RU2292112C1 - Device for generating subnanosecond pulses - Google Patents

Abstract

FIELD: pulse engineering; generation of subnanosecond pulses for locating devices, charged-particle accelerators, and lasers.

SUBSTANCE: proposed device has pulse-voltage charging source, shaping line, two peaking switches, high-resistance shaping line, output shaping line, and transmitting line; mounted on first electrode of second peaking switch is additional electrode electrically connected to first electrode that encloses it and is disposed coaxially with this electrode.

EFFECT: reduced rise time of subnanosecond pulses.

5 cl, 5 dwg

Description

The invention relates to a pulse technique and can be used to create subnanosecond pulses, for example, in location systems, in charged particle accelerators, lasers.

Known devices for the formation of high-voltage voltage and current pulses in which the formation of pulses with a nanosecond duration is achieved by using low-inductance capacitors and sharpening switches connected to the output of the pulse voltage generators (GIN) Arkadyev-Marx [1].

When the GIN is triggered, a voltage pulse appears at its output, the amplitude of which is close to n · U _cm , where n is the number of GIN stages, U _cm is the charging voltage of the GIN stage. This pulse is applied to a low-inductance capacitor connected to the output of the GIN, the capacitor is charging. At a certain point in time, when the amplitude of the voltage pulse across the capacitor is close to n · U _cm , the sharpening switch breaks through and the low-inductance capacitor begins to discharge to the load. The electrical capacitance of this capacitor is selected so that the stored energy is sufficient to form the front of the pulse and its amplitude. The rest of the pulse is generated due to the energy stored in the storage capacitors of the GIN. Since the switching time of the switch-sharpener is short, and the inductance of the discharge circuit: low-inductance capacitor - capacitor-sharpener - the load is quite low, a high-voltage pulse with a short (nanosecond) front is formed on the load. A peculiar compensation of the high GIN inductance occurs during the formation of the pulse front.

The disadvantage of this device is the insufficiently high response speed of the switch-sharpener due to small overvoltages on it. When generating pulses with subnanosecond fronts, two or more pulse exacerbation stages are used to increase the switching speed of the switches.

A device for generating high-voltage nanosecond pulses [2], comprising a primary energy storage device - a pulse transformer, a first forming line (PL), a first switch-sharpener, a second PL, a second switch-sharpener, a transmission line (PL), a load.

The device operates as follows. After the operation of the pulse transformer, the first PL is charged and the next breakdown of the first switch-sharpener is broken. The first PL discharges to the second PL within a few tens of nanoseconds, and a strong overvoltage arises on the second switch-sharpener due to the rapid increase in voltage. As a result, the second switch-sharpener works in fractions of a nanosecond. Submarine without distortion transmits a pulse to the load, on which a pulse is formed with a front in a fraction of nanoseconds. The pulse duration is determined by the electrical lengths of the forming lines.

The disadvantage of this device is that at high voltage levels (from hundreds of kilovolts to megavolts), the insulation distances in the coaxial design of the sharpener switch significantly affect the switching time of the second sharpener switch and lead to an increase in the duration of the edges and pulse widths due to the influence of inductance, the so-called pulse switching loop.

A device for generating picosecond voltage pulses [3], where significant compensation of the inductance of the switching loop is achieved due to the conical narrowing of the electrodes of the switch-sharpener and the outer shell of the coaxial PL in the device. The described device contains a primary energy storage device - a pulse transformer, FL, the first switch-sharpener, a transforming line (TFL) connected to the storage forming line (NFL), the second switch-sharpener, PL, load.

When the control signal is supplied, the primary energy source (pulse transformer) is turned on, the first PL is charged and the first switch-sharpener is broken down and the first PL is discharged to the TFL connected to the NFL. After the voltage near the maximum increases on the NFL, the second switch-sharpener breaks through and a pulse with a short edge propagates to the load on the submarine. Since the inductance of the spark is large enough because of its small (fraction of a millimeter) diameter, inhomogeneity is formed in the zone of the spark gap due to a jump in the wave impedance Z of the _sparks , which is equal according to [4]

where ε is the dielectric constant of the working medium of the switch-sharpener,

D is the diameter of the discharge chamber,

d _u - spark diameter.

Smooth narrowing of the internal and external conductors of the sharpening switch can improve the coordination of the first NFL with PFL and reduce the structural inductance of the elements of the electrode system in the discharge circuit by reducing the difference in the diameters of the spark and the electrodes of the second switch-sharpener.

The disadvantage of this device is that a further decrease in the duration of the pulse front is limited by a sufficiently large structural inductance of the capacitance of the conical NFL in the discharge circuit.

