US3381890A - Vacuum apparatus - Google Patents

Description

y 7, 1968 CHIKARA HAYASHI 3,381,890

VACUUM APPARATUS Filed Dec. 29, 1965 5 Sheets-Sheet 1 CHIKARA HAYASHI y 7, 1968 CHIKARA HAYASHI 3,381,890

VACUUM APPARATUS Filed Dec. 29, 1965 5 Sheets-Sheet 2 loh INVENTOR.

CHIKARA HAYASHI BY WWW" May 1953 CHIKARA HAYASHI 3,381,890

VACUUM APPARATUS Filed Dec. 29, 1965 5 Sheets-Sheet 5 INVENTOR.

CHIKARA HAYASHI AMWMW y 7, 1963 CHIKARA HAYASHI 3,381,890

VACUUM APPARATUS 5 Sheets-Sheet 4 Filed Dec. 29, 1965 Fig. 6

INVENTOR.

CHIKARA HAYASHI IZI b ,AW LMMW y 1968 CHIKARA HAYASHI 3,381,890

VACUUM APPARATUS Filed Dec. 29, 1965 5 Sheets-Sheet 5 INVENTOR.

CHIKARA HAYASHI MMW United States Patent 3,381,896 VACUUM APPARATUS Chikara Hayashi, Yokohama-sin, Japan, assigns: to Nihon Shinku Gijitsu Kahushiki Kaisha (Japan Vacuum Engineering (30., Ltd), Yokohama, Japan Filed Dec. 29, 1965, Ser. No. 546,108 Claims priority, application Japan, Dec. 30, 1964, 39/74,583; Jan. 8, 1965, 40/590 4 Claims. ((11. 23069) ABSTRACT OF THE DISCLUSURE In a glow discharge vacuum apparatus characterized by electrodes disposed in a magnetic field for the ionization of traces of gas contained therein, the provision of a radioactive energy emitting body to accelerate ionization in said device, a target for said emissions, said target, when struck by said emissions, being adapted to emit into the system emissions of an energy lower than the energy of the emissions from the radioactive body.

This invention relates to vacuum apparatus such as a getter ion pump and/or a glow discharge vacuum guage. The principle of the vacuum apparatus will be explained with reference to a getter ion pump and a glow discharge vacuum guage.

A getter ion pump generally comprises a pump chamber, an anode and cathode located in the pump chamber, means for impressing voltages between the anode and cathode, and means for establishing a magnetic field in the pump chamber as principal elements, and has as a characteristic function the evacuation of the pump chamher to a clean high vacuum. In starting the getter ion pump, it is required to pre-evacuate the getter ion pump to a intermediate vacuum. Then, the electrons suspended in the space between the anode and cathode will come into collision with the netural gaseous molecules in the pre-evacuated pump chamber, then the molecules are divided into the electrons and the positively charged molecules or atoms and the positive ions thus formed travel towards and impinge against the cathode under the influence of the voltage impressed. By the impingement of positive ion a part of the material forming of the cathode is sputtered in particles, and the sputtered particles fly in the pump chamber and then deposit on the surface of the member surrounding the cathode such as, for example, the anode, cathode or envelope to form a getter layer. Since the getter layer has a function to entrap the gaseous molecules in the pump chamber, the pressure in the pump chamber and in the interior of a vacuum apparatus connected to the pump chamber is lowered, consequently the vacuum apparatus is evacuated. On the other hand, the electrons newly produced by the ionization of the neutral molecules are useful for successive ionization and excitation of other neutral molecules. Since the magnetic field established in the pumping chamber has a function to confine the electrons in the space between the anode and cathode, they travel a long path before they arrive at anode thus the occasion of ionization and excitation of the neutral molecules is successively increased. With such an increase of the electron or successive ionization and excitation of the neutral molecules and the confinement of the electrons due to the magnetic field, the pumping operation may be maintained. The operation of Patented May 7, 1968 the getter ion pump above mentioned is generally believed as true by those skilled in the art, and is realized in generating high vacua without containing impurities or foreign matters such as, for example, 1()"'10 mm. Hg. However, previous getter ion pumps have been imperfect in that the start of pumping is difiicult or the time required for from the switching on of the pump to anormal pumping operation is long, especially where the pumping chamber has been previously evacuated to a very high vacuum.

