US3228589A

US3228589A - Ion pump having encapsulated internal magnet assemblies

Info

Publication number: US3228589A
Application number: US316694A
Authority: US
Inventors: William J Kearns
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1963-10-16
Filing date: 1963-10-16
Publication date: 1966-01-11
Anticipated expiration: 1983-01-11
Also published as: GB1073168A; FR90880E; FR1415012A; GB1158486A; US3325086A

Description

Jan. 11, 1966 w. J. KEARNS 3,228,589

ION PUMP HAVING ENCAPSULATED INTERNAL MAGNET ASSEMBLIES Filed Oct. 16, 1963 3 Sheets-Sheet 1 lNVENTOFI WILLIAM J. KEARNS,

HIS ATTORNEY.

ION PUMP HAVING ENCAPSULATED INTERNAL MAGNET ASSEMBLIES Filed OCt- 16, 1963 W. J. KEARNS Jan. 11, 1966 3 Sheets-Sheet 2 INVENTOR WILLIAM J. KEARNS,

BY ms ATTORNEY.

W. J. KEARNS Jan. 11, 1966 ION PUMP HAVING ENCAPSULA'I'ED INTERNAL MAGNET ASSEMBLIES 3 Sheets-Sheet 3 Filed Oct. 16, 1963 LQAD LINE CURVE QZQUUM tml MEN-:4 qmmlm MAGNETIC FIELD GAUSSE'S DEMAGNETIZATION SLOPE 8/H ENERGY PRODUCT DH X10 ALNICO 5 ALNICO 8 BAR/UM FERRITE I 400 DEMAGNETIZING FORGE (H) osnsrzns FIG.9.

INVENTOR WILLIAM J. KEARNS,

HIS ATTORNEY.

United States Patent 3,228,589 HGN PUMP HAVING ENCAPSULATED INTERNAL MAGNET ASEMBLIES William J. Kern-us, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed Oct. 16, 1963, Ser. No. 316,694 Claims. (Cl. 230-69) This invention relates to ionic vacuum pump apparatus and more particularly to ionic vacuum pumps incorporating a plurality of encapsulated magnets utilized in an internal modular arrangement within ionic pump apparatus being evacuated.

The continuous and increasing use of ion-type vacuum pumps has led to the requirement that these pumps have increased capacity and efficiency while at the same time be of an economical and simple design. Commensurate with the efliciency and capacity requirements are those desirable pump configurations which provide widespread or flexible applications of the pump to varying or different uses or demands.

The ion-type vacuum pump does not lend itself readily to ordinary scaling up or interchangeable techniques since these techniques lack a complete underlying theoretical understanding of the operative concepts involved, and this understanding is necessary in order to establish changes which provide increased pump capacity or wide applicability of the pumps to varying and differing applications.

Accordingly, it is an object of this invention to provide an improved ionic vacuum pump.

It is another object of this invention to provide an improved magnet assembly for ionic vacuum pumps.

It is a further object of this invention to provide an improved plural magnet structure configuration for ionic vacuum pumps.

It is yet another object of this invention to provide modular magnet and electrode assemblies for ionic vacuurn pumps.

It is yet another object of this invention to provide an improved ion vacuum pump employing a peripheral-like or curved row of magnets within the pump enclosure.

It is still another object of this invention to provide an improved ionic vacuum pump employing a separately assembled circular row of encapsulated magnets within an ionic pump enclosure subjected to low pressure conditions.

It is still another object of this invention to provide an ionic vacuum pump with a stacked array of magnet assemblies with an add-on feature.

It is still another object of this invention to provide an improved ionic vacuum pump structure which provides a choice of easily replaceable magnet and electrode assemblies and therefore a choice of pump capacities to be obtained.

It is yet another object of this invention to provide a circular closed row of specifically shaped encapsulated magnets within a circular evacuating chamber in a triode ionic vacuum pump.

It is yet another object of this invention to provide a magnet and electrode structure which will function in any vacuum enclosure large enough to contain the mentioned parts and which does not require a specially shaped container.

Briefly described, this invention in one preferred form includes a cylindrical enclosure member subjected to evacuating conditions, with a circular row of specifically shaped encapsulated and vacuum sealed magents therein. The circular row of magnets is positioned adjacent to but spaced from the inner periphery of the enclosure member and concentric therewith. The encapsulated magnets "ice are also retained in lateral spaced-apart relationship peripherally, and in each space between magnets there is positioned an anode-cathode assembly to provide, in overall configuration, a circular row of interdependent ionic pump configuration cooperatively acting to remove gases from the defined peripheral enclosure.

