US3315125A

US3315125A - High-power ion and electron sources in cascade arrangement

Info

Publication number: US3315125A
Application number: US287817A
Authority: US
Inventors: Frohlich Heinz
Original assignee: Siemens AG
Current assignee: Siemens Schuckertwerke AG; Siemens AG
Priority date: 1962-11-20
Filing date: 1963-06-14
Publication date: 1967-04-18
Anticipated expiration: 1984-04-18
Also published as: GB1060309A; DE1208420B; CH412124A; NL298175A

Description

April 18,- 1967 HIGH-POWER ION AND ELECTRON SOURCES IN CASCADE ARRANGEMENT Filed June 14,. 1963 H. FRCHLICH 3,315,125

United States Patent Office 3,L'-ll5,l25 Patented Apr. 18, 1967 3,315,125 HIGH-POWER ION AND ELECTRON SOURCEfi lN tCAS CADE ARRANGEMENT Heinz Friihlich, Nurnberg, Germany, assignor to Siemens- Schuckertwerlre Alrtiengescllschaft, Berlin-Siemensstadt,

Germany, a corporation of Germany Filed June 14, 1963, fier. No. 287,817 priority, application Germany, Nov. 20, 1962,

8 82,505 8 Claims. (Cl. 315-111) My invention relates to high-power ion and electron sources and more particularly ion and electron sources based upon the principle of the so-called du-oplasrnatron sources known from German Patent 1,059,581.

Such high-power ion and electron sources are capable of producing electron streams of up to about amperes, and when fed with hydrogen, can produce ion streams of up to about 1 ampere in continuous operation. However, for many technical uses, in high-vacuum melting ovens for metals with high melting points for example a greater electron output is desired. Thus, there are melting ovens of up to 600 kilowatts power rating which require three sources with three acceleration and vacuum systems for the normally employed voltages of 20 kv. On the other hand, the production of ions by these sources is insufiicient for special purposes, such as ionic drives for space travel. In order to produce more intense ion streams, it has been suggested that straight or ring-shaped emission slots be made in the duoplasmatron. Such slotted designs, however, are usually not suitable for technical use as an electron source. It is diflicult, furthermore, to construct cathodes of suitable shape, efiiciency, useful life span, and service reliability for the expanded arc discharge occurring in such sources, since arc currents of about 100 amperes have to be kept under control.

An object of my invention is to provide a high-power ion and electron source assembly employing the principle of duoplasmatrons to produce very intense ion streams without requiring specially shaped cathodes.

Another object of the invention is to provide a source assembly with at least two stages in which all but the first stage require no cathode structure at all.

A further object of the invention is to provide an assembly of the above-described character which because of its ability to produce ion streams of relatively great intensity, makes new fields of application where high discharge currents are desired or required, accessible for use of sources on the duoplasmatron principle.

With the above and other related objects in view, and

in accordance with my invention, I provide at least two component sources arranged in cascade, and have the electrons emitted from the preceding source constitute a virtual cathode of the following source, the discharge currents of the component sources increasing by the use of volume ionization from stage to stage. Only one cathode of normal size for an emission current in the order of 10 amperes is then required in the first stage of the cascade, while a current many times greater can be drawn from the last stage of the cascade. Other features which are considered as characteristic for the invention are set forth in the appended claims. The invention, however, both as to its construction and method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is explanatory and shows diagrammatically a sectional view of the upper part of a duoplasmatron source; and

Claims FIG. 2 is a two-stage embodiment of the invention shown partly diagrammatically and partly in section.

Referring to the drawings and first particularly to FIG. 1 there is shown an electron beam 1 which is emitted from a source S through an aperture 1a in an anode 3 with an energy of up to 30 electron volts. A discharge chamber 2a is connected to this source S and has a gas pressure approximately equal to the pressure in the source. The electrons ll .emitted by the source serve as a virtual cathode for the discharge 2 in the discharge chamber 2a, which is enclosed by a pulling anode 4 at one end and a cylindrical wall 5. A direct current source 6 energizes the discharge.

