US2405069A - Pulse generating system - Google Patents

Description

July 30, 1946. TONKS 2,405,069

PULSE GENERATING SYSTEM Filed Feb. 23, 1942 2 Sheets-Sheet l MAGNETRON CIRCUIT CURRENT SOURCE TWEWM 2 To DIRECT CURRENT SOURCE T0 PRIMARY TIMING SYSTEM Inventbr:

Lewi Ton ks,

M I I by His Attorney July 30, 1946. TONKS 2,405,069

PULSE GENERATING SYSTEM Filed Feb. 23, 1942 2 Sheets$heet 2 SURCE F fi 1 ULTRA VIOLET fillr 64 LIGHT z MAGNETRON T H, CIRCUIT TO PRIHARY Tmme SYSTEM T Ihventor:

Lewi TOfi' k8.

His Attorney.

Patented July 30, 1946 UNITED STATES PULSE GENERATING SYSTEM Lewi Tonks, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application February 23, 1942, Serial No. 432,009

1 12 Claims.

My invention relates to pulse generating systems, particularly to such systems employing spark gaps as switching mechanism, and the obiect of the invention is to provide improved systems of this character which produce pulses at a relatively high rate and operate at a high charging voltage, and which supply a large value of instantaneous power with a high order of timing precision of sparking of the switch means proper.

In pulse generating systems for supplying instantaneous high power at a rapid rate which have been proposed and used heretofore in an extended range of applications, difliculties have been encountered in obtaining pulses of the required power and repetition rate and at the same time with the desired timing accuracy.

In accordance with my present invention these disadvantages are overcome by the provision of a pulse generating apparatus in which a charged capacitive storage element is connected to a load by a spark gap arrangement or assembly providing two spark gaps in series, and in which a predetermined initial apportionment of the voltages across the two gaps is changed or disturbed at the desired triggering instant thereby to cause breakdown of the spark gaps and to initiate the discharge, through the load, of a pulse from the storage element.

In one embodiment of my invention an alternating current source is arranged to charge the storage element at each cycle through a rectifier, and during the interval at each cycle when the voltage of the alternating current source is reversed the spark gap switch means is triggered thereby initiating the discharge of the storage element through the load. The capacitive storage element is preferably of such character as to produce a discharge pulse of substantially rectangular wave form and for this purpose may comprise a section of a suitable transmission line.

In this embodiment of the invention the initial apportionment of the voltages is disturbed or changed to initiate the discharge by reducing to a substantial degree, preferably close to zero, the

potential initially impressed on one of the conductive electrode members which provide the two spark gaps. The reducing of the potential is accomplished by pulsing positive the control electrode of a space discharge device normally in cutoil. condition connected to the spark gap electrode member, the conduction periods of the space discharge device being synchronized, through timing means which may comprise a multivibrator and a primary or initial timing device connected thereto with the frequency of the alternating current source which charges the storage element. Instead of the alternating current source a direct current source may be employed to charge the capacitive storage element and in this case the timing means above mentioned may be utilized to control the positive pulsing of the space discharge device control electrode.

In another embodiment of the invention the l predetermined initial apportionment of the voltages across the two gaps is changed or disturbed not by reducing close to zero the potential initially impressed on one of the electrode members but by impressing a voltage pulse thereon,

preferably from an inductance arranged to be charged periodically from a space discharge device having a pulse timing means associated therewith which may include a multivibrator.

The novel features which are considered to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings wherein Fig. 1 is a diagrammatic representation of a pulse generating system, powered from an alternating current source, in which my invention has been embodied; Fig. 2 is a detailed illustration of a spark gap switching assembly in accordance with my invention; Fig. 3 illustrates a voltage pulse produced in accordance with my invention; Figs. 4 and 4a illustrate systems similar to that of Fig. 1 but powered from a direct current source: and Fig. 5 illustrates a modification of the embodiments shown in Figs. 1 and 4.

In Fig. 1 the numeral l designates a ca acitive element adapted to be charged periodically from an alternating current source through a transformer 2, a rectifier 3 and an inductance 4 shunted by a resistor 5, and to be discharged during the reverse period of the current source through a load element such as a resistor 6, across which 0 may be connected a desired output or utilization tion. For illustrative purposes the utilization circuit is shown herein as including a magnetron upon the anode-cathode circuit of which the pulses from resistor 6 are impressed and which is connected to an antenna to transmit therefrom rapidly repeated short-duration pulses of intense microwave radiation utilized, for example, in the detection of distant objects.