The inventor found that such difiiculties may be obviated by providing a radiation source, such as an electron radiation source, ion radiation source or electromagnetic wave source of appropriate energy, within the pump chamber to supply primary electrons useful for triggering and stabilizing the discharge in the pump, In conventional sputter ion pump, the electrons in the pump chamber at its start are believed to be generated naturally by the influx of cosmic rays or by field emission or by photo emission. In such a case, the chance of collision of the electrons with the neutral molecules are lessened with decreasing the pressure in the pump, until at least successive increment of the electrons are not expected. This fact is the cause of making the start of pumping difiicult and the time up to the normal pumping operation long. Some conventional Penning discharge vacuum gauge is provided with hot filament usable for emitting triggering electrons. Hot filament, however, evolves much gases in ultra-high vacuum, thus this is not recommendable in ultra-high vacuum use. In view of this fact, the provision of the radiation source in the pump chamber is very effective for improving the performance of the getter ion pump, provided the source is located at a right position with appropriate potential.

As to the radiation source, several radioactive substances may be used, but the preferable source is a solid body formed of radioactive substances or containing such substances, because said solid body does not emit any impurity to contaminate the vacuum atmosphere. The most satisfactory substance is a solid, radioactive element of a type able to eifect fl-decay or emit ,B-rays such as, for example, Ni or Sr or their respective isotopes. However, the energies of the electrons successively emitted from these elements are not constant, but variable in intensity, while they are so high as in the order of several ten kev. to several hundred kev., consequently in case these elements are used without any special arrangement as a radiation source for the getter ion pump, the electrons emitted therefrom travel through the pump chamber so fast and probably only once that the ionization of the neutral molecule is not effectively enhanced. In order to obtain sufiicient enhancement of the ionization of the neutral molecules, the triggering electrons coming into the discharge space should be of relatively low initial velocity that they may oscillate between electrodes many times. According to the present invention the electron emitting source consists of a radioactive element and a member (referred to as an auxiliary pole hereinafter) receiving the electrons emitted from the electron emitting source. The auxiliary pole emits secondary-electrons of relatively low energies. By providing the electron emitting source capable of emitting the secondary-electrons in the getter ion pump, the performance of the getter ion pump is found to be greatly improved.

It should be noted that though the explanation of the electron emitting source has been made with reference to Ni and Sr in the foregoing, the source should not be limited to these substances, but the element emitting a-rays or -rays may be used in place of the electron emitting element as a source.

This principle may be applied to a glow discharge vacuurn guage. The glow discharge vcauum guage generally comprises a vacuum measuring member, an anode and cathode located in the casing of the vacuum measuring member, means for impressing voltages between these electrodes, means for generating a magnetic field in the vacuum measuring member, and means for measuring the electric current passing through. the circuit connecting the anode and cathode at the exterior of the casing, and has characteristics able to measure the pressure under high vacuum in a vacuum apparatus Whose interior communicates with that of the vacuum measuring member. Upon connecting the vacuum measuring member to the vacuum apparatus, the electrons suspended or floating in the space between the anode and cathode come into collision with the neutral molecules, and ionize them for separation into electrons and positive ions. The positive ions thus formed travel towards the cathode and collide thereon. The electrons produced by this collision (referred to as daughter-electrons or secondary-electrons hereinafter) are useful for ionization, dissociation and excitation of other neutral molecules, as described hereinafter. On the other hand, the magnetic field established in the vacuum measuring member confine electrons in the space between the anode and the cathode to create an electron cloud composed of many oscillating electrons there. As the ionization of the neutral molecules is continued, the electron clouds becomes so thick with regard to electrons that finally a portion of the charged electrons get enough energy to reach the anode. On the other hand, the electron cloud is continuously supplemented with the electrons newly produced by both the ionization of the neutral molecules and the electrons emitted from the cathode by the impingement of the positive ions or photons thereon. In the cases where the dissipation of the electrons is continuously balanced with the supply of the electrons, a stationary discharge current will be created there. The intensity of the electric current varies according to the density of the neutral molecules, namely the pressure in the vacuum measuring member.

