US2105463A

US2105463A - Vacuum tube

Info

Publication number: US2105463A
Application number: US228233A
Authority: US
Inventors: Henry G Cordes; Bertha L Cordes
Original assignee: Individual
Current assignee: Individual
Priority date: 1927-10-24
Filing date: 1927-10-24
Publication date: 1938-01-18
Anticipated expiration: 1955-01-18

Description

Jan. 18,1938. H. G. CORDES VACUUM TUBE Filed Oct. 24, 1927 5 Sheets-Sheet 1 F E L;

awn d E M Mm ma rm N E V m? H I e. rm

H. G. CORDES Jan. 18, 1938.

VACUUM-TUBE Filed Oct. 24, 1927 5 Sheets-Sheet 4 IN V EN TOR Hz/7r 6. Cordas wgdfigw A TTO NE YS H. G. CORDES Jan. 18, 1938.

VACUUM TUBE 5 Sheets-Sheet 5 Filed 001;. 24, 1927 s s a v. d r R 0 TWO RC T m M m6 v9 Mr M r H Y B with a mercury Patented Jan. 18, 1938 VACUUM TUBE Henry G. Cordes, Palo Alto, can; Bertha L.

Cordes, owner by decree of court Application October 24, 1927, Serial No. 228,233 30 Claims. (01.175-354) This invention relates generally to devices utilizing electrical discharges .thru gases, and is particularly applicable to mercury vapor vacuum tubes. The devices herein described are capable of being used for the rectification of high voltage alternating'current or for the production of high frequency uni-directional current discharges from a source of continuous uni-direccan be rectified by intermittent discharges thru tional current.

It is an objectof this invention to devise means for more eifectively controlling current discharges thru gases, particularly current discharges thru ionized mercury vapor.

It is a further object of this invention to devise a mercury arc rectifier capable of rectifying higher voltages than has heretofore been pos- 81 e.

It is a further object of this invention to devise a mercury vapor tube capable of interrupting flow of relatively large currents of high P tential.

It is a further object of this invention to devise improved means whereby relatively small currents may be utilized for -piloting or controlling relatively large current discharges.

It is a further object of this invention to devise a'mercury arc vacuum tube which will not permit aninverse flow of current when used together with reactive circuits.

Further objects of the invention appear from the following description in which I have set forth the preferred embodiments of my invention; It is to be understoodthat the appended claims are to be accordeda range of equivalents consistent with the state of the prior art.

Referring to the drawings:

Figure 1 is a side elevational view in cross section illustrating a mercury vapor vacuum tube incorporating theprinciples of this invention.

Fig. 2 is a view similar to Fig. 1 but showing a modified form 'of the anode chamber and its associated electrodes.-

Fig. 3 is a view similar to Fig. 1 showing a further modification of the invention, and also showing the manner in which the device may be utilized for the generation of high frequency oscillations.

.Fig. 4 is a view similar to Fig. 1 showing a further modification of the invention, this modification differing in construction of the mercury pump and the details of the control electrodes.

Fig. 5 is a cross sectional detail illustrating another modified form of anode chamber and its associated electrodes, capable of being utilized h vapor tube such as shown in Figs. 6 and '7 are details in cross section showing modified forms of ionizing anodes.

Fig. 8 is a detail shownin cross section of another modified form of anode chamber and associated electrodes, capable of being utilized with a vacuum tube such as shown in Fig. 1.

Fig. 9 is a cross sectional elevational view showing a further modified form of tube.

Fig. 10 is a crosssectional detail taken along the line l0l0 of Fig. 9.

The value of alternating current voltage which mercury vapor in a vacuum tube is limited by ,arc-back when the inverse voltage exceeds a cer tain maximum value or by excessive inverse 'Geissler discharge current when-the discharge frequency is high. For this reason it has been.

. impossible in the past to utilize mercury vapor -reduce high frequency inverse current to a negligible value when producing high frequency unidirectional discharges.

It is well known that a low pressure of gas, either in the form of non-condensable (fixed gas) or condensable gas (vapor), is essential in a mercury vapor tube when it is desired to avoid ex-, cessive inverse current. Consequently, in mercury vapor tubes for rectifying high voltages, it has been the practice to keep the gas pressure as low as possible. However, when the gas pressure is decreased below a certain point a phenomenon known as fading occurs in rectifiers. Fading consists in an anode failing to pass current during part or all of a positive half-cycle due to the establishment of a high initial resistance in the discharge path space, that is, the space acts as an insulator until breakdown is produced by a relatively high positive potential impressed on the anode. In addition to low gas pressure, fading is known to be increased by lengthening the discharge path, by reducing its cross-sectional area, or by placing bends in it. The cause of fading is generally attributed to the formation of a static charge on the glass wall of a low pressure part of the discharge path.

. has been known as a means for neutralizing the static charge. My invention comprises means for reducing the gas pressure to a lower value than has heretofore been used and providing more eflective means 'toneutralize the static charge.

