US2145727A - High voltage discharge apparatus - Google Patents

Description

`Fan. 31, 1939. w L LLOYD, JR

HIGH VOLTAGE DISCHARGE APPARATUS Filed Dec. 28, 1937 Pfg. 2.

Inventor: Wi|| L Lloyd JV., b iwf/176.1%@ y His Attorney.

llllllllll//lllll I Patented e 3i, i939 HHGH VOLTAGE DISCGE APPARATUS Will L. Lloyd, Jr., Pittsfield, Mass., assigner to General Electric Company, a corporation of New York Application December 28, 1937, Serial No. 182,084

Claims.

The present invention relates to improvements in high voltage discharge apparatus. While not limited thereto, it is especially applicable to apparatus for generating high velocity X-rays or 5 cathode rays. In this latter connection, it is primarily useful with multisection discharge tubes of the general type described in Brasch and Lange Patent #2,043,733, granted June 6, 1936.

In accordance with the Brasch and Lange patent referred to, the discharge envelope is made up of a plurality of sequentially arranged capacitive elements, each comprising a pair of annular platelike conducting members spaced by interposed insulating members. The conducting members are of such area as to provide appreciable capacitance between adjacent members and function to govern the potential distribution along the length of the envelope. My present invention provides improved means for energizing a tube of this type.

It has been previously proposed to energize high voltage apparatus by the use of a multistage impulse circuit or generator comprising a plurality of groups of condensers, resistances, and

spark gaps, these elements being so arranged that the condensers can be charged in parallel through the resistances and discharged in series upon the breakdown of the spark gaps. However, such equipment, as conventionally employed, presents the disadvantage that both the impulse generator and its connections to the discharge tube are difilcult to insulate and render shock-proof.

It is an object of this invention to provide means for so combining a discharge device and impulse generator as greatly to simplify the insulation of the complete equipment.

In a preferred embodiment this is accomplished by utilizing the capacitive elements of a discharge tube of the multisection type hereinbefore referred to as the capacitances of an impulse circuit associated with the tube. By this means the discharge tube is, in effect, made its own impulse generator.

The features of novelty which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the drawing in which Fig. 1 represents diagrammatically one embodiment of the invention as applied to a cathode ray tube and Fig. 2 shows 5% diagrammatically the use ci' the invention in (Cl. Z50-146) connection with an X-ray tube having a pool type cathode.

Referring particularly to Fig. 1, there is shown an enclosing casing having insulating side walls IU and upper and lower end walls il and l2 of 5 conducting material. Arranged centrally within the casing and coterminous therewith there is provided a multisection discharge tube having an incandescible cathode i3, which is only schematically indicated. As shown, the tube envelope 10 comprises a plurality of annular platelike conducting members id which are insulatingly spaced by means of interposed insulating members i5. It will be understood, of course, that the arrangement illustrated is entirely schematic 15 and that many practical features of the discharge tube are not shown. The actual construction of the tube may suitably follow the arrangement described by Brasch and Lange in their aforesaid Patent #2,043,733. The tube as a 20 Whole may be immersed in a dielectric medium having a dielectric strength greater than that of air. Such medium may comprise, for example, oil or high pressure gas or vapor provided as a filling for the casing I0. 25

The conducting members llt are arranged transversely to the axis of the discharge envelope and in the arrangement shown extend partially inside and partially outside the envelope. They are preferably of such area as to provide appre- 30 ciable capacitance between adjacent members so that the envelope comprises a series of capacitive elements sequentially arranged. It is an important function of such elements to govern the potential distribution along the axis of the discharge path so as to prevent the occurrence of creepage discharges.

In order to establish a high potential between the end plates il and I2 of the casing il) and thereby to energize the discharge tube, I provide a multistage impulse circuit or generator. This comprises high resistances I8 connecting alternate ones of the conducting members Ill, spark gaps i9 connected between certain adjacent conducting members and capacitances 2G. 45

In accordance with my invention, the capacitances indicated by dotted line condensers 20 are provided by the inherent capacity coupling existing between adjacent conducting members lli. This is readily feasible if the members ld are of relatively great area and if the dielectric medium existing between them has a high specic inductive capacity. The spark gaps i9 may be enclosed in separate discharge vessels within the casing ill or may be positioned Outside the casing' and connected to the appropriate conducting members Il by conductors leading thereto. The resistances I8 may also be arranged either within or without the casing as circumstances may require.

In the use of the device, energy is supplied to the impulse generator from a direct current source 23 which may have a potential only a small fraction of that required to eiect the desired operation of the discharge tube. With the connections illustrated, this source will be effective to charge the various capacitances in parallel through the resistances I8. After a critical voltage has been attained by the capacitive elements, breakdown of at least one of the spark gaps I3 will occur. Such breakdown will change the voltage distribution of the system in such a way as immediately to cause a breakdown of the remain-v ing spark gaps. Since this operation is equivalent to short circuiting the gaps, it will result in placing the condensers 20 in series across the discharge tube so that the sum of their voltages will be impressed between the cathode I3 and the cooperating electrode structure at the other end of the tube. Assuming the cathode to be in an electron emitting condition, an impulse discharge will occur which will result in the production of high velocity electrons. 'Ihese may be utilized in the production of X-rays or for any other desired purpose. (With an apparatus such as that shown in Fig. l, the electrons may be projected through a window 25 provided at the lower end of the tube and may be utilized as cathode rays.) The transient effects of the impulse discharge are prevented from adversely affecting the power source 23 by the use of choke coils 26 connected in series therewith.

