SU1660071A1 - Method of control over gas-discharge commutation instrument with cold cathode - Google Patents

Description

The invention relates to the control of gas-discharge devices for devices pulse technology of medium and high power. The purpose of the invention is to increase the resistance of the device to current overload. The goal is achieved by applying a voltage pulse to the first control electrode with an amplitude sufficient to ignite the discharge between the cold cathode and the first control electrode. A control pulse is supplied to the second control electrode, and the control pulse is fed to the first third of the control pulse decay. The length of the leading edge of the control pulse should not exceed half the duration of the decline of the starting pulse, and the duration of the control pulse is equal to the required pulse duration of the anode current. 2 Il.

the control electrode of the starting voltage pulse with an amplitude sufficient to ignite the discharge between the cold cathode and the first control electrode, and the control pulse to the second control electrode, the control pulse is fed to the first third of the start pulse decay, the leading edge of the control pulse not exceeding half the duration of the drop the starting pulse and the duration

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control pulse - equal to the required pulse duration of the anode current.

FIG. 1 is a diagram explaining the method for controlling a cold cathode gas-discharge switching device; in fig. 2 - diagrams of voltages on the electrodes of the device and anode current.

The anode of the device 1 from the source 2 of high voltage through the load 3 serves a positive voltage of 1020 kV. Source 2 is usually a capacitive energy storage device with a charge device. Device 1 contains, in addition to the anode and the cold cathode, the first and second control electrodes, and inside the device shell is hydrogen at low pressure (1-10 Pa) ..

The first control electrode from the pulse generator 4 serves a starting voltage pulse with an amplitude sufficient for igniting the discharge between the cold cathode and the first control electrode. FIG. 2, the starting pulse is shown in the upper voltage profile of the first control electrode ϋι. After that, a starting superdense glow discharge is installed in the device with a maintenance voltage of about 300 V at a current of one to ten amperes. Depending on the design of the cold cathode assembly - the first control electrode in the device can be installed various types of self-glow discharge. If this node is a reversed gas magnetron, then a glow discharge in the crossed electric and magnetic fields is installed in the device. If the first control electrode is made in the form of a flat grid, and the cathode is in the form of a cylinder with an open end, then a polokathod form of a super-dense glow discharge is installed in the device. It is possible to use in the device other variants of the cathode assembly, which provide for the facilitated establishment of an independent superdense glow discharge. The starting pulse may have a shape close to a rectangular one, but the use of trapezoidal and exponential pulses is permissible. The duration of the starting pulse and the starting discharge is 1-5 μs. To reduce the statistical instability of the establishment of the start discharge to the first control electrode, it is advisable to apply a constant positive bias voltage through the ballast resistance 5 from source 6 with a voltage of 400-500 V to establish a preparatory discharge with a current of about 10 mA.

The start discharge is designed to create a plasma in the cathode assembly, which further provides the required current in the anode circuit of device 1. It is necessary that the current of the starting discharge (pulse) does not exceed the critical value for this device. Otherwise, the starting discharge causes the ignition of an independent glow discharge between the anode and the cathode and the transition of the device to the usual thyratron mode, in which the current in the anode circuit is limited almost exclusively by the load resistance. The critical current decreases with increasing gas pressure and the permeability of the electrodes shielding the anode from the cathode assembly of the device. The magnitude of the critical current is determined experimentally, it is approximately an order of magnitude higher than the working value of the current of the starting discharge.

In the first third of the decline of the starting pulse serves a control pulse from a pulse generator 7 to the second control electrode, and the duration of the leading edge of the control pulse does not exceed half the duration of the decline of the starting pulse. FIG. 2, the average plot represents the course of the voltage change on the second control electrode g. The duration of the control pulse is approximately equal to the required pulse duration of the anode current. The lower plot in FIG. 2 shows the change in anode current 1a. The amplitude of the control voltage pulse is 0.5-2 kV. By varying the amplitude of the control pulse, the amplitude of the anodic current pulse is adjusted.

In device 1, the anode node — the second control electrode is similar to the anode-grid node of the tacitron with a heated cathode, i.e. the second control electrode also has a low permeability and performs the functions of the unlocking and locking grid electrode. To improve the locking properties of the second control electrode, a negative bias can be applied to it, as in tacitrons, but this is not necessary.

