DE1514990A1 - Hollow cathode - Google Patents

Description

Description au dom patent application from the company

IWIiEBD AIHCRAFT CORPORATION, 400 LIaLn Street, Easu Hartford,

Connecticut, V.St.A.

concerning
Hollow cathode

Priority »December 10, 1964 - 7th St.A.

The invention relates to an annular hollow cathode and insbeeoudere ο Ine perforated cathode, soft an achGlboriföz'juigoii electron beam radially inward from a slot opening on the inside Emits circumferential surface *

BoI conventional processes a ma generating Elektronenbündein wcrdon Eliifctrunen au a curse of the upper through-heated cathode oiner

Emits β L ο ti free aotat. Wasan in a hollow cathode

by Freiauttton from Elakfcronon ala follow dae Zuaomiaonatoßeo faster electrons with iJaniuo lekii len in the Hollow cathode

The previously known flea cathodes uuifaaaen a geeohloueenan Hohläsylinder aue wire mesh; or perforated on the mefcaii »it aintr circle opening in one end face. When the cathode is set to a high negative potential in suction on the exercise, orgespenni; iofc, what;?; as anod *; whirls, oo - a glow discharge is initiated.

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Bti corrugated combinations of cathode dimensions and height of the pressure is a well bundled · * electron bundle higher Generated current density, where β without 11a Slektrohen from the opening emerge from the hollow cathode. The electron beam can be focused on energy density by means of electromagnetic lenses which are comparable to those in conventional electron beam welding devices.

The subject of the invention is a hollow cathode which is essentially ring-shaped and produces a thin, disk-shaped bundle of electrons. The electrons are emitted from a circular opening in the cathode and are accelerated radially inward towards the workpiece with an energy which approximately corresponds to the voltage lying on the discharge path, which is usually in the kilovolt range. If the MQVküt'dük consists of metal, an anode can serve. If , on the other hand, it is an insulator, the electrical circuit sB is fully completed by means of a remote control unit on the surface of the surface and through the conduction through tine reutliee vtialie plaaaa to a distant area. The ring-shaped cathode can be used for rsraohioden-like purposes, eg for tails, for soldering, for zone melting, also for pulling fibers and for evaporating and knocking down the vapors.

The hollow shell according to the invention is rorsugawelea ale hollow Hingköi-por or in a similar form formed and laced on drmht,

usually made of refractory metal, the cathode

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is held at a negative potential in relation to the anode, whereby the inode is either the workpiece or a metal file that carries the torrent, such as the load-bearing components. Electrons are emitted outside the ring-shaped slot in the inside of the toroid. When operating the cathode, the pressure of the exercise is generally reduced to a level of 0.1 micron Hg. The little-loved eYacuated laraer is then filled again with an inert Qaa, such as helium or argon, or a bit of any Gao that I can bear with the workpiece at the temperature used. With a suitable pressure, which is usually in the range of 1 to 1000 microns Hg, a hollow cathode discharge can be initiated and, by means of a potential diffusion, several thousand volts can be maintained between the cathode and anode or remote control. Under these conditions, a well-focused slectron bandage is required! au · dom ringi Orwigen school: Esiit and collides with the workpiece, and swar smooth uii deeeon unifang.

There are also modified cathode forms tiiid arrangements τβτ-turn »sB invortierto cathodes, whose Kltk.tronenliUrtdei rudißl. na oh auJien geric: htn1 aind, Kcthoden with all directed el "ktiOnenbündeln" MehrfHChlalhoden odar 7-vbup / ^ ongisresif Fathoö * »n, R (m1 · Cathodes« it ■:;. r- - ^ eliutSi'j £, on Qutirnol-iip M df Ku ilsfn, Abn »t '» eung «n or Foreen $ um u:. ^ G <! Rciißi {; gofcT-nsi» · ff < ^s i ■ ■ ■ ⁴ - UcΛ ■ <· vu f »..Lirf> 1 ßen odnr edit.

ffegcnetaud "df r Frf tJiduii ^ · let ιΰη * · ir ■ -"t.'jM.-ni> S d: <- ü rJ ugf Wrmlge Bohlhcu «^ asit ίυ ^ Ιιϋ ο« ··, j> criorif ^; ' . (■. ■> · ^; ίΐ »· ^ · η, · ,. ■ \ <) ti> much rswnh) at

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non-conductive; as well as for metallic workpieces IKBt. You cathode according to the invention can be welded, Soldering, zone melting, fiber drawing, and evaporation and deposition of the vapor use and can have an irregular shape for the processing of irregular work pieces. the Cathode according to the invention can also be used for welding or for • Other processing operations in the interior of a pipe or a Use workpiece ··.

