RU2705207C2 - Electron accelerator based on ferroelectric plasma cathode - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to accelerator equipment, plasma physics, radiation physics, and can be used in atomic physics, medicine, chemistry, solid state physics, where it is important to obtain beams of charged particles with required energy parameters and controlled duration. Electron accelerator based on ferroelectric plasma cathode (CEP cathode) comprises electrically connected energy accumulator, pulse shaper in form of single forming line (OPL) and discharge unit, diode with BOT cathode, separate transmitting line providing transfer of voltage pulse from energy accumulator to cathode for creation of plasma on its surface. Discharge assembly is a single uncontrolled discharger; uncontrolled discharger is connected to the electric circuit between the OPL and the diode through the matching resistance, and provides switching of the OFL to the diode gap with the BOT cathode; energy storage unit is represented by a pair of pulse voltage generators interconnected by fiber-optic communication lines through a synchronization unit, which provides switching of these generators with different delay times, wherein one of the accumulator generators is electrically connected to the OPL of the pulse former through the capacitor, and the second generator is connected to the separate transmitting line; OPL is electrically connected to the DC voltage generator through a matching resistor.

EFFECT: technical result is enabling possibility to vary energy of beam electrons and duration of beam generation (duration of electron flow current pulse).

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Description

The invention relates to the field of accelerator technology, plasma physics, radiation physics and can be used in atomic physics, medicine, chemistry, solid state physics, where it is important to obtain charged particle beams with the necessary energy parameters and adjustable duration.

A device is known (G. Rosenman and D Shur. Elektron emission from ferroelectrics // J of Appl. Phys. V. 88 N 11 2000 pp 6109-6161 1]), designed to produce electron beams - an electron accelerator based on ferroelectric plasma (BEP ) cathode. The accelerator includes a source of high-voltage pulses - a pulse generator, a high-voltage transformer, a transmission line, a BOT cathode and an anode forming a diode gap.

The disadvantage of such an accelerator is that

1. Electron emission from the surface of the BOT cathode begins with a certain delay after applying a voltage pulse to the diode gap, and this leads to the fact that the duration of the current pulse of the electron beam turns out to be rigidly attached to the accelerating voltage pulse from the source of high voltage pulses.

2. Characteristically, it is not possible to vary widely the magnitude of the accelerating voltage applied to the diode gap of the accelerator, due to the specifics of the pulse generator used.

Closest to the claimed device is an electron accelerator using a BOT cathode (G.A. Month of Physics – Uspekhi, 2008, vol. 178, No. 1, pp. 85-108). It consists of a charge capacitor electrically connected together, a spark gap (forming an energy storage device); pulse transformer; accumulative glycerin line in the form of a single forming line (OFL), sharpening a spark gap and a cutting spark gap (discharge node) (forming a pulse shaper together); voltage dividers; cathode power cable (a separate cable (transmission line) that provides the transmission of a voltage pulse from the energy storage to the cathode to create a plasma on its surface); cathode and anode, forming a diode with a BOT - cathode.

When the spark gap of the energy storage device is triggered, the capacitor is discharged to the winding of the pulse transformer, while the storage glycerin line is charged. When the sharpening spark gap is triggered, a voltage pulse appears on the diode. By changing the length of the gap of the cutting spark gap, you can change the pulse duration. When the spark gap of the energy storage device is triggered, the voltage necessary for plasma formation on the cathode surface, which comes earlier than the high-voltage pulse, providing acceleration of electrons, is supplied through the cable to the discharge circuit of the cathode.

The main disadvantages of this system are:

1. The inability to vary over a wide range the magnitude of the accelerating voltage applied to the diode gap of the accelerator, which makes it impossible to vary the energy of the electron beam.

2. The inability to change the duration of the electron stream (the duration of the current pulse of the electron stream).

The technical problem is to obtain electron beams of various durations in a wide energy range.

The technical result consists in providing the ability to vary the energy of the electron beam and the duration of the beam (the duration of the current pulse of the electron beam).

