US3448333A - Process for initiating an arc between electrodes in a plasma gun - Google Patents

Process for initiating an arc between electrodes in a plasma gun Download PDF

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Publication number
US3448333A
US3448333A US554170A US3448333DA US3448333A US 3448333 A US3448333 A US 3448333A US 554170 A US554170 A US 554170A US 3448333D A US3448333D A US 3448333DA US 3448333 A US3448333 A US 3448333A
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Prior art keywords
gas
electrodes
mixture
arc
electrode
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Expired - Lifetime
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US554170A
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English (en)
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Kenneth Arkless
Alan Lawrence Hare
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British Titan Products Co Ltd
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British Titan Products Co Ltd
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/48—Generating plasma using an arc
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/52—Generating plasma using exploding wires or spark gaps

Definitions

  • a process for initiating an are between electrodes in a plasma gun is disclosed.
  • a gaseous mixture is introduced between the electrodes, which gaseous mixture has a lower breakdown potential than its constituents.
  • the mixture comprises the primary gas to be heated and an additional gaseous constituent.
  • the arc can be initiated at a lower potential than would have otherwise been possible.
  • the present invention relates to improved apparatus and processes for heating gases by means of an electric discharge between electrodes.
  • One apparatus which utilizes this principle is the plasma gun which, in one form, consists of at least two electrodes connected to a suitable source of electrical energy, which may be a source of direct or alternating current, but which is preferably a source of direct current.
  • a central solid electrode projecting toward the centre of a disc electrode.
  • the disc electrode in such guns is usually provided with an orifice through the centre as an outlet for the gas which is heated by passage through the discharge between the electrodes and the arc is formed between the tip of the central electrode and the inner edge and/or the inner wall of the orifice through the other electrode.
  • the central electrode is the cathode.
  • the gas to be heated is generally introduced into such a gun around the central electrode either in helical flow (for example by the introduction of the gas tangentially to the wall of the chamber containing the central electrode) or in laminar flow (for example by the introduction of the gas through a number of orifices surrounding the central electrode). Alternatively a mixture of such flows may be provided.
  • Plasma guns of the type referred to above are described, for example, in our co-pending US. application Ser. No. 256,386, filed Feb. 5, 1963, and now abandoned.
  • the electrodes in the plasma gun may be tubes, preferably coaxial tubes placed in end to end relationship and the are being formed between the in teriors of the electrodes.
  • the gas to be heated may be introduced into the chamber surrounding the adjacent ends of the electrodes, preferably through a number of inlets directed tangentially to the walls of the chamber to impart a helical flow to the gas before passing through the discharge.
  • the gas may conveniently be directed through the interior of one of the tubes forming an electrode to the atmosphere.
  • the gas to be heated may be introduced Patented June 3, 1969 through one tubular electrode and withdrawn through the other.
  • plasma gun as used in this specification, therefore, is meant a device whereby a gas is heated to a high temperature by its passage through an electric are between electrodes.
  • Plasma guns are generally designed to operate in a stable manner once the arc has been initiated but the initiation of the arc presents considerable practical difficulties because the voltage required to initiate the arc is much greater than that required to maintain the are once the latter is established. The voltage required to initiate the are, therefore, must exceed the breakdown potential of the gas between the electrodes. Power units can be designed to provide the high voltages necessary to initiate the are (as well as to maintain the are) but this greatly increases the cost of the power unit.
  • auxiliary circuits to provide high frequency discharges of short duration between the electrodes.
  • Such auxiliary circuits require careful construction and, again, considerably increase the cost of the installation. Furthermore, there is a danger that the high frequency discharge may damage the main power unit connected to the electrodes.
  • Another method of initiating the arc in plasma guns which has been used is the insertion between the electrodes of a metal wire or the like whereby the metal is rapidly heated and thus produces ions which assist in providing a path for the are which may then become established.
  • a variation of this method is the provision of a third electrode, for example a carbon electrode which is in electrical contact with one electrode and which is momentarily advanced, for example pneumatically, until it contacts the other electrode thereby completing the circuit.
  • This short circuit initiates the are by a temporary reduction of the gap between the electrodes, thus increasing the potential gradient between the electrodes until it exceeds the breakdown potential of the gas.
  • Unreliability in the operation of a plasma gun is a particularly serious disadvantage when the plasma gun forms part of a complex chemical plant which relies upon the gun as a source of heat.
  • the invention is a process for initiating an are between electrodes comprising passing a primary gas to be heated between electrodes connected to a suitable source of electrical energy and introducing, between the electrodes, a secondary gas or gas mixture in such a manner that it forms, either when mixed with the primary gas or by itself, a gaseous mixture between the electrodes which has a lower breakdown potential than that of its constituents and of the potential drop between the electrodes.
  • the invention is also a plasma gun for heating a gas to a high temperature comprising at least two electrodes adapted for connection to a source of electrical energy; at least one inlet for the gas to be heated by passage between the electrodes and an outlet for the heated gas, characterized in that there is provided a conduit, the wall of which is in electrical contact with one electrode and which is so positioned as to direct a gas introduced through the conduit between the surfaces of the electrodes and means to introduce a gas into the said conduit.
  • the gas mixture which has a lower breakdown potential than that of its constituents may be formed either by introducing a single secondary gas into the space between the electrodes in such a manner that it mixes with the primary gas to be heated, passing between the electrodes, and forms with this gas a mixture of the correct proportions to obtain the desired low breakdown potential, or by introducing a secondary gas mixture, for example a preformed mixture between the electrodes.