The invention is illustrated below with reference to the ohmic drawings additionally described in several examples!

Figure 1 shows a perforated. Hollow cathode of known type.

FIG. 2 shows a typical ring-shaped hollow cathode system. FIG. 3 shows a detail of a preferred annular buried cathode.

FIG. 4 shows the mode of operation of the ring-shaped hollow cathode.

FIG. 5 shows a hollow cathode with a workpiece in cross section as well as the generated electron beam bundle.

FIG. 6 shows additional spatial arrangements of hollow cathodes according to the invention.

The known hollow cathode according to FIG. 1 comprises a closed one hollow cylinder 10 made of wire mesh. In one end face of the cylindrical cathode 10 is a circular Opening 12 incised. If the cathode in relation to the anode,

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«Etir * dl« environment or the workpiece, is negatively biased, a glow discharge is initiated and a new one is created Electron-carrying electron bundle 14 "Because of the special geometry of the cathode 10, most electrons get through" ■ are located in the part of the plasma within the cylinder, as a bundle 14 through the opening to the outside. Also, these ! Electrons approximately corresponding to the total voltage of the discharge path accelerated in a very close to the opening 12 lying area. Therefore all weak electric fields, which are present in the surrounding plasma, have which fills the container, a negligible effect on the energy or the direction of the electron bundle T4. One in that The workpiece 16 lying on the electron beam 14 can be heated, welded or otherwise with the electron beam 14 to edit. This can be focused by electromagnetic lenses (not shown). A discharge generally occurs only one at pressures below 1000 microns Hg.

Pigur 2 schematically shows an annular hollow cathode discharge system according to the invention and FIG. 3 shows the structure of a hollow cathode according to the invention. The annular hollow cathode 20 is made, for example, of stainless steel in the shape of a wire mesh with a wire thickness of 25 microns (10 mil) and a size of 40. Cathodes made in this way have an outer diameter D _Q , which is typically 1.3 to 4 faohe dee inner Durohsfessers D is ₁ , whereby these ratios do not apply as limits. The height H of the cathode does not appear to be

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However, the size of the opening A can be critical, as will be explained below. Even the ffand-aloke and the vasohene width βoheint do not give any noticeable influence on UmM "-. Have tin bundles.

The cathode 20, the workpiece 22 and the associated supporting parts are accommodated in an airtight container 24 which is made, for example, of glass or other suitable material. The cathode is held by an arm 26 which can also act as a negative connection line for the cathode r ^ ev. The workpiece 22 is held by means of a metal arm 30 on which two adjustable O.sm.mgiieder 28 and 28 'are attached. If the workpiece 22 is made of metal »kamt et. be grounded to serve as an anode BU . ^ e In Figi'i "3 iat # a separate anode 32 ry ^^. is.3 5 r.uiu Λϊΐ je-iir place within the container 24. The anode küzsji & iuo positive voltage supply and an anode holder 34 u» rt »is ^ e?> o Figure 5 shows in cross section the rseu & through the cathode 20 • M» vjßf't. forketück the 22 focus wobbled Elektronenbilndel,

The container 24 is first evacuated by means of a vacuum pump 36, Once the pressure is correct, a source of gas is connected to create a gas atmosphere. As gas can be helium, hydrogen, nitrogen or argon or any other ^ lcla A suitable gas is used for the workpiece concerned <efu

The theory of the * mode of operation of the hollow cathode, as it has been known so far can be explained with reference to FIG. There are several

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Eohiedliohe modes of operation. The desirable mode of operation, i.e. is the mode of operation in which an electron beam is generated similar to an abnormal glow discharge by making a positive one BspannungB-Strom-Charalrterietik and a transition in • Shows an arc-like mode of operation, sometimes called the "fountain" mode, where the energy level is increased. the Voltage or the current at which this transition takes place depends Clay of the geometry of the cathode, of the gas used and of the Gas pressure.

