US3316443A - Magnetic field controlled apparatus with means to oscillate electrons for the ionization of gas molecules - Google Patents

Description

p 25, 1967 L. K. HANSEN 3,316,443

MAGNETIC FIELD CONTROLLED APPARATUS WITH MEANS TO OSCILLATE ELECTRONS FOR THE IONIZATION OF GAS MOLECULES Filed Aug. 23, 1961 0739 m 9,; q/ I a/ lj! F 19,3

a l I I-I V 114, aa

ar h Zia/mm lbw-veg:

United States Patent Calif.

Filed Aug. 23, 1961, Ser. No. 133,407 1 Claim. (Cl. 315-111) This invention relates to apparatus for producing charged particles and more particularly relates to apparatus for providing a controlled and efiicient production of charged particles. The apparatus is especially adapted to be used as a source for indicating the number of molecules of gas in an enclosure or as an ion source or a vacuum pump.

As apparatus has become increasingly complex in construction and sensitive in operation, it has become necessary at times to determine with considerable precision the number of molecules in an enclosure. For example, in oil refining and in other types of chemical processing, the number of molecules in an enclosure often has to be determined in order to control the proper operation of the chemical process at successive instants of time. As another example, vacuum techniques are being used increasingly to control various operations. Such vacuum techniques require that the vacuum be maintained with precision. Because of this, the number of molecules in an enclosure has to be determined with considerable accuracy.

Various attempts have been made to produce equipment for measuring with precision the number of molecules of gas in an enclosure. Although the efforts to de velop satisfactory equipment for providing such measurements have been considerable, they have not borne complete success. For example, a common equipment now in use for measuring the number of molecules of gas in an enclosure includes an electrode which is spaced relatively close to the electrically grounded walls defining an enclosure and which is subjected to high voltages such as in the order of 2,000 volts. Because of the relative disposition of the electrode and the walls defining the enclosure and because of the voltage difierence between the electrode and the walls defining the enclosure, positive ions are repelled by the electrode with considerable energy toward the walls defining the enclosure to produce a secondary emission of electrons from the walls. These electrons are then accelerated from the walls defining the enclosure so as to strike molecules of gas and produce an ionization of such molecules. The positive ions produced as a result of such ionization are then repelled by the electrode to the walls defining the enclosure to produce a further emission of electrons on a secondary basis from the wall.

The apparatus described in the previous paragraph has certain inherent disadvantages. Since the positive ions are attracted to the walls defining the enclosure to produce a secondary emission of electrons, the walls become contaminated by the positive ions. This is especially true when molecules of different gases are introduced at successive times into the enclosure. The walls defining the enclosure also tend to become contaminated as by adsorption of molecules of the different gases in the enclosure and as by chemical reaction between the walls defining the enclosure and the molecules of the different gases in the enclosure. As the walls defining the enclosure become chemically contaminated, the rate of secondary emission of electrons from the walls varies so as to cloud the interpretations of any output indications obtained from the apparatus.

A further disadvantage results from the fact that sparklng often occurs between the electrode and the walls definlng the enclosure because of the close spacing and considerable voltage difierence between the electrode and the walls. This sparking is especially prevalent after a con siderable number of charged particles have been produced within the enclosure. Since the sparking produces further charged particles, it also tends to cloud the measurements of the charged particles produced from molecules of gas within the enclosure. The measurements are further clouded because the sputtering of electrons from the walls defining the enclosure tends to alter the surface of the walls and affect the subsequent emission of electrons from the walls.

In copending application Ser. No. 126,554 filed by Kenneth R. MacKenzie, apparatus is disclosed and claimed for overcoming the above disadvantages. The apparatus produces charged particles without any secondary emission of electrons from the walls defining the enclosure. The apparatus provides a pair of electrodes, both of which are connected to receive a relatively low voltage such as +200 volts. Since the electrodes are at a relatively low voltage, no sparking or sputtering occurs even when a considerable number of charged particles are present within the enclosure.

In the ionization gauge disclosed and claimed in copending application Ser. No. 126,554, two electrodes are disposed in spaced relationship to each other and are provided with a configuration to retain electrons within the electrodes. Each of the electrodes is provided with an opening which faces the opening in the other electrode so that the electrons are able to move in a reciprocal path between the electrodes through the openings in the electrodes. A direct voltage is applied to the electrodes to retain electrons within the enclosure and to inhibit the movement of the electrons toward the walls defining the enclosure. An alternating voltage is also applied to the electrodes such that the alternating voltage on one of the electrodes has an opposite phase to the alternating voltage on the other electrode.