It is essential to the invention that the discharge 2, within the proper range of operating voltage between the extraction anode 4 and the source anode 3, is of the type operating without a cathode spot (burning spot). Since the electrons 1 are emitted with considerable energy from the source S, there is also no necessity for formation of a cathode drop. As a result, in the aforementioned voltage range, the discharge burns with a positive voltage characteristic so that no ballast resistance is necessary for limiting the current in the circuit. The ions impinging on the source anode 3 distribute themselves on the entire surface thereof. The above-described operating conditions constitute the stable duoplasmatron operation.

It has been found that, by utilizing the volume ionization in the discharge 2, a discharge current of double or treble the amount of the emission current of the virtual cathode ll can be drawn in the discharge 2 under stable operating conditions, so that the discharge current is equal to or larger than the arc current in the source. This elfect is to be attributed to the development of electrons by ionization processes. Only when a critical value of the extraction voltage is exceeded does the discharge change to a true are discharge with a negative characteristic.

This phenomenon can be utilized by arranging a plurality of sources in cascade one behind the other, so that each source acts as a virtual cathode (in the electronoptical sense) for the following source. The are current is thereby multiplied without requiring a correspondingly large incandescent cathode.

As can be seen in FIG. 2, the first or preceding stage includes a cathode flange 7 of non-magnetic material, for example refined or stainless steel, on which is mounted an insulating bushing 8 through which extend cathode lead elements 9 that are electrically connected to a cathode It). An intermediate electrode 11 insulated by a ring 14 from an outer covering 12 and from an anode plate 13a that is formed with an emission opening 13, is cooled by cooling pipes 15 and is provided with a canal 16 which cooperates with the anode plate to produce a magnetic pole-shoe lens for guiding the plasma through the emission aperture 13. The

lens

13a, 16 is magnetically energized by a coil 17 which is energized from a non-illustrated direct current source. A low-voltage incandescent discharge takes place between the cathode 10 and the anode plate 13a when a gas pressure of at least 10- mm. Hg is gas feed pipe 13. The gas flows through the emission aperture 13, and, in the illustrated embodiment of FIG. 2, ultimately flows out of any emission opening 30. The gas feed pipe or inlet 18 may, however, also be connected to the upper stage of the device or any added intermediate stage. The low-voltage discharge is fed across a stabilizing resistor by a current source 19, which can have a potential of between 200 to 300 volts. The shielded construction shown in the drawing basically corresponds to the construction disclosed in the previously 3 described German Patent 1,059,581 in which I am named as the inventor.

The intermediate electrode 11 that is shown in FIG. 2 as being connected to the casing 12 through the switch 21 and the resistor 22, is biased to such a negative potential with respect to the casing that the electron stream from the intermediate electrode is equal to the ion stream. The combined arc stream flows, in this case, through the emission opening 13 from the cathode it) with a slight percentage loss and with a regulated potential of about 30 volts. Investigations have shown that double layers (potential jumps) arise in the plasma, that is in the canal 16, which accelerate the electrons to this velocity in the direction of the emission aperture 13.

Due to the constriction or pinching of the plasma by the magnetic pole-shoe lens, i.e. by the spiralling of the electrons in the inhomogeneous magnetic field of the lens, an intense ionization of the gases occurs between the opening of the canal to and the emission aperture 13 which leads to a positive plasma potential with respect to the anode. A positive potential hill is therefore formed, reaching its maximum directly over the canal opening from which the ions are accelerated in the direction of the canal and in the direction of the emission aperture. For electrons, instead of a positive potential hill there is a potential trough, and in this trough the electrons that are formed by ionization action in this range oscillate and further intensify the ionization.