This invention will be better understood when taken in connection with the following description and the drawings in which FIG. 1 is a cross-sectional view of one preferred embodiment of this invention.

FIG. 2 is a top view of the embodiment of FIG. 1.

FIG. 3 is a partial view of one anode structure which is employed in the embodiment of FIG. 1.

FIG. 4 is a partial view of one cathode structure which is employed in the embodiment of FIG. 1.

FIG. 5 is an illustration of supporting and mounting means for an anode-cathode assembly of this invention.

FIG. 6 shows a series of curves indicating pumping speed vs. magnetic field strength in an ionic vacuum pump.

FIG. 7 illustrates a hysteresis curve for a permanent magnet material.

FIG. 8 illustrates a series of curves of unit property characteristics of magnet materials in Alnico 5, Alnico 8 and barium ferrite magnets.

FIG. 9 is a schematic illustration of a magnet circuit.

One measure of efficiency of an ion pump is the ratio of the pumping speed to the pump volume or weight. It is a continuing desirable feature of ionic pumps that this ratio be increased to more optimum or maximum values. It has been discovered that this ratio may indeed be increased to approach optimum values by utilizing a plurality of encapsulated magnets which, together with their cooperating electrode structures, are positioned within the evacuation enclosure. The enclosure may thus be of simple design and minimum weight. Referring now to FIGS. 1 and 2, there is shown a preferred embodiment of an ionic pump utilizing the specific features of this invention.

In FIG. 1 ionic pump 10 includes in one preferred form, a cylindrical enclosure or cylinder 11 suitably supported by one or more support or mounting

members

12 and 13. Enclosure member 11 is ordinarily a gas-impervious material, preferably a metal, for example stainless steel, which may be formed by a hydroforming process so that no welds or seams are necessary. In one ion pump in accordance with the practices of this invention, enclosure member 11 is a closed bottom hydroformed stainless steel cylinder or can about 20 inches internal diameter, about 20 /2 inches height and about A inch thick. Enclosure member 11 is provided with a top or cover assembly 14 which may be suitably sealed by suitable flange gasketing arrangements 14' or by welding to the enclosure member 11 to provide a vacuum tight volume. In order to provide attachment and flow communication of enclosure 11 with a structure to be evacuated, cover assembly 14 is provided with a large neck conduit or flanged aperture member 15. Enclosure 11 together with cover assembly 14 constitutes the ionic pump housing which houses the magnet assemblies 16 and anode-cathode electrode assemblies 17.

As best shown in FIG. 2, magnet assemblies 16 are arranged in a peripheral array of circular row, in lateral spaced-apart relationship to each other, and also concentrically positioned in enclosure 11 to define a central open space 18. Each of the magnet assemblies 16 as illustrated is positioned adjacent but spaced from the internal periphery or wall of the enclosure 11, and each magnet assembly is of the illustrated trapezoidal cross-sectional configuration with the smaller faces directed inwardly or towards the center of enclosure 11. By means of this arrangement and magnet configuration the lateral or ad jacent spaces between magnets are equal coextensively in length, width and height, and open channel or flow spaces are provided around the magnet assemblies 16 for increased pumping efficiency.

Heretofore the positioning of a magnet within the confines of an evacuated enclosure or pump introduced the inherent problems of outgassing of the magnetic material and gas leakage detection. For these more important reasons the magnets have usually been mounted on the outside of a given vacuum enclosure member. However, many of the design criteria of ionic pumps are highlydependent on the magnetic field strength between adjacent magnets, and it is obvious that such magnetic field strength is in turn dependent upon the spacing of the magnets. The introduction of extraneous material between magnet assemblies thus increases the space between the magnet assemblies While at the same time decreasing the field strength and the pumping efiiciency of the pump. For example, it is generally considered each inch of gap space requires inch of magnet length between the gaps. The far reaching effect of the practice of introducing extraneous material between magnets is to require proportionately more magnet material which occupies useful pump space, and the overall volume for a given capacity pump is increased or pump capacity decreased. It is further undesirable to introduce extraneous metal members between adjacent magnets, for example by suitably forming the enclosure 11 to provide a pcripheral row of indentations and thereafter positioning the magnets in the indentations. A desirable feature of these pumps is to have as much unrestricted flow area as possible and eliminate all unnecessary curves, corners or projections which may inhibit free-flow conditions. The mentioned indentations detract from conductance or free-flow conditions.

