Abstract: The invention provides a plasma welding or brazing process in which a direct current pilot arc is maintained throughout the process. The process comprises the steps of setting a pilot arc power supply (6) to a relatively high level, generating a high voltage spark discharge between a non-consumable electrode (14) of a plasma welding or brazing torch (2) and a nozzle (18) of said torch in order to start the flow of a pilot arc current, detecting the pilot arc current and reducing the pilot arc current to a relatively low level. The invention further provides apparatus for carrying out plasma arc welding, comprising a plasma welding torch, a controller and a power supply. The controller further comprises means for detecting the flow of a pilot arc current and or a main arc current and means for reducing this current on detection.

Abstract: A plasma reactor system with controlled DC bias for manufacturing semiconductor wafers and the like. The reactor system includes a plasma chamber, a plasma generating coil and a chuck including a chuck electrode. The chuck supports a workpiece within the chamber. The plasma reactor system further includes a pair of generators, one of which supplies a radio frequency signal to the plasma generating coil. The second generator delivers a RF signal which to the chuck electrode and acts to control DC bias at the workpiece. Peak voltage sensor circuitry and set point signal circuitry controls the power output of the generator, and a matching network coupled between the generator and the first electrode matches the impedance of the RF signal with the load applied by the plasma. DC bias determines the energy with which plasma particles impact the surface of a workpiece and thereby determines the rate at which the process is performed.

Abstract: An apparatus for dissociating gases includes a plasma chamber that may be formed from a metallic material and a transformer having a magnetic core surrounding a portion of the plasma chamber and having a primary winding. The apparatus also includes one or more switching semiconductor devices that are directly coupled to a voltage supply and that have an output coupled to the primary winding of the transformer. The one or more switching semiconductor devices drive current in the primary winding that induces a potential inside the chamber that forms a plasma which completes a secondary circuit of the transformer.

Abstract: A plasma apparatus separately measures multiple plasma jets upstream of where the plasma jets converge into a combined plasma stream. The separate plasma jets can be separately adjusted to place the separate jets in a configuration that provides the combined stream with desired properties for a plasma treatment. The system can include an injector for a neutral jet that becomes part of the combined plasma stream. With an injector, the positions of the plasma jets can be measured relative to the injector so that the plasma jets and the neutral jet are properly aligned to form a combine plasma stream having the properties desired.

Abstract: A plasma-assisted processing system has a lifting mechanism capable of vertically moving a microwave power unit and a waveguide to adjust the level of a planar slot antenna disposed on an expanded lower end part of the waveguide. A space extending under the antenna is surrounded by a shielding member. An optical sensor having an array of photosensors is disposed on the outer side of a window formed in the side wall of a vacuum vessel to monitor the lower limit level of a cease region for a plasma (cease level). An ideal distance between the cease level and the antenna is determined beforehand and the level of the antenna is adjusted on the basis of a measured cease level so that the antenna is spaced the ideal distance apart from the cease level. Since the difference between the cease level and a level X0 for the cutoff density of an X-wave is fixed, the level X0 may be monitored instead of the cease level.

Abstract: A method of controlling an output of a generator is provided. The output provides an output signal having a settling time to a load having an impedance. The settling time of the output signal is determined. The output signal is amplitude modulated with a modulation waveform. A sense signal is generated that is representative of the modulated output signal. The sense signal is sampled at a sampling time based upon the settling time of the output signal. A digital representation of the sampled sense signal is generated. The amplitude modulation of the output is controlled based upon the digital representation of the sampled sense signal.

Abstract: A plasma reactor system with controlled DC bias for manufacturing semiconductor wafers and the like. The reactor system includes a plasma chamber, a plasma generating coil and a chuck including a chuck electrode. The chuck supports a workpiece within the chamber. The plasma reactor system further includes a pair of generators, one of which supplies a radio frequency signal to the plasma generating coil. The second generator delivers a RF signal which to the chuck electrode and acts to control DC bias at the workpiece. Peak voltage sensor circuitry and set point signal circuitry controls the power output of the generator, and a matching network coupled between the generator and the first electrode matches the impedance of the RF signal with the load applied by the plasma. DC bias determines the energy with which plasma particles impact the surface of a workpiece and thereby determines the rate at which the process is performed.

Abstract: An apparatus and method for producing an exhaust processor comprising: a clamping device for applying a predetermined clamping pressure to clamp a case or other component of the exhaust processor about a substrate or other component of the exhaust processor to define a gap between the case and substrate; a measuring device for measuring a size of the gap during application of the predetermined clamping pressure, the measuring device including a clamping pressure control system for adjusting the predetermined clamping pressure of the clamping device in response to the gap measurement so that the gap size is within a predetermined range; and a welder for welding a portion of the case component to an other portion of the caset when the gap size is within the predetermined range. The measuring device also includes a camera for measuring the gap size.

Abstract: A process for operating a plasma torch having an improved start up and shut down sequence to substantially increase electrode element life. The first shut down mode is controlled such that plasma gas flow through the swirl ring and nozzle prevents the formation of an oxide layer upon the electrode. The shut down method is especially useful for torches which operate at 100 amps or greater. The inclusion of an aluminum jacket surrounding the electrode outer walls has been found to contribute to the ability to avoid formation of oxide layers on the electrode.