The operation of the glow discharge vacuum guage is well known to those skilled in the art, and has been satisfactory for meausring high vacua as low as mm. Hg or lower. However, the previous glow discharge vacuum guage has been defective in that the start of operation is slow, especially in the high vacuum or that sometimes the discharge is not effected and/or even the discharge once initiated often extinguish or becomes unstable. These difficulties are caused by the insufiiciency of the number of the electrons initially existing in the vacuum measuring member, as explained hereinbefore. Therefore, the function of the glow discharge vacuum guage with an electron emitting source is essentially similar to that of the getter ion pump.

Therefore, it is an object of the present invention to provide a novel and useful getter ion pump including a source adapted to emit secondary-electrons of relatively low energies.

Another object of the present invention is to provide a novel and useful glow discharge vacuum guage comprising a source adapted to emit secondary-electrons of relatively low energies.

Although the primary application of this radiation induced secondary-electron emitter will be concerned with vacuum guage and vacuum pump, similar apparatus based on this principle will be useful for various purposes including design and construction of ion sources for mass spectrometers or partial pressure detectors. Therefore the object of this invention should be understood to pro- 4- vide a novel means to establish a stable electron cloud by using radiation induced electron source.

The invention will now be described with reference to the accompanying drawings wherein:

FIG. 1 is a vertical sectional view of one preferable type of a getter ion pump of the present invention.

FIG. 2 is a partial sectional view showing a modified arrangement of an anode and cathode of the present invention.

FIG. 3 is a similar view to FIG. 2, but shows another modified arrangement.

FIG. 4 is a similar view to FIG. 1, but fragmentarily shows a further modified arrangement.

FIG. 5 is a vertical sectional view of one preferable type of a glow discharge vacuum guage of the present invention.

FIG. 6 is a diagrammatic sectional view illustrating the operation of the vacuum measuring member shown in FIG. 5.

FIG. '7 is a similar view to FIG. 6, but shows a modified arrangement.

FIG. 8 is a similar view to FIG. 6, but shows another modified arrangement.

FIG. 9 shows a further modified glow discharge vacuum guage of the present invention.

FIG. 10 shows a furthermore modified glow discharge vacuum guage.

Referring to PEG. 1, there is shown an embodiment of a getter ion pump of the present invention generally indicated at 10 A casing 12 defining a pump chamber 11 is rectangular in cross-section and made of a material easy to emit a secondary-electron such as stainless steel and provided with mounting bores 13 at its left side wall and a connecting port 14 at its right side wall. An anode 26] located in the casing 12 is cylindrical formed, and a cathode 15 associated with the anode 20] comprises an upper plate 21f facin an upper opening 22 of the anode 20f in spaced relation therewith and a lower plate 23 facing a lower opening 24 of the anode 20 in spaced relation therewith. The anode 20 is rigidly held at its left side by a supporting rod 19 of good electric conductivity which passes through the center of the upper mounting bore 13 and sealingly fixed thereto by means of an insulator 29 and seal 30. The upper and lower plates 211'- and 231 of the cathode 151 are connected each other by a connecting rod 50 of good electric conductivity and the assembled cathode 15 is supported at the edge of the lower plate 23 by a supporting rod 51 passing through the lower mounting bore 13 and sealing fixed thereto in a similar way to the upper connecting rod 19.

The materials of the cathode 15 and anode 20f are the same as those of the previous getter ion pump, namely, for the cathode 15 is provided with plate containing or composed of reactive substance such as any Mo, C1, W, Ta, Nb, Fe, Ti, Zr, Ni, Ba, Al, Th, Mg, Ca, or Sr, and/ or a material coated with such a substance, while for the anode 25 f is used either reactive substance or conventional structural material such as stainless steel.

In the lower plate 23f of the cathode 15; is provided an inverted conical opening 52 radially spaced from its center, and to the lower face of the bored portion is secured a radioactive element 28f. The radioactive element 28f comprises, as an example, an annular plate 54 of non-radioactive substance with a bore 53 larger than the lower opening of the inverted conical opening 52 in diameter, and an annular radioactive plate 56 secured to the lower face of the annular non-radioactive plate 54 and having a bore 55 of a diameter larger than that of the bore 53, these bores 53 and 55 being coaxially aligned with the inverted conical opening 52.