The problem to which the invention is directed, is to reduce the duration of the front of subnanosecond pulses.

The technical result is to provide more efficient transfer of energy to the load in the technique of forming subnanosecond pulses.

The problem is solved due to the fact that in the device for generating subnanosecond pulses containing a charging pulse voltage source, forming a line (PL), the high-voltage conductor of which is connected on one side to the output of the charging pulse voltage source, and on the other hand, to the first switch a sharpener connected through a high-impedance FL with a high-voltage current lead of the output FL, which through a second switch-sharpener is connected to a high-voltage current lead of a transmission line (PL), sub li ne the output to the load, wherein the electrical conductors potential-forming lines and PL are their housings and connected to each other, on the first electrode of the second switch-sharpener secured additional electrode having a first electrode galvanic contact, covering it and disposed coaxially with them.

The additional electrode may be made in the form of a hollow cylinder.

The additional electrode may be made in the form of a hollow truncated cone.

The second electrode of the second switch-sharpener can be made located in the cavity of the additional electrode.

The length of the additional electrode can be determined from the condition

where t _ph - the duration of the pulse front in the design of the device without an additional electrode;

v is the speed of light in the dielectric medium of the second switch-sharpener.

The installation of an additional electrode on the first electrode of the second switch-sharpener causes the formation of two additional electrical capacitances with low structural inductance due to the reduction of the discharge loop due to the selection of the optimal sizes of the discharge circuits formed by the capacitance C ₃ between the additional electrode and the external current lead, the capacitance C ₄ between the additional electrode the second electrode of the second switch-sharpener, the spark channel and the load. At the time of switching, the additional electrode together with the spark channel forms the smallest possible in size and, accordingly, inductance oscillatory circuit, which allows to increase the current growth rate through the spark channel after its formation. This, in turn, leads to an increase in the rate of increase in voltage in the submarine and at the load. Fast electromagnetic processes in this circuit can reduce the duration of the front of the current pulse due to the energy stored in the capacitances C ₄ and C ₃ . The travel time of the electromagnetic wave t ₀ on the surface of the additional electrode is determined by the formula:

where l _about - the total path length of the wave;

ν is the propagation velocity of an electromagnetic wave in a dielectric medium.

Since the wave is formed after the breakdown of the second switch-sharpener, the total path length of the wave l _about from the breakdown point (the top of the conical electrode) is approximately:

where l is the length of the additional electrode;

d is the inner diameter of the additional electrode mounted on the first electrode of the second switch-sharpener.

Accordingly, the travel time t ₀ to the end of the additional electrode is:

where l is the length of the additional electrode, l = l _o -d / 2;

ν is the propagation velocity of an electromagnetic wave in a dielectric medium;

d is the inner diameter of the additional electrode mounted on the first electrode of the second switch-sharpener.

The duration of the pulse front depends on the switching time of the second switch-sharpener and the travel time of the wave along the additional electrode, i.e. length and diameter of the additional electrode. The pure switching time t _{k of the} sharpening switch in the subnanosecond time range is practically impossible to measure, therefore, in the calculations it was specified by a certain function of t _pho . The dimensions of the additional electrode and, accordingly, the electric capacitances C ₃ and C ₄ must be selected in such a way as to provide sufficient energy input for the vibrational emission of electromagnetic energy at the top of the current pulse (voltage) and increase the steepness of the pulse front.

Experiments and calculations showed that there is a certain range of lengths of the additional electrode, in which the duration of the pulse front in the device with the additional electrode will be shorter than the duration of the pulse front in the device without the additional electrode.

This range is defined as follows. For different pressure values and different insulation distances in the device for generating subnanosecond pulses without an additional electrode, a voltage pulse is recorded at the load using a voltage divider built into a coaxial submarine. The waveform determines the pulse front duration t _pho (t _pho = 0.38 ns at a pressure of 60 atm and an interelectrode distance of 4 mm, t _pho = 0.42 ns at a pressure of 40 atm and an interelectrode distance of 6 mm, t _pho = 0.48 ns at a pressure of 30 atm and an interelectrode distance of 8 mm). Change the length of the additional electrode from 5 to 80 mm in increments of 5 mm. For each step of the length of the additional electrode, the value t ₀ / t _pho = l _o / νt _{pho is} calculated by calculation. For each resulting point, a voltage pulse is recorded at the load and the value of t _f is determined for the subnanosecond pulse generating device with an additional electrode. The result obtained experimentally is confirmed by calculation. The obtained curves 1, 2, 3 for different values of t _fo (figure 4).