Because of the introduction of an alternating voltage to the pair of electrodes in opposed phase relationship, the electrons in one of the electrodes are initially attracted to the second electrode so as to strike molecules of gas and ionize such molecules during their movement. In the next half cycle of the alternating voltage, the electrons in the second electrode are attracted to the first electrode so as to strike and ionize further molecules of gas in the electrode. In this way, a cumulative number of molecules of gas are ionized in the successive half cycles of the alternating voltage.

Means are also included in the ionization gauge disclosed and claimed in copending application Ser. No. 126,554 for channeling the flow of electrons between the first and second electrodes so that the electrons are not able to strike the electrodes or the walls defining the enclosure. Means are also included in the ionization gauge for returning any electrons secondarily emitted from the walls defining the enclosure to such walls so that such electrons cannot be used in ionizing molecules of the gas within the enclosure. In this way, the electrons produced from the molecules of gas within the enclosure are efficiently used to produce further electrons without any secondary emission of electrons from the electrodes or the walls defining the enclosure.

This invention provides an improvement over the ionization gauge disclosed and claimed in copending application Ser. No. 126,554. In this invention, a grid is disposed between the first and second electrodes to control the movement of the electrons in the reciprocal path between the electrodes. The grid is biased at a negative voltage relative to the constant component of the voltage on the electrodes so as to normally prevent the movement of electrons between the electrodes. However, upon the application of an alternating voltage to the electrodes in the opposing phase relationship, the potential on one of the electrodes decreases toward the potential on the grid so as to reduce the bias imposed by the grid. At the same time, the alternating voltage causes the potential on the second electrode to rise relative to the voltage on the grid. In this way, electrons are able to move from the first electrode toward the second electrode only in that portion in each half cycle of the alternating voltage when the biasing effect of the grid is removed. The electrons can receive an optimum amount of energy by having their transfer thus delayed until a maximum voltage difference is established between the anodes. This optimum amount of' energy is desirable in order to increase the rate at which the molecules of gas are ionized by the electrons striking such molecules.

Furthermore,,by delaying the movement of the electrons, between the electrodes, the electrons oscillate for an increased period of time within each electrode. Since 5 gauge constituting one embodiment of this invention;

- FIGURE 2 is a schematic view, partially in'section and partially in block form, illustrating the construction of the embodiment'shown in FIGURE 1; and

FIGURE 3 is a schematic view, partially in section and partially in block form, illustrating a second embodiment of the improved ionization gauge constituting this invention.

In the embodiment of the invention shown in the drawings, an enclosure is formed from an electrical conductor, such as brass or stainless steel, which has. non magnetic properties. The enclosure 10 may be in the form of a cylinder and is at a suitable reference potential such as ground. The enclosure 10 is provided with a conduit 12 to receive molecules of gas from any suitable source (not shown).

A pair of electrodes 14 and 16 are disposed within the enclosure 10. Each of the electrodes 14 and 16 is preferably in the form of a cylinder with the axis of the cylinder defining each electrode corresponding to the axis of the cylinder defining the enclosure 20. The electrode 14 is provided with a pair of openings 20 and 22 at its opposite faces and the electrode 16 is provided with a pair of openings 24 and 25 at its opposite faces.

7 By. way of illustration, the electrodes 14 and 16 may be provided with a diameter in the order of 1 /2 inches and with an axiallength in the order of /2 inch. The electrodes 14 and 16 may be separated from each other by a distancein the order of /2 inch. Theopenings 20,

22, 24 and 25 in the electrodes 14 and 16 may be axially aligned with the electrodes themselves and may be provided with diameters in the order of inch.

The electrodes 14 and 16 are connected to the opposite ends of a winding 32, the center tap'of which is connected to receive a suitable potential such as +200 volts from a source of direct voltage. The electrodes 14 and 16 also receive analternating voltagebecause of .the'

magnetic coupling between a winding 36 and the winding 32. The'winding 36 receives the alternating voltage from a source 38 at a suitable frequency such as two .megacycle s per second. a

The alternating voltage introduced to the electrodes 14 and 16, may have a peak amplitude in the order of +50 volts, although peak amplitudes as low as 20 volts or lower or as high as volts or higher may also be used. The introduction of alternating voltage at the particular frequency such as 2 megacycles per second is facilitated by connecting a capacitor 34 across the winding 32 to produce a tank circuit resonant at the particular frequency. The alternating voltage introduced to the electrode 14 has a displaced phase relationship relative to the alternating voltage introduced to the electrode 16. This phase displacement is preferably A grid 26 is disposed between the electrodes 14 and 16 in equally spaced relationship to the electrodes. The grid 26 is provided with a hollow annular configuration and is disposed with its center on the axis defining the electrodes 14 and 16 and the enclosure 10. The grid erties. The grid is connected to the source 30 to receive a suitable biasing voltage such as +100 volts when direct potentials of +200 volts are applied to the electrodes 14 and 16.