The material of the annular non-radioactive plate 54 should be one of that easily secured to the cathode 15;, while the material of the annular radioactive plate 56 is an element effecting p-clecay, preferably of Ni or Sr effecting 100% fi-decay and having a long half value period and a high energy. The material coated with Ni or Sr may be used for the annular plate 56.

The casing 12f is grounded at 34 to maintain its voltage at nil. The anode is electrically connected to a voltage impressing means 32 through a terminal 31 and a lead wire, and the voltage impressing means 32 is grounded at 33 so as to be maintained at a potential usually between 1 kv. and 7 kv. relative to the earth. The cathode 15 is connected to another voltage impressing means 57 through a terminal 59 and a lead wire, and the voltage impressing means 57 is grounded at 60 so as the cathode be maintained at a potential usually between l0 v. and 200 v. relative to the earth.

Magnets 35 disposed above and below the upper and lower walls respectively are permanent magnets 0r electromagnets to generate a magnetic field parallel to the axis of the anode 20f in a cylindrical space 36 enclosed with the anode 20f, and the intensity of the magnetic field is normally maintained at 500 g. or more, as way of example.

In operation, the outlet port 37 is connected to a valve 38 of a vacuum apparatus 39 and another valve 40 of an auxiliary vacuum pump 41 by a T conduit 37, and then the auxiliary vacuum pump is operated to evacuate the pump chamber to a certain vacuum such as, for example, 10' mm. Hg, the voltage impressin means 32 and 57 are energized to impress a voltage between the anode and cathode, and the magnets 35 generates a magnetic field in the space 36. The annular radioactive plate 56 of the radioactive element 28 always emits radiations (referred to as primary-electrons hereinafter).

Most of the primary-electrons travel toward a wall portion 58 of the casing 12] (illustrated in dashed-lines, and referred to as an auxiliary pole hereinafter) facing the annular radioactive plate 56 and come into collision therewith or effect scattering thereof to cause the auxiliary pole to emit secondaryelectrons. When the primary-rays emitted from the radioactive element 28 are electrons, the energy of the secondary-electrons emitted by virtue of said primary-electrons is less than that of the primary-electrons. Some of the secondaryelectrons emitted from the auxiliary pole 58 pass through the circular bores 55, 53 and 52. The secondary electrons thus are formed and come into the space 36 can not reach cathode, because they do not have enough initial energy to overcome the negative potential impressed on the cathode. Neither can they reach anode, because of the impressed magnetic field. Thus the secondary electrons oscillate in the space 36. This means long trajectory of the secondary electrons which in turn greatly enhance the probability of ionizing collision with neutral molecules in the space 36. Consequently, even if the number of electrons originally suspended in the pump chamber were very samll and not enough to cause the self-sustaining discharge, the secondary electrons build up to suflicient number for triggering and stabilizing the discharge in the space 36 accompanying ionization of neutral atoms or molecules therein. Thus the positive start of pumping, the shortening of the time which is required to reach the normal operation of the pump, and the improvement in pumping efiiciency may be accomplished. In addition, the annular radioactive plate 56 is positioned away from the axis of the anode 20f to cause the secondary-electrons to travel diagonally in the space under the anode 20f in order to increase the occasion of collision with the neutral molecules. On the contrary, in the case where the annular radioactive plate 56 is located near the center of the axis of the magnetic field, and cause the secondary-electrons to travel along the axis of the magnetic field, almost of them will travel the vicinity of the axis and ionizes the neutral molecules existing there alone, consequently the multiplication of the electrons will be reduced in some degree in comparison with the former way. However, it should be noted that since the characteristic feature of the present invention resides in the provision of the secondary-electrons, the present invention is never limited to the course of the secondaryelectrons.

To maintain the auxiliary pole for emitting the secondary-electron at a higher voltage than that of the cathode 15 also serves for lengthening the path of the secondary-electrons. On the other hand, when the voltage of the auxiliary pole 58 is equal to or lower than that of the cathode 15 the fact that the improvement in pumping efilciency is not so much as in the former is proved by experiment. However, it should be noted here that, in case of using a ,B-source, the source 56 can be put at the position 58 instead of 56. Any fl-ray source emits electrons having various energy. In other words fl-radiation are of continuous spectra in energy. Therefore electrons emitted directly from a fi-source and of suitable energy for passing through the hole 52 are essentially the same as the secondary electrons discussed above.