The effects of charging conductors which are insulated from, and placed adjacent to, the discharge path has been published. The phenomena caused by the effects consists in either decreasing or increasing the breakdown valueof the discharge path space. In terms of the well known concepts of charged elements and of space charge of the electron theory, the breakdown value is decreased by increasing the number of positive ions in the discharge path space and it is increased by decreasing-the number of positive ions. In other words, the breakdown value varies with the negativity of the space charge. I have found that the breakdown value can be thus varied more effectively as the rarefaction of the space is increased, Fading is attributed to the collection of positive ions from the space by the wall of the discharge path, especially when the rarefaction is high. I reduce undesired negativity by making the space more positive.

The starting band, or the filamentary exten-- sion of the anode, in a mercury vapor lamp to start the discharge constitutes a well known means for decreasing the breakdown value of the path space. On the other hand, metallic rectifier tubes are often constructed so that the anode is surrounded by the metal of the tube which is at the potential of the cathode and therefore tends to attract positive ions from the space around the anode; this tends to increase the breakdown value of the discharge path space. It is customary practice to place a shield around the anode to reduce the tendency of the metal to make the space charge too negative.

One feature of my improvement consists in establishing a desired breakdown value of the discharge path space and then cyclically varying this value to attain the result desired.

The breakdown-value-control surface may be either a metallic conductor placed in the discharge path space or a conducting sheath placed adjacent to the glass opposite to the space. In

the first case the discharge current may concentrate at one point on the metallic conductor which may thereby become a source of secondary electron emission. In the second case a charge is distributed over the entire glass surface thus avoiding concentration and secondary electron emission. The sheath acts in a manner equivalent to a number of condensers (capacitive impedances) each in series with a metallic control conductor. Undesirable concentration of the discharge current may also be avoided by uti lizing a high resistance conductor in a manner hereinafter described. The terms control surface and control conductor, as here used, control space charge including wall charge effects as distinguished from control of the state of ion emission from the cathode whether produced] by heating the mercury, by passing a keep-alive current to the cathode, or by passing a. pilot spark to the cathode,

To prepare a tube in the practice of this invention, I initially outgas the tube and electrodes r to a very high degree and provide means, after sealing oil, to maintain the required low gas pressure in the anode end of the discharge path which will hereinafter be termed the anode chamber by restricting the flow of mercury vapor into the anode chamber, by providing a cooling medium such as water or other refrigerant to cool the anode chamber, by providing diffusion and condensation pump action, and by providing Sprengel pump action.

The restriction of mercury vapor flow has been side of the constricted part of the discharge path. The high pressure side when viewed thru water and pyrex glass has a yellowish-white glow while the low pressure side has a' bluish glow which indicates much greater diffusion of the discharge.

I- have found that a great tendency for high frequency intermittent discharges to take place is produced by an abrupt change in the crosssectional area.of the discharge path at the low temperature produced by a, cooling medium.

The practice of producing diffusion and condensation pump action in a mercury vapor tube is old. The novel feature of my invention comprises a higher vapor pressure in the cathode chamber than has heretofore been used to supply pumping vapor. I provide an external heater to heat thru a glass heat-conductor the cathode mercury both to produce a preliminary pumping action and to reduce the breakdown value of the discharge path space by increasing the vapor pressure in the cathode chamber. The heater also reduces the breakdown value when the rectified current is too small to maintain the cathode mercury at the proper temperature.

Another novel feature is a miniature Sprengel pump which removes permanently non-condensable gas from the operating part of the tube. The return-flow of condensed mercury passes thru a miniature fall tube and non-condensable gas is thereby compressed and liberated in a separate chamber which is sealed by mercury from the main part of the tube. Any mercury vapor tube may be made self-evacuating during operation by providing the tube with such a pump.

Referring now to that embodiment of the invention illustrated in Fig. l, I have shown a vacuum tube II which is made of pyrex and which is evacuated to a high degree. The upper part of the tube is formed to provide an anode chamber I2 while the lower part is formed to provide a cathode chamber l3. Cooperatively associated with the anode chamber is an anode I4 to which is connected the lead-in terminal Hi. The anode is cylindrical in form and is made of pressed graphite, altho it may be made of metal and may assume another form. The cathode chamber is formed to provide a receptacle for the cathode mercury H to which connection is made by the lead-in terminal N! which is grounded.

The anode chamber is cooled by means of a jacket l9 thru which cold water is circulated. The cathode chamber is heated by an electrical heater 2| supplied with current thru

terminals

22 and 23. A heat insulating medium 24 is employed for minimizing transfer of heat from the cathode chamber or from the heater to the anode chamber. In addition to the usual anode and cathode, I provide a breakdown control surface by means of which I control discharges thru the anode chamber. In Fig. 1 the control surface is formed by the inner surface of the water-cooled glass which is charged by displacement current flowing to or from the conducting water in the cooling jacket l9.

Instead of having an unrestricted path for mercury vapor between the anode and cathode chambers, the mercury vapor from the cathode chamher is discharged into the lower part of the anode chamber thru a suitable tube 21, the discharge end of which is substantially smaller in diameter than that of the anode chamber l2. Positioned over the end of tube 21 is a vapor-deflecting cap 28 which is suitably supported (not shown) so that its periphery is spaced as shown from the anode chamber wall. This cap or deflector serves as a means for restricting flow of mercury vapor from the cathode to the anode chamber, directs vapor flow away from anode l4, and separates the anode. chamber which lies above the rim of the cap'from the condensing chamber which is disposed below said rim. The deflected mercury vapor is condensed as it contacts with the cooled wall below the cap. The condensed mercuryis returned to the cathode chamber by way of one or more fall tubes 29 which discharge into a suitable trap 30; the mercury from this trap being returned to the cathode chamber thru tube 3|.

