US 3579027 A
Description (OCR text may contain errors)
l 9 l 2 l o O5-l8-7l XR 3,579,027
 Inventor Maximilian Pater Primary ExaminerRaymond F. Hossfeld Vienna, Austria A uorney Glascock, Downing &- Seebold [2|] Appl. No. 710,175
 Filed Mar. 4, 1968  Patented May 18, 1971 ABSTRACT: An ignition device for high efficiency plasma  Assignee Gebr. Bohler & Co. Aktiengesellsclum producers, which device precludes the necessity for extremely Vienna, Austria high voltages to produce the initial ignition of the plasma  Priority Mar. 3, 1967 producer by providing high specific ionic densities between  Ami. the electrodes thereof. The ignition device consists of an an- [3l] A203l/67 nular passage surrounding a rod electrode and through which ionizable gas is passed. The cylindrical wall which defines the outer periphery of the annulus continues axially beyond the 54) IGNIIING AID FOR nlcu EFFICIENCY PLASMA a first Passage- A PRODUCERS further cylmdncal wall forms a second larger dlametered tubular passage beyond said first tubular passage. An are is 7 Claims, 1 Drawing Fig.
struck between the rod electrode and the cylindrical wall forming the second tubular passage, which are has electric 2 1. e lines of force in the form of a cone with the apex pointing up- [5 i IIZIL Cl H01] stream the direction of the flgw of the ionizable gas. The cone-  313/197, shaped age has an azimuthal magnetic field on the inside and h 315/! l 219/121 outside thereof, and as the gas goes through the arc it is partially ionized and the opposite charge carriers are radially  Refcnm CM separated by the azimuthal magnetic field. By virtue of the UNITED STATES PATENTS separation, there is less tendency for the opposite charge car- 2,508,954 5/1950 Latour et al. 313/231X riers to recombine, and consequently there is a higher specific 3,370,198 2/1968 Rogers et al. 3 15/ l l l ionic-density when the gas is introduced between the elec- 3,425,223 2/ i969 Browning 60/203 trodes of the high efficiency plasma producer.
III] Patented May 18, 1971 I 3,579,027
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Br ML 7 "M IGNKTKNG All) FOR HIGH EFFICIENCY PLASMA PRODUCERS Apparatus for the production of plasma operates, in general, with the help of an electric arc through which the gas to be converted into plasma is directed, and by which it is ionized. High efficiency apparatus of large size have at least one complication in that there is too great a distance between the electrodes, and the initial ignition of the plasma producing arc can be accomplished only with the greatest of difficulty.
A way for overcoming this difficulty consists, for example, in the production of a short duration high induction voltage between the electrodes, but this measure carries the disadvantage of the great number of coil windings necessary for this purpose. l-ligh resistance occurs in the part of the apparatus providing the current. Another possibility, difficult to place in practice, could consist of a primary arc to be ignited between a cathode and an auxiliary graphite electrode, which are is transmitted to a second electrode, and then the auxiliary electrode can be removed.
An electric arc ignition apparatus is already known in which separate ignition electrodes have been utilized and through which, for example, a condenser is discharged. The quasineutral plasma which has been produced from this discharge is directed between the electrodes of the electric arc and serves for the preliminary ionization, whereby naturally a considerable part of the positive and negative ions produced is lost, in proportion to the distance to betravelled, on account of recombination of the opposite charge carriers.
If however, in accordance with the instant invention, the gas to be ionized is directed through an are having the shape of a cone, or in the extreme case through an approximately discshaped arc, an azimuthal magnetic field is produced, leading to a separation of different charge carriers in the plasma, and also after a dissipation of the electrons there is an excess of positive charge carriers. On account of this dissipation of their negative counterparts over long distances, the positive charge carriers have no opportunity to neutralize, so that in comparison with the already known procedures, there results the advantage of maintaining for a longer period the ionized state of the auxiliary gas stream.
A further advantage of this invention in comparison with the already known procedures, consists in the possibility of operating with considerably lower voltage for ionization.
The method according to the invention consists therefore in the fact that the medium to be ionized is directed through a conical arc, and in the extreme case, a disc-shaped are when viewed along the electrode. The ions produced therein are led into the space between the electrodes of the high efficiency plasma producer to be ignited, so that the voltage necessary to produce the initial ignition is greatly lowered on account of the relatively high specific ionic densities. This method may be carried out by an apparatus which contains essentially the elements of an ordinary electric ignition sparkplug, namely, a central electrode preferably in rod form; an isolating body surrounding it at least partially; a counterelectrode which is shaped so that between it and the rod-shaped electrode there burns a conic or in the borderline case a disc-shaped arc; as well as additionally a stopping or securing device, a gas feeder, and a gas channel going through the sparking area. These types of plasma sparking plugs can be screwed into any plasma producer and changed in a simple way and manner at any time. The necessary auxiliary sparking voltage can be realized with less effort due to the smaller requirements for the operation of the plasma spark plug. The required electric current produced by passing a gas medium to be ionized through an arc-shaped cone and in the extreme case a disc, and thereafter the gas medium in at least a partially ionized state is brought into the space between the electrodes of the high efficiency plasma producer.