The capacitive storage element I is constituted preferably by a section of transmission line of such character that the discharge therefrom each connected to a common lead 9 and with the 3 other sides of adjacent condensers connected by inductances III. The operation of the element I in forming a square pulse will be understood if this element is looked upon as an approximation to a uniform transmission line having uniformly.

distributed inductance and capacity of total amounts L and C respectively. It is well known that if such a line, open at thegfar end, is charged to a potential V and then discharged through a resistance R=JL7U current value and duration will To discharge the storage element I through the load 6, in accordance with the present invention a switching means is provided comprising a plurality of spark gap members or conductive electrode members in the present embodiment three in number, II, I 2, and I3, providing two spark gaps I4 and I6 in series with the storage element I and the load 6. The constructional features of the switching means comprising spark gap members II to I3 will be explained in detail hereinafter in connection with Fig. 2. The voltages initially impressed across the spark gaps I4 and I5 are preferably equally apportioned as by resistors I6 and I! connected respectively between member II connected to the capacitor element I and the intermediate member I2, and between the intermediate member I2 and member I3 connected to the load 6. A capacitor I8 for balancing the distributed capacity of member I2 is shown connected between members I and I2 but is not always necessary.

The numeral I9 designates a space discharge device, normally in cutoff condition, the anode 20 of which is connected to the intermediate spark gap member I2, and the cathode 2| of which is connected to ground through a bypass condenser 22. To cause space discharge device I9 to become periodically conducting, thereby to reduce periodically close to zero the potential of spark gap member I2, a means is provided to impress a positive pulse upon the control electrode 23 of the latter space discharge device. Any suitable means may be utilized for this purpose. Preferably, however, an inductance 24 shunted by a damping resistor 25 and included in the anode circuit of a space discharge device 26, normally in cutoif condition, is provided which is connected through a condenser 21 to the control electrode 23 of discharge device I9 to supply the positive pulse thereto. A relatively large leak resistance 28 is connected between the control electrode 23 and cathode 2| of space discharge device I9 to suppress to a sufficient extent a positive reversal of the potential impressed thereon.

To initiate the supplying of the pulse from inductance 24 to the control electrode 23 of device I9 and to maintain synchronization of thi pulse and the frequency of the above-mentioned alternating current source, a space discharge device 23 of the gas filled type arranged to operate in a usual sweep circuit 30, or saw tooth wave generatlng circuit, is preferably employed in connection with a multivibrator 3 I. Potentials are supplied to the control electrode 32 of device 29 through a transformer 33 to initiate periodic operation of the discharge device 29 and thereby to cause negative potentials in synchronism with the frequency of the alternating current source to be impressed upon an input electrode of the multivibrator.

By adjusting the cathode bias of gas filled device 29 the pulse phase relative to the voltage from the alternating current source may be r 8- ulated over nearly a full degrees.

The pulse rate of the multivibrator is thus synchronized, by connection to circuit 30, with the predetermined frequency, and the output circuit of the multivibrator is in turn connected through a. capacitor 34 and resistor 35 to the control electrode 36 of space discharge device 26 to impress short pulses at this frequency upon the latter electrode.

Danger of overloading of the anode circuit of device 26 which is likely to occur unless the current-passing interval, or interval during which current is traversing inductance 24, is maintained at a small fraction of the total time period of each pulse is avoided, since current-passing intervals of the required short duration in device 26 are obtained corresponding to the short pulses readily obtainable from the multivibrator and impressed upon the control electrode 36.

Any conventional means other than as above described for maintaining synchronization of the pulse from inductance 24 and the frequency of the alternating current source may be employed.

In the operation of the system illustrated in Fig. 1, the transformer 2 charges the capacitive element or transmission line section I once per cycle through rectifier 3 and inductance 4. After charging is complete and during the interval when the voltage of transformer 2 is reversed, the switching means constituted by 'the spark gap members or spark electrode members II to I3 is triggered, thus applying to the load 6 one-half of the voltage of transmission line I in the form of a wave approximating a square wave.