  • the gases will mingle to give concentration gradients which may be considered in the form of a large number of gas mixtures containing various concentrations of their constituent gases between the electrodes and, in the present invention, the secondary gas or gas mixture is introduced into the plasma gun in such a manner that at least one resulting gas mixture exists between the electrodes containing the correct proportion of gases to give the desired low breakdown potential.
  • the secondary gas or gas mixture which is introduced between the electrodes is preferably introduced through a conduit, the wall of which is in electrical contact with one of the electrodes, and which directs the gas or gas mixture at the face of the other electrode.
  • a conduit the wall of which is in electrical contact with one of the electrodes, and which directs the gas or gas mixture at the face of the other electrode.
  • One particular method of producing such an arrangement is by drilling a hole through the wall of the gun, through a portion of one electrode and at such an angle that gas issuing from the interior end of the conduit is directed upon the face of another electrode between which the are is to be formed.
  • a tube or the like may be inserted in the hole to facilitate variation of the velocity and/or direction of the gas flow.
  • the distal end of the conduit is normally provided with means to introduce the secondary gas or gas mixture into the conduit, for example this may comprise a connection to a gas supply pipe.
  • the wall of the conduit for the secondary gas or gas mixture may not be in electrical contact with an electrode and so positioned that the second gas or gas mixture is directed between the faces of the electrodes.
  • the conduit may be of any suitable cross section and may, for example, terminate in the gun in a slot, annulus or porous plug. Alternatively, there may be a number of such conduits or even a single conduit which may terminate in a number of orifices of the type mentioned above.
  • the end of the conduit should preferably not project into the arc (when initiated) in order to avoid excessive erosion of the conduit.
  • By such means it may be possible to use a conduit of smaller internal diameter (particularly where the space between the electrodes is large) and thereby reducing the amount of secondary gas or gas mixture required to initiate the arc.
  • the optimum diameter of the conduit will depend, inter alia, upon: the number of conduits; the distance between the electrodes; the composition of the gas mixture required to give a low breakdown potential; the amount of gas to be introduced between the electrodes and the pressure available for its introduction.
  • a conduit or conduits having an internal diameter in the range of about /2 to and particularly in the range of to have been found convenient, although larger diameter conduits may be desirable, particularly where the electrode gap is large.
  • the secondary gas or gas mixture which is introduced into the space between the electrodes (between which the arc is to be initiated) in order to reduce the breakdown potential must be such a nature that, if it is a single gas, it forms with the primary gas, a gaseous mixture having a lower breakdown potential than that of either of the constituents of the mixture and, if a gas mixture, then that mixture of gasses must be such that it provides a lower breakdown potential between the electrodes than any of the constituents of the mixture or of the primary gas.
  • the process of the present invention depends upon the formation of a zone or zones of a gas mixture between the electrodes which is characterised by the presence of a major gaseous constituent having a high metastable potential (for example the secondary gas or gas mixture) and a minor constituent(s) having a lower ionization potential (for example the primary gas or a constituent of the secondary gas mixture) than the metastable potential of the major constituent.
  • a major gaseous constituent having a high metastable potential for example the secondary gas or gas mixture
  • a minor constituent(s) having a lower ionization potential for example the primary gas or a constituent of the secondary gas mixture
  • the voltage applied across the electrodes is believed to give rise to metastable molecules of the major constituent (which have a relatively long life when compared with ionized molecules) and these interact with molecules of the minor constituent thereby causing their ionization.
  • the ionization of the molecules of the minor constituent is believed to be maintained by their high dilution and/or by further ionization due to their interaction with the metastable molecules of the major constituent, thus creating a pathway for the flow of current between the electrodes which rapidly increases to form a self-sustaining are. This are is then transferred to the primary gas, and the flow of secondary gas or gas mixture is discontinued.
  • Gases which have a high metastable potential are helium (19.8 electron volts) and neon (16.6 electron volts).
  • Argon which is less suitable, has a metastable potential of 11.5 volts.
  • Primary gases or gases which may be introduced through the conduit as a component of a secondary gas mixture and which are very suitable for use in the present invention as ionizing gases (particularly with helium or neon as the secondary gas) are hydrogen, oxygen, nitrogen, argon (where this is not used as the secondary gas), chlorine, carbon monoxide, carbon dioxide, ammonia, hydrogen chloride, nitrogen oxides, sulphur dioxide, and methane which have ionization potentials in the range of about 10 to 15 electron volts.
  • the local concentration of the secondary gas between the electrodes should be greater than and preferably greater than by volume to obtain the minimum breakdown potential, the ionizing gas or gases forming the remainder of the mixture.
  • a primary gas such as nitrogen may be passed between the electrodes to which electrical power is supplied and helium or neon, as the an orifice diameter) at 50 p.s.i.g. and the introduction of this gas mixture was controlled by a solenoid valve.
  • Example 3 The process described in Example 2 was repeated except that oxygen was introduced as the primary gas in place of nitrogen.
  • Example 4 The process of Example 2 was repeated using helium neon and argon separately as primary gases without the introduction of a secondary gas. In no case could the are be initiated either at 1500 or at 3000 volts open circuit voltage.
  • step (b) is formed by mixing a substantial amount of at least one secondary gas with said primary gas and wherein said are transfer in step (c) is effected by discontinuing the mixing of secondary gas with said primary gas.
  • the secondary gas is a gas other than said primary gas and is selected from the group consisting of helium, neon, argon and mixtures thereof.
  • a process as claimed in claim 5 wherein the concentration of secondary gas comprises at least by volume of the mixture.
  • step (b) is a mixture of at least two gases other than said primary gas and wherein said are transfer is efiected by feeding primary gas between said electrodes through said arc, and discontinuing feeding of said gas mixture.
  • step (:b) comprises a mixture of at least one member selected from the group consisting of helium and neon with an ionizing gas.
US554170A 1965-06-15 1966-05-31 Process for initiating an arc between electrodes in a plasma gun Expired - Lifetime US3448333A (en)