The technical result is achieved by the fact that, in contrast to the known electron accelerator based on a ferroelectric plasma cathode (BOT cathode), containing an energy storage device electrically connected with each other, a pulse shaper in the form of a single forming line (OFL) and a discharge unit, a diode with a BOT cathode , a separate transmission line that provides the transfer of a voltage pulse from the energy storage to the cathode to create a plasma on its surface, in the proposed accelerator, the discharge unit is a single n controlled arrester; an uncontrolled arrester is connected to the electric circuit between the OFL and the diode through a matching resistor and provides switching of the PLL on the diode gap of the diode with the SEC cathode; the energy storage device is represented by a pair of pulsed voltage generators connected to each other by fiber-optic communication lines through a synchronization unit, which provides switching of these generators with different delay times, moreover, one of the storage generators is electrically connected to the OFL of the pulse shaper through the capacitance, and the second generator is connected to a separate transmitter lines; OFL is electrically connected to a DC voltage generator through a resistor.

The proposed circuit, due to the time difference between the ignition discharge on the surface of the SEC cathode and accelerating pulses, and also due to the presence of two different power sources of the electron accelerator circuit, allows changing the duration of the current pulse. A current pulse can exist only under the simultaneous action of both ignition and acceleration pulses, which makes it possible to vary the duration of the electron flux within the range 0≤t of the _beam ≤t _{acceleration pulse} under the condition t _{acceleration pulse} ≤t _{ignition pulse}

That is, technically, the approach is implemented due to a fundamentally new system of power supply and accelerator control. For this purpose, instead of the energy storage device in the form of a capacitor and an arrester, an energy storage device is used, which is a pair of pulse voltage generators connected in a certain way, which allows organizing two different power supply circuits in the inventive accelerator. One of them performs a preliminary breakdown along the ceramic surface of the cathode in order to create a plasma on this surface, which is a source of electrons. Another is designed to form an electrical impulse of the required amplitude and duration of the accelerating electron beam.

In the claimed design, the synchronization unit through a fiber optic communication line (fiber) is connected to the first pulse voltage generator having a lower amplitude voltage value. From another output, the synchronization unit is connected to another generator with a large amplitude voltage. The latter is connected through a capacitance to a single forming line (OFL). A DC voltage generator is galvanically connected to the same end of the OFL by a decoupling resistor. The resistance of the terminating resistor in total with the resistance of the diode should be equal to the wave resistance of the OFL ρ = R _c + R _d , where R _c is the nominal load resistance - terminating resistor, R _d is the resistance of the diode.

Using OFL, consistent with the resistance of the terminating resistor and the resistance of the diode, allows you to generate pulses of high accelerating voltage on the diode.

Varying the magnitude of the voltage generated by the pulse voltage generator with a large amplitude voltage, and adjusting the uncontrolled arrester, you can change the magnitude of the accelerating voltage, which affects the magnitude of the accelerating voltage and uniquely characterizes the energy of the electron beam.

The pulse duration of the OFL loaded on the terminating resistor is equal to the double range of the electromagnetic wave along the line. By changing the length of the PL, it is possible to change the duration of the electron beam.

This system has the ability to control the pulse duration, which is realized due to the ability to change the delay time between the voltage pulse creating a plasma on the cathode surface and the accelerating voltage pulse. This is done by changing the delay time between switching a pair of pulse voltage generators using a synchronization unit.

All the signs together work on the claimed technical result and allow you to generate accelerating voltage pulses with the ability to adjust the electron energy of the beam and the duration of the generation of the beam.

In FIG. presents a circuit diagram of the inventive accelerator, where

1 - pulse generator with a lower amplitude value of the voltage;

2 - a separate transmission line;

3 - DC voltage generator;

4 - pulse generator with a large amplitude voltage value;

5 - block synchronization;

6 - decoupling resistor;

7 - capacity;

8 - OFL;

9 - uncontrolled arrester;

10 - SES-cathode;

11 - terminating resistor;

12 - electron beam.