The puncture of the types of discharge can be compared with How common glow discharges work. The entire voltage gradient of the discharge lies in a normal glow discharge in an area close to the cathode, this area being called

Cathode fall is known. The characteristic thickness D of the

The case of the cathode depends on the gas pressure, the type of gas and the cathode material and the applied voltage. The high potential sin of this area can be seen with the eye through the separation parts »Wipe a dark area of the discharge space nearby the cathode, the so-called cathode dark roughness, and a bright area, the so-called cathode glow light. The equipotential lines for such a stress distribution run parallel to the cathode.

If dl * annular opening A of the hollow cathode by less than the Factor 10 is smaller than the thickness D_ of the cathode trap, so will

the potential distribution is not significantly disturbed by this.

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This occurs at low pressures and / or low voltages Under these operating conditions, the cathode works like a solid cathode without a diaphragm, and there is practically no discharge takes place inside the cathode, since the interior thereof is at the cathode potential. Therefore, no electron beam is formed either. Likewise occurs within the cathode among these Conditions only a very low glow light.

If the opening Λ in the ring-shaped hollow cathode is approximately equal to the thickness D., the opening disturbs the potential distribution and consequently part of the cathode trap lies within the cathode. These relationships are shown in FIG. The potential drop within the cathode usually comprises a small fraction of the total cathode drop. In addition, the special shape of the cathode makes it extremely unlikely that electrons formed by ionization in the cavity will exit it through any holes, with the exception of the relevant opening. Electrons emitted from the inside of the wire mesh 44 by secondary emission are also likely to be trapped in the inner photential region. Even with a discharge of a few kilovolts, the maximum potential within the cathode is probably less than 100 volts. Electrons that are trapped within this potential space, forming a secondary discharge which brings with it a considerable generation of ion Elektro.-NEN pairs due to the electron bombardment, gon cat h ode 'em ittierte Se ^ ind & g.elektronen are the main source for electrons that serve to hold the discharge inside the cathode

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The school ions that are formed outside the cathode are another main source of secondary electrons.

According to FIG. 4, the disturbed potential distribution in the vicinity of the opening A is reminiscent of a concave lens. The field lines running normal to the equipotential lines converge in the vicinity of the opening. Electrons located in the cavity drift towards the opening, in which the electric field is relatively weak. In the area of the opening they are accelerated by the full cathode fall and thus achieve a high directional speed approximately in the longitudinal direction of the field lines. In this way, the hollow cathode, which is provided with perforated walls, creates a highly concentrated, low-energy electron blind. It is therefore very desirable to keep the potential drop within the cathode at a fraction of the total cathode drop. For this reason, the opening A should be slightly smaller than the dioke D ₀ . However, the opening A must not be made too small, since otherwise, as already mentioned above, no electron beam will be formed.

If the opening A is significantly larger than the thickness D _{ß of} the cathode trap, then the entire cathode trap lies within the cathode. Electrons emitted from the interior of the cathode surface are accelerated by almost the entire discharge voltage at a fairly short distance from the wall. Relatively few electron orbits run through the opening. Most of the electrons are trapped in the deep potential area inside the cathode

and can only emerge in which it comes zn clashes and / or

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The repeated reflections from the walls of the potential area electrons lose electrons when they collide with atoms in elastic collisions and then drift towards the opening sa _v in the relatively weak field prevailing. Therefore, a sioalioh intense plasma is formed inside the cathode and many ion-electron pairs are sucked into the cathode rim duroh Blektronenbeeohufi The thus sucked ions are accelerated directly to the cathode wall. In such a mode of operation of _t which is known as arc discharge, the cathode is often bi "ium annealing is rhltit * ^n, from which aan seen that a beträftlisher Änergieverlust produced at the cathode. Therefore, ei is the right operation in the general α lives w'lsBchenawerf.

Yertiaohe with Ringkathodec _f which fixed (non-interrupted) walls have, haban shown that at the eelben Oasdruok and wider same voltage, the cathode has With fixed winds a lower Intladung · »stream and a lower efficiency of the ElektronenbUndeleraeugung than the perforated cathode of gleiohen Dimensions · The contribution of the perforations is usually due to a pressure flow phenomenon. The mode of operation of a long cathode with solid walls can be improved by providing direct ventilation to the cathode. The perforation Ia Asa fiaissi, however, nooh have further weekly effects on the cathode.