A grid 52 is disposed between the electrode 14 and the wall defining the upper face of the enclosure 10. The grid 52 may be provided with a hollow annular configuration and is disposed with its center on the axis common to the cylindrical electrodes 14 and 16. The grid 52 is made from a suitable material, such as brass or stainless steel, which has non-magnetic properties. The grid 52 is connected to receive a suitable negative potential such as l00 volts from the source 30. A grid 50 having a construction corresponding to that of the grid 52 is disposed between the electrode 16 and the bottom wall defining the enclosure 10. The grid 50 is disposed in axially aligned relationship with the grid 52 and is connected to receive the potential of 100 volts from the source 30.

The charged particles within the enclosure 10 are subjected to a magnetic field as by a pair of magnetic poles 40 and 42. The pole 40 may constitute a north pole and the pole 42 may constitute a south pole. The poles 40 and 42 are disposed at opposite ends of the enclosure 10 along'the axis common to the electrodes 14 and 16 and the walls defining the enclosure 10. By way of illustration, the poles 40 and 42' may beconstructed to produce a magnetic fieldin the order of 100 gausses although the poles may be constructed to produce increased magnetic fields up to 1000 gauses and even higher. Although the poles '40 and 42 are preferably formed from permanent magnets, it should be appreciated that the polesmay also constitute electromagnets in which magnetic fields are produced by passing an electrical current through coils disposed around the poles.

Some electrons always exist within the enclosure 10. These electrons tend to be attracted into the spaces'defined by the electrodes 14 and 16 since the electrodes 14 and 16 receive positive potentials and since the electrodes 14 and 16 have substantially no electrical field within the spaces definedv by the electrodes. During the time that no alternating voltage is introduced from the source 38 to the electrodes 14 and 16, the electrons tend to oscillate in'a random. pattern Within the spaces defined by the electrodes.

Upon the introduction of an alternating voltage from the source 38 to the electrodes 14 and 16, the voltage on one of the electrodes tends to rise at the same time that the voltage on the other electrode is falling. This potential difference causes the electrons within one of the 1 in the electrode 16 when the electrons strike such molecules of gas.

In the next half cycle of the alternating voltage from the source 38, the potential on the electrode 14 rises above the potential on the electrode 16. This causes the electrons within the electrode 16 to be attracted toward the electrode 14. When the electrons reach the electrode 14, they strike molecules of gas within the electrode 14 so as to ionize such molecules.

In this way, a progressive number of electrons is produced in each successive half cycle of the alternating voltage from the source 38. As the number of electrons within the enclosure increases, the probability increases that the electrons will strike molecules of gas and ionize such molecules. Because of this, a cumulative number of electrons is produced from the molecules of gas in the successive half cycles of the alternating voltage from the source 38.

The electrons move in a reciprocal path between the electrodes 14 and 16 through the openings 22 and 24 in the electrodes without tending to strike the walls of the electrodes. This results from the action of the poles 40 and 42 in channeling the movement of the electrons parallel to the axis common to the electrodes 14 and 16 and the walls defining the enclosure 10. The poles 40 and 42 provide such a channeling action on the electrons because the lines of magnetic flux between the poles arein a direction parallel to the axial line common to the electrodes 14 and 16 and the walls defining the enclosure 10.

The grid 26 is instrumental in insuring that the electrons strike molecules of gas with sufficient force to ionize the molecules. This results from the bias introduced to the grid 26 from the source 30 relative to the positive potential applied to the electrons 14 and 16 from the source to obtain the movement of the electrons between the electrodes 14 and 16 only in the portions of each alternation where the potential has an increased value relative to the value of the potential at the initiation of each alternation. The bias on the grid 26 relative to the potential on the electrodes 14 and 16 prevents electrons from moving between the electrodes 14 and 16 during the time that no alternating voltage is introduced to the electrodes from the source 38.

