US2792524A - Gaseous arc high frequency generator - Google Patents

Description

May 14, 1957 E. D. MGARTHUR 2,792,524

GASEOUS ARC HIGH FREQUENCY GENERATOR Filed April 30. 1952 STAR TING VGLTAGE His Attorney.

United States Patent F Elmer D. McArthur, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application April 30, 1952, Serial No. 285,192 7 Claims. (Cl. 315-40) My invention relates to gaseous are high frequency generators of a type sometimes known as are constriction oscillators.

If an arc is forced to fiow through a constricting orifice, the are will quench or extinguish itself at a very rapid rate when the current density in the orifice reaches a certain limit. This limit is believed to correspond to a con dition of complete ionization of the gaseous medium in the orifice so that upon increase of applied voltage the electrons and ions are completely removed and the are discharged suddenly collapses. It is known that with proper conditions, namely relatively low gas pressure, high voltage between the arc electrodes, and orifice dimensions preferably less than the mean free path of the electrons within it, the rate of the collapse of the are discharge is very high, containing frequency components in the ultra-high frequency range. A train of high frequency damped oscillations in the circuit associated with the discharge electrodes is accordingly established following each discharge collapse. The rate of repetition of the discharge current buildup and collapse can be variously controlled, and various attempts have been made to utilize the high frequency energy periodically generated.

It is an object of my invention to provide an improved ultra-high frequency generator of the arc constriction type.

It is another object of my invention to provide an improved method of exciting an ultra-high frequency resonator.

It is a further object of my invention to provide a generator utilizing the high frequency components of the collapse of a self-extinguished are.

It is a still further object of my invention to provide a series of ultra-high frequency damped oscillation trains at a desired repetition rate.

In carrying out my invention an ultra high frequency output cavity resonator adapted to be excited by the collapse of a magnetic field established within the resonator is positioned near the path of a self-extinguished gaseous are. In a particular embodiment described herein an output resonator positioned between the cathode and anode of a gaseous discharge device has an opening extending through the resonator to both provide the arc constricting means and an efficient excitation gap for exciting the resonator. Each time the arc is quenched a train of oscillations is established in the output circuit, the rate of damping depending principally upon the load coupled to the resonator. The repetition rate of the oscillation trains is determined as desired by the circuit constants chosen for the charging circuit.

The features in the invention desired to be protected herein are pointed out in the appended claims. The invention itself, together with its further objects and advantages, may best be understood by reference to the following description, when considered in connection with the appended drawings in which Fig. 1 is a sectional view of an oscillator arrangement embodying my inven- Patented May 14, 1957 tion and Fig. 2 is a curve illustrating the charging and discharging rate.

Referring now to Fig. l, a discharge device 1 is illustrated having a mercury pool cathode 2 and an anode 3 spaced to provide a path for gaseous arc discharge between them. A hollow metallic cavity resonator 4 is positioned in the discharge path between the cathode 2 and anode 3. An opening 5 extending through the resonator provides a restricted passageway for the arc discharge, preferably defined by the inner surfaces of two coaxial cylindrical members 6 and 7. A generally toroidal shape is thus imparted to the resonator 4. the cylinders 6 and 7 comprising its inner periphery. As shown in the drawing, the axis of rotation of the resonator is thus coaxial with that of the arc constricting orifice or passage 5 through which all of the gaseous arc current of the discharge device must pass.

In the particular form shown in the drawing the upper and lower resonator cylinders 6 and 7 have their opposing ends connected to the inner peripheries of upper and lower annular members 8 and 9, respectively, which in turn are connected at their outer peripheries to the ends of an outer cylinder 10. To facilitate coupling to the electric discharge, the facing ends of the inner cylinders 6 and 7 are spaced to provide a narrow circular or annular excitation gap 11 along the inner periphery of the toroidal resonator. The gap, that is, the planes of either gap edge, may therefore be considered as transverse or normal to the flow of discharge current. A relatively simple means for exciting the resonator is thus provided in which an electric field may exist across the gap between the upper and lower members 6 and 7 while a circular magnet field concentric with the resonator axis is established within the resonator. The cross section of the resonator chamber may be circular, rectangular, or otherwise configured, so long as standing waves may be established at the desired output frequency.