As described above, the puncture of a hollow cathode old perforated walls in the electron bundle mode is analogous to a

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abnormal source discharge. The secondary discharge which la inside tor hollow cathode takes place »and Al · thus Terbundene Brseugung τοη Ioasn-Blektroaen-Pasxen gives noon «In · sueäteliohe Quell · for Slsktrontn and · 1η · greater capacity to conduct electricity with a flat Π11 — ntieilTini The most effective operation results in ei oh, if the electricity ▼ on the Of catch the τοη the outer surface of the cathode outgoing Current VvMAtIiClI exceeded. The external stream "represents a loss stream" since it does not contribute in any way to the bundle of winds. However, ions outside the cathode are

Perforations «ad duroh the opening accelerates ond hit the inner wall of the cathode »eo dal be freiceeetit on this Sslcandixelvktronsn. IeI a cathode with a certain total Vltomwadorohorwonaag (open Vllohea) is the one in the Inner Rana Cathode penetrating Ion Etrom la weeentliohen independently τοη the oharmfcterietleohen hole size ·· of the perforations. This is because » that the ions are accelerated evenly by the cathode fall and therefore received a sufficiently high population that theirs Paths are not significantly disturbed by the fine structure that electrical suffers in the immediate vicinity of the cathode perforations effective initial τοη electrons in the discharge within the Cathode, however, requires that a substantial part of the potential drop takes place in the interior close to the inner wall of the cathode. • Therefore, a more effective start-up of the blsktroasm is seen if the · characteristic Loohgrußs of the perforations (I> orohbrsohi] ngsn) ringsrt becomes »without the openwork flat sslbst su indsrn. Bs The result is an increased efficiency of the air bundle suction with a reduction in the characteristic hole size.

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In electron beam operation, an annular hollow cathode with perforated walls has a positive voltage-current characteristic. For a given cathode, the voltage-StroB operating range is heavily dependent on the gas pressure or better said τοη the class density. Tests have shown that the transition Enters a high current arc discharge at higher pressures » when the discharge capacity is increased. It has also been shown dafi is the maximum voltage that can be generated over a discharge path in the Electronium bundle mode of operation can be maintained with increasing pressure falls. Further, for a given pressure, lower currents are obtained using solid walls instead of perforated walls Used. However, cathodes with solid walls can be used at higher Press before an arc discharge occurs in them. This can have some advantages for certain applications. At the same pressure and voltage, both the measured beam power and the input power τοη are cathodes with perforated walls a little higher for larger cathodes. A cathode with solid walls works at significantly lower power than any perforated cathode regardless of size. The beam power8-effect8g * ad is for all cathodes with perforated would find the same. There are efficiencies τοη 75 pounds in the case of annular Cathodes have been obtained. As an effective measure to increase dta Shielding, inter alia, the ring-shaped hollow cathode has proven to be efficient in such cathodes.

Figure 6 shows modified Aasführungsformen a cathode according to Invention. In the arrangement according to FIG. 6a, the cathode 70 is

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inverted, eo that the electron beam is directed radially outwards and therefore welds the inside of the pipe 72 or a similar workpiece. The end of the tube 72 must of course be sealed be. In the arrangement according to FIG. 6B, the cathode 70 is not arranged in a plane, but at an angle, so that the electron bundle is not focused in the plane of the cathode, but on an area of the workpiece that is remote from this area 72. The electron bundle here has a cone shape.

FIG. 6C shows the use of superimposed cathodes 70 and 70 ', which can act on the workpiece 72 at the same time. One of the cathodes has a circular cross-sectional shape. The cathodes can be designed to be movable in relation to the cathode holder its Figure 6D shows the use of a cathode 70 with a axially directed electron beam "which strikes the workpiece 72 in a circle"

Numerous variations of the cathode of the invention can be used for use with irregularly shaped workpieces. FIG. 6E shows an irregularly shaped cathode 70 which is used together with an irregularly shaped workpiece 72. It is also possible to use cathodes with an irregular transverse shape, as shown, for example, in FIG. 6F. Other cathode shapes can easily be devised without any inventive considerations! sB cathodes of different geometry, for example triangular or trapezoidal cathodes, cathodes with different widths of the opening or with irregularly shaped openings or with a

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partially covered opening.