In order to prevent outgassing of the magnet material or any gas leakage therefrom during future operation of the pump, each magnet assembly 16 is encapsulated by an encapsulating material 19 as illustrated in FIG. 2. Such a material 19 may be either metallic or non-metallic provided it performs the function of encapsulating or vacuum sealing the inner magnet material without gas leakage. Accordingly, material 19 may be of stainless steel in folded sheet form or as a seamless can, channel or enclosure, having a wall thickness of about .060 inch, and suitably vacuum sealed. In one practice of this invention encapsulating material 19 is in sheet form and suitably folded about individual columns of magnets for welding along the backside of the assemblies as at 20. Referring again to FIG. 1, each magnet assembly 16 includes one or more individual magnets 21-24, the particular number being chosen with respect to availability of the magnets and the economic circumstances of their manufacture. At each end of the magnet assemblies 16 a block 25 of stainless steel is suitably welded to encapsulating material 19 so that each magnet assembly is provided with an encapsulating envelope. The thicker blocks 25 lend structural rigidity to the magnet assemblies and further provide attaching means therefor.

As described, encapsulation is employed to prevent outgassing of the magnetic material during pump operation, a problem previously deterring the use of internal magnets subjected to high vacuum conditions. The magnet assemblies 16 are prepared by evacuating the encapsulating envelope to only a few microns of mercury internal pressure, baking out the magnets at a temperature at least as high as that to be encountered in intended use, and then backfilling the encapsulating envelope with a gas such as helium which is used as a tracer gas in the event of leakage of the envelope at a future time. Backfilling is limited to between about 100 microns to a few torr of helium. Evacuated conditions in the magnet assemblics is also desirable to prevent dimensional &

changes in the gap between magnets during future pump operation under varying conditions.

Each magnet assembly .thus represent-s a column of enclosed stacked magnets, and in a preferred embodiment of this invention for a 1000 liter/sec. pump, ten magnet assemblies are employed within enclosure 11. The crosssectional dimensions of the trapezoid magnets are: a base of about 4V2 inches, a face of about 2 /2 inches and about 3 inches therebetween. The use of a smooth cylindrical configuration for the outer enclosure member 11, together with the thin encapsulating material 19 about the magnet assemblies 16 provides an optimum clearance or lateral spacing between each pair of magnet assemblies 16 of about 1.625 inches.

In order to maintain the individual magnet assemblies 16 in their illustrated peripheral position (as shown in FIG. 2), the magnet assemblies 16 are premounted in a module type assembly. More particularly, and referring to FIG. 1, the magnet assemblies 16 in the form of columns are positioned in a peripheral row between and perpendicular to the plane of atying ring 26 at the base of the circular row of magnet assemblies 16, and a tying ring 27 at the top of the circular row of magnet assemblies 16. These tying rings 26 and 27 are in the form of circular outgassed stainless steel disks having very

large apertures

28 and 29 respectively therethrough. These

rings

26 and 27 define a washer-like or annular flange structure to which magnet assemblies 16 are attached. Various suitable attachment devices may be employed to afiix a magnet column assembly 16 to tying rings 26 and 27. For example, bolts 30 may pass through apertures in the rings and threadedly engage blocks 25 or studs on blocks 25 may pass through the rings et cetera.. Ring 26 or ring 27 may then be suitably attached to the enclosure 11 also by a threaded, connection illustrated generally for example at 31. Tying rings 26 and 27 in their respective relationship provide rigid lateral space relationship of the magnet assemblies while at the same time performing the function of providing an integral modular structure, or unit assembly 32 of the ring of magnets. The magnet assemblies 16 unit or module 32, including the

rings

26 and 27 and the mounted magnet assemblies 16, greatly facilitates general handlings of the magnets since the modular or unit structure is a pre-assembled item. The number of magnets may vary from as low as three to as many as ten (FIG. 2). A lower limit of four magnet assemblies is preferable.

The modular structure or unit assembly 32 of the magnet assemblies 16 is an important feature of this invention since these unit assemblies may be made inv a wide variety of predetermined shapes and sizes, not only for standardization purposes but also for interfitting or" replacement relationships in the same or different pumps. or as a pumping unit in a large vacuum enclosure. In'. this manner the overall capacity of a given ion pump may be changed by merely inserting Within the enclosure: 11 of FIG. 1 the proper magnet unit assembly which: will provide the pump with, for example, a liter/sec.,. 250 liter/see, 500 liter/see,- or 1000 liter/sec. capacity. In this respect for example a given modular structure: magnet unit assembly of a height H may provide 100 liter/sec. capacity and a height of 2H may provide a. 250 liter/sec. capacity, et cetera. Therefore, one may reduce or increase the capacity of this pump merely by inserting or removing the type of magnet structure described. By the same token, a given pump design may be scheduled or assembled for varying pump requirements merely by the insertion of the proper and standard modular magnet unit assembly.