Both electrodes, between which the conical arc burns, do not necessarily have to be part of the plasma ignition spark plug. In the preferred form, the plasma producer in which the plasma ignition spark plug is fixed, serves as a counterelectrode. If the ignition spark plug electrode has been shaped as a rod electrode, as in the case with the usual electric spark plug, it is advantageous to make the isolating body which is surrounding it long enough to over reach the electrode tip in order to prevent a backfiring of the spark.
Referring now to the drawing, it will be seen that the ignition aid comprises a rod electrode 1 which is connected to a current source and is contained in an isolating cylindrical body 2. An annular securing means 3 for the ignition aid is screwed into a plasma producer 5, and preferably the plasma producer acts as a counterelectrode and is also connected to the current source. The gas to be ionized is introduced through a coupling 6, down through a gas feeding annular channel 4 and through a conical are 7 which is struck between the end of rod electrode 1 and the inner cylindrical wall surface of the plasma producer 5. The lower portion of the cylindrical isolating body 2 continues axially beyond the end of rod electrode 1 into a cylindrical space defined by the inner wall surface of plasma producer 5. Therefore it will be seen that the path of the gas introduced through coupling 6 is first through the annular channel 4, then through two axially succeeding tubular passages 8 and 9, respectively formed by the inner wall surface of the lower portion of the isolating cylindrical body 2 and the inner cylindrical wall surface of plasma producer 5. The cone-shaped arc 7 has an azimuthal magnetic field on the inside and outside thereof, and as the gas goes through the arc it is partially ionized and the opposite charge carriers are radially separated by the azimuthal magnetic field. By virtue of the separation, there is less tendency for the opposite charge carriers to recombine, and consequently there is a higher specific ionic density when the gas is introduced between the electrodes of the high efficiency plasma producer.
In many instances, it is desired to use a material which emits electrons in the manufacture of the electrodes. On account of the relatively high heat exposure of the isolating body, it should preferably consist of a high heat resistant materials.
The method according to the present invention makes possible the safe ignition of gas discharges in plasma producers of large dimensions, with easy manipulation thereof and the guarantee of uniform conditions and functioning of the apparatus.
l. A method of igniting a high efficiency plasma producer with relatively low voltage comprising the steps of passing a stream of ionizable gas through an ignition aid, said gas following a path defined by a rod electrode and a surrounding isolating body of said aid; producing an electric arc discharge between the end portion of said rod electrode and a counterelectrode radially spaced and axially beyond said rod electrode; the electric lines of force of said are being inclined in the form of a cone with the apex thereof pointing upstream the direction of flow of said ionizable gas in at least that area of said are through which said gas passes thereby producing an azimuthal magnetic field, whereby said gas passing through said inclined arc is at least partially ionized; radially separating, by virtue of said azimuthal magnetic field, the opposite charge carriers in said partially ionized gas to minimize recombination of said carriers and thereby create a high specific ionic density in said gas; and then introducing said high specific ionic density gas into the area between the electrodes of the high efficiency plasma producer.
2 A method as claimed in claim 1 wherein backfiring of said arc is prevented by extending said isolating body axially beyond said end portion of the rod electrode to form a first tubular passage and further providing a second and radially larger tubular passage, coaxial with the first, and formed by said high efficiency plasma producer acting as said counterelectrode, immediately in the direction of gas flow beyond said first tubular passage, so said gas flows along said path and successively through said two tubular passages.
3. A high efficiency plasma producer ignition aid utilizing relatively low voltage comprising an isolating body having an inner cylindrical wall in which a rod electrode is concentrically mounted and radially spaced to form an annular passage, said cylindrical wall extending axially beyond one end of said rod electrode forming a first tubular passage;.a second cylindrical wall coaxial and of larger diameter than the first forming a second tubular passage immediately succeeding said first tubular passage; means for feeding ionizable gas to the end of said annular passage opposite said one end of said rod electrode; means. for applying electric potentials having opposite signs respectively to said rod electrode and said second cylindrical wall to form an arc having electric lines of force inclined in the form of a cone with the apex thereof pointing upstream the direction of flow of said ionizable gas in at least that area of said are through which said gas passes so that said gas passing through said inclined arc is partially ionized and the opposite charge carriers are radially separated by an azimuthal magnetic field to form a high specific ionic density in said gas, which high specific ionic density gas is then introduced to the electrodes of the high efficiency plasma producer.
4. An ignition aid as claimed in claim 3 wherein at least one of the electrodes consists of electron emitting material.
5. An ignition aid as claimed in claim 3 wherein said first cylindrical wall is made of heat resistant material.
6. An ignition aid as claimed in claim 3 further comprising a securing device about said isolating body to secure said ignition aid to said high efficiency plasma producer.
7. An ignition aid as claimed in claim 3 wherein said second cylindrical wall is part of the high efficiency plasma producer.