As can be seen, there is quite pronounced minimum pulse front duration values for different t values under certain _pho t ₀ / t _fo. Obviously, for small lengths of the additional electrode l, the energy stored in the capacitors formed by the additional electrode and the current path with zero potential C ₃ and the additional electrode and the second electrode of the second switch-sharpener C ₄ is not enough to reduce the duration of the pulse front. For large lengths of the additional electrode l, the forming line formed by the additional electrode and the main electrodes cannot be discharged faster than the travel time of the electromagnetic wave along the additional electrode. If this time is significantly greater than the value of t _k , the pulse front is elongated.

As follows from figure 4, the minimum values of t _f are at a ratio of t ₀ / l _fo within (0.08-0.24),

From here we get:

t ₀ / t _pho = 0.08-0.24,

t ₀ = (0.08-0.24) t _fo

taking into account (1) t ₀ = l ₀ / ν,

l ₀ = t ₀ ν,

determines the total wavelength

Based on the foregoing, the determination of the optimal value of the length of the additional electrode is reduced to the following. According to the presented formula, having previously measured the duration of the pulse front in the device for generating subnanosecond pulses without an additional electrode, the total wavelength l _{about is} determined. From (2) determine the length of the additional electrode l = l _o -d / 2, which must be installed in the switch-sharpener to reduce the duration of the pulse front. The diameter of the additional electrode d is chosen mainly for reasons of ensuring the electric strength of the medium between the additional electrode and the sharpening switch electrode connected to the coaxial transmission line.

The implementation of an additional electrode in the form of a hollow cylinder allows you to most effectively reduce the duration of the pulse front.

The implementation of the additional electrode in the form of a truncated cone allows you to strengthen its capacitive connection with the main electrodes of the switch-sharpener and increase the slope of the pulse.

The implementation of the second electrode of the second switch-sharpener located in the cavity of the additional electrode allows the most optimal way to reduce the duration of the pulse front by reducing the wave impedance in the discharge channel.

Figure 1 shows the overall design of a device for generating subnanosecond pulses.

Figure 2 presents the design of the second switch-sharpener with the implementation of the additional electrode in the form of a hollow cylinder.

Figure 3 presents the design of the second switch-sharpener with the implementation of the additional electrode in the form of a hollow truncated cone.

Figure 4 presents the dependence of the duration of the pulse front in the submarine (or at the load) on the ratio t _o / t _fo for different values of t _fo .

Figure 5 presents the waveforms of voltage pulses on the PL, submarine and switch sharpeners.

A device for generating subnanosecond pulses contains a charging source of pulse voltage 1 (Fig. 1), PL 2, forming an electric capacitance C ₁ , a high-voltage conductor 3 of which is connected on one side to the output of the charging source of pulse voltage 1, and on the other hand, to the first electrode 4-sharpener first switch 5, second electrode 6 which is connected via a high photoluminescence with a high current lead 7 8 9 PL output constituting the capacitance c ₂ (2) made, e.g., in the form of a conical Kwak ialnoy forming line. The high-voltage conductor 8 (Fig. 1) of the output FL 9 through the second switch-sharpener 10 is connected to the high-voltage conductor 11 of the PL 12 connected to the output 13 at the output. The conductors with zero potential 14, 15, 16 of the forming lines 2, 9 and PL 12 are their bodies and connected to each other. An additional electrode 18 is attached to the first electrode 17 of the second sharpening switch 10, having a galvanic contact with the first electrode 17, covering it and located coaxially with it. The installation of an additional electrode 18 causes the creation of two additional electric capacitances with low structural inductance, formed by an additional electrode 18 and a current path with zero potential 15 C ₃ (Fig. 2) and an additional electrode 18 and a second electrode 19 of the second sharpening switch 10 C ₄ . There is also a capacitance between the electrodes 17, 19 of the second switch-sharpener 10 C ₅ .

The additional electrode 18 may be made in the form of a hollow cylinder (figure 2).

The additional electrode 18 can be made in the form of a hollow truncated cone (figure 3).

The second electrode 19 of the second switch-sharpener 10 can be performed located in the cavity of the additional electrode 18 (figure 3).

The length of the additional electrode 18 can be determined from the condition

l _o = (0.08-0.24) t _pho ν (Fig. 4)

where t _ph - the duration of the pulse front in the design of the device without an additional electrode;

ν is the speed of light in the dielectric medium of the second switch-sharpener.