Between each spaced-apart magnet assembly 16 there is positioned an anode-cathode electrode assembly 17 to provide ionic pumping means between adjacent magnet assemblies 16. As illustrated in FIG. 5, each of the electrode assemblies 17 included spaced-apart cathode elec trodes 33 and 34 with an intermediate electron and ion transparent grid-type anode 35. In one preferred form of this invention anode 35 comprises a square grid structure, as illustrated in FIG. 3, composed of a plurality of longitudinal strips 36 and transverse strips 37. These strips are provided with spaced transverse slots along their longitudinal length and thereby the strips interengage with each other to provide the familiar eggcrate type or general honeycomb structure. In one operative practice of this invention these

strips

36 and 37 were on the order of about 7 /2 inches length, /2 inch width, and were made of .012 inch thick titanium.

Other anode electrode configurations may also be employed in this invention in addition to the composite grid or honeycomb design. For example, a plurality of separate and. discrete anodes may be employed, or suitable open meshes, a plurality of spaced meshes, et cetera. One or more of the anode grid structures are provided to extend vertically along the full height of the magnet column assemblies 16 although the capacity of the pump may be varied where less anode structure is employed. It is preferred, however, to have similar heights for magnets as well as electrodes.

The

cathode electrodes

33 and 34 are positioned one on each side of the grid anode 35 as shown in FIG. 2. The construction of the cathodes is best shown in FIG. 4 where each

cathode

33 and 34 in one preferred example comprises an electron and ion transparent honeycomb or grid structure of long thin titanium strips 38 and 39 of about .008 to .015 inch thickness and /s inch height or depth to provide a nominal dimension of about inch across the individual grid openings, as compared to about /2 inch across the individual grid openings of the anode 35. Each of the

cathodes

33 and 34 is enclosed within a suitable supporting frame 40.

The supporting means for an anode-cathode assembly 17 may best be described as follows. All metal parts are of stainless steel or other material of non-magnetic and gas-free characteristics. In FIG. 1 a series of metal supports or columns 41 are suitably attached to

rings

26 and 27 for example by threaded connection means 42. The anode-cathode assemblies 17 are then attached to and supported by supports 41 as illustrated in FIG. 5. Referring now to FIG. 5, the individual attaching means for an anode 35 may comprise a suitable machine screw 43 which passes through an aperture in an end strip 36 of anode 35, an aperture through support 41, and threadedly engages a cylindrical electrically insulating alumina or ceramic block 44 on the opposite side of support 41. A metal sputter cap or shield 45 is fitted over the exposed end of block 44. Thereafter a U-shaped clip 46 is suitably attached to block 44 by means of screw 47 passing through clip 46 and threadedly engaging block 44. The upstanding or extending arms of clip 46 are in parallel relationship to anode 35, and frame 40 containing a

cathode

33 or 34 is attached thereto by means of a screw 48 passing through an arm of clip 46 and threadedly engaging frame 40. In order to maintain established spaced relationship at the unsupported ends of the anode 35 and

cathodes

33 and 34, suitable small clips are welded across the unsupported ends of

cathodes

33 and 34 as illustrated. Sputter shield 45 prevents short circuiting of the anode and cathodes due to sputtered cathode material. In one preferred form of this invention as illustrated, a pair of the described attaching means (other than support 41) is employed for each anode-cathode assembly 17, and a pair of anode-cathode assemblies 17 is attached to each support 41 in end-to-end or vertical relationship. As can be seen in FIG. 1, a disengagement of connections 42 on a rod 41 permits removal of a mounted vertical pair of electrodes.

In order to facilitate mounting and dismounting of the anode-cathode assemblies in enclosure 11, and to provide proper electrical connection thereto, a plurality of supports 41 may be suitably joined together by means of one or more connecting strips 49 as illustrated in FIG. 2 to provide an electrode unit assembly. Referring to FIG. 2, stainless steel strip 49 is 30 inches long, inch wide by .035 inch thick, and contains transverse slots therein which are adapted to be slidably engaged under screws 47. As illustrated in FIGS. 1 and 2, five vertical pairs of electrode assemblies are laterally joined together as a unit in a row by four connector strips 49. Referring again to FIG. 1, cover assembly 14 includes electrical connection means 50 and 51 which are adapted to provide suitable electrical connections from an external source of electrical power to the pump. From one of the connection means for example 50 an electrical stainless steel wire lead 52 connects to an upper connector strip 49, with a jumper stainless steel lead 53 connecting to a lower strip 49. The electrical connection is, therefore, made to upper and lower anode-cathode assemblies as a unit and to /2 the number of units or five laterally adjacent units. The same connection is utilized for the remaining five units. A suitable ground connection 52 is made to the enclosure 11 to complete an electrical circuit and establish the desired electrical potential.