It should also be noted here that there are various means for keeping the secondary electron source at a positive potential relative to the cathode. Therefore any method or means to keep the secondary electron source, including the ,B-ray source as mentioned above, at a positive potential relative to the cathode are usable according to the principle covered by this invention. Autobiasing is, for example, one of such method well known to those skilled in the art.

FIG. 2 shows a modification of the present invention wherein a cathode 15g in the form of a cylinder having open opposite ends is located in a casing 10g with a connecting port 14, and auxiliary poles 58g of annular plate are disposed in and adjacent the edges of the open ends of the cathode, and an anode 20g is disposed on the axis of the cathode 15g. These poles are spaced each other and mounted in a casing 16g. A supporting rod for each pole sealingly and insulatingly passes through the casing 10g and is connected at its end outside of the casing 10 to a voltage impressing means (not shown) and a radioactive element 28g is mounted on the inside face of the cathode 15g. In this modification, the arrangement of the anode and cathode may be interchanged in such a manner that the cathode of rod is disposed on the axis of the anode of cylinder.

FIG. 3 shows another modification wherein a vertical cylindrical anode 20h having open opposite ends is located in a casing 10/1 with a connecting port 14, and an upper plate 21h of a cathode 15h and an auxiliary pole 5811 are horizontally disposed in and adjacent the upper edge of the anode 2011, and in and adjacent the lower edge of the anode 20h a lower plate 23h and a radioactive element 28h are located in line. Means for supporting the poles and the arrangement of the supporting means are similar to FIG. 2.

In these modifications, the secondary-electrons are emitted, of course, from the auxiliary poles 58g (FIG. 2)

and 28/1 and 58h (FIG. 3) respectively.

FIG. 4 shows another modification which differs from the pump of FIG. 1 in the point that a unit of the radioactive element of 28 and the annular radioactive plate 56 of FIG. 1 are replaced by a single radioactive element 28k mounted on a portion of the casing 12k facing an inverted conical bore 52k in .a cathode 15k. A space 58k in the vicinity of the bore 52k formed in the cathode 1 5k is maintained at a positive potential relative to the cathode, but a negative potential relative to both an earthed radioactive element 28k and a positive anode 20k, as a consequence, the electrons of low energy emitted from the radioactive element 28k will be confined in the space 58k of negative potential so as not to enter a space 36 between the cathode and anode, while the electrons of medium and high energies similarly emitted from the active element 28k will enter the space 36 after passing through the space 58k and the electrons of extremely high energy among them will travel straight toward the opposite cathode plate and will collide therewith, and the other ones will dissipate their energies before reaching the opposite cathode and is urged to travel in the opposite direction, and then in the original direction so as to oscillate between the spaced cathodes 15k until they collide with the neutral molecules existing there. While the electrons other than ones of medium energy are of course serviceable for the purpose of emitting the secondaryelectrons from the portions of the pump chamber which are attacked by the electrons, the most important characteristic feature of this modification resides in the fact that the space 58k maintained at a negative potential 'act as a sieve or filter for the electrons coming into this region. =In the case of FIG. 4, the radioactive element 28k substantially serves as an auxiliary pole for emitting the secondary-electrons and may be considered as .a sort of the auxiliary pole. Furthermore, it is noted that the lower cathode plate 15 with a single bore :52 may be replaced by one with a plurality of bores, namely, a reticulated cathode plate, and that a plurality of the spaced radioactive elements may be provided on the inner surface of the casing 12k.

It is added that the oxide, carbide or boride of alkaline earth metal having a strong electron emitting characteristic may be used for the auxiliary pole in the pump illustrated in FIGS. 1 to 4, and that a suitable sheet metal coated with these substances may also be used therefor. In the case where such kind of highly efficient emitter contains an amount of radioactive substance, the radioactive element emits the so-called primary electrons which in turn may be converted into the production of the secondary-electrons. This kind of combined emitter is efiiciently used as the secondary electron emitter. In this case, however, both secondary electrons and some primary electrons are emitted from the auxiliary pole shown in 'FIG. 1 or from 28k shown in FIG. 4. Furthermore, a composite element consisting of a radioactive element such as Ni and a film of semi-conductive material such as Si or Ge may be used in place of the auxiliary pole. In this case, a portion of the secondary electrons from the auxiliary pole travel toward the anode through the film, and the other electrons activate the semi-conductive film so as to emit electrons of low speeds which also serve for the purpose of the ionization of the neutral molecules.