Fall tube 29 is of relatively small diameter so that Sprengel pump action is produced by condensed mercury dropping down thru the 'same. This Sprengel pump action assists the condensation pump action in reducing the pressure in the anode chamber and transfers permanently non-condensable gas from the main part of the tube to the gas-chamber 35. I have found that the mercury in trap 30 in the lower end of fall tube 29 which seals the gas in chamber 35 from the main part of the evacuated space of the tube is outgassed to a greater degree than the mercury ll of the cathode to which it is returned. The resistance 15 represents the resistance of the water (not shown) from the ground.

' In order to explain the operation of the device. it will be assumed that terminals l6 and I8 are connected to a suitable source ofcurrent while by means of a double throw switch 32 terminal 26 may be connected either to terminal 16 orto terminal 33'upon which controlling potentials are applied. The cathode chamber is heated by supplying alternating current to the

terminals

22 and 23 until the mercury vapor pressure in the cathode chamber attains a value of the order shown in the drawings which corresponds to a breakdown value of potential of the order of 1500 volts. Assuming now that switch .32 is open, that an alternating potential of about 15,000 volts is applied to terminals l6 and i8, that pumping action is'taking place due to the mercury vapor flowing down past the rim of cap 28 and condensing, and that cold water is flowing from a grounded source thru supply tubing and jacket iii to cool the anode chamber and charge the water negatively with respect to the anode M which increases the negativity of the discharge path space, then no breakdown will take place to initiate a current flow from the anode to the cathode. Now if conductors l5 and 26 are connected together by switch 32, flow of current will occur in one direction'only and. the device will operate emciently as a rectifier. At a current density of about one half ---ampere per square inch, the discharge is bluish between anode I 4 and the rim of the'vapor defiector 28 while it is yellowish-white between the deflector and thecathode ii. The usual cathode spot is formed on the cathode provided the external resistance in the supply circuit permits suficient current to flow. If switch 32 is opened again while alternating potential is being applied, the half-wave current discharges between the anode and cathode immediately stop.

In order to illustrate another mode of operation, it will be presumed that a direct current positive potential is impressed on terminal I6 with respect to terminal 18 and switch 32 is thrown to connect

conductors

26 and 33. Due to the water being connected to l8 thru high resistance, a discharge'does not take place as long as displacement current fiows from the anode chamber to the water. However, if a positivepotential is Jacket I9 to the.

placed on conductor 33 so that the flow of displacement current ceases then breakdown takes place between anode and cathode. I have found that because of the inherent properties of my device unidirectional discharges may take place at-relativelyhigh frequencies as controlled by potentials appliedto conductor '26. The device may therefore be employedfor the generation of radio frequency oscillating current.

I have found that it is practicable to supply fresh water to jacket l9 thru about ten feet of rubber tubing and discharging the water thru similar tubing. By operating the tube under such conditions, the external resistance (represented by l5) of the two rubber tubes in parallel between the control terminal 26 and the cathode terminal I8 is about one megohm which allows suiiicient current to pass to operate the tube in the manner described above.

The facts and theory with which I explain the operation of the device is as follows: During a positive half-cycle on the anode, with switch 32 open, current cannot be started to flow from anode ll to mercury cathode l1 due to the high negativity of the space charge produced -by the water in the water-jacket l9 which is electrically connected to the cathode thru the resistance I 5 mentioned above. Closing switch 32 upward connects the water in the jacket to the anode 14 which changes the charge of the water from negativeto zero with respect to the anode; in other words, closing switch 32 neutralizes the high negativity and produces a lower breakdown value of the discharge path.. During the half-cycle that the anode is negative with respect to the cathode and the water is similarly charged, the increase of breakdown value caused by the presence of the water acts to prevent inverse discharge which, in turn, determines the range of rectification. The water-cooled wall collects positive ions without producing an objectionable rise in temperature which is prevented by the presence of both the cooling medium and the distributed collection area; these positive ions would, in the absence of the charged wall, bombard the anode and thereby produce a condition favorable to inverse current.

The vacuum necessary for the tube will vary depending upon the potentials with which it is to be operated. During the process of evacuating my tube I have found that when the fixed gas pressure is still relatively high, a crest potential of say 14,000 volts will not be rectified, as an inverse discharge takes place whether the switch 32 is open or closed. When the gas pressure as shown by a McLeod gage connected to the high pressure part of the tube has attained a fairly low value, say of the order of one bar, then the discharge with switch 32 open is erratic and may be accompanied by inverse discharge to a certain extent. Under this condition ofvacuum the inverse discharge ceases when switch 32 is closed to connect conductors I6 and 26. The tube will 'function'fairly efiiciently under this condition of vacuum altho slight fluctuations will occur in the rectified current. However, the factor of safety against inverse discharge is small. I prefer to carry the vacuum to a higher degree which .produces a condition in which no discharge can the vacuum is preferably carried to a degree at which no discharge will occur at such potential vious modifications of Fig. 1 may be made as,-

for example, passing a. non-conducting cooling liquid thru jacket IS in which a metallic film on glass is disposed to serve as a control conductor to influence breakdown value of the anode chamber.