One of the overriding features in an ion pump is the magnet assembly, and upon the magnet assembly depends most of the operating parameters of the pump. Included among the important factors affecting the choice of a suitable magnet material are the etfect of the magnetic field on the pumping speed of the pump and the environment to which a pump may be subjected, for example high bakeout temperatures or mechanical shocks, et cetera. FIG. 6 is illustrative of a series of curves showing the dependence of the speed of an ionic pump on the associated magnetic field. From an inspection of these curves it can be seen that the pumping speed increases for increased magnetic field, especially for the higher voltages for a given set of pump electrodes up to about for example 3000 gausses. Beyond this field. strength, the increase in pumping speed may not justify the economics of higher magnetic field strength. A, B and C represent area dimensions of opposed spaced magnet poles.

The magnets employed in the practice of this invention are permanent magnets produced from permanent magnet materials which are characterized by a very wide hysteresis loop such as is shown schematically in FIG. 7. Referring now to FIG. 7 the heavy dashed line illustrates the initial magnetizing curve. If the magnetizing force denoted as H increase-s beyond the saturation level H there is no further increase in the induction B. When the current is reduced, B does not retrace the dashed line but remains high and crosses the axis H at zero at a high value B the residual induction. In order to reduce B to zero a high demagnetizing field equal to the coercive force I-I must be applied, resulting in the curve B H in the second quadrant. The shape of this curve B H the demagnetization curve, is determined entirely by the ma netic properties of the permanent magnet material. In the ionic pumps of the present invention the preferred materials are Alnico 5, Alnico 8, and in some instances barium ferrite, the choice depending upon the nature of the pump service and. the required gap length. For small ionic pumps Alnico 5 is generally used because it is relatively inexpensive and can be cast into a variety of useful shapes. (Permanent Magnets and Their Applications, R. 1. Parker & R. J. Studders, Wiley & Sons, New York, 1962).

The demagnetization curves for these materials are shown in FIG. 8 which is the second quadrant of the total hysteresis loop showing the relationship of the magnetizing force H and the residual induction B. Superimposed on these curves are the contour lines of constant energy product BE in units of gaussoersteds. The contour line tangent to the demagnetization curve of a particular material establishes the maximum energy product (maximum gaussoersted). The maximum energy point on the demagnetization curve is the operating point of the magnet where the maximum field is obtained for a minimum magnet volume. The sloping straight lines 2 L H L H Since flux lines are continuous the following relationship also holds:

(3) A B A B =0 Solving for L and A in

equations

2 and 3 respectively and multiplying each side together yields the important equation which shows the significance of the maximum energy product BH. That is, the minimum magnet volume, and hence weight, is achieved for a given magnetic requirement if the magnetic design can be arranged so that the material is working at or near its maximum energy prodnot.

For most ion pumps the required gap length or distance L is usually about 1 /2 inches and the required gap area is from about 9 sq. in. to 50 sq. in. depending on the speed rating of the pump. Also, in most ion pumps the area of the magnet face A is equal to A the area of the gap. Therefore B/H is determined by the ratio of the magnet length to gap length only. Returning now to FIG. 5 and using the relationship B. =B H to determine the slope of the load line, we find that the maximum energy product for Alnico 5 occurs at slopes of 21 for Alnico 5, 6 for Alnico 8 and 1.2 for barium ferrite. For gap fields up to 1500 or 1600 gausses, barium ferrite magnets are probably the most efficient to use since the length of the magnet (i.e., in the direction of magnetization) is roughly equal to the length of the gap. It is particularly useful for magnetic circuits containing a number of gaps and magnets in series to form a closed loop as in many multiple stack ion pumps. Alnico 5 is seen to require the greatest amount of magnetic material for a given gap length. However, it is also capable of producing the highest field in the gap and fields of 5000 gausses are not uncommon in Alnico 5 magnets with large gaps. Alnico 8 has a demagnetization curve approaching the straight line of barium ferrite but has a much higher induction so that a reasonably high field can be produced in gaps suitable for ion pumps without excessively long magnets. Thus a magnetic circuit with multiple gaps can easily be obtained using Alnico 8 with fields up to 2500 gausses.