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GB25193/65A GB1112444A (en) 1965-06-15 1965-06-15 Plasma gun gas heating process

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US (1) US3448333A (xx)
JP (1) JPS4826264B1 (xx)
BE (1) BE682580A (xx)
DE (1) DE1539691C2 (xx)
FR (1) FR1538972A (xx)
GB (1) GB1112444A (xx)
NL (1) NL6608277A (xx)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3541379A (en) * 1967-09-11 1970-11-17 Ppg Industries Inc Method for initiating gaseous plasmas
US4156828A (en) * 1977-03-18 1979-05-29 Deutsche Forschungs- Und Versuchsanstalt Fur Luft- Und Raumfahrt E.V. Glow discharge apparatus and a method of operating same
US4691109A (en) * 1986-01-28 1987-09-01 Rca Corporation Apparatus and method for producing ions
US4697085A (en) * 1986-01-28 1987-09-29 Rca Corporation Apparatus and method for producing ions
US5367871A (en) * 1992-07-27 1994-11-29 General Electric Company Aircraft engine ignition system
CN114158173A (zh) * 2021-11-30 2022-03-08 西北核技术研究所 一种用于抑制预脉冲电流的丝阵负载结构

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2926840A1 (de) * 1979-07-03 1981-01-22 Siemens Ag Strahlenaustrittsfenster
US4549065A (en) * 1983-01-21 1985-10-22 Technology Application Services Corporation Plasma generator and method

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3229155A (en) * 1960-12-20 1966-01-11 William C A Carlson Electric arc device for heating gases
US3255379A (en) * 1963-07-26 1966-06-07 Giannini Scient Corp Apparatus and method for generating light

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3229155A (en) * 1960-12-20 1966-01-11 William C A Carlson Electric arc device for heating gases
US3255379A (en) * 1963-07-26 1966-06-07 Giannini Scient Corp Apparatus and method for generating light

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3541379A (en) * 1967-09-11 1970-11-17 Ppg Industries Inc Method for initiating gaseous plasmas
US4156828A (en) * 1977-03-18 1979-05-29 Deutsche Forschungs- Und Versuchsanstalt Fur Luft- Und Raumfahrt E.V. Glow discharge apparatus and a method of operating same
US4691109A (en) * 1986-01-28 1987-09-01 Rca Corporation Apparatus and method for producing ions
US4697085A (en) * 1986-01-28 1987-09-29 Rca Corporation Apparatus and method for producing ions
US5367871A (en) * 1992-07-27 1994-11-29 General Electric Company Aircraft engine ignition system
CN114158173A (zh) * 2021-11-30 2022-03-08 西北核技术研究所 一种用于抑制预脉冲电流的丝阵负载结构
CN114158173B (zh) * 2021-11-30 2023-09-01 西北核技术研究所 一种用于抑制预脉冲电流的丝阵负载结构

Also Published As

Publication number Publication date
GB1112444A (en) 1968-05-08
NL6608277A (xx) 1966-12-16
DE1539691B1 (de) 1973-11-29
DE1539691C2 (de) 1974-06-20
JPS4826264B1 (xx) 1973-08-08
FR1538972A (fr) 1968-09-13
BE682580A (xx) 1966-12-15

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