RU2666353C1 - Sub-nanosecond electrons accelerator - Google Patents

Abstract

FIELD: physics.SUBSTANCE: invention relates to the sub-nanosecond duration electron beams generation equipment. Generator contains the generating and transmitting coaxial lines, sharpening and cutting discharge gaps, the generating line is connected to the nanosecond high-voltage pulses source, at that, between the forming and transmitting lines the second generating line is further introduced with the second sharpening discharge gap formation. Second generating line consists of two sections, of which the first, high-resistance section, is located on the first generating line side, and the second, the low-resistance section, is the short accumulation line located on the transmitting line side. Both sharpening discharge gaps are formed by gaps between the lines, the short accumulation line inner and outer conductors surfaces in the zone of the minimum gap between the conductors are made equidistant, transmitting line is made long, with the wave resistance increase towards the accelerating tube, wherein the accelerating tube comprises metal housing and current lead, forming line with the wave resistance equal to the transmitting line output section wave resistance. Current lead is fixed to the housing by means of ceramic hollow conical insulator, at that, the gap resistance between the accelerating tube anode and cathode, is at least in two times exceeds the transmitting line output section wave resistance.EFFECT: technical result is increase in the voltage pulse amplitude at the gap between the accelerating tube anode and cathode.4 cl, 4 dwg

Description

The invention relates to techniques for the formation of electron beams of subnanosecond duration and can be used to create subnanosecond electron accelerators of the megavolt range. These accelerators are widely used to determine the temporal resolution of nanosecond detectors of pulses of electronic and bremsstrahlung, as well as high-speed measuring ropes, to obtain ultrashort light flashes, etc.

Subnanosecond electron accelerators are known (Zheltov K.A. Picosecond high-current electron accelerators. - Moscow: Energoatomizdat, 1991. - P. 93-105), containing a source of nanosecond high-voltage pulses and an oil-filled shaper, in which the front and shortening pulses to fractions of a nanosecond. These pulses then go to the accelerator tube, where subnanosecond electron beams are generated.

The disadvantages of these accelerators is that breakdowns of the interelectrode gap of the sharpening arresters occur in the environment of transformer oil. In this case, periodic pumping of oil through the shaper is required and it is necessary to withstand a long time (several minutes) of exposure between pulses: accelerators require stationary installation, otherwise the adjustments and settings of the generator are violated.

Closest to the claimed one is a subnanosecond electron accelerator (Mesyats GA, Yalandin MI High-power picosecond electronics // Uspekhi Fizicheskikh Nauk. 2005. T. 175, No. 3. P. 225-246) containing a source of nanosecond high-voltage pulses, gas-filled shaper of subnanosecond voltage pulses and accelerator tube. The shaper contains forming and transmitting coaxial lines, sharpening and cutting off the discharge gaps, the forming line is connected to a source of nanosecond high-voltage pulses.

The use of compressed gas as the working medium of commuting sharpening and shearing discharge gaps can significantly reduce the exposure time between pulses and provide a frequency mode of operation of these accelerators, which can also be portable and work in any position.

The disadvantages of these accelerators are the relatively low energy of the electrons in the beam (not higher than 300 keV), which is associated with the mandatory coordination of the resistances of the transmission line and the accelerator tube, as well as with the specifics of breakdown of gas gaps, in which the increase in electric strength with a decrease in the duration of the applied voltage pulse occurs significantly in less than in transformer oil. In this case, voltage pulses with an amplitude, respectively, of not more than 300 kV, are supplied to the accelerating tube.

When creating this invention, the problem was solved of creating a frequency subnanosecond electron accelerator with electron energies above 0.8 MeV.

The technical result is to increase the amplitude of the voltage pulse in the gap between the anode and cathode of the accelerating tube.