If the choice of a magnet material were to be based solely on the maximum energy product, barium ferrite would be a desirable material. However, according to the curves in FIG. 7 it is more desirable to use larger fields than 1500 gausses. In addition many pumps are subjected to bakeout processes to at least 250 C. and on some occasions to 400 C. For high or bakeout temperatures the ferrite magnets must be removed from the pump to prevent demagnetizing, whereas Alnico magnets may be baked to 500 C. safely. Removing large magnets from their magnetic circuit is quite difiicult because of the large mechanical forces involved. Therefore, because of the considerations of high field and high temperature cam rn m pability, Alnico 8 is a preferred optimum magnet material for larger ion pumps. The design equations given above do not include the problem of leakage flux and are presented to show the various parameters important to the design of ion pumps.

To provide a series of ion pumps in the range of 100 liter/sec. to 2500 liter/sec. and higher without requiring excessive design variations, a modular approach as described is used. The magnet modules or unit assemblies themselves include two sizes, a small liter/sec. module having a magnetic field area of about 3 inches by 3 inches and a large nominal 50 liter/ sec. module having a magnetic field area of about 3 inches by 7 /2 inches. It is desirable that both of these triode-type magnet pumping units have a close spacing between the collector surfaces of about 1% inches. The modular concept may provide a series of magnet units and anode-cathode units or sub-units where the units are interchangeably mounted in a suitable enclosure.

If the protrusion of the enclosure or vacuum wall which usually surrounds the electrode space could be eliminated 'or reduced considerably, less magnet material would be needed to produce the required field. The protrusion of the vacuum enclosure wall has been eliminated in the design of the magnet assemblies of this invention by encapsulating the magnets themselves in thin wall stainless steel envelopes or cans and placing them inside of the vacuum enclosure. Thus there is no need for any part of the heavy enclosure wall 11 to project or protrude into the space between magnets. The cans are evacuated and baked to remove the water vapor and gases from the metal casings so that on subsequent heating the can will not experience an internal pressure. The cans are backfilled with helium to a few torr pressure so that they can be leak checked and are then sealed off by welding a stainless steel tubulation.

Magnetizing a ring magnet unit may be carried out by magnetizing each magnet element separately and then assembling the individual magnets in assembly 16, or magnetizing the entire modular unit 32 with the magnet assemblies 16 bolted in place. The first method is easier as far as obtaining a high field in each magnet. However, when the magnets are removed from the magnetic circuit employed for magnetizing, the field drops along the demagnetization curve, and when reassembled as part of the magnet unit, the final gap field will be somewhat lower than that which could be obtained if the magnets retained their original magnetism. There is also the problem of handling large magnets capable of producing fields in excess of 2000 gausses. For example each magnet assembly 16 in the 1000 liter/sec. ring magnet weighs pounds, and the total magnet unit 32 weighs over 450 pounds. The magnetic forces attracting each unit may be several hundred pounds, adding a certain element of danger to the handling problem.

To avoid these difficulties the magnet assembly is magnetized as a unit by placing it into a toroidal field and reducing the reluctance of the gaps with soft iron keepers. The most important result of this method is that the magnetic field is quite uniform across the gap because the toroidal magnetizing field coincides exactly with the desired field pattern. The fringing field produced by the magents represents wasted magnetic energy and is a disturbance to meters and instruments. The ring magnet assembly of this invention produces a low fringing field considering the field strength produced in the gap. Its intensity varies around the circumference of the magnet assembly, being a maximum along the centerline of a gap and a minimum along the centerline of a magnet. For example, about four inches from the pump wall the maximum fringe field is gausses and about six inches away it is less than about 10 gausses.

This invention thus provides a magnet construction which permits the use of the attractive properties of Alnico magnets and particularly Alnico 8. By eliminating the protrusion or heavy vacuum or enclosure wall from between magnet spaces the amount of magnet material has been minimized. By using internal encapsulated magnet assemblies a drawn seamless stainless steel shell can be used for the pump casing. Encapsulation may take the form of magnets or magnet material which has been suitably impregnated or otherwise treated to reduce outgassing under pumping conditions. There is no need to disassemble the magnet unit assembly for bakeout since the magnet material can be baked at 400 to 500 C. The conductance or pumping path to the electrodes is quite large, permitting the full utilization of the pumping elements capability. For example, the ring magnet assembly together with the pumping elements may be mounted directly inside of large vacuum systems with no conductance limitation due to connecting piping. The magnet assembly and position in this invention utilizes magnet material at as high an efiiciency as possible thereby providing a high pump speed to weight ratio for the pump.