In Fig. 2, I have illustrated a modified form of Fig. l in which an internal control electrode is employed to decrease the breakdown value of the discharge path by neutralizing the efiects on its value produced by the charging of the water in jacket l9, and during the following halfcycle to aid by charging the water to produce an increase of breakdown value with respect to inverse current. The anode chamber 2l2 of the tube 2 is provided with an elongated internal control electrode 33; connection is made to 36 by means of lead-in terminal 31. The anode 2 is arranged adjacent the upper end of 36, is cylindrical in shape, and surrounds electrode 36.

228, similar in construction and function to the deflector 28 shown in Fig. 1. The electrode 36 is constructed so as to have relatively high resistance between its upper and lower ends, this resistance being greater for tubes adapted to be used upon the higher potentials. In practice I have obtained good results by making the electrode 36 of glass covered with a thin film of metal.

suitable resistance material which will retain its resistance when high potentials are impressed on its terminals and which will not be attacked by mercury vapor. The upper end of tube 221 which discharges vapor from the cathode chamber has a restricted discharge orifice 38 which both increases the velocity of the vapor and establishes a greater difference of vapor pressure in the discharge path. I have found that the abrupt change in the cross-sectional area of the discharge path from that in the anode chamber to that in constriction 38 provides a condition which facilitates the production of high frequency discharges.

The anode chamber 2|2 is cooled by means of water-jacket 2l9. By means of switch 39 the liquid of this jacket may be connected in parallel with control electrode 36. A three-way switch 41 connects the control electrode directly to the anode terminal [6, or to this terminal in series with condenser 42, or, as in Fig. 1, to terminal 33. The mercury I1 is heated by heater 2| thru the glass wall of the tube which serves as a heat conductor.

The theory with which I explain the operation of the arrangement shown in Fig. 2 is substantially the same as that with respect to Fig. 1. When the potential of the anode H4 and of the control electrode 36 is increasing positively with respect to the cathode, a discharge takes place from the lower end of electrode 36 at the breakdown voltage of the high pressure vapor which may be in the neighborhood of 2000 volts. After such breakdown each element of area of the electrode 36 primes an adjacent element above it so that the discharge from electrode 36 climbs up until it initiates a main discharge from the anode 2 in a manner similar to the well known filamentaryextension-of-the-anode method of starting a mercury vapor lamp. In other words the initial discharge from electrode 36 neutralizes the neg- Thev lower end of 36 is expanded to form a deflector However I may use instead a rod con- .structed of carborundum or silicon or any other ative space charge in a sheath adjacent to its surface and this sheath increases in thickness as the current increases. The high resistance in series with the control surface 36, or of the water between conductor 26 and'the glass adjacent to space 212, tends to prevent the flow of a parasitic high frequency current in a circuit comprising .anode 2; the presence of the resistance, I have found, increases the inverse breakdown value of the main discharge path, and tends to prevent puncture of the glass. In general, the flow of parasitic high frequency current thru the main anode must be prevented.

In accordance with the above mode of operation, an equivalent of the control eljgptrode 36 may be formed by utilizing a number of separate conductors of progressively increasing length; the shortest cdnductor terminating near the anode 2H and the longest terminating near the defieetor 228. The shortest of these conductors may be connected to the anode terminal IE or to some external source of controlling potential, and the remainder may be interconnected in series by high resistances or small condensers. Each conductor would then initiate a. discharge from the conductor immediately above it and therefore progress upwardly and initiate a discharge from the anode.

The resistance of the electrode 36 will vary with different conditions of operation. For example its resistance may be about one megohm when 10,000 volts effective are being rectified. One factor in the selection of the proper resistance for electrode 36 is that in order to pilot the discharge upwardly the resistance per unit length of electrode 36 should be greaterthan the resistance per unit length of sheath space. By sheath space I refer to the relatively low resistance sheath formed about electrode 36 in which the negative space charge is neutralized and which initiates a main discharge. Another factor which requires that the resistance of electrode 36 be high is that a feeble inverse discharge passes from the cathode to the lower end of 36 at about the same voltage as that which initiates a discharge in the preceding half-cycle. This feeble inverse current increases the negativity of the space charge thus protecting the anode from a large inverse current discharge.

It will be noted that switch 4| may be thrown so as to connect electrode 36 with terminal l6 in series with condenser 42. This arrangement is sometimes desirable as it reduces the effective current flowing thru electrode 36 and also permits a reduction in the resistance of this electrode. The electrode 36 may be used to the exclusion of the connection 26 to the water in jacket 2|9, or it may be used in conjunction with the same by closing switch 39.

A characteristic feature common to all the discharge path breakdown control surfaces is illustrated by the glass surface of the discharge path opposite the water in jacket M9, by the surface of electrode 36, and by the equivalent electrodes herein described. In each of the illustrations the control surface consists of a plurality of elemental control surfaces arranged so that the elements of surface are interdependent. For example assume that a decrease of breakdown value is to be produced by electrode 36 to initiate a discharge to anode 2M from cathode IT. The piloting discharge, that is, the electron flow, passes first from the cathode to the nearest-to-cathode end of electrode 36 where the vapor pressure is relatively high and spreads to other elements of surface toward the anode as is the case in starting a mercury vapor lamp by means of a filamentary extension of the anode. The upper elements therefore depend on the lower for a relatively low breakdown value and the lower elements depend on the upper to pilot more effectively the discharge to the anode. It is thus seen that a discharge can be initiated at a relatively low potential thru a discharge path which has a relatively high breakdown value due to length, bends, and low pressure by means of a plurality of elemental control surfaces connected to the piloting potential source so that the impedance'in the piloting circuit is decreased as the piloting discharge spreads towards the anode.