The grid 26 also prevents the electrons from moving between the electrodes 14 and 16 during the time that the alternating potential from the source 38 has established a relatively low voltage difference between electrodes 14 and 16. In this way, the electrons are able to move between the electrodes 14 and 16 only as the alternating potential from the source 38 approaches its peak value in each half cycle. Because the electrons are able to move between the electrodes 14 and 16 only at the peak of the alternating voltage from the source 38, the electrons acquire in their motion between the electrodes 14 and 16 an optimum amount of energy. This insures that the electrons will strike molecules of gas within the electrodes 14 and 16 with increased probability of ionizing such molecules. The grid 26 is accordingly instrumental in assuring that the ionization gauge constituting this invention operates efficiently in producing electrons and positive ions from the molecules of gas within the enclosure.

The grid 26 is also instrumental in another important way in assuring that the ionization gauge constitutmg thls invention operates efficiently in ionizing the molecules of gas within the enclosure 10 at an optimum rate. This results from the operation of the grid 26 in each half cycle of the alternating voltage from the source 38 in delaying the movement of the electrons between the electrodes 14 and 16. This delay causes the electrons to remain an increased length of time within one of the electrodes 14 and 16 in each half cycle of the alternating voltage. During the time that the electrons remain within each of the electrodes 14 and 16, they have an oscillatory movement because of the opposing forces produced on the electrons 'sion of electrons from the walls.

by the electrodes. Because of their oscillatory movement within each of the electrodes 14 and 16, the electrons have an increased opportunity to strike molecules of gas and ionize such molecules.

The electrons moving in the reciprocal path between the electrodes 14 and 16 do not strike the walls defining the enclosure 10. This results from the positive potential on the electrodes 14 and '16 relative to the potential on the walls defining the enclosure 10. It also results from the considerable distance between the electrodes and the walls defining the enclosure 10.

The positive ions produced from the molecules of gas from the enclosure 10 may tend to drift toward the walls defining the enclosure 10 since the grounded potential on the walls defining the enclosure 10 is negative with respect to the positive potential on the electrodes 14 and 16. The positive ions will generally not strike the walls defining the enclosure 10 with a sufficient force to produce a significant secondary emission of electrons from such walls. The reason is that the potential difference between the electrodes 14 and 16 and the walls defining the enclosure 10 is relatively low.

As will be seen, the openings in the grid-s 26, 50' and 52 are greater than the openings 20 and 22 in the electrode 14 and the openings 24 and 25 in the electrode 16. Because of the increased openings in the grids 26, 50 and 52, any electrons secondarily emitted from the grids are inhibited from moving in a path which would cause them to join the electrons moving in a reciprocal path between the electrodes 14 and 16.

Any electrons secondarily emitted from the walls defining the enclosure 10 are repelled by the grids 50 and 52 so as to return to the walls. In this Way, the electrons secondarily emitted from the walls defining the enclosure 10 are prevented from moving into the region within the electrodes 14 and 16 to join the electrons produced from the molecules of gas within the enclosure. Because of this, only the electrons produced from the molecules of gas within the enclosure 10 are instrumental in producing the ionization of other molecules of gas within the enclosure into electrons and positive ions.

The apparatus constituting the invention has certain important advantages. It provides an efficient production of electrons from the molecules of gas within the enclosure 10. The electrons are produced entirely from the molecules of gas within the enclosure 10 and are not obtained from any secondary emission of electrons from the electrodes 14 and 16 and the walls defining the enclosure 10. This causes the apparatus constituting this invention to constitute a source of charged particles whereby an improved control is obtained over the production of the charged particles in comparison to the sources now in use.

Since the electrons are produced entirely fro-m molecules of gas, the walls defining the enclosure 10 cannot be contaminated chemically with positive ions obtained from molecules of the different gases within the enclosure 10. Even if the walls defining the enclosure 10 in the apparatus constituting this invention should be contaminated by the molecules of the different gases, this does not affect the operation of the apparatus since the charged particles in the apparatus are not obtained from the walls.

Contamination has been troublesome in the apparatus of the prior art since the positive ions obtained from the molecules of the different gases within the enclosure have been intentionally directed in the prior art to the walls defining the enclosure so as to produce a secondary emis- Since molecules of different gases are introduced into the enclosure at different periods of time, the walls defining the enclosure in the apparatus of the prior art eventually become contaminated with these different molecules. This has prevented the apparatus of the prior art from providing a sensitive and accurate indication as to the number of molecules of gas within the enclosure. This has been especially true since contamination of, the walls affects the number of electrons secondarily emitted by each positive ion from the walls defining the enclosure in the apparatus of the prior art.