If the intermediate electrode 11 is connected by the switch 21 to the negative pole of the generator 19 through a resistor 23, the intermediate electrode 11 is given a strong negative potential with respect to the anode 13a. Ionic wall losses in the canal 16 are thereby increased and theion stream from the positive potential hill to the canal becomes larger. The plasma gradient thereby becomes greater and the electrons are accelerated even more strongly toward the emission opening 13. The ions formed by ionization action can then also be accelerated and emitted so that it is possible to draw an electron current even from the first stage that is about 30 to 50% greater than the cathode emission. The intermediate electrode thus has a potential that is somewhat similar to the cathode potential.

The anode plate 13a is cooled with water or a similar suitable coolant circulated through a bore 24 formed therein. With an emission aperture 13 of a diameter of 1.3 to 1.4 millimeters in the first stage, an electron current of about amperes can be produced.

The electron current then enters the second stage which is separated from the first stage by an insulating ring 25. Between the casing 12 of the first stage and the casing 26 of the second stage, there is an electromotive force supplied by the generator 27, no ballast resistor being required in the circuit. In further respects, generally, the construction elements of the second stage correspond to those of the first stage and require no additional explana tion.

It is essential, however, that the discharge in the second stage diifers from the discharge in the first stage in that it burns with a positive voltage characteristic. The voltage of the generator 27 can be so adjusted that with the aid of an intermediate electrode 28 held at a negative potential (when switch 29 is in the lower position), an electron current is emitted through the opening 30 that is two to three times larger than the emission current out of the opening 13. An ion reverse current strikes the ion plate 13a of the first stage along its entire cooled surface. This is true generally for the anodes of all the stages just so long as the arc in each has the described characteristic.

The geometry of the pole-shoe lens in the second and following stages can be so constructed that the density of the stream in the respective emission opening may have a predetermined value, for example may remain constant. The larger the emission opening is, the more easily can it be accorded a canal-like characteristic because the wall losses of electrons become relatively small and therefore permit better heat removal. The size of the beam cross section is determined by suitable choice of the number of ampere windings of the energizing coil.

In contrast to the normal single-stage duoplasmatron in which the plasma cross section and the cross section of the emission opening must conform with each other as much as possible to avoid neutral gas losses, in the present invention, with the exception of the upper stage, as shown in FIG. 2, the cross section of the emission openings is larger than the plasma beam cross section. The heat load of the respective anodes is thereby decreased, and adjustment of. the gas pressure in the individual stage is facilitated.

The inner walls of the canals of the pole-shoe lenses that are located in the intermediate electrodes can be provided with thin metal cylinders for heat-insulating the canal walls, which, due to ion impact, are consequently heated to such a high temperature that they emit electrons. These electrons contribute to the increase of the combined emission of the particular stage. In FIG. 2 there is schematically shown a metal cylinder 31 with a heat insulator 32.

While the invention has been illustrated and described as embodied in a particular high-power ion and electron source assembly, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing from the spirit of the present invention and within the scope and range of equivalents of the following claims.

I claim:

1. A high-power ion and electron source, comprising in combination, a preceding stage including an energizable anode, cathode and intermediate electrode, said intermediate electrode defining a chamber in which an ionizable gas is received, and cooperating with said anode and cathode, when respectively energized, for ionizing the gas and for discharging electrons through an aperture formed in said anode, and at least one succeeding cathodeless stage, otherwise substantially similar to the preceding stage, said preceding and succeeding stages being arranged in cascade, the electrons discharged by the preceding stage being received in the chamber defined by the intermediate electrode of the cathode-less succeeding stage and forming a virtual cathode for the same, the discharge currents of said stages being increased from stage to stage through volume ionization of the gas.

2. A high-power ion and electron source, comprising in combination, a preceding stage including an energizable anode, cathode and intermediate electrode, said intermediate electrode defining a chamber in which an ionizable gas is received, and cooperating with said anode and cathode, when respectively energized, for ionizing the gas and for discharging electrons through an aperture formed in said anode, and at least one succeeding cathode-less stage, otherwise substantially similar to the preceding stage, said preceding and succeeding stages being arranged in cascade, the electrons discharged by the preceding stage being received in the chamber defined by the intermediate electrode of the cathode-less succeeding stage and forming a virtual cathode for the same, the anode of the succeeding stage being biased with respect to the virtual cathode to attract the electrons thereof, and means for adjusting the attracting voltage of the anode of the suc ceeding stage so that a discharge current with a positive voltage characteristic and without cathode voltage drop is maintained, the discharge currents of said stages being increased from stage to stage through volume ionization of the gas.