While this invention has been described with reference to particular and explementary embodiments thereof, it is to be understood that numerous changes can be made by those skilled in the art without actually departing from the invention as disclosed, and it is intended that the appended claims include all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

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

1. For use in an ionic pump employing a plurality of spaced magnets with intermediate anode-cathode assemblies a magnet unit assembly comprising in combination,

(a) a plurality of magnets of tapered cross-section,

(b) encapsulating means sealing separate magnets,

(c) supporting means supporting a plurality of said encapsulated magnet-s in spaced-apart relationship in row form curving to permit the smaller faces of said tapered cross-section to face in a converging direction,

(d) said support means tying said magnets into a rigid integral modular structural unit whereby all magnets may be handled as a unit.

2. The invention as recited in claim 1 wherein said row is a peripheral row.

3. The invention as recited in claim 1 wherein said row is a circular row with the said smaller faces of said magnets facing the center thereof.

4. For use in an ionic pump employing a plurality of spaced magnets with intermediate anode-cathode assemblies a magnet unit assembly comprising in combination,

(a) a plurality of magnets of trapezoidal cross-section,

(b) encapsulating means sealing separate magnets,

(c) upper and lower ring supporting means supporting therebetween a plurailty of said encapsulated magnets in spaced-apart relationship in a closed circular row with the smaller faces of said trapezoidal crosssection facing the center of the defined circle,

((1) said support means releasably securing said magnets into a rigid integral modular structural unit whereby all magnets may be handled as a unit.

5. The invention as recited in claim 4 wherein said magnets are encapsulated in a stainless steel shell, said shell being evacuated and containing a minor amount of a tracer gas.

6. The invention as recited in claim 5 wherein said magnets are made of Alnico material.

7. For use in an ionic pump including a plurality of spaced magnets and anode-cathode assemblies, a magnet unit assembly comprising in combination,

(a) a pair of flat stainless steel ring members in spacedapart concentric relationship,

(b) a plurality of columnar magnet assemblies of trapezoidal cross-section positioned between said 10 ring members in equi-distant circumferential relationship with the smaller faces facing the center of the defined circle,

(c) stainless steel envelope encapsulating means encapsulating each of said magnet assemblies,

((1) each of said magnet assemblies being evacuated and partially filled with helium tracer gas,

(e) means releasably securing said rings and said magnet assemblies into a rigid unit capable of handling as a single structure for mounting in an ionic pump.

8. An ionic vacuum pump comprising in combination,

(a) an enclosure member adapted to be subjected to high vacuum conditions,

(b) a row of laterally spaced apart anode-cathode assemblies in said enclosure,

(c) a row of laterally spaced apart sealed encapsulated magnets in said enclosure between said anode-cathode structures with one magnet between each pair of said anode-cathode assemblies in said row to provide a magnetic field to increase ionization,

((1) means releasably securing said magnets in a unitary relationship so that insertion and withdrawal of said magnets from said enclosure takes place as a single unit,

(e) and means electrically connecting a plurality of said laterally spaced apart anode-cathode assemblies together inside said enclosure member.

The invention as recited in claim 8 wherein said row of encapsulated magnets is a peripheral row.

10. The invention as recited in claim 8 wherein said peripheral row represents a closed circle.

11. The invention as recited in claim 10 wherein each of said encapsulated magnets is of trapezoidal cross-section with the smaller faces facing the center of said circle.

12. The invention as recited in claim 11 wherein at least four encapsulated magnets are employed.

13. The invention as recited in claim 11 wherein ten encapsulated magnets are employed.

14. An ionic vacuum pump comprising in combination,

(a) an enclosure member adapted to be subjected to high vacuum conditions,

(b) a plurality of spaced anode-cathode assemblies in said enclosure,

(0) a plurality of sealed encapsulated magnets in said enclosure,

(d) one of said encapsulated magnets being positioned on each side of said anode-cathode assemblies to provide a magnetic field therebetween to increase gas ionization,

(e) each of said cathodes having substantial transparency with respect to gas ions between adjacent magnet assemblies,

(f) means operatively connecting said magnet assemblies into an electrical circuit so that the opposed faces of said magnet assemblies operate as ion collectors,

(g) and means releasably securing said magnets in a unitary relationship so that insertion and withdrawal of said magnets from said enclosure takes place as a single unit.

