US3735197A

US3735197A - Rectifier

Info

Publication number: US3735197A
Application number: US00171588A
Authority: US
Inventors: V Pakin
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-08-13
Filing date: 1971-08-13
Publication date: 1973-05-22
Anticipated expiration: 1990-05-22

Abstract

A rectifier which consists of two coaxial cylindrical electrodes separated by a working gap filled with a low pressure gas and which is controlled by a magnetic field having an axial component; said rectifier being provided with at least one control winding disposed on the external surface, with respect to the working gap, of any of the electrodes and fed with a pulse current, the duration of the current pulses being such that the control magnetic field is removed by the instant the working current pulse switched by the rectifier terminates.

Description

United States Patent [191 Pakin RECTIFIER [76] Inventor: Vadiln Nik'olaevich Pakin, Zhemchuzhnaya ulitsa 24, kv. 35, Novosibirsk, U.S.S.R.

[22] Filed: Aug. 13, 1971 21 Appl. No.: 171,588

[52] US. Cl. ..3l5/348, 313/157, 313/161 [51] Int. Cl ..H0lj 17/14 [58] Field ofSearch ..313/157, 161;

[56] References Cited UNITED STATES PATENTS l/l97l 10/1968 9/1971 Hofmann et a1 ..313/16l Wasa et al. ...3l5/344 X Hofmann ..3l3/l57 X May 22,1973

Primary Examiner-Roy Lake Assistant Examiner-James B. Mullins Attorney-Eric H. Waters et a1.

[57] ABSTRACT A rectifier which consists of two coaxial cylindrical electrodes separated by a working gap filled with a low pressure gas and which is controlled by a magnetic field having an axial component; said rectifier being provided with at least one control winding disposed on the external surface, with respect to the working gap, of any of the electrodes and fed with a pulse current, the duration of the current pulses being such that the control magnetic field is removed by the instant the working current pulse switched by the rectifier terminates.

2 Claims, 3 Drawing Figures Patented May 22, 1973 3,735,197

2 Sheets-Sheet 1 ZJZA 0 r1 Z (3 Z 2 FIE. J

Patented May 22, 1973 2 Sheets-Sheet 2 N GE RECTIFIER This invention relates to gas-discharge devices and, more particularly, to rectifiers designed for use in acceleration and plasma techniques and in electric engineering.

Known in the art is a rectifier consisting of two coaxial cylindrical electrodes separated by a working gap which is filled with a low-pressure gas and which is controlled by a permanent magnetic field having an axial component.

The rectifying properties of this device are due to the fact that a permanent magnetic field having an axial component is produced near one of the electrodes, the cathode, by a ferrite block; this magnetic field quickly collapses towards the other electrode, the anode, at which it is practically equal to zero. The gap between the anode and the cathode and the gas pressure are selected so that the length of the mean electron path in the gas in the absence of a control magnetic field should be close to the size of the gap, owing to which the rectifier is capable of withstanding high voltages of any polarity. The presence of an axial component in the control magnetic field results in the fact that at the forward polarity of the electrodes the electron path in the gas near the cathode sharply increases, each electron produces several ionizing events, and an avalanche builds up through which the rectified current passes. At the reverse polarity ofthe electrodes, the electrons leaving the anode are quickly accelerated and, when reaching the region of the magnetic field, bend and increase their path in the gas very little, so that the rectifier withstands a high reverse voltage.

A disadvantage of this rectifier is that it is a diode uncontrollable in time. Another disadvantage is that a ferrite block of a definite shape producing a magnetic field of a definite intensity is rather difficult to manufacture, while the presence of a permanent magnetic field in the anode-to-cathode gap increases the deionization time of the rectifier after the passage of the working current pulse, which imposes considerable limitations on the rate of rise of the reverse voltage at the rectifier. This rectifier is further disadvantageous in that the working current is applied from one end of the electrodes, which fact, when the working current pulse has a large duration and high intensity, may cause the plasma to be ejected from the working zone by the magnetic pressure of the working current to the free end so that a pinch effect and quick destruction of the electrodes may result.

An object of the present invention is to obviate the above mentioned disadvantages by providing a rectifier which is controlled by a pulse-type magnetic field, has a small deionization time, is simple in construction, easy to manufacture and reliable in operation.

With this object in view, the rectifier according to the invention is provided with at least one control winding disposed on the external surface, with respect to the working gap of any of the electrodes and fed with pulse current, the duration of the current pulses being such that the control magnetic field is removed the instant the working current pulse switched by the rectifier terminates.

The control winding should be preferably made bifilar, the winding pitch being larger than the working gap between the electrodes.

It is also preferable that the control winding should be made sectional.

To enable the control magnetic field to penetrate into the working gap and effectively to remove the control field the instant the working current pulse terminates, the electrodes should be preferably made from a material having a sufficiently high resistivity and low permeability for the given thickness of the electrode walls and the duration of the control magnetic field pulse.