As disclosed in c-opending application Ser. No. 126,554 the apparatus constituting the invention may be used as an ion source or as a vacuum pump in addition to its use as an ionization gauge. When the apparatus constituting this invention is used as an ion source, the positive ions produced within the enclosure from the molecules of gas within the enclosure are channeled through,

an opening in the enclosure to output apparatus which uses the ions. When the apparatus constituting this invention is used as a vacuum pump, the ions produced from the molecules of gas within the enclosure 10 are channeled through the opening in the enclosure and are collected after passing through such opening. Since the ions are withdrawn from the enclosure, the molecules of gas in the enclosure 10 eventually become considerably reduced in number.

The embodiment shown in FIGURE 3 operates on the same general principles as the embodiment shown in FIG- .URES 1 and 2. However, in the embodiment shown in FIGURE 3 the electrons move in an arcuate path between the electrodes rather than in a linear path as in the embodiment shown in FIGURES 1 and 2. In the embodiment shown in FIGURE 3, a pair of electrodes F100 and .102 are disposed relative to one another in a manner similar to the relative disposition of the electrodes 14 and 16 in the embodiment shown in FIGURES 1 and 2. Each of the electrodes 100 and 102 is provided witha substantially frusto-conical configuration wherein the bases of the 'fr-ustrums in the electrodes 100 and 102 face each other. The electrode 100 is provided with openings 104 and 106 respectively corresponding to the openings 20 and 22 in the. electrode 14, and the electrode 102 is provided with openings 108 and 110 respectively corresponding to the openings 24 and 25 in the electrode 16.

Grids 11 2,. 11 4 and 116 respectively correspond to the grids 26, 50 and 5 2 in the embodiment-shown in FIG- URES 1 and 2. The grids 1'12, 114 and 116 have a construction, con-figuration and relative disposition similar to the construction, configuration and relative disposition of the grids 26, 50 and 52 in the embodiment shown in FIGURES l and 2. A'pair of magnetic poles 120 and 122 respectively correspond to the poles 40 and 42 in the embodiment shown in FIGURES 1 and 2. The poles are provided with hemispherical configurations at their ends, as indicated at 124 and 126 in FIGURE 3.

Because of the configuration of the electrodes 100 and 102 andbecause of the hemispherical pole faces 124 and 1 26, the electrons travel in an arcuate path as indicated in broken lines at 130 in FIGURE 3. The path of the electrons tends to diverge during the movement of the electrons from each of the electrodes 100 and 102 toward the grid 112. The electrons tend to converge during their movement past the grid 112 toward the electrodes 100" and 102. Since the electrons tend to converge during their movement toward each of the electrodes 100 and 102, they tend to become focussed so as to be maintained upon the electrodes and 102 and on the grid 1:12.

Although this application has been disclosed and illustrated with reference to particular applications, the principles involved are susceptible of numerous other applications which will be apparent to persons skilled in the art. The invention-is, therefore, to be limited only as indicated by the scope of the appended claim.

What is claimed is:

In combination for obtaining a controlled production of charged particles from a plurality of molecules, a source of direct voltage, first means coupled electrically to the source of direct voltage and provided with an extended length in a first direction and constructed to provide a substantially uniform electrical field along the extended length in the first direction and provided with an opening for a movement of electrons through the first means in the first direction, second means coupled electrically to the source of direct voltage and provided with an extended length in the first direction and constructed to provide a substantially uniform electrical field along the extended length in the first direction and provided with a second opening to obtain a movement of electrons in the first direction through the second opening, the second means being displaced relative to the first means in the first direction to obtain a movement of electrons in the first direction'between the first and second means through the openings in the first and second means, means coupled electrically to the first and second means tointroduce alternating voltages to the first and second means with the phase of the alternating voltage introduced to the first means being displaced relative to the phase of the alternating voltage introduced to the second means to obtain avmovement of electrons in the first direction between the first and second means through the openings in such means and to obtain the production of charged particles from the molecules as a result of such movement,

third means disposed between the first and second means in the first direction to control the movement of electrons in the first direction between the first and second means,

and means coupled electrically to the third means to bias the third means relative to the first and second means for obtaining a movement of electrons between the first and second means only in a limited portion of each half cycle of the alternating voltage and with suflicient energy to ionize molecules.

References Cited by the Examiner JAMES W. LAWRENCE, Primary Examiner.

RALPH G. NILSON, GEORGE N. WESTBY, Examiners.

C. O. GARDNER, D. E. SRAGOW, V. LAFRANCHI, Assistant Examiners.

Images