The orifice or passageway 5 has a diameter which is preferably less than the mean free path of electrons in the gaseous discharge, this measurement being dependent upon the prevailing operating pressure of the ionizable gas employed. The length of passageway 5 is also preferably long with respect to the mean free path to facilitate arc quenching at readily attained current densities. While the cylinders 6 and 7 are separated by the gap 11 to provide a convenient excitation means, the gap is unnecessary to the arc restriction function and for the purposes of description of the operation of the invention, the orifice function may be considered as unaffected by the relatively narrow excitation gap 11. On the other hand upper cylinder 6, for example, can alone be dimensioned to define the critical or limiting orifice, and if desired, can be independent of the resonator and separate- 1y supported.

in order to complete the envelope of the discharge device 1, the cathode 2 and the anode 3 are respectively supportingly sealed from the resonator by insulating members. Thus the mercury pool cathode 2 is suitably contained in a cup-shaped metallic member 12, the edge of which is sealed to the lower end of a glass cylindrical envelope portion 13. The upper edge of the glass sealing ring 13 is sealed to the edge of a metallic sealing ring 14 whose other end is hermetically secured, as by welding, to the lower surface 9 of the resonator 4. The anode 3 is suitably supported from a resilient sealing ring 15 having its inner edge hermetically secured around the anode and its outer edge sealed to the upper end of a second glass sealing ring 16. The lower end of the glass ring is sealed to one edge of a metallic sealing ring 17 whose other edge is hermetically secured to the upper surface 8 of the resonator 4. It is obvious, of course, that other envelope arrangements for the discharge device 1 may be employed without departing from my invention.

As shown in Fig. 1, an output coupling means comprising a concentric transmission line section 18 is utilized to supply wave energy from the resonator to the desired load, such as, for example, an antenna. The outer conductor of the line section 18 is hermetically secured to the outer surface 10 of the resonator and the inner con ductor extends into the resonator with its end bent over to contact the inner surface of the resonator. A dielectric insulator, which may suitably comprise a glass bead 19, is sealed between the concentric conductors to close the envelope opening.

The anode 3 is preferably positioned close to the orifice defining means so that the electric field potential in the orifice can be readily increased upon increase of anode potential. As shown in Fig. l, the lower end of the anode is adjacent but spaced from the upper inner cylinder 6 of the resonator. The anode itself is preferably hollow to permit circulation of a fluid coolant near the active anode surfaces. Accordingly a cover plate 20 secured to the top of the anode covers a central bore and carries input and output tubes 21 and 22 which are suitably connected to a source of Water or other fluid coolant. Additional cooling means, of course, may be provided in the device 1 as required for particular duty cycles.

When mercury is used as the ionizable medium, a starting electrode 23 is preferably employed in order to establish the cathode spot. Accordingly the electrode 23 is positioned within the device 1 in contact with the surface of the mercury pool and is supported by a conductor rod 24 extending through the cathode cup 12 and insulatingly sealed therein. The starting circuit is entirely conventional and may suitably comprise a circuit for providing a high voltage impulse when the circuit is closed. If an ionizable gas, such as hydrogen or one of the inert gases, for example, are employed instead of mercury vapor, then no such starting means need be employed.

When a source of direct current voltage, such as a battery 25 is connected between the cathode and anode of the discharge device, a gaseous arc can be established with the aid of the starting electrode 23. A portion of the arc length is necessarily confined in the limited cross section area of the orifice defined by the opening in the resonator 4. While the orifice dimensions depend upon the desired maximum current density, the diameter of the orifice is preferably less and its length greater than the mean free length of the electron path in mercury vapor at the operating vapor pressure. So long as the applied voltage is higher than the arc drop, the current of the arc discharge, and hence the current density through the orifice, increases until a condition of complete ionization is obtained in the orifice. At this point when the voltage is further increased, further ionization cannot be produced and the electrons and positive ions are instead swept out of the space within the orifice, evacuating it to a very high degree. As a result the discharge is very quickly quenched. For example, I have found that with currents in the order of 100 amperes per square centimeter, the arc collapses at a rate in the order of amperes per second. It is this discharge rate, rather than the low frequency charging rate, which is utilized in exciting the resonator.