3. A high-power ion and electron source, comprising in combination, a preceding stage including an energizable anode, cathode and intermediate electrode, said intermediate electrode defining a chamber in which an ionizable gas is received, and cooperating with said anode and cathode, when respectively energized, for ionizing the gas and for discharging electrons through an aperture formed in said anode, and at least one succeeding cathode-less stage, otherwise substantially similar to the preceding stage, said preceding and succeeding stages being arranged in cascade, first energized external circuit means connecting the anode and cathode of the preceding stage, and second energized external circuit means interconnecting the anode of the preceding and succeeding stages, only said first external circuit means including a ballast resistance, the electrons discharged by the preceding stage being received in the chamber defined by the intermediate electrode of the cathode-less succeeding stage and forming a virtual cathode for the same, the discharge currents of said stages being increased from stage to stage through volume ionization of the gas.

4. A high-power ion and electron source, comprising in combination, a preceding stage including an energizable anode, cathode and intermediate electrode, said intermediate electrode defining a chamber in which an ionizable gas is received, and cooperating with said anode and cathode, when respectively energized, for ionizing the gas and for discharging electrons through an aperture formed in said anode, and at least one succeeding cathode-less stage, otherwise substantially similar to the preceding stage, said preceding and succeeding stages being arranged in cascade, voltage means connecting the anode and the intermediate electrode of each stage respectively, and biasing said intermediate electrode strongly negative with respect to its anode, the electrons discharged by the preceding stage being received in the chamber defined by the intermediate electrode of the cathode-less succeeding stage and forming a virtual cathode for the same, the discharge currents of said stages being increased from stage to stage through volume ionization of the gas.

5. A high-power ion and electron source, comprising in combination, a preceding stage including an energizable anode, cathode and intermediate electrode, said intermediate electrode defining a chamber in which an ionizable gas is received, and cooperating with said anode and cathode, when respectively energized, for ionizing the gas and for discharging electrons through an aperture formed in said anode, and at least one succeeding cathode-less stage, otherwise substantially similar to the preceding stage, said preceding and succeeding stages being arranged in cascade, voltage means connecting the anode and the intermediate electrode of each stage, respectively, and biasing said intermediate electrode strongly negative with respect to its anode, and means for adjusting the bias between said intermediate electro-de and said anode, respectively, the electrons discharged by the preceding stage being received in the chamber defined by the intermediate electrode of the cathode-less succeeding stage and forming a virtual cathode for the same, the discharge currents of said stages being increased from stage to stage through volume ionization of the gas.

6. A high-power ion and electron source, comprising in combination, a preceding stage including an energizable anode, cathode and inter-mediate electrode, said intermediate electrode defining a chamber in which an ionizable gas is received, and cooperating with said anode and cathode, when respectively energized, for ionizing the gas and for discharging electrons through an aperture formed in said anode, and at least one succeeding cathodeless stage, otherwise substantially similar to the preceding stage, said preceding and succeeding stages being arranged in cascade, voltage means connecting the anode and the intermediate electrode of each stage, respectively, and biasing said intermediate electrode strongly negative with respect to its anode, and switching means for selectively disconnecting said voltage means from said anode and intermediate electrode, respectively, and connecting said anode and intermediate electrode to one another across a ballast resistance, the electrons discharged by the preceding stage being received in the chamber defined by the intermediate electrode of the cathode-less succeeding stage and forming a virtual cathode for the same, the discharge currents of said stages being increased from stage to stage through volume ionization of the gas.