The device operates as follows. After turning on the charging source of the pulse voltage 1 (Fig. 1) at time t ₁ , the capacitance C _{1 of the} first forming line 2 is charged (curve 1) (Fig. 5). The electric strength of the main gap between the electrodes 4, 6 of the first switch-sharpener 5 (Fig. 1) is determined by the geometry of the gap and the properties of the insulating medium in the working volume and is selected so that breakdown of the gap occurs at a voltage close to the maximum value. In the event of a breakdown between the electrodes 4, 6 of the switch 5 at time t ₂ (Fig. 5), the capacitance C ₂ (Fig. 2) of the conical forming line 9 is rapidly charged (curve 2) (Fig. 5). In parallel, the charging of electric capacitances formed by an additional electrode 18 and a current path with zero potential 15 C ₃ (Fig. 2) and an additional electrode 18 and a second electrode 19 of the second switch-sharpener 10 C ₄ (curve 3), as well as the interelectrode capacitance C ₅ ( curve 3) (Fig. 5). At the time of breakdown t _{3 of the} second switch-sharpener 10 (Fig. 1), the additional electrode 18 together with the spark channel forms the smallest possible in size and, accordingly, inductance oscillatory circuit. The discharge of the structural capacity C ₄ (FIG. 2) begins to occur through the spark channel of the second switch-sharpener 10 (curve 3) (FIG. 5). An electromagnetic wave begins to propagate along the inner surface of the additional electrode 18, the travel time of which is determined by the formula:

where l ₀ is the total path length of the wave;

ν is the propagation velocity of an electromagnetic wave in a dielectric medium.

Since the wave is formed after the breakdown of the second switch-sharpener 10, the total path length of the wave l _o from the breakdown point (the top of the conical electrode) is approximately:

where l is the length of the additional electrode 18;

d is the inner diameter of the additional electrode 18, mounted on the first electrode 17 of the second switch-sharpener 10.

Accordingly, the travel time t to the end of the additional electrode is:

At time t ₄ (Fig. 5), the wave, reaching the end of the additional electrode 18, is reflected and the recharging of capacitance C ₄ (Fig. 2) begins, ensuring the formation of the lower part of the pulse front, part of the wave, being refracted, passes into PL 12 (curve 4) (Fig. 5). At the same time, the discharge of capacitance C ₃ begins (FIG. 2), ensuring the formation of the peak front of the pulse. Fast electromagnetic processes in the oscillatory circuit allow the formation of a steep front of the current pulse due to the energy stored in the capacitances C ₄ and C ₃ .

At time t ₅ , the discharge of capacitances C ₂ begins, providing a corresponding pulse duration at load 13.

The creation of two additional electric capacitances C ₄ and C ₃ with a low structural inductance allows increasing the current growth rate through the spark channel after its formation. This in turn leads to an increase in the rate of rise of voltage in the transmitting coaxial line and the load.

Information sources

1. Kremnev V.V., Mesyats G.A. Methods of multiplication and transformation of pulses in high-current electronics. Novosibirsk: Nauka, 1987, p. 108.

2. Burger I.W., Baum C.E., Prather W. D. Disign anol Development ob a High Voltage Cooaxial Hygrogen gwitch. Proceeding ob SPIE, 2002, V.4720, p. 43-58.

3. Zheltov K.A. Picosecond high-current nanosecond accelerators. M .: Energoatomizdat, 1991, p. 21.

4. H. Meinke, F. Gundlach. Radio technical reference. Moscow, Gosenergoizdat, 1961, p. 131.

Claims (5)

1. Device for generating subnanosecond pulses, containing a charging source of pulse voltage, forming a line (PL), the high-voltage conductor of which is connected on one side to the output of the charging source of pulse voltage, and on the other hand, to the first sharpening switch connected via a high-resistance PL to high-voltage conductor output FL, which through the second switch-sharpener is connected to the high-voltage conductor of the transmission line (PL) connected to the output to the load, and The potentials of the forming lines and submarines with zero potential are their bodies and are connected to each other, characterized in that an additional electrode is mounted on the first electrode of the second sharpening switch, having a galvanic contact with the first electrode, covering it and located coaxially with it. 2. The device according to claim 1, characterized in that the additional electrode is made in the form of a hollow cylinder. 3. The device according to claim 1, characterized in that the additional electrode is made in the form of a hollow truncated cone. 4. The device according to any one of claims 1 to 3, characterized in that the second electrode of the second switch-sharpener is made located in the cavity of the additional electrode. 5. The device according to any one of claims 1 to 3, characterized in that the length of the additional electrode is determined from the condition

where t _ph - the duration of the pulse front in the design of the device without an additional electrode; v is the speed of light in the dielectric medium of the second switch-sharpener.

Images