The specified technical result is achieved in that, in comparison with the known subnanosecond electron accelerator containing a source of nanosecond high-voltage pulses, a gas-filled shaper of subnanosecond voltage pulses and an accelerator tube, the shaper contains forming and transmitting coaxial lines, sharpening and cutting off the discharge gaps to the nanosecond, of high-voltage pulses, new is that between the generating and transmission lines tionary introduced second shaping line to form a second sharpening discharge gap, wherein the second shaping line consists of two portions, of which the first, high-resistance portion is positioned on the first side of the forming line, and the second low resistance. represents a short storage line located on the side of the transmission line, both sharpening discharge gaps are formed by gaps between the lines, the surfaces of the internal and external conductors of the short storage line in the zone of the minimum gap between the conductors are made equidistant, the transmission line is long, with increasing wave resistance towards the accelerating tube, and the accelerating tube contains a metal casing and current lead, which form a line with a wave resistance equal to the wave resistance of the output section of the transmission line, and the current lead is fixed to the housing by means of a ceramic hollow conical insulator, while the resistance of the gap between the anode and cathode of the accelerating tube is at least twice the wave resistance of the output section of the transmission line.

In addition, the first section of the second forming line has a wave impedance 3-10 times greater than the wave impedance of the second section of the same line.

The lengths of the equidistant surfaces of the inner and outer conductors of the short storage line do not exceed 0.03 m.

The length L of the transmission line meets the condition L≥c⋅Т / 4. where c is the speed of light in vacuum, T is the minimum value of the time interval between the generation of the first and repeated electron pulses of the accelerator.

The second, low-resistance section of the second forming line (short storage line) is called short because of its small length (not more than 0.03 m) and ensures the formation of a subnanosecond voltage pulse when discharged to the transmission line. The discharge duration is equal to the time τ of the double pulse path along the equidistant section of the short line. In a gas-filled line, τ = 2 × l / s, where l is the length of the equidistant section of the short line, and s is the speed of light in vacuum. When l = 0.03 m, τ = 0.2 ns.

The transmission line is called long, because its length L is many times greater than the length l of the short storage line. The condition L≥c⋅T / 4 takes into account the fact that repeated electron pulses appear after a four-fold run of subnanosecond voltage pulses between the cutting discharge gap and the cathode of the accelerating tube. In this case, the minimum value of the time interval T between the generation of the first and repeated electron pulses of the accelerator is determined by the time during which the transient response of the object under study attenuates.

In the inventive accelerator, charging a short storage line is produced from the first forming line through the first high-resistance section of the second forming line after the breakdown of the first sharpening gap. Due to the short length and small capacity of the short line, its charging time does not exceed 1 ns (in the prototype accelerator, the charging time of the forming line is 10 ns). This allows you to increase the breakdown voltage of the second sharpening gap and thereby increase the voltage amplitude of the subnanosecond pulse coming into the transmission line.

The passage of a pulse along a transmission line with wave impedance increasing towards the accelerator tube is accompanied by a transformation of the subnanosecond voltage pulse with an increase in its amplitude, which leads to an increase in the voltage amplitude at the gap between the anode and cathode of the accelerator tube.

Exceeding the resistance of the gap between the anode and cathode relative to the resistance of the output section of the transmission line by at least two times also leads to an increase in the voltage amplitude at the gap between the anode and cathode of the accelerating tube.

The shear discharge gap serves to reduce the cut-off duration of the subnanosecond voltage pulse by closing the gap when it is broken at the top or front of the pulse. Increasing the amplitude of the subnanosecond voltage pulse coming into the transmission line creates the need to increase the length of the cutting discharge gap, which in the prototype accelerator will lead to pulse broadening due to an increase in the inductance of the spark breakdown channel. In the inventive accelerator, the presence of a high-resistance section of the second forming line allows decoupling of the low-resistance section from the first forming line and provides an effective fast cut of the subnanosecond pulse even with an increased inductance of the spark breakdown channel.