A suitable air blast directed through the spark gaps I4 and I6 removes the ionization products resulting from the discharge thereacross and reestablishes control or reopening of the circuit at the spark gaps after each sparking period.

Referring to Fig. 2, in the spark gap switching means illustrated in detail therein, the spark gap or electrode members II, I2, and I3 are mounted in spaced relation on a frame 31. One of the electrode members, II, upon which the highest potential is impressed, is supported on the frame by a terminal member 38 which may be rigidly fixed thereto. The intermediate electrode member I2 is supported by a terminal member 39 fastened to a block or sliding member 40 of suitable form movable laterally with respect to the frame to adjust the position of member I2 with respect to member I I. The third electrode member I 3 is supported by a terminal member 4| movable laterally in the frame to adjust the position of member I3 with respect to member I2. The main bodies 42, 43 and 44 of the spark gap members II to I3 are formed of a suitable electrically conducting material to which tungsten can be soldered. The members 42 to 44 are roughly elliptical in cross sectional outline, tapering at an angle of approximately five degrees from near the axis of the spark gaps toward the opposite ends in order to reduce the tendency to formation of sparks not in the line of the axis of the gaps l4 and II.

In the high potential member 42 and the intermediate member 48 are formed air ducts which, when the bodies are of solid metal, may comprise holes 45 and 46 extending from the center to one end of the bodies, and holes 4'! and 48 at right angles to the holes 46 and 46 and extending from the inner ends thereof to an outer face of the bodies. To conduct an air blast through the air ducts, the terminal members 88 and 36 are preferably tubular and are in connection respectively with the holes 45 and 46.

Electrodes 46 and 68 having preferably the form of rounded rods connected respectively interiorly of members II and I 2, extend respectively through holes 41 and 48 and project therefrom a short distance, electrode 48 being directed toward member l2 and electrode 58 toward member I 8.

On the faces of members l2 and il toward which electrodes 49 and 68 respectively extend are soldered or otherwise secured tungsten plates or bosses and 62. A suitable means (not shown) is provided for producing a blast of air or other suitable gas through the air ducts and in the spark gaps l4 and I5. Instead of being formed from a solid block as shown in Fig. 2, the main spark gap bodies 42 to 44 may be spun or pressed from sheet material, and to prevent undesired or outlaw sparks from their surfaces because of rusting, the surfaces may be plated with gold or silver, for example.

In a practical application of the invention constructed and operated as described in connection with Figs. 1 and 2, .the charging circuit was powered from a 490 cycle alternating current source.

The charging voltage from transformer 2 was 68 kilovolts, 34 kilovolts being applied to the load 6. Substantially instantaneous power of 4.6 megawatts was delivered from the transmission line I, which had a capacitance of 2300 micromicrofarads and an impedance of 233 ohms. The curve of the discharge pulse applied to the non-inductive load constituted by the resistance Shad the form, approximating a rectangular wave. shown in Fig. 3, the pulse lasting approximately only 1.1 microsecond with a precision of sparking proper of a fraction of second. The space discharge device I8, included in the gap trigger circuit, was of the type RK65; space discharge device 26, included in the pulse amplifier circuit, of the GL813 type; and space discharge device 28, included in the master pulse circuit, of the 884 type. The r. m. s. value of voltage impressed on the control electrode 32 .of the latter device, type 884, from the transformer 33 ranged from 0.2 volt to 2.5 volts. The spark gaps l4 and I5 were approximately five-eighths inch in length at the 68 kilovolts across the gaps, and an air pressure of from one to two pounds per square inch (gauge) in the supply line sufliced to remove ionization products and to reestablish control after the occurrence of the spark.

In the above described practical application of the pulse generating system illustrated in Fig. l, the charging voltage was limited as above mentioned to a value of 68 kilovolts. It is to be understood that such limiting of the voltage was not caused by the spark gap switching arrangement provided in accordance with my present invention but primarily by the characteristics of the high voltage transformer 2 and secondarily by the danger of spark-over to frame elements or other low voltage elements with increase of charging voltage. It will be understood that by the employing of a suitable higher voltage transformer or like means connected to the storage element I and by proper precautions in design to preclude the occurrence of spark-over, still higher instantaneous power atan increased charging voltage may be obtained from the system herein described in connection with Fig. 1.