Fig. 3 shows a further modification of the invention, and illustrates the manner in which the tube may be used for the generation of high frequency oscillations. The lower end of the tube in this instance is provided with a pocket 43 within which is disposed the electrical heating element 44. This construction permits the mercury 3|! to surround the heater, thus aflording more efllcient transfer of heat. The exterior of the lower tube portion is preferably provided with a jacket 46 of heat insulating material. The water jacket 3 I 9, is preferably constructed of some suitable metal such as nickel iron or chrome iron alloy, and is sealed as at 41 to the glass of the cathode chamber, and at 48 to the adjoining walls of the anode chamber. This arrangement makes possible a lowerpressure in the anode chamber 3l2 than can be obtained by the use of a glass jacket for the reason that the metal more effectively conducts the heat to the cooling liquid. Another advantage is that this metal jacket may serve as an electrode and for this purpose I have shown a terminal conductor 49 connected to the walls of the same.

The control electrode 336 in this instance consists of a hollow glasstube having a hollow deflecting cap 328 formed upon its lower end'. Positioned within this tube and within the hollow cap 328, there is a conductor 53, which is connected to an external terminal conductor 31. Arranged adjacent to and preferably surrounding a lateral extension 54 of the tube 5| there is the anode 3M to which is connected the terminal conductor l6.

In conjunction with 'the tube 329 for returning condensed mercury to the cathode chamber, I may utilize a cleanup bulb 56 which may contain in auxiliary electrode of tungsten, activated charcoal or other material for absorbing gases. After draining thru tube 329 the mercury is returned to the cathode chamber thru a suitable trap 330. The control electrode 336, or anode extension, functions in the same manner as thecontrol electrode shown in Fig. 2. When the anode M4 is charged positively with respect to the cathode, no discharge will'take place if switch 32 is opened due to the negativity of the space charge, but

when this switch is closed to connect the anode and the control electrode, a discharge will take place between the anode and cathode due to the decrease of negativity of the space charge produced by current from conductor 53 acting thru the

glass

328 and 336. The pilotingaction of the control electrode 336 is substantially the same as that previously described with respect to Figs. 1 and 2.

The use of the'metallic water jacket 3l9 makes it possible to use a keep-alive current between this jacket and the cathode. For example I have shown a source of direct current potential as represented by the battery 51, connected across the terminals 48 and I8. With this arrangement a current is continuously passed from the water Jacket to the cathode. thus keeping the mercury vapor in the cathode chamber continuously ion-' ized. The alternating current to be rectified may then be impressed across terminals I 6 and 49 as anode and water jacket, and the water jacket or terminal 49 may begrounded as indicated by ground connection 58. Ifthe tubeshowninr lgdistobeusedexclusively as a rectifier of high voltage alternating current, the conductor 53 may be connected-directly to the anode 3 within the tube.

One circuit with which the device shown in Fig. 3 may be used for the generation of high frequency discharges has been shown. In this v indicated by transformer 50, i. e. across the case a suitable source of direct current, such as a generator 59, has its positive lead connected to anode 3 by way of switch 55 and its' negative lead connected to the "keep-alive anode or jacket 3!!! by way of switch 60, a suitable high frequency choke 6| being inserted in series with the positive lead. An oscillatory circuit consisting of inductance 62 and capacitance 63 is likewise connected across the anode 3H and jacket 3i9. A suitable master oscillator 64 is coupled across the keep alive anode or jacket 3l9'and control electrode 336, as by means of stabilizing circuit 66. The output or work circuit, as indicated at 61, is suitably coupled to the oscillatory circuit as by means'of inductance". The high frequency controlling impulses impressed upon. the controlling electrode 336, initiate a series of current discharges from the anode to the cathode at a frequency dependent upon the frequency of the stabilizing circuit 66.

The cathode ionizing current flowing from the water jacket 3!!! to the cathode 3 will reduce the potential required to initiate a discharge between the anode and the'water jacket. If this ionizing current is sufficiently large the current passed thru the heater 44 may be reduced to zero; in other words the heater may be used only. for starting purposes. 1

In the modification shown in Fig. 4, no means has been provided for utilizing pump action of the mercury for reducingthe pressure in the anode chamber. The reduction of pressure in the anode chamber in this instance is produced solely by cooling the anode chamber and by providing a greater restriction between the anode and cathode chamber. For example the tube 421 whichv leads mercury vapor from the cathode chamber is provided with a very small discharge orifice 438. Instead of utilizing the liquid in the cooling jacket 9 for forming a control electrode, I provide in this instance an external metal sleeve H which is connected to the terminal conductor 26. This construction permits the use of non-conductive cooling liquids, such as cold oils.