Abstract: A process for operating a plasma torch having an improved start up and shut down sequence to substantially increase electrode element life. The first shut down mode is controlled such that plasma gas flow through the swirl ring and nozzle prevents the formation of an oxide layer upon the electrode. The shut down method is especially useful for torches which operate at 100 amps or greater. The inclusion of an aluminum jacket surrounding the electrode outer walls has been found to contribute to the ability to avoid formation of oxide layers on the electrode.

Abstract: The present invention is constituted of a lower electrode structure (1) comprising a base table (2) formed of a conductive material, an electrostatic adsorption member (3) formed on the base table (2) and having a dielectric layer (4) on which the substrate to be mounted and within which an electrode (5) electrically isolated from the base table (2) is housed, first wiring (7) having an end connected to the electrode (3) of the electrostatic adsorption member, a direct-current source (8) connected to the other end of the first wiring (7), second wiring (10) having an end connected to the base table (2), a high frequency source (11) connected to the other end of the second wiring (10), a third wiring (14) for connecting the first wiring (7) and the second wiring (10), and a capacitor (13) formed on the third wiring (14). Plasma processing is performed by disposing the lower electrode structure (1) in the chamber (21).

Abstract: Multiple plasma jet path sensing positions and multiple localized steering magnetic fields for each plasma jet leg in an atmospheric plasma jet control system are described for a precise control over positions of plasma jet legs as well as their directions in a vertex zone, where a hot gas stream is generated for treatment of a semiconductor device. With a plasma jet generator system in accordance with the invention precise control over the plasma jet legs enables one to virtually eliminate plasma jet path instability at the vertex region.

Abstract: A plasma processing method comprises the steps of supplying a low-frequency bias to a first electrode carrying a substrate, and supplying a high-frequency power to a second electrode facing the first electrode, wherein the low-frequency bias is supplied to the first electrode in advance of starting plasma by the energy of the high-frequency power, with an electric power sufficient to form an ion-sheath on the surface of the substrate.

Abstract: A method of controlling an output of a generator is provided. The output provides an output signal having a settling time to a load having an impedance. The settling time of the output signal is determined. The output signal is amplitude modulated with a modulation waveform. A sense signal is generated that is representative of the modulated output signal. The sense signal is sampled at a sampling time based upon the settling time of the output signal. A digital representation of the sampled sense signal is generated. The amplitude modulation of the output is controlled based upon the digital representation of the sampled sense signal.

Abstract: A plasma apparatus separately measures multiple plasma jets upstream of where the plasma jets converge into a combined plasma stream. The separate plasma jets can be separately adjusted to place the separate jets in a configuration that provides the combined stream with desired properties for a plasma treatment. The system can include an injector for a neutral jet that becomes part of the combined plasma stream. With an injector, the positions of the plasma jets can be measured relative to the injector so that the plasma jets and the neutral jet are properly aligned to form a combine plasma stream having the properties desired.

Abstract: A method of controlling an output of a generator is provided. The output provides an output signal having a settling time to a load having an impedance. The settling time of the output signal is determined. The output signal is amplitude modulated with a modulation waveform. A sense signal is generated that is representative of the modulated output signal. The sense signal is sampled at a sampling time based upon the settling time of the output signal. A digital representation of the sampled sense signal is generated. The amplitude modulation of the output is controlled based upon the digital representation of the sampled sense signal.

Abstract: An impedance matching circuit for a plasma source includes: a first network including: a first coil; and a RF power supply applying a first voltage to the first coil; and a second network including; a second coil grounded having a second voltage, the second voltage being lower than the first voltage; first and second reactive elements, one end portion of the first and second reactive elements being connected to each end portion of the second coil, respectively; and a load connected to the other end portions of the first and second reactive elements, phases at two end portions of the load being different from each other.

Abstract: A system for converting DC power (22) into an RF electromagnetic field in a processing chamber, the system being composed of: a coil (16) constructed to surround the processing chamber; and an RF power generator (20) including a free-running oscillator (26) having a DC power input and an RF power output, the power output connected to a load impedance which includes the coil for supplying RF current to the coil at a frequency which is dependent on the load impedance.

Abstract: An apparatus for dissociating gases includes a plasma chamber that may be formed from a metallic material and a transformer having a magnetic core surrounding a portion of the plasma chamber and having a primary winding. The apparatus also includes one or more switching semiconductor devices that are directly coupled to a voltage supply and that have an output coupled to the primary winding of the transformer. The one or more switching semiconductor devices drive current in the primary winding that induces a potential inside the chamber that forms a plasma which completes a secondary circuit of the transformer.

Abstract: A method and apparatus for plasma cutting includes a cutting power supply, preferably a buck converter, and a compressor. The cutting power supply provides power to a plasma torch, and the compressor provides air to the torch. The air compressor is integrated into the plasma cutter, and includes a compressor motor, preferably with a buck convertor power supply, or having the motor windings are part of the buck converter that is the cutting power supply. The motor is regulated regulator to a fixed setpoint or a user setpoint by a compressor regulator in response to a feedback signal, preferably a compressor motor voltage feedback signal. The compressor also turns the compressor on and/off in response to a trigger and/or cutting current feedback signal and has an on/off circuit responsive thereto in various alternatives.

Abstract: A device for stopping a bleeding in living tissue in humans and animals by forming a necrotic layer in the tissue comprises a member for generating a dynamic plasma flow capable of wholly or partially penetrating an outer, porous layer of the necrotic layer. The device also has an electrosurgical generator arranged to transfer electric energy to the inner