Referring to FIG. showing an embodiment of a glow discharge vacuum guage 110 of the present invention, the vacuum guage 110 includes a vacuum measuring member 111 which comprises a vertical, substantially closed cylindrical casing 113 made of glass and having a connecting port 112 as its lower portion, an auxiliary pole 114 of rod supported at its upper portion by the top wall of the casing 113 and coaxially extending in and with the casing 113, a cylindrical, open cylindrical cathode 116 provided with a plurality of openings 115 coaxial ly surrounding and spaced from the auxiliary pole 114, and an open cylindrical anode 117 coaxially surrounding and spaced from the cathode 116, and also spaced from the casing 113. The cathode 116 and anode 117 are supported in position by supporting rods 119 and 120 of good conductivity, rigidly secured, by means of soldering, to the lower end portions of the cathode 1'16 and anode 117 and sealingly passing through the bottom wall of .the casing 113 and terminating at 119 and 120 respectively, each of the rods 119 and 120 being rigidly fixed to the bottom wall. On the inner surface of the cathode 16 are secured a plurality of radiation sources 121 at places such as the circumferences of the openings 115. With the vacuum measuring member 111 is prepared a cylindrical magnet 122 coaxially surrounding the casing 113. The outer end 123 of the auxiliary pole 114 is grounded at 124 through a leading wire. The outer end 125 of the supporting rod 119 is connected to a cathode voltage impressing means 127 with an ampere meter 130 through a leading wire, and the outer end of the supporting rod is connected to an anode voltage impressing means 128 and the two voltage impressing means 127 and 128 are connected to each other through a leading Wire which is earthed at 129. The anode voltage impressing means 128 is designed to provide a direct current voltage ranging from 1 to 7 kv. between the outer end 126 and the earth 129, and the cathode voltage impressing means 127 is designed to provide a direct current voltage ranging from -1100 to -5 v. between the outer end and the earth 129 With this arrangement the above-mentioned voltages are provided between the anode 117 and the auxiliary pole 114, and between the cathode 116 and the auxiliary pole 114 respectively. It is noted however that these values of voltage are taken by way of example and not part of the present invention, and that instead of the direct current voltage, a half-wave or full-wave rectified current voltage and/or alternating current voltage may be used.

Materials forming the anode 117 and cathode 116 are similar to those used in the prior glow discharge vacuum guage such as magnetron vacuum guage, namely, Mo, Re, W, Ta, Fe, Ni, Pt, Au, Ir, Al, or Cu and/or their respective alloys are used for the anode 117 and cathode 116. For the auxiliary pole 114 are used the above enumerated materials and/ or the oxides, carbides or borides of alkaline earth metal. In addition to these substances, some lined materials wit-h these substances may also be used for the anode 117, cathode 118 and auxiliary pole 114.

The radiation source 121 is formed of solid radioactive substances, alloys and mixtures composed of radioactive substances and/or some lined materials with the radioactive substances.

In one preferable embodiment of the materials, Pt or Au coated M0 is used for the anode 117 and the cathode 116, ThO lined tungsten is used for the auxiliary pole 114, and Ni is used for the radiation source 121.

The magnet 122, either permanent magnet or electromagnet is used so as to establish a magnetic field of intensity of 500-3000 kg. in the interior of the vacuum measuring member 111, specially in the region or space 131 between the anode 117 and cathode 116. The operation of this vacuum guage resembles that of the prior glow discharge vacuum guage, specially that of the magnetron vacuum guage. Upon connecting the connecting port 112 to a vacuum tank whose pressure is measured, impressing the above-mentioned voltages between the cathode 116, anode 117 and auxiliary pole 114, and energizing the electromagnet to establish the magnetic field of the abovementioned intensity, as illustrated in FIG. 6, radiation rays 132 are emitted from the radiation sources 121 and collide against the auxiliary pole 114, and cause the auxlliary pole 114 to emit secondary-electrons 133 acting as a trigger. The greater portion of these electrons 133 arrives at the region 131 after passing through the openings 115 and works in like manner as the floating electrons in the prior glow discharge vacuum guage, in other words, these secondary electrons 133 act as the triggers to produce a discharge-in-magnetic field in the region 131 between the cathode and anode. Since these trigger electrons 133 are successively supplied to these, the discharge never extinguish but the measurement of high vacua and the stabilization of the discharge current indispensable for measuring are accomplished.