In the operation of the modification shown in Fig. 4, the oriflce 438 between the cathode and anode chambers permits a very small amount of mercury vapor to pass from the cathode into the anode chamber and all of this mercury is condensed in the lower part of the anode chamof 1 ampere the diameter of this orifice may be.

about millimeter when the crest potential to be rectified is of the order of 15,000 volts. It is to be understood that the anode chamber must be made longer, or the diameter of the orifice smaller, as the voltage to be rectified is increased. Under best operating conditions an arc discharge will not pass from the anode to the cathode until switch 32 is closed to connect togethercontrol and anode electrodes, and intermittent discharges can be stopped by opening this switch. The initial potential, or the potential necessary upon the control electrode for causing a discharge between the anode and the cathode, may be decreased by increasing the current thru the electrical heater 42I.

Fig. shows a modification of the construction shown in Figs. 1 and 3, particularly with respect to the construction of the control electrode, and to the arrangement of maintaining a condition of ionization in the cathode chamber. As in the construction of Fig. 3 the electrode provided by the cooling jacket 5!!! does not extend close enough to'the anode for dielectric current passing thru it to break down the initial resistance of the anode chamber caused by fading due to the low gas pressure produced by the cooling medium. The break down of this resistance is accomplished however by utilizing an external metal sheath or coating '12 which surrounds that part of the tube adjacent to the anode 5l4l, and which also surrounds at least a portion of the jacket 5l9. By means of conductor 13, this coating 12 is connected together with terminal 28 from jacket 5l9. The. tube 521 leading from the cathode chamber is provided with a restriction or orifice 538, similar to the orifice shown in. Figs. 2 and 3. Positioned over the end of this orifice there is an inverted cap-shaped deflector 528' which is preferably made of insulating material such as glass, and is supported from the depending glass tube 16. Extending downwardly into tube 521 thru the orifice 538, there is a conductor 11, which for convenience, may be sealed into the deflecting cap 528 and connected to the terminal conductor 49.

In the operation of that modification of the invention shown in Fig. 5, a keep alive current may be applied across the cathode and conductor 49, so as to maintain the vapor in the cathode in ionized condition. The heat developed by this ionized current passing thru the mercury vapor, superheats the vapor which passes up thru the orifice 538. By means of this device I have been able tosubstantiallyreduce the reignition potential of the device.

Fig.6 shows a modified form of the ionizing anode shown in Fig. 4. The anode I! in Fig. 5

' may cause overheating of the walls of the oathode chamber. To prevent deleterious results due to such overheating, I provide the upper end of the tube 621 with a tip or shield 18 which is made of some material capable of withstanding a high temperature, as for example graphite or tungsten. This tip 18 is provided with an orifice 638 thru which extends the ionizing anode 611, this anode being preferably constructed of metal capable of withstanding high temperature, such as tungsten. In this improved construction the nature of the tip 18 and the ionizing anode permits the vapor passing up thru the orifice 638 to be highly superheated.

Fig. 7 shows another modified form of the ionizing anode shown in Fig. 6. In this case the vapor deflecting cap I28 is elongated and-the tip I18 terminates short of the electrode 111. The tip H8 is preferably constructed of quartz, which is fused to the tube 121 by a graded quartz to pyrex joint 8|. The high fusing temperature of quartz permits a high current density in the orifice 138, and the high temperature of this orifice superheats the vapor passing thru it.

In Fig. 8, I have shown a modification of the construction shown in Fig. l in that the anode may be directly cooled by circulating liquid. This anode. M4 is constructed of hollow metal thru which water may be circulated thru the intake and discharge pipes 83 and 84. The lower end of the electrode is of course sealed, and a metal to glass sealed joint 85 is provided between a flange on the anode and the adjacent walls of the tube.

The use of a water cooled anode is desirable in that it reduces the pressure within the anode chamber 8l2 and thereby increases potential required to produce an inverse discharge. The defleeting cap 828 in this instance is of slightly modified construction in that it is supported by a tungsten wire 86 extending down thru orifice 838 and secured to the wall of tube 821.

' Fig. 9 shows a modfiication of the construction shown in Figure 1 in which the cathode chamber M3 is extended and is surrounded by part of the anode chamber 9l2, as is shown. In this case to form a complete control electrode, a shield 912 surrounds the Walls of the anode chamber SH and also surrounds at least a portion of the cooling jacket Bill. The electrical heater 944 is disposed within a horizontal pocket 943 and is thus surrounded by the mercury 9H. Mercury vapor from the cathode chamber is discharged thru tube 921 at a point in the space surrounded by the cooling jacket GIS, and the tube at this point is tipped so that the condensed mercury may drain back into the cathode chamber thru a drain tube 929 As in the case of Figure l, the walls of the cathode chamber are preferably provided with a heat insulating jacket 946.

I claim:

l. The method of operating a mercury vapor tube having anode and cathode chambers comprising: establishing a high resistance in the anode chamber by cooling the chamber to the extent that said resistance'cannot be broken down by a potential of ten thousand volts in the presence of a heated cathode chamber, and breaking down said resistance by piloting a discharge thru said chambers.