To prevent the plasma from being ejected to the ends of the electrodes and increase the operational reliability of the rectifier, the working current should be preferably applied symmetrically to both ends of the electrodes.

For symmetrical application of the current to the electrode ends, disk flanges should be preferably attached at the electrode ends to which the working current should be symmetrically fed along the circumference.

For reliable protection of the insulators against the plasma ejected from the discharge gap and for reduction of the size of the insulators, the current should be preferably applied with the help of coaxial cylinders of a diameter much smaller than the diameter of the working electrodes, said cylinders being attached at the electrode ends.

The invention will be better understood from the following description of its specific embodiment when read in connection with the accompanying drawings, in which:

FIG. 1 is a sectional view of a rectifier with disk flanges at the electrode ends, according to the invention;

FIG. 2 is a sectional view of a rectifier with coaxial cylindrical leads, according to the invention;

FIG. 3 is a time graph illustrating the operation of the rectifier, according to the invention.

The rectifier shown in FIG. 1 comprises an outer electrode 1 and an inner electrode 2 designed as coaxial stainless steel cylinders separated by a gap 3 and terminating in

shaped disk flanges

4 and 5 which are isolated from each other by shaped ring insulators 6 and used so as to symmetrically apply the working current to the

electrodes

1 and 2 of the rectifier simultaneously from both ends.

A helical groove provided on the outer electrode 1 accommodates a bifilar control winding 7 made from an insulated copper strap. The pitch of the control winding 7 is made several times (e.g. four times) larger than the size of the gap 3. The control winding 7 is sectionalized. The rectifier is also provided with pipe connections 8 and holes 9 for feeding the gas to, and evacuating it from, the working gap 3.

Apart from these components the rectifier shown in FIG. 2 comprises coaxial cylinders 10 and 11 which are attached on the

disk flanges

4 and 5 and which have diameters much smaller than those of the

electrodes

1 and 2.

The time graph in FIG. 3 shows a curve 12 and a the control current pulse terminates and the instant t =t to the moment at which the working current pulse terminates or, in other words, drops to zero.

The rectifier operates as follows.

At the instant i= a control current pulse is applied to the control winding 7. The magnetic field produced by the control current penetrates through the wall of the electrode 1 and at the instant I, which is determined by the voltage at which the rectifier reaches a critical value a breakdown occurs in the rectifier due to a sharp increase in the electron path in the gas. I

At current densities up to about 3A/cm the rectifier operates with a glow discharge completely controlled by the magnetic field, the voltage drop across the discharge being equal to or greater than 350 V. As the current density increases the glow discharge passes to an arc discharge with a voltage drop of about 100-50 V. Since the arc discharge is not controlled by an external magnetic field, this field may be removed after the arc is struck and the discharge is extinguished the first time the working current passes through zero. As at the instant t the magnetic field is removed, the electron path in the gas is small and close to the size of the working gap 3 and the rectifier safely withstands a high voltage of any polarity. If, however, by the instant 1 corresponding to the zero working current the magnetic field is not removed, the electron path remains large, the deionization and ion recombination time is great and the rectifier passes current in the reverse direction, forward direction and so on, until the control magnetic field is removed and the arc is naturally extinguished the first time the working current passes through zero after the removal of the control field.

The advantage of the present invention is that the rectifier is controlled in time, practically irrespective of the electrode polarity and, therefore, can be used for switching single pulses of any polarity or successive trains of pulses of any polarity. Another advantage of the rectifier described herein is that its magnetic control means is easy to manufacture as being in the form of a conventional winding made from conductors. The shape and connection of the winding are immaterial, though a bifilar winding with a pitch several times larger than the size of the working gap is preferable.

The rectifier has a small deionization and ion recombination time as the control field is absent at the instant the working current pulse terminates.

Owing to the fact that current is symmetrically applied from both ends of itselectrodes the rectifier has a reliable balanced construction with leads having small spurious inductance and low resistance.

The use of a sectional winding enables the rectifier to operate with an arc discharge in the gas even at low working currents without current interruption.

What is claimed is:

1. A rectifier comprising an insulator; a first cylindrical electrode; a second cylindrical electrode disposed coaxially with respect to said first electrode and separated therefrom by said insulator; there being provided a working gap between said electrodes, a low-pressure gas filling said gap; said electrodes having external surfaces and opposite ends; a control winding to produce a pulsed control magnetic field having an axial component with said working gap, said control winding being disposed on the external surface, with respect to said working gap, of at least one of said electrodes; and means for the axial, symmetrical supply of current to be switched simultaneously to both ends of both electrodes, said means being in the form of disk flanges secured on both ends of said electrodes.

2. A rectifier as claimed in claim 1 comprising coaxial cylinders and wherein said disk flanges are coupled with the co-axial cylinders which have a substantially small diameter than said electrodes.