An increase in the amplitude of the charging voltage of the short storage line entails the need to increase the minimum gap between the conductors of the line to ensure sufficient electrical strength. The implementation of the surfaces of the inner and outer conductors of the short storage line in the zone of minimum clearance between the conductors is equidistant allows you to make a short line with equal electrical strength in the specified area and with an increased charging voltage to eliminate breakdowns between the conductors of the line.

The use of a ceramic conical insulator in the accelerator tube makes it possible to place the tube directly in the atmosphere of compressed gas. A hollow conical insulator has high mechanical strength, but the wall thickness is many times smaller than the radial size of the insulator in any section, which ensures the passage of a subnanosecond voltage pulse through the insulator with virtually no distortion.

The presence in the tube of a metal casing and current lead, which form a line with a wave impedance equal to the wave resistance of the output section of the transmission line, ensures that the high-voltage subnanosecond pulse travels up to the jam between the anode and cathode without distortion due to the absence of inhomogeneities that lead to pulse broadening and a decrease in its amplitude ,

Thus, in the present invention, all of these features are directed at increasing the amplitude of the voltage pulse in the gap between the anode and cathode of the accelerating tube, and therefore the indicated technical result is realized.

In FIG. 1. FIG. 2. FIG. 3 shows the design of the high-voltage block of the inventive subnanosecond accelerator, the output section of the transmission line with an accelerator tube attached to it, and a fragment of the shaper of the subnanosecond voltage pulses with forming and transmitting lines, as well as sharpening and cutting gaps, where the following elements are indicated:

1 - source of nanosecond high voltage pulses;

2 - sealed housing;

3 - the first forming line;

4 - the second forming line;

5, 6, 7 - sections of the transmission stepped line;

8 - accelerating tube;

9 - the first sharpening gap;

10 - second sharpening gap;

11 - retractable electrode;

12 - cutting clearance;

13, 14 - insulators;

15 - inductor;

16 - frameless inductor;

17 - reference insulators of the transmission line;

18 - high-resistance section of the second forming line;

19 - low-resistance section of the second forming line (short storage line);

20 - collet;

21 - current lead;

22 - the gap between the cathode and the anode;

23 - cathode;

24 - anode;

25 - accelerator tube body;

26 - ceramic insulator;

A - equidistant surface of the conductors of the short storage line.

In FIG. Figure 4 shows the waveform of the electron current outside the window of the accelerating tube.

The inventive subnanosecond accelerator includes a source of 1 nanosecond high-voltage pulses and a shaper of subnanosecond pulses, which contains a sealed housing 2. the first forming line 3. the second forming line 4. transmitting a stepped line divided into sections 5. 6 and 7, as well as an accelerator tube 8 Between lines 3 and 4, there is a first sharpening gap 9, between line 4 and section 5 of the transmission step line a second sharpening gap 10. The gap between the side surface of section 5 and the retractable electrode ohm 11 is a shear gap 12. Line 4 is mounted on insulators 13 and 14. The insulator 14 is simultaneously the frame of the inductor 15, which serves to suppress the pre-pulse when charging the stray capacitance of the electrodes forming the sharpening gap 9. Line 3 is electrically connected to the output of source 1 through frameless inductor 16. Sections 5. 6 and 7 of the transmitting stepped line are fixed in the shaper housing on the supporting insulators 17.