Am application of the ring-shaped hollow cathode according to the invention butt welding of pipes is also the same or different Materials such as aluminum, stainless steel, Kovar, titanium and niobium. This leaves welds with a high tensile strength produce. If daa workpiece in relation to the center line offset from a symmetrical cathode, the could The area of the workpiece furthest away from the cathode a Become overheated so that you have to borrow for an exact alignment.

»These are other areas of application of the ring-shaped hollow cathode Soldering, ablation and sputtering and zone heating. E.g. the property of a ring-shaped carbon cathode, which can be used with this Let both insulators and conductors heat up, for zonal cleaning (refining) of ceramic materials and for drawing Use crystals, such as those made of clay. Bring the ring-shaped Hollow cathode in a dome-shaped magnetic field thereby widen the heated zone.

You ring-shaped hollow cathode can also be used to remove the heat for drawing fibers from Pyrex * H Vycor * ^, fused silica and other similar materials. The cathode can be turned on use for heating tungsten and fused silica or other substrates of chemical evaporation and precipitation

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Si-ring-shaped hollow cathode according to the invention generates a well-focused electron bundle with high energy density • in a mechanically simple electron acceleration system, «• loh ·· no · critical · evasion required. Ea let not necessary di · Electrically heat the cathode so that the service life of the cathode is increased. It is also not necessary to have a hooh « keep vacuum system ready, creating a diffusion pump • RU.brigt, as · required · with other electron tank systems is. Tone special part of the gate is the Umetand that the ring-shaped Hollow cathode used both in directional conductors and in metals w «n can» without the need for any special accessories Ut.

Si · invention can be used in many ways within the framework of modify the general idea of the invention, see B. in terms of the geometric shapes of the cathode.

In the claims, the expression is intended to be "annular" or "substantially ring-shaped "mean a substantially closed shape and also include irregular shapes, a.B. the shape of a "C, one "U", a polygon, an ellipse, a circle, etc.

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Claims (1)

~ 16 - 15U990 Claims 1. Hollow cathode, characterized by an essentially ring-shaped hollow metal component which has a narrow opening which is calibrated at least over part of its surface and extends, inter alia, the center of the component. 2. Hollow cathode according to claim 1, characterized in that the Opening extends continuously over the surface of the metallic component. 3. Hollow cathode according to claim 1 or 2, characterized in that at least part of the wall of the component is perforated. 4 «hollow cathode according to claim 2 and 3, characterized in that the metallic component has a cross-sectional shape, dit a forms a substantially closed planar figure which is interrupted by a narrow circumferential slot which forms part of the through opening. 5. hollow cathode according to claim 1 to 4, characterized in that deJ the cross section of the component with the azimuthal position around the center of the component with respect to the area and the geometric shape changes. 6. hollow cathode according to claim 4 and 5, characterized in that daft the Umfaugenschutz in its orientation and in the area · with the azimuthal position varies around the center of the component. 009830/0202 BUILD uRiQINAL -π- 15.H990 7 »Boring cathode according to claims 1 to 6, characterized in that» that the component has the Torrn of a body, which by the circumferential movement of an essentially closed plane! a closed path is created which runs around an axis lying in the plane of the figure. 8. Hollow cathode according to claim 7 »daduroh characterized» that the plane figure is a rectangle and contains an opening in one side of the same. 9 «hollow cathode according to claim 7» characterized »that the flat figure is curvilinear " 10 »Hollow cathode according to claims 1 to 9» characterized » that it is operated in a container in which a low pressure can be generated and which contains an electrode so that a potential difference can be established between the metallic component of the cathode and the electrode »in order to bring about an electron discharge from the opening» 11. Hollow cathode naoh claim 10, characterized in that the Container is filled with a gas of a predetermined pressure. 12. Hollow cathode naoh claim 10 or 11, characterized by » that it is used for processing workpieces »which in dtr Orbit of the electron beam are arranged. 009830/0202 J3 hollow cathode according to claims 10 to 12, characterized in that that the workpiece is used as an electrode and in the container is arranged. 14 · Hollow cathode according to claim 10 to 12, characterized in that that the workpiece is an insulator. 009830/0202 Blank page