Since the circuit, diagrammatically illustrated in FIG. 5, comprising the voltage impressing means 127 and 128, the ampere meter and the earth 124 and 129 is a conventional one, a detailed explanation is omitted, but it is noted that the discharge current is introduced directly or after amplified to the ampere meter 130 which indicates indirectly the pressure Within the vacuum tank.

As to the modified glow discharge vacuum guages it will be explained hereinafter.

The modification illustrated in FIG. 7 differs in construction from FIG. 5 in the point that the modification comprises an anode 117a of rod, a cylindrical perforated cathode 116a located coaxially with the anode 117a in the spaced relation thereto, and a cylindrical auxiliary pole 114a surrounding coaxia-lly wit-h and spaced from the cathode 116a. In this modification, radiation rays 132a travel outwards from radiation source 121a mounted on the outer surface of the cathode 116a, and collide against the auxiliary pole 114a. The secondary-electrons 133a emitted by this collision from the auxiliary pole 114a travel inwards, pass through openings 115a and arrive at a region 131a between the cathode and anode.

Another modification illustrated in FIG. 8 includes a box-shaped auxiliary pole 11% with a connecting port 11%. instead of the auxiliary pole 114a of FIG. 7. Supporting rod 12Gb and 11% carrying an anode 117b and cathode 11Gb respectively pass through the Wall of the box-shaped auxiliary pole 114b with seal and insulation. Therefore, the auxiliary pole 11-4b serves as a casing corresponding to the casing 113 of FIG. 5. Radiation source 1211) and other elements are arranged in similar way to. those in FIG. 7, and trigger electrons 13-3b travel in the direction of the arrow.

Further modification illustrated in FIG. 9 includes a horizontal anode 1170 of rectangular frame, a cathode consisting of horizontal upper and lower plate 1160 and 1160" spaced from the anode 1170 respectively, a horizontal auxiliary pole plate 1140 transversely aligned in the spaced relation with the upper anode plate 116s, and a radiation source plate 1210 transversely aligned in the spaced relation with the lower anode plate 1160'" and facing the auxiliary pole plate 1140. The electrodes 1170, 1160 and 1140 are housed in a glass casing 1130 along with the radiation source 1210 and supported by supporting rods 1200, 1190 and 1180 respectively in the same way as FIG. 5, and the radiation source 1210 is carried by a bent rod 132a secured to the bottom of the casing 113a. An electromagnet 1220 located outwardly of the casing 1130 comprises an upper and lower electrodes 122a and 122s" facing the upper and lower cathode plates 1160' and 1160". With this arrangement, as illustrated by the arrows radiation rays 132a travel towards the auxiliary pole 1140, while the trigger electrons arrive at a discharging region 1310 which is define-d by the anode 117a and the upper and lower cathode plates 1160' and 1160".

On the other hand, the current measured in each of the vacuum guages as above-mentioned, strictly speaking, is the sum of the current owing to the emission of the trigger electrons from the radiation sources and the current produced by the ionization of the neutral molecules caused by the collision of the trigger electrons against the neutral molecules. When the guage comes to its critical operation region the number of the neutral molecules in the guage is substantially kept at a very small constant value, in consequence the current based on the ionization of the neutral molecules sets in a very small stationary cur-rent. For the accurate measurement of the vacuum it is desired to measure this stationary current alone and to prevent the flowing of the trigger electrons into the current measuring means.