2. A vacuum tube having: anode and cathode electrodes for the passage of current periodically and intermittently therebetween, a discharge path between said electrodes thru an ionizable vapor, a surface capable of assuming a varying electrical charge positioned adjacent said path, means for connecting said surface to the anode comprising impedance of high enough value to prevent the flow of objectionable parasitic variable current therethru when sixty cycle alternating voltage is impressed on said electrodes, and means for artificially reducing the vapor pressure in the vicinity of said surface.

3. A mercury arc vacuum tube arranged to pass current periodica y, intermittently, and unidirectionally compr c a solid anode in an anode chamber, a liquid-cooled wall arranged to reduce the vapor pressure in said chamber, and a cathode of mercury arranged to be periodically reignitedwith the aid of a heat conductor adjacent said mercury, and a source of heat of surficiently high temperature to heat said mercury thru said conductor to the extent that the potential required to be impressed between said electrodes to produce said reignitions is reduced.

4. A mercury vapor arc rectifier tube comprising an anode in an anode chamber, a mercury cathode in a cathode chamber, means for liquid cooling to reduce the vapor pressure in said anode chamber, means for heating said cathode by causing emission of electrons therefrom intermittently and periodically, and means for heat insulating said cathode chamber to the extent required to keep said cathode hot enough to allow breakdown between said electrodes at the operating voltage of the rectifier.

5. An arc vacuum tube arranged to pass current unidirectionally and intermittently to a cathode during operation thereof comprising an anode chamber, a cathode chamber containing mercury, means for vaporizing the mercury, and means including a suitable vapor-flow path for restricting the flow of mercury vapor from said cathode chamber to the extent that the vapor pressure in said cathode chamber is high enough to be broken down by the operating voltage.

6. The method of operating a vacuum tube containing an anode, a cathode of mercury, and

a discharge path therebetween, which comprises: heating said mercury to the extent that self-ignition takes place at the operating voltage of the tube and simultaneously cooling part of said path to the extent that said voltage cannot produce inverse current of excessively large'value.

7. The method of operating a vacuum tube provided with a cathode, an anode, a discharge path containing vapor, and a plurality of piloting elements arrangedlongitudinally along said path, which comprises: establishing a relatively high pressure-gradient in said path, producing a discharge from the piloting element nearest the cathode to initiate a discharge from the next adjacent piloting element, and so on toward the anode until a main discharge from the anode to the cathode is initiated, and repeating said initiation of the main discharge periodically.

8. A vacuum tube comprising: an anode, a cathode, a discharge path therebetween containing vapor, a cooling medium adjacent to at least a part of said path, a discharge-path control electrode comprising a plurality of elemental control surfaces disposed along said part at points having a substantially different electrical breakdown value with respect to the cathode and at least one of said values being influenced by cooling, and impedances in series with each of said surfaces arranged so that when a positive potential with respect to the cathode is impressed on said electrode the discharge starts from one of said surfaces and progresses to another of said surfaces having a higher breakdown value.

9. A mercury vapor tube comprising an electrode of mercury, means for vaporizing said mercury, a mercury-vapor condensing surface, andmeans including a receiving gas chamber maintained at less than atmospheric pressure for producing Sprengel pump action with mercury from said condensing surface.

10. The method of operating a vacuum container containing a pool of mercury which comprises heating the mercury to vaporize it, reducing the temperature of the vapor to condense it, and compressing fixed 'gas and storing it at a pressure below atmospheric to produce Sprengel pump action while returning said condensed mercury to said pool.

11. A vacuum tube comprising an electricaldischarge path, a flow of relatively high pressure vapor in part of said path, a main condensing surface, and a vapor deflector arranged todeflect said flow toward said surface and to divide said path into highpressure and low pressure parts.

12. The method of decreasing the inverse current caused by the high value of the frequency of alternating potential impressed-upon a discharge path between an anode disposed adjacent to low pressure vapor, and a cathode, which comprises: heating the cathode, establishing an initial dielectric strength of said path sufiiciently high to prevent breakdown by the operating potential in the presence of the heated cathode, and impressing a potential of a positive average-value such as the operating-potential on the anode with respect to the cathode while alternately producing at said frequency a decrease and an increase in the electrical breakdown value of said path to thereby decrease the inverse current flow.

13. The method of reducing the pressure of fixed gas adjacent to an anode before starting to operate a vacuum tube having a solid anode and a vaporizable cathode, which comprises the following two steps in a convenient order: heating the cathode to produce a suitable pressure of vapor, cooling a space between the anode and the cathode to reduce the gas pressure adjacent the anode then and thereby, producing diffusion pump action with said vapor to further reduce said gas pressure, and the final step ofstarting intermittent flow of current from said anode.

14. A vacuum tube arranged to pass current periodically, intermittently, and unidirectionally, comprising: an anode, a cathode, a discharge path therebetween containing gas, and a discharge-path control conductor extending in and along said path from a point having a relatively high electrical breakdown value to a point having a lower value with respect to the cathode and possessing sufficient impedance to render inverse current flow negligible, said lower value being influenced by the residual ionization produced by a preceding discharge thru said path.

15. A vacuum tube arranged to pass current periodically, intermittently, and unidirectionally, comprising: an anode, a cathode, a discharge path therebetween containing vapor, an electrical breakdown control surface adjacent to at least a part of said path, and cooling means capable of reducing vapor pressure in said part; said surface being charged to a potential having a negative average-value with respect to the anode and the anode being periodically charged positively with respect to the cathode.