The principle of operation of the inventive accelerator is as follows. After the source 1 of the nanosecond high-voltage pulses is triggered, the first forming line 3 does not charge through the inductor 16 for a time of 5-10. After that, the first sharpening gap 9 breaks through and connects the line 3 to the second forming line 4 through its high-resistance section 18. During the time, less than 1 ns, the short storage line 19 (low-impedance portion of the second forming line) is charged. After charging, a second sharpening gap 10 breaks through and connects the short storage line 19 to the transmission line section 5. In this case, a quick discharge of the short line 19 to the transmission line section 5 occurs, as a result of which a voltage pulse of subnanosecond duration is generated in the transmission line. At the top of this pulse, a cutting gap 12 breaks through and a shortening of the cut of the subnanosecond pulse occurs with an additional decrease in the pulse duration. Further, this pulse propagates along sections 5, 6 and 7 of the transmission step line, and at each transition of one step to the next, with a higher wave impedance, the pulse transforms with increasing voltage amplitude. After passing through the transmission line, a subnanosecond pulse passes through collet 20 to the current lead 21 of the accelerator tube 8. In this case, at the gap 22 of the accelerator tube, the voltages of the incoming and reflected pulses are added, which with a relatively high resistance of the gap 22 leads to further) increase the voltage pulse across the gap and increase the maximum electron energy in the output beam. The voltage amplitude in the gap between the anode and cathode of the accelerating tube ultimately reaches a value close to the amplitude of the charging voltage of the first forming line 3, while the amplitude of the subnanosecond pulse coming into section 5 of the transmission line is approximately half that.

The inventive subnanosecond electron accelerator was manufactured and tested with the following parameters of some nodes:

- voltage source of nanosecond high-voltage pulses - 900 kV;

- wave impedance of the high-resistance section of the second line forming line - 90 Ohms;

- the length of the generators of the equidistant surfaces of the short storage line is not more than 0.015 m;

- wave impedance of the short storage line - 18 Ohms;

- length of the transmission line - 0.97 m;

- wave resistance of the output section of the transmission line - 60 Ohms;

- wave impedance of the casing and current input of the accelerating tube - 60 Ohms;

- the resistance of the gap between the anode and cathode of the accelerating tube is more than 200 Ohms.

The accelerator provides the generation of electron beams with a frequency of 30 pulses per minute with a maximum electron energy in the beam of at least 800 keV and a current amplitude of about 2 kA. In FIG. Figure 4 shows a typical waveform of the electron current outside the window of the accelerating tube. The horizontal scan is 0.5 n / division, the duration of the subnanosecond pulse at half maximum amplitude is 0.23 ns. The time interval T between the generation of the first and repeated electron pulses of the accelerator is T = 13 ns.

Claims (4)

1. A subnanosecond electron accelerator containing a source of nanosecond high-voltage pulses, a gas-filled shaper of subnanosecond voltage pulses and an accelerator tube, a shaper contains a coaxial line forming and transmitting, sharpening and cutting off the discharge gaps, the forming line is connected to a nanosecond high-voltage pulse source, which differs between and the transmission lines additionally introduced a second forming line with the formation of the second sharpening p a gap, and the second forming line consists of two sections, of which the first, high-resistance section, is located on the side of the first forming line, and the second, low-resistance, is a short accumulation line located on the side of the transmission line, both sharpening discharge gaps are formed by gaps between lines, the surface of the inner and outer conductors of the short storage line in the zone of the minimum gap between the conductors are made equidistant, the transmission line is made long, with growing wave resistance towards the accelerating tube, the accelerating tube containing a metal casing and a current lead, which form a line with a wave resistance equal to the wave resistance of the output section of the transmission line, and the current lead is fixed to the body by means of a ceramic hollow conical insulator, while the gap resistance between the anode and the cathode of the accelerating tube is at least twice the wave resistance of the output section of the transmission line. 2. The subnanosecond electron accelerator according to claim 1, characterized in that the first section of the second forming line has a wave resistance 3-10 times greater than the wave resistance of the second section of the second forming line. 3. The subnanosecond electron accelerator according to claim 1, characterized in that the lengths of the equidistant surfaces of the inner and outer conductors of the short storage line do not exceed 0.03 m. 4. The subnanosecond electron accelerator according to claim 1, characterized in that the length L of the transmission line meets the condition L≥с⋅Т / 4, where c is the speed of light in vacuum, T is the minimum value of the time interval between the generation of the first and repeated electron pulses of electronic accelerator pulses.

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