Referring to Fig. 4, in the embodiment of my invention illustrated therein a direct current source instead of an alternating current source is employed as a power supply. The switching means comprising spark gap or electrode members H tol3 of Fig. 4 may be identical with that described in connection with Fig. 1, the triggering being accomplished, as in Fig. 1, by reducing to a substantial degree the potential of the intermediate member l2 through a space discharge device whose control electrode is pulsed positive by an inductance 24 in the anode circuit of a second space discharge device 26 the energizing of the control electrode 36 of which is provided by the multivibrator 3|. The energizing pulse from the multivibrator can in turn be released by a negative pulse impressed, from any suitable or usual primary or initial timing system (not shown), upon the terminal 53. As a result the power pulse is generated at a time subsequent to the primary pulse by an interval which is of the order of one microsecond, but for successive pulses this interval is the same within less than 10- seconds. Other known means may be employed for energizing the discharge device l9 at time intervals which may be varied,'in a usual or known manner, through wide limits.

As in Fig. 1, in Fig. 4 a capacitive storage element 54 is provided adapted to be charged from the power source, and to be discharged periodically, by triggering the spark gap switching means, through a load such as resistance 6. The capacitive storage element 54 may be the same as that designated by the numeral I in Fig. 1, or, instead, a capacitive element 55 in series with a transmission line 56 having a plurality of inductance capacity sections, at least six in number, may be employed. The direct current source is adapted to be connected by a switch 51 through an inductance 58 and a rectifier 58 to the capacitive storage element 54, and through a switch 51a interconnected with switch 51 to the space discharge device 26 to supply anode current thereto.

The interconnected switch means including switches 51 and 51a is so arranged that in initiating the supply of current to the storage element 54 and to the space discharge device 2'6, the switch 51 closes first and the switch 51a closes a few milliseconds later. The closing of switch 51 initiates an oscillation involving the inductance 58 and capacity 55, the period of this oscillation being determined by the respective inductance and capacitance values of these elements. During the first half period of the oscillation the current flow is in one direction only, rising to a maximum and falling to zero. Meanwhile the charge on the capacity 55 is rising continuously until at the instant of zero current the capacity is charged to twice the direct current voltage of the source, and from this instant on the capacity retains the charge because the rectifier 59 prevents reversal of the current and a continuation of the oscillation. At a, subsequent time, as assured by the later closing of switch 51a, the gap fires, the capacity 55 discharges through the gap and the recharging automatically takes place. As long as the recharging time, represented by the half period of the oscillation, is less than the pulse interval, the above described action continues automatically. This type of charging may be called half sine wave charging, referring to the shape of the capacity voltage wave during the charging time.

Another type of charging than the half sine wave type above described may be employed in the method of powering from a direct current source shown in Fig. 4. In this other type of charging, the series connection comprising the inductance 58 and the capacity 55 has a natural period whose half value is greater instead of less than the pulse interval. In this latter type of charging, when the switch 51 is closed transient conditions obtain in the circuit for a short time, but a steady state is reached in which the ourrent through inductance 58 never falls to zero and consists of a constant current upon whichare superimposed humps consisting of portions (less than half) of sine waves. Corresponding thereto the voltage wave on the condenser 55 approximates to a sawtooth with a linear rise and an abrupt fall, the linear rise being modified in accordance with the variation of the charging current. the smaller are the variations in current and the more nearly linear is the rise of voltage across the capacity 55. With this method the rectifier 59 is not necessary and, as shown in Fig. 4a, is absent from the system which is otherwise as shown in Fig. 4. This latter type of charging may be called straight line charging.

In a practical application of the invention constructed essentially as described in connection with Fig. 4 except that, instead of the storage element 54 of Fig. 4, the storage element I of Fig. 1 was employed, the charging voltage applied to the storage element was approximately 65 kilovolts and the pulse voltage applied to the load resistor 6 approximately 32 kilovolts. In this system a pulse rate up to a rate of the order of 3000 per second was obtained with an accuracy of firing relative to the multivibrator pulse, and hence to the timing signal from any master or primary signal system connected to terminal 53 to control the multivibrator, of better than 10- second.

