal at the sensor, which is used to generate an electrical synchronization pulse, the delay of which is determined by the rise time of the leading edge of the sensor and is less than 40 ps. The inventive method was tested experimentally.

Thus, the presented data indicate that the following set of conditions are met when using the proposed method:

1. The process implementing the claimed method is intended for use in high-voltage pulse technology for precise synchronization of devices.

2. For the claimed method and device, in the form in which it is given in the claims, the possibility of its implementation has been confirmed.

Claims (5)

1. A method for generating a synchronization pulse for a high-voltage spark gap with a laser trigger, which consists in using part of the trigger laser radiation to probe the discharge gap entering the interferometer, the measuring arm of which passes through the discharge gap, and the reference arm of which is configured to provide destructive interference conditions, which determines the absence of an optical signal in a state of anticipation of the operation of a high-voltage spark gap, and causes its appearance when plasma appears in the discharge gap due to the mismatch of this condition. 2. A device for generating a synchronization pulse for a high-voltage spark gap with laser triggering, containing a window for introducing laser radiation into the discharge gap, coaxially located electrodes placed in a sealed housing filled with gas with a pressure from 0.1 MPa to 10 MPa, characterized in that it contains a splitter of the triggering laser radiation, splitting the laser beam into two beams, the first of which is used to create plasma on one of the electrodes of the high-voltage spark gap, and the second is used to interferometrically determine the presence of plasma in the discharge gap. 3. The device according to claim 2, characterized in that it contains an interferometer, the optical axis of the measuring arm of which passes through the discharge gap. 4. The device according to claim 3, characterized in that the interferometer is configured to create destructive interference conditions in the discharge standby mode in the discharge gap of the device. 5. The device according to claim 2, characterized in that the synchronization pulse is formed due to the appearance of an optical signal due to the violation of the condition of destructive interference when plasma appears in the discharge gap.

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