The second control electrode is located away from the cold cathode, for example, shifted axially relative to the cathode assembly, made in the form of an inverted magnetron. This leads to the fact that when a control pulse is applied to the second control electrode, a difficult glow discharge develops with a maintenance voltage of more than 1 kV, which can be called semi-independent. The current of this discharge (the current manager

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pulse) is not more than 20% of the current discharge start. A difficult glow discharge occurs when the amplitude of the control pulse exceeds the minimum critical value for this device. Therefore, even if a positive bias is applied to the first control electrode and a preparatory discharge is maintained, when the control pulse is applied with an amplitude less than 10 times the minimum critical value, the current to the anode does not occur, while the second control electrode is able to maintain a difficult glow discharge with a high voltage and after the end of the 15 start pulse.

If the amplitude of the control pulse exceeds the maximum critical value, an independent super-dense glow discharge with an increased concentration of charged particles develops on the second control electrode. This leads to the transition of the entire instrument to the usual tacitron and even thyratron mode, in which the current in the anode circuit is determined 25 only by the load resistance. The critical maximum amplitude of the control pulse is 2.5–5 kV and decreases with increasing pressure. The minimum and maximum critical amplitudes of the control electrode are determined experimentally.

When implementing the proposed control method, a device with a cold cathode combines the properties of an electrovacuum lamp, operating in the mode of saturation of the cathode current, and a gas-discharge device. It can not only control the beginning and end of the passage of the anode current, but also the amplitude of the latter. 40 For this purpose, the device uses difficult forms of low-pressure glow discharge. Due to the fact that the amplitude of the anode current depends only on the current of the starting discharge on the first control electrode 45 and the amplitude of the control im-. pulse on the second control electrode, increases the resistance of the device to current. Vym overload. In fact, with a sharp change in the load resistance, for example, its sparking, breakdown, the current in the anode circuit remains almost unchanged. This prevents destruction due to the spark and arc discharges of the load itself (most importantly, if there is a load of any generator vacuum tube), in addition, an overload of the high anode voltage source and a pause in the operation of the radio pulse device are excluded.

Regulation of the anode current using the second control electrode is due to the following, due to the fact that the discharge to this electrode is difficult, and the electrode itself is a fine-structured grid, i.e. grid with holes of small diameter (<1 mm), the thickness of the space charge layer in the holes of the grid is an essential part of the diameter of the hole. Therefore, the anode field practically does not penetrate into the space between the anode and the second control electrode and does not affect the physical processes in this space. The anode current is formed by those electrons that did not hit the second control electrode and slipped through the holes in it. If you increase the diameter of the holes in the control electrode or reduce the thickness of the space charge layer by increasing the current to the electrode above the critical value, the anode field penetrates through the second control electrode and an independent discharge is established between the cathode and the anode, while the positive effect is not achieved.

A semi-independent discharge to the second control electrode is maintained only at the trailing edge of the starting pulse, when in the gap between the cold cathode the first control electrode is set to the mode of excess conductivity, i.e. when the current in the circuit of the first control electrode is less than the ion current to the cathode. If, apply control pulses to the second electrode at the top of the starting pulse. then, for transferring the discharge to this electrode, such a high amplitude of the control pulse is required, at which an independent superdense glow discharge is established on the anode. Due to the rapid deionization of the plasma of the start discharge (its decay occurs faster than exponentially), it is necessary to immediately apply a control pulse to the second control electrode, and the greater the delay in the supply of the control pulse, the smaller the amplitude of the anode current. From an energetic point of view, the supply of a control pulse to the first third of the decline of the starting pulse is acceptable. Proceeding from this, it is necessary that the duration of the leading edge of the control pulse does not exceed half the duration of the decline of the starting pulse.

In the worst case, when

control pulse is applied at the end

the first third of the decline of the starting pulse, and

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the duration of the front of the control pulse is equal to half the duration of the fall, the amplitude of the anode current is less than 10% of the amplitude of the current of the starting pulse.

Claims (1)

FORMULA AND A C A R E T U N A METHOD FOR MANAGING GAS DISCHARGE switching device with a cold cathode, which consists in applying to the first control electrode of the starting voltage pulse with an amplitude sufficient to ignite the discharge between the cathode and the first control electrode and supply control pulse to the second control electrode, characterized in that, in order to increase the resistance of the device to current overloads, the control 5, a pulse is formed of positive polarity and is fed to the first third of the decline of the starting pulse, and the length of the leading edge of the control pulse does not exceed half the duration of the 10-step spa and the starting pulse, and the duration of the control pulse is set equal to the required anode current pulse duration. 15 Phi g.1 1660071