Referring to Fig. 5 the modification of my invention illustrated therein mayv comprise a capacitive storage element I adapted to be charged from a suitable source of power, for example a direct current. source, and to be discharged through a load resistor 6, connected to a magnetron I, for example, as in Figs. 1 and 4, by a switching means having spark gap members II, I2 and I3 providing spark gaps 50 and 5| corresponding to the spark gaps I4 and I5 of the embodiment of my invention illustrated in Figs. 1

and 4. So far as the switching operation is concerned, the load resistor 6 may be grounded at either end, the nature of the output circuit connected thereto determining the proper grounding point. Gap 6| is made longer than gap 60, preferably substantially twice the length thereof, and across one of the gaps 60 is connected a resistor 62.

As in the embodiment shown in Figs. 1 and 4, in the modification illustrated in Fig. 5 the spark gap switching means is triggered by changing or disturbing the apportionment of the voltages applied across the spark gaps.

In Fig. 5, however, instead of reducing the potential on the intermediate spark gap member I2 to a substantial degree or close to zero, a pulse The larger the value of the inductance 58 of relatively high voltage is impressed upon the member I2 to accomplish the triggering action. For thi purpose preferably at least three space discharge devices 63, corresponding to device 28 of Figs. 1 and 4, arranged in parallel and of the GL813 type for example, are adapted to provide the required energization of an inductance 84, corresponding to inductance 24 of Figs. 1 and 4. The anode circuit of the devices 63 is supplied from the direct current source, and the energizing of the control electrodes of the paralleled devices 63 is produced by a suitable timing means which preferably includes a multivibrator and a primary or initial timing system associated therewith as in Fig. 4.

In the operation of the pulse generating system shown in Fig. 5 the initiation of the spark discharge from the capacitive storage element I is accomplished by suddenly exceeding the breakdown voltage across the gaps 60 and 6| by means of the self-induction pulse from the inductance 64 in the anode circuit of the space discharge devices 63. Reliability of firing across the gap 60 and 6| is increased, if desired, by irradiating the gaps continuously from a source of ultraviolet light, represented conventionally by the rectangle 65, such as a quartz mercury lamp or a spark in air. during a phase interva1 which includes at least the firing instant. An air blast across the gaps is necessary to clear the space of all ions before a succeeding firing instant.

My invention has been described herein in particular embodiments for purposes of illustration. It is to be understood, however. that the invention is susceptible of various changes and modifications and that by the appended claims I intend to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim a new and desire to secure by Letters Patent of the United States is:

1. In combination, a capacitive device adapted to store electric energy in electrostatic condition and to produce a discharge voltage pulse approximating rectangular wave form, an electrical power source, means to connect said source to said capacitive device to store a charge therein, a load, three spark gap members providing two spark gaps in serie with said capacitive device and said load, and means to initiate discharge of said device through said load including an electron discharge device having an electrode connected to at least one of said spark gap members abruptly to change the potential of one of said members and thereby to change the initial apportionment of voltage across said gaps.

2. In apparatu for generating rapidly repeated electric pulses, a capacitive element adapted to store electric energy in electrostatic condition and to produce power pulses, an electrical power source, means to connect said source to said capacitive device to store a succession of charges therein, a load, three spark gap members providing two spark gap in series with said capacitive device and said load, and means to initiate the discharge in succession from said capacitive element of said pulses through said load, said lastnamed means including an electron discharge device having an electrode connected to the intermediate of said spark gap members and arranged by its discharge abruptly to change the potential of said intermediate member thereby to change the initial apportionment of voltage acros said gaps.

3. A pulse generating apparatus comprising a capacitive storage element, a load device, means for periodically charging said torage element, at least three sparking electrodes spaced apart to provide at least two spark gaps in series between said storage element and said load device, and means for initiating periodic discharge of said storage element across aid gaps and through said load device comprising an electron discharge device electrically connected between two of said sparking electrode across one of said gaps and timing means for periodically rendering said discharge device conductive.