The voltage induced in reactive circuits with such a rapid change of current is very high. This rate of change is very effectively utilized in exciting the resonator as the resonator is both inductively coupled to the arc current in view of the circular magnetic field about the path are discharge and capacitively coupled to the space charge whose potential gradient changes very quickly upon current collapse. Upon collapse of the arc current, the low frequency magnetic field within the resonator is reduced to zero at a very rapid rate, and

the electric field along the arc increases at a corresponding rate to the low frequency peak or open circuit charging voltage. As the resonator is thus elfectively excited by the rapid collapse of the arc discharge and is otherwise isolated from the input circuit, the direct current energy of the input system is effectively and efficiently translated to ultra-high frequency waves. The duration of the excitation, or rate of damping of the high frequency output waves depends upon the figuire of merit or Q of the resonator, which in most cases will be in part determined by the resistance of the output circuit to which the resonator is coupled.

As will be noted in Fig. 1 an intermediate tap of the voltage source 25 is connected to the resonator 4 to pro vide a slightly positive voltage thereto with respect to the cathode. In that way the lower surface 9 of the resonator 4 within the discharge device serves as a holding anode to maintain the cathode spot after the discharge current through the orifice 1's extinguished. Series resistance 26 is preferably employed to limit this current to a small value. It is to be understood, however, that the voltage applied to the anode 3, is very large both with respect to the holding voltage and the normal voltage drop across the gaseous arc in order that the quenching process may be maintained. A conventional holding anode may be employed instead, if desired. As further shown, for purposes of convenience, so far as insulation of the output system is concerned, the resonator 4 is connected to ground, the cathode thus being negative with respect to ground.

The repetition rate of the train of damped oscillations depends upon the time required for the discharge to build up to its maximum value and the time for the stored energy in the input circuit to be dissipated so that a discharge may again be established Within the device 1. The time required for the discharge to inquenching point is dependent upon the time constant of the direct current charging circuit. To control this constant an inductor 27 and an adjustable resistor 28 are shown connected in circuit with the voltage between its positive terminal and The anode-cathode capacitance of the device 1 is normally too small to increase the charging time materially, but must be considered when very fast charging rates are desired. The charging time may accordingly be varied from a maximum value when the resistance of the resistor 28 is set at zero ohm to a minimum value determined by the amount of resistance it is desired to insert. If very short charging times are desired, the inductance may be reduced to that inherent in the circuit conductors. Since some energy is stored in the inductance and capacitance of the charging circuit, the time for this energy to be dissipated must be included in determining the repetition rate.

Referring to Fig. 2 the variation of discharge current with time is illustrated. As may be seen upon application of operating voltages, the arc current builds up to a maximum value corresponding to complete ionization within the arc restricting opening. Upon collapse of the arc current the energy stored in the charging circuit is the charging process again begins. It is obvious, of course, that the time constant of the charging circuit may be variously arranged according to well-known principles to produce the desired repetition rate, which is the restriction oscillator frequency.

Each time the discharge are collapses, the output resonator 4 is excited at its resonant frequency, thus producing a train of ultra-high frequency oscillations which are damped at a rate dependent upon the resonator loading. As desired, the output oscillations, whose frequency is many times the repetition rate of the discharge arc, may be damped out in a fraction of the repetition period, or they may persist until the next occurrence of the arc collapse, when the resonator is again excited, although not necessarily in phase with the previous oscillatory train. Thus, it may be seen that the fre quency and damping rate of the output circuit energy are substantially independent of the arc constriction repetition rate established by the charging circuit.

While the invention has been described by reference to a particular embodiment thereof, it will be understood that numerous modifications may be made by those skilled in the art without departing from the invention and I therefore aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure Patent of the United States is.

1. In combination, a gaseous discharge device comprising an envelope, a cathode electrode and an anode electrode having facing surfaces spaced from each other within said envelope, means interposed between said cathode and anode including a hollow resonator aper tured to provide a passageway therethrough and an orifice defining member for restricting the cross section area of a portion of the path of a gaseous arc discharge between said electrodes, and means coupled between said electrodes for applying a potential between said electrodes in excess of that required for complete ionization of the medium within said orifice whereby the discharge cur rent is extinguished and the resonator is excited to provide an output at a frequency determined by said resby Letters onator.