7. A high-power ion and electron source, comprising in combination, a preceding stage including an energizable anode, cathode and intermediate electrode, said intermediate electrode defining a chamber in which an ionizable gas is receive-d, and cooperating with said anode and cathode, when respectively energized, for ionizing the gas and for discharging electrons through an aperture formed in said anode, and means for combining at least part of the ionized gas and electrons in said preceding stage into a plasma beam and guiding said beam toward the aperture in said anode, and at least one succeeding cathodedess stage, otherwise substantially similar to the preceding stage, said preceding and succeeding stages being arranged in cascade, the electrons discharged by the preceding stage being received in the chamber defined by the intermediate electrode of the cathode-less succeeding stage, said electrons forming a virtual cathode for the same, the discharge currents of said stages being increased from stage to stage through volume ionization of the gas, the cross section of the aperture formed in the anode of each stage being larger than the cross section of the plasma beam in the respective stage except for the last stage of the cascade.

8. A high-power ion and electron source, comprising in combination, a preceding stage including an energizable anode, cathode and intermediate electrode, said intermediate electrode defining a chamber in which an ionizable gas is received, and cooperating with said anode and cathode, when respectively energized, for ionizing the gas and for discharging electrons, said intermediate electrode having an end wall formed with a canal communicating with said chamber and being in registry with an aperture formed in said anode, said canal being provided with a peripheral heat-insulating thin metal layer, and at least one succeeding cathode-less stage, otherwise substantially similar to the preceding stage, said preceding and succeeding stages being arranged in cascade, the electrons discharged by the preceding stage being received in the chamber defined by the intermediate electrode of the cathode-less succeeding stage and forming a virtual cathode for the same, the discharge currents of said stages being increased from stage to stage through volume ionization of the gas.

References Cited by the Examiner UNITED STATES PATENTS 2,975,277 3/1961 Von Ardenne 315-111 X 3,033,984 5/1962 Fisher et al 250-833 3,137,801 6/1964 Brooks et a1 313-161 X JAMES W. LAWRENCE, Primary Examiner. S. A. SCHNEEBERGER, Assistant Examiner.

Claims

2. A HIGH-POWER ION AND ELECTRON SOURCE, COMPRISING IN COMBINATION, A PRECEDING STAGE INCLUDING AN ENERGIZABLE ANODE, CATHODE AND INTERMEDIATE ELECTRODE, SAID INTERMEDIATE ELECTRODE DEFINING A CHAMBER IN WHICH AN IONIZABLE GAS IS RECEIVED, AND COOPERATING WITH SAID ANODE AND CATHODE, WHEN RESPECTIVELY ENERGIZED, FOR IONIZING THE GAS AND FOR DISCHARGING ELECTRONS THROUGH AN APERTURE FORMED IN SAID ANODE, AND AT LEAST ONE SUCCEEDING CATHODE-LESS STAGE, OTHERWISE SUBSTANTIALLY SIMILAR TO THE PRECEDING STAGE, SAID PRECEDING AND SUCCEEDING STAGES BEING ARRANGED IN CASCADE, THE ELECTRONS DISCHARGED BY THE PRECEDING STAGE BEING RECEIVED IN THE CHAMBER DEFINED BY THE INTERMEDIATE ELECTRODE OF THE CATHODE-LESS SUCCEEDING STAGE AND FORMING A VIRTUAL CATHODE FOR THE SAME, THE ANODE OF THE SUCCEEDING STAGE BEING BIASED WITH RESPECT TO THE VIRTUAL CATHODE TO ATTRACT THE ELECTRONS THEREOF, AND MEANS FOR ADJUSTING THE ATTRACTING VOLTAGE OF THE ANODE OF THE SUCCEEDING STAGE SO THAT A DISCHARGE CURRENT WITH A POSITIVE VOLTAGE CHARACTERISTIC AND WITHOUT CATHODE VOLTAGE DROP IS MAINTAINED, THE DISCHARGE CURRENTS OF SAID STAGES BEING INCREASED FROM STAGE TO STAGE THROUGH VOLUME IONIZATION OF THE GAS.