In addition to the capacitances 20 already referred to as existing between certain of the conducting members, there exist similar capacitances 20 between the remaining members. However, these play little part in the operation of the impulse circuit since they are shunted by the spark gaps I9 during the discharge period. Their effect, if any, is a helpful one in that the current which they discharge across the spark gaps tends to reduce the voltage drop in such gaps.

The apparatus which I have described in the foregoing has the advantage of combining the discharge tube and impulse generator in a single unit which can be completely enclosed in a common casing. For that reason it is relatively easy to render the whole assembly shock-proof and safe for hospital or other use. Furthermore, the inherent capacitance of the discharge tube is now assigned a useful function rather than being, as formerly, an objectionable load on the energizing system.

In Fig. 2 I have illustrated a modified use of .the invention as applied in connection with an X-ray tube having a pool type cathode and X-ray producing target 3 I. As shown, this target is arranged opposite a glass window 32 adapted to transmit X-rays without substantial obstruction. The discharge envelope is constituted, as in the case previously described, of conducting members 34 alternated with insulating portions 33 and is enclosed in a casing 35. The various conducting members are connected by resistances 36, spark gaps 31, and their inherent capacitances 38 in the same manner as specified in connection with Fig. 1.

If all of the conducting members are arranged to extend into the interior of the envelope (as in Fig. 1) it is clear that during the discharge period, the electron stream will be forced to traverse pairs oi.' adjacent members which are at the same potential. (This is due to the fact that certain members are substantially directly connected by the breakdown of the spark gaps.) Since this condition has a tendency to cause defocusing of the electron stream. it is advantageous in some cases to arrange the conducting members in the manner illustrated so that only alternate members extend into the discharge space. In cases where charging of the inner surface of the envelope wall is not a problem, it may even be desirable to have all the conducting members arranged outside the envelope.

In application Serial No. 147,287, filed June 9, 1937, in the name of K. H. Kingdon, it is explained that an X-ray producing discharge may be developed in a pool type discharge device by the use of an energy source which is adapted to provide current to the device at a rate in excess of that at which electrons ca n be supplied by the cathode during the initial discharge period. Since an impulse generator constitutes an ideal example of an energy source of the type speciiied it will be seen that the combination described in the foregoing paragraphs is a highly advantageous one.

While I have described my invention by reference to particular structures it will be understood that many modifications may be made by those skilled in the art without departure from the invention. I, therefore, aim in the appended claims to cover all such modifications as fall within the true spirit and scope 0f the foregoing disclosure. Wherever reference is made in the claims to an impulse circuit or generator, I wish it to be understood that I refer to one of the known arrangements of resistances, capacitances and spark gaps which are conventionally designated by that name.

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

1. A discharge apparatus comprising an elongated discharge tube including a series of sequentially arranged capacitive elements forming constituent parts of the tube envelope, discharge electrodes associated with the tube, and a multistage impulse circuit for impressing a high potential between said electrodes, each stage of said circuit comprising at least one of said capacitive elements as a principal capacitance thereof.

2. Discharge apparatus comprising a discharge envelope constituted o-f a plurality of alternately arranged conductive and non-conductive members, the conductive members being of suiiicient area so that appreciable capacitance exists between adjacent members, t Scharge electrodes associated with the envelope and a multistage impulse circuit 'for impressing a high potential between said electrodes, each stage of said circuit including the capacitance existing between a pair of adjacent conductive members as the principal capacitance thereof.

3. Discharge apparatus comprising a discharge envelope including a series of vsequentially arranged capacitive elements as constituent parts thereof, discharge electrodes associated with the envelope, a multistage impulse circuit including conventionally connected resistances, capacitances and spark gaps for impressing a high potential -between said electrodes, the capacitance 0f each stage of the circuit being provided by one of the capacitive elements of the discharge tube,

and a common casing enclosing said discharge 'Il envelope and the operative elements of said Iimpulse circuit.

4. Discharge apparatus including an elongated being disposed transversely to the axis of the envelope so as to govern the potential distribution therealong, cooperating discharge electrodes within the envelope, a multistage impulse circuit consisting of the capacitances provided between adjacent ones of said conducting members in combination with resistances and spark gaps properly connected to said members, and connections between the terminals of the impulse v:zzircuit and the said cooperating discharge elecro es.

5. X-ray apparatus comprising an X-ray tube including an anode and a cathode, a plurality of platelike conducting members insulatingly spaced along the discharge path between the anode and cathode for controlling the potential distribution therebetween, each of said members having an opening therein to permit the passage of a discharge therethrough, and a multistage impulse circuit for causing an X-ray producing discharge between the anode and cathode, said circuit consisting of the capacitances provided between adjacent ones of said platelike members in combination with resistances and spark gaps properly connected tosaid members.

WILL L. LLOYD, JR.

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