16.'A vacuum tube constructed with fused insulation-to-metal joints to prevent air-leakage, comprising: an anode, a cathode, a discharge path therebetween containing vapor, and a surface capable of being charged disposed adjacent to at least a part of said path. in combination with a cooling medium arranged to cool said part; the anode and said surface being simultaneously charged negatively with respect to the cathode and the anode being charged to a negative average value with respect to the cathode.

17. The method of operating a vacuum tube 'containing mercury which comprises heating the mercury to produce vapor at a pressure corresponding to a relatively low electrical breakdown value, and cyclically impressing a potential of said value on the vapor to break it down periodically by simultaneously decreasing the negativity of the space charge of the vapor as described and increasing the ionization at the cathode at the beginning of each cycle.

18. A vacuum tube containing mercury vapor and comprising a condensing chamber having wall surface heated only by vapor, a cathode of 7 mercury, an anode, and a discharge path therebetween provided with a constricted part having the property of tending to interrupt periodically the flow of continuous current thru said part; a potential of positive average value being impressed on the anode with respect to the cathodeand of high enough crest-value to break down said part after each interruption of current therethru.

19. A vacuum tube for passing current intermittently, periodically, and unidirectionally between electrodes, comprising: an anode in an anode space, a discharge path terminating at the anode and containing vapor, cooling means for reducing the pressure in saidspace by cooling at least part of said path, a surface adjacent to, and between the terminals of, said path and arranged for increasing the electrical breakdown value thereof, and a surface adjacent to, and between the terminals of, said path and arranged for neutralizing the effect of said increase.

20. The method of operating a vacuum tube containing mercury and provided with electrodes, which comprises: heating mercury in a vacuum to the extent that self-ignition would take place between an anode and said mercury at the operating voltage which voltage is of such a value that self ignition would not occur without heating the mercury and impressing the operating voltage between an anode and the heated mercury to pass current periodically, intermittently, and unidirectionally therebetween.

21. A vacuum tube for passing current periodically, intermittently, and unidirectionally thru vapor, comprising: vapor, an anode, a cathode, a discharge path therethru and therebetween having a high pressure-gradient, a control surface adjacent to the high pressure end of said path capable of decreasing the electrical breakdown value of the path, and a control surface adjacent to the low pressure end of said path capable of increasing the electrical breakdown value of the path to prevent inverse current.

22. The method of operating a mercury vapor tube containing two electrodes and a discharge path therebetween divided into high and low pressure parts by a condensing chamber disposed adjacent to said path, which comprises the step of decreasing the electrical breakdown value of the path at a point therein differing in pressure from that surrounding either of said electrodes to initiate a main discharge therethru.-

23. In a vacuum tube: a condensing chamber, an anode, and a discharge path terminating at said anode; said path containing vapor, and being divided into high and low pressure parts by passing adjacent to said chamber, and a composite surface comprising a plurality of elemental surfaces disposed in said parts, each capable of decreasing the electrical breakdown value of the path to aid initiation of a main discharge therethru.

24. The method of reducing the voltage required to initiate electron flow thru a discharge path between two electrodes, containing vapor,

\ and divided into high and low pressure parts by a condensing chamber 'disposed adjacent to said path, which comprises the step of decreasing the electrical breakdown value of the path at a plurality of points therein between the electrodes.

25. A vacuum tube arranged to pass current periodically, intermittently, and unidirectionally from an anode charged to a positive average potential with respect to a cathode comprising said anode, said cathode, a discharge path therebetween containing vapor, a cooling medium arranged to reduce the pressure of vapor in the anode end of said path, and a surface capable of increasing the potential required to initiate current flow from the anode combined with a con ductor, having high impedance and capable of conducting continuous current, connected between said surface and a source of potential having a negative average value with respect to said anode.

26. The method of outgassing mercury having all of its surfaces exposed to a pressure less than atmospheric in a vacuum container which comprises: maintaining a foreign gas pressure in said container of the low value described, evaporating mercury from a pool of mercury in said container to produce mercury vapor, impressing a potentialexceeding one thousand volts on said vapor with respect to a charged surface to aid in dissociating said gas and vapor, condensing said vapor, and collecting said condensed mercury in a pool containing only mercury so treated while permanently removing foreign gas from said vapor.

27. A mercury vapor container constructed with fused insulation-to-metal joints to maintain the low pressure described comprising: a pool of mercury constituting a source of vapor, means including a charged surface for electrifying the vapor, means for condensing said vapor before it reaches said surface, and means for forming a second pool of mercury consisting entirely of said condensed mercury and having all of its surfaces exposed to less than atmospheric pressure.

28. A vacuum tube comprlsing a mercury cathode, an anode, a condensing chamber, a discharge path between the anode and the cathode, means including said chamber for dividing said path into high and low pressure parts, and means for reducing the value of a transient positive voltage required to be impressed on the anode with respect to the cathode to initiate unidirectional discharge in said path combined with a source of transient voltage capable of producing breakdown of the path during each positive half-wave impulse.

29. In a system for electron discharge a vacuum tube comprising an anode and a discharge path terminating at said anode and containing a single, cooled, constricted passageway inclosing a surface capable of collecting positive ions proximate thereto, and electrical energy supply for