15. An ionic vacuum pump comprising in combination,

(a) an enclosure member adapted to be subjected to high vacuum conditions,

(b) a plurality of spaced anode-cathode assemblies in said enclosure,

(-c) a plurality of scaled encapsulated magnets in said enclosure and between said anode-cathode assemblies with one magnet on each side of said anode-cathode assemblies to provide a magnetic field to increase ionization,

(d) each of said cathode having substantial transparency with respect to gas ions between adjacent magnet assemblies,

(e) means operatively connecting aid magnet assemblies into an electrical circuit so that the opposed faces of said magnet assemblies operate as ion collectors,

(f) and means releasably securing said magnets in a unitary relationship so that insertion and Withdrawal of said magnets from said enclosure takes place as a single unit.

16. An ionic pump comprising in combination,

(a) an integral modular magnet assembly unit comprising a series of laterally spaced magnets releasably secured in a circle relationship,

(b) an integral anode-cathode unit comprising a series of laterally paced cathode-anode-cathode electrode assembly units releasably secured in a circle relationshi (c) 5nd means slida-bly engaging and attaching said units in interleaved relationship with said spaced magnets to provide a series of interdependent ionic pumping elements.

17. An ionic pump comprising in combination,

(a) an enclosure member,

(b) an integral modular magnet assembly unit comprising a series of laterally spaced magnets releasably secured in a circle relationship, in said enclosure member,

(c) an integral anode-cathode unit comprising a series of laterally spaced cathode-anode-cathode electrode assembly units releasably secured in a circle relationship,

(d) and means slida-bly engaging and attaching said units in interleaved relationship to provide a series of interdependent ionic pumping elements in said enclosure member.

18. In a triode ionic vacuum pump a single unitary electrode assembly comprising in combination,

(a) a central electron transparent multicellu-lar grid anode,

(-b) a pair of electron transparent multice'llular grid cathodes positioned one on each side of said anode and electrically connected and (6) means insulatingly joining said cathode electrodes to said anode electrode as a single unitary electrode assembly.

19. In a triode ionic vacuum pump a single unitary electrode assembly comprising in combination,

(a) a planar electron transparent multicellular grid anode, (b) a pair of electron transparent multic-ellular planar grid oath-odes positioned one on each side of and parallel With said planar grid anode and electrically connected together,

(c) means insulatingly joining said planar cathodes to said anode at only one end thereof, and

(d) means maintaining the other end of said cathodes in spaced relationship to each other.

20. In a triode ionic vacuum pump a single unitary electrode assembly comprising in combination,

(-a) a planar electron transparent multicellular grid anode having substantial depth and individual grid openings of a predetermined size,

(b) a pair of planar electron transparent multicellular cathode grids having substantial depth and positioned one on each side of said plan-ar grid anode and electrically connected together,

(-0) said planar cathodes having substantial depth and grid openings of a predetermined ize smaller than the grid openings of said anode,

(d) means attaching said grid anode to a support means at only one end thereof,

(e) a pair of spaced apart electrical insulators attached to said support means at said one end,

(f) and means attaching the said planar cathodes to said insulators and (-g) means at the other end of said support attaching said cathodes together to maintain their spaced reiationship.

References Cited by the Examiner UNITED STATES PATENTS MARK NEWMAN, Primary Examiner.

WARREN E. COLEMAN, Examiner.

Claims

8. AN IONIC VACUUM PUMP COMPRISING IN COMBINATION, (A) AN ENCLOSURE MEMBER ADAPTED TO BE SUBJECTED TO HIGH VACUUM CONDITIONS, (B) A ROW OF LATERALLY SPACED APART ANODE-CATHODE ASSEMBLIES IN SAID ENCLOSURE, (C) A ROW OF LATERALLY SPACED APART SEALED ENCAPSULATED MAGNETS IN SAID ENCLOSURE BETWEEN SAID ANODE-CATHODE STRUCTURES WITH ONE MAGNET BETWEEN EACH PAIR OF SAID ANODE-CATHODE ASSEMBLIES IN SAID ROW TO PROVIDE A MAGNETIC FIELD TO INCREASE IONIZATION, (D) MEANS RELEASABLY SECURING SAID MAGNETS IN A UNITARY RELATIONSHIP SO THAT THE INSERTION AND WITHDRAWAL OF SAID MAGNETS FROM SAID ENCLOSURE TAKES PLACE AS A SINGLE UNIT,