2. In combination, a gaseous discharge device comprising an envelope, a cathode electrode and an anode electrode having facing surfaces spaced from each other within said envelope, means interposed between said cathode and anode including a hollow resonator aper tured to provide a passageway therethrough and an orifice defining member for restricting the cross section area of a portion of the path of a gaseous arc discharge between said electrodes, and a direct current charging circuit coupled to said electrodes for applying a potential between said electrodes in excess of that required for complete ionization of the medium within said orifice whereby the discharge current is extinguished and the resonator is excited to provide an output at a frequency determined by said resonator, said charging circuit and said discharge path having a time constant establishing the repetition rate of said resonator excitation.

3. In combination, a gaseous discharge device comprising an envelope containing an ionizable medium, a cathode electrode and an anode electrode having facing surfaces spaced from each other within said envelope, a cavity resonator having a resonant frequency having at least a portion thereof positioned between said cathode and said anode, said resonator being apertured to provide a passageway therethrough for constricting the cross section area of a portion of the path of a gaseous are discharge between said electrodes, and means coupled to said electrodes for applying a potential between said electrodes in excess of that required for complete ionization of the medium within said orifice whereby the discharge current is extinguished and the resonator is excited to provide an output at said resonant frequency.

4. In combination, a gaseous discharge device comprising a cathode electrode, an anode electrode spaced from said cathode electrode to provide a discharge path therebetween, a cavity resonator of a generally toroidal shape tuned to a resonant frequency positioned between said anode and said cathode having a central opening therethrough defining a constricted orifice for a portion of the discharge path between said electrodes, means coupled to said electrode for applying a potential between said electrodes in excess of that required for complete ionization of a gaseous arc discharge within said orifice whereby said discharge is quenched and said resonator is excited to provide an output at said frequency, and means for coupling said resonator to an output load circuit.

5. in combination, a gaseous discharge device comprising a cathode, an anode spaced from said cathode to provide a discharge path therebetween, a cavity resonator of a generally toroidal shape tuned to a resonant frequency and positioned between said anode and said cathode with the central opening therethrough defining a constricted orifice for a portion of the discharge path between said electrodes anode and cathode, an input circuit means including a source of direct current voltage coupled to said anode and cathode for applying a potential between said anode and cathode in excess of that required for complete ionization of a gaseous are discharge within said orifice whereby said discharge is quenched and said resonator is excited at said resonant frequency by the collapsing electric and magnetic fields of the quenched arc discharge. said input circuit together with said discharge path having a time constant establishing the repetition rate of the quenching of the arc discharge, and means for coupling said resonator to an output load circuit.

6. In combination, a gaseous discharge device comprising a cathode, an anode spaced from said cathode to provide a discharge path therebetween, a cavity resonator of a generally toroidal shape having a resonant frequency positioned between said anode and said cathode having a central excitation opening therethrough defining a constricted orifice for a portion of the discharge path between said electrodes, means coupled to said cathode and resonator for applying a potential between said cathode and said resonator to establish a gaseous arc therebetwecn, and means for exciting said resonator comprising means coupled between said anode and cathode for applying a potential between said anode and said cathode in excess of that required for complete ionization of a gaseous arc discharge within said orifice where by said discharge is suddenly quenched to excite said resonator and provide an output at said frequency.

7. In combination. a gaseous discharge device comprising a cathode, an anode spaced [rom said cathode to provide a discharge path tbcrcbetwecn. a cavity re sonator of a generally toroidal shape positioned between said anode and said cathode having a central excitation opening therethrough defining a constricted orifice for a portion of the discharge path between said electrodes, means coupled to said cathode and resonator [or applying a potential between said cathode and said resonator to establish a gaseous arc thercbctwccn. means for exciting said resonator comprising means coupled between said anode and cathode for applying a potential between said anode and said cathode in excess of that required for complete ionization of a gaseous arc discharge within said orifice whereby said discharge is suddenly quenched at a repetition rate difiering from the resonant frequency of said cavity resonator, and means for coupling said resonator to an output load circuit.

References Cited in the file of this patent UNITED STATES PATENTS

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