4. In a system for discharging a charged device, three conductive elements providing two spark gaps in series with said device, the conductive element having one extreme of potential and the intermediate conductive element each having a duct formed therein and each having an electrod mounted within and projecting from the corree sponding duct, each of said electrodes being conductively connected to the corresponding conductive element, said ducts being adapted to be traversed by a gas to remove ionization products from said spark gaps subsequent to said spark discharge.

5. In a system for discharging a charged device, a plurality of conductive elements providing two spark gaps in series with said device, one of said elements at each gap having a duct formed therein and an electrode of refractory material conductively connected thereto mounted within aid duct and projecting therefrom into the gap, the other of said element at each gap having attached thereto a member formed of conductive refractory material to receive the spark discharge from the electrode of the corresponding other element, said ducts being adapted to be traversed by a gas to remove ionization products from said gaps.

6. In combination, a capacitive device, an alternating current source, means including a rectliler to connect said source to said device to store a charge therein, a load, three spark gap member providing t'wo spark gaps in series with said device and said load, a space discharge device having its anode connected to the intermediate one of said spark gap members, means connected to the control grid of said space discharge device to cause,

said space discharge device to become conducting periodically thereby to reduce substantially the potential of said intermediate member, and means operatively associated with said current source and said last-named means to maintain synchronization of the conduction periods of said space discharge device and the frequency of said source.

7. In combination, a capacitive device, a source 01' direct current, a load, means comprising an inductance and a rectifier to connect said source to said capacitive device to store a charge therein, three spark gap members providing two spark gaps in series with said capacitive device and said load, a space discharge device having its anode connected to the intermediate one of said spark gap members, and timing means connected to the control grid oi said space discharge device to cause said space discharge device to become conductive periodically thereby to reduce substantially the potential of said intermediate member.

8. In combination, a capacitive device, a source of direct current, a load, means comprising an inductance to connect said source to said capacitive device to store a charge therein, three spark gap members providing two gap in series with said capacitive device and said load, and means to change the potential of the intermediate one of said members from the initial potential thereof, said last-named means comprising a space discharge device having its anode connected to said intermediate member and timing means connected to the control grid of said space discharge device.

9. In apparatus for generating rapidly repeated electric pulses, a capacitive element adapted to store electric ener y, an inductive element, a direct current power source, means including said inductive element for connecting said source to said capacitive element to store a succession of charges therein, sai capacitive element and said inductive element being included in an oscillatory charging circuit having a, half period of oscillation longer than the time interval between said pulses, a load, and means for applying the stored electric energy to said load from said capacitive element at substantially'equal time intervals.

10. In apparatus for generating electric pulses at a given rate, a capacitive element for storing electric energy, an inductive element, a direct current source, a rectifier, an oscillatory charging circuit including in series said rectifier and said capacitive and inductive elements, said elements having respectively such values 01 capacitance and inductance that the half period of oscillation of said charging circuit is somewhat less than the time interval between pulses at said desired rate, a load, a plurality of spark gap members providing two spark gaps in series with said capacitive element and said load, and means to initiate said pulses from said capacitive element through said load comprising timing means operatively associated with one of said gap members to change periodically at said given rate the voltage impressed across said gaps from the initial voltage apportionment between said gaps.

11. In apparatus for generating rapidly repeated electric pulses, a capacitive element adapted to store electric energy, a direct current power source, mean to connect said source to said capacitive device to store a succession of charges therein, the time period of charging being equal to or less than the interval between pulses, a load, three spark gap members providing two spark gaps connected in series with said capacitive device and said load, and mean including an electron discharge device for producing an abrupt change of potential of one of said spark gap members thereby suddenly to change the potential distribution across said gap and initiate a pulse discharge thereacross from said capacitive element through said load, and means independent of said direct current power source for periodically initiating a discharge of said electron discharge device.

12. In combination, a capacitive device, a current source, a load, means to connect said source to said capacitive device to store a, charge therein, and means to initiate discharge of said device through said load comprising three spark gap member providing two spark gaps in series with said capacitive devic and said load, an inductance adapted to impress a voltage pulse upon the intermediate one of said spark gap members, at least one space discharge device having said second-named inductance connected in the anodecathode circuit thereof, and timing means connected to the control grid of said space discharge device to initiate periodically the flow of energizing current through said second-named inductance and to cut off said current flow suddenly a short time interval after each initiation thereof.

LEWI TONKS.

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