FIG. shows a furthermore modified or improved glow discharge vacuum guage adapted to the end as above-mentioned. The vacuum guage includes a casing 113d having a connecting port 112d and serving as an auxiliary pole. In the casing 113d are arranged a vertical, open cylindrical anode 117d and a cathode 116d consisting of an upper and lower plates 116d and 116d" facing the upper and lower edges of the cathode 116d. The upper cathode plate 116d has an opening 115d radially spaced from its axis and a radiation source 121d mounted on the periphery of the opening 115d, and the lower cathode plate 116d" has an opening 140. At the portion of the casing 113a underneath the opening 140 is provided a downwardly extending, elongated tubular member 141 which passes through the central bore 142 of a lower magnet 122a. and receives at the lower portion adjacent its bottom an ion collecting means 143. The ion collecting means 143 is carried by a rod 144 sealingly and this arrangement, radiation rays 132d emitted from the insulatingly passing through and fixed at the bottom. With radiation source 121d travel outwardly and collide with the inner face of the casing 113d, as illustrated by the arrow and cause the casing 113d to emit electrons 133d. The emitted electrons 133d pass through the opening 115d and then reach at a region 131d between the cathode 116d and anode 117d to ionize the neutral molecules existing there. A portion of the ions thus formed is drawn to the lower cathode plate 116d" by virtue of the potential thereof and most of the drawn ions 134d travels through the openings in the elongated tubular member 141, and finally deposits on the ion collecting means 143, while the trigger electrons 133d which have arrived at the region 131d are not subjected to the attraction force of the lower cathode plate 116d" by virtue of the electrostatic field, and have little chance to enter the tu bular member 141 so as to deposit on the ion collecting means 143.

A penetrant mesh electrode may, however, be added just underneath the hole 140 so that no electrons might escape from the hole 140 to the tube 141.

Ion collector 143 can be replaced by a multiplier, if necessary.

As is obvious from the foregoing explanation, the radiation source may be made of any material or substance able to emit appropriate radiation rays. Even the case where the radiation source emits electrons, the secondary electrons emitted from the auxiliary pole is of sufficiently low energy which is important for the electrons to take a long oscillatory trajectory which in turn assures increased opportunity of ionization of the neutral molecules and the maintenance of the ionization thereof that are the object of the present invention. Though the explanation was made in such a manner that the auxiliary pole is maintained at a positive voltage relative to the cathode, but a negative voltage relative to the anode, this relation as to the voltage should be broadly varied in accordance with the geometrical arrangement of the members constituting the vacuum measuring member or their materials or the sorts of the radiations or their energies, and so, it may be happened to maintain the auxiliary pole at a negative voltage relative to the cathode. For example, if additional electron repeller electrodes made of fine mesh grid are prepared inside the cathode plates, the auxiliary pole can be kept at a negative potential to the cathode. In this case the cathode receives positive ion passed through the repeller electrodes, but the electrons emitted from the auxiliary pole repelled by the repeller and oscillate in the discharge space. Though the electron emission from the auxiliary pole may be effected by the back-scattering of the same owing to the collision of the electrons from the radiation source against the same, the essential purpose of the auxiliary pole resides in the fact that it may emit electrons when attacked by the radiation rays. Considering thus, it may be said that the radiation source and the auxiliary pole constitutes in cooperation with each other an electron emitting means. The principle of the present invention is to provide a electron supply means adapted to accelerate the dischargein-magnetic field and maintain the same, therefore the present invention may be applied to all vacuum equipment requiring efficient ionization in gas phase, especially in ultra-high vacuum where impurity gas evolution from hot cathode is prohibited.

What I claim is:

1. In a glow discharge vacuum apparatus characterized by electrodes for the ionization of traces of gas contained therein and means fro producing a magnetic field between said electrodes, a radioactive energy emitting body afiixed within said apparatus to accelerate ionization therein and a target to receive the emissions from the radioactive body, said target being of a composition whereby it emits I 1 into the system emissions of lesser energy than that of the radioactive body when struck thereby.

2. A device in accordance with claim 1 wherein the radioactive body is disposed on one of the electrodes.

3. A device in accordance with claim 1 wherein one of said electrodes is provided with .an opening and the radioactive body is annular and disposed on said electrode in registry with the opening.

4. A device in accordance with claim 1 wherein the target is a rod disposed axially of the electrodes.

References Cited UNITED STATES PATENTS Mellen 324-33 X Donath et a1. 32433 X Jepson 230-69 Mackenzie 23069 10 ROBERT M. WALKER, Primary Examiner.

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