The device operates as follows

The DC voltage generator U _g 3 through the decoupling resistor 6 charges the OFL and puts the uncontrolled arrester into a pre-breakdown state when the condition U _g <U _{pr is} fulfilled, where U _pr is the breakdown voltage of an uncontrolled arrester 9. Pulse voltage generators were used as pulse generators [1] .

In the initial position, the pulse voltage generators 1 and 4 are in a charged state. At the initial moment of time, from the synchronization unit 5 via a fiber-optic communication line (fiber), the pulse generator is first switched with a lower amplitude voltage value. The high-voltage voltage pulse generated by him with a duration of τ amplitude U ₁ is transmitted through a transmission line 2 to the SEC cathode 10, as a result, a surface breakdown occurs on the ceramic surface of the cathode, creating a plasma that is the source of electrons for the accelerator. With a certain delay Δτ, a pulse generator with a large amplitude voltage value U _{2 is} launched from the synchronization unit through the optical channel. The pulse generated by him through the capacitance 7 is supplied to the OFL 8. It is important to note that the pulse from this generator exceeds the voltage of the constant voltage generator U ₂ > U _CR > U _g , which leads to a confident breakdown of the uncontrolled spark gap 9. Further, the high voltage pulse U ₁ , from the OFL through the matching resistor 11 enters the accelerating gap of the diode of the electron accelerator, which leads to the formation of the electron stream 12. The resistance of the matching resistor in total with the resistance of the diode should equal the wave resistance OFF ρ = R _c + R _d , where R _c is the nominal load resistance - terminating resistor, R _d is the diode resistance.

The electron accelerator is made as follows.

OFL is made of a piece of coaxial cable KVI - 100.

As a pulse voltage generator with a lower amplitude value of voltage 1, a generator was used that has the following characteristics:

- response delay: ± 2 ns;

- pulse duration voltage: 10 kV;

- front of the generated pulse: up to 5 ns;

- voltage pulse delay: 500 ns.

The generator with a large amplitude value of voltage 4 is the second pulse voltage generator, the characteristics of which are as follows:

- output voltage: from 60 to 80 kV;

- front of the generated pulse: up to 5 ns

- response delay ± 2 ns.

To improve the stability of operation of the uncontrolled spark gap 9, the single forming line 8 is in a charged state. The charge of this line is carried out by a source of constant voltage 3-25 kV through a decoupling resistor 6-100 kOhm. To eliminate the direct current coupling of the forming line and the second pulse voltage generator 4, a capacitor 7 K15-10 3300 pF × 31.5 kV was used. The resistor 6 limits the current of the generator 4 and eliminates its influence on the generated output pulse. Upon reaching the voltage at which the breakdown of the spark gap occurs, a voltage pulse of negative polarity is formed on the accelerating gap. Verification showed the possibility of controlling the duration in the range from 5 ns to 1 μs and the energy of the beam electrons in the range from 2 keV to 40 keV.

Thus, due to the proposed improvements in the power supply circuit of the electron accelerator and accelerator control compared to the prototype, it is possible to control such parameters as the electron energy of the beam and the duration of beam generation (duration of the current pulse of the electron beam).

Claims (1)

An electron accelerator based on a ferroelectric plasma cathode (BOT cathode), containing an energy storage device electrically connected with each other, a pulse shaper in the form of a single forming line (OFL) and a discharge unit, a diode with a BEP cathode, a separate transmission line that provides the transmission of a voltage pulse from energy storage to the cathode to create a plasma on its surface, characterized in that the discharge unit is a single uncontrolled discharger; an uncontrolled arrester is connected to the electric circuit between the AFL and the diode with the SEC cathode through a matching resistance and provides switching of the AFL to the diode gap of the diode; the energy storage device is represented by a pair of pulsed voltage generators connected to each other by fiber-optic communication lines through a synchronization unit, which provides switching of these generators with different delay times, moreover, one of the storage generators is electrically connected to the OFL of the pulse shaper through the capacitance, and the second generator is connected to a separate transmitter lines; OFL is electrically connected to a DC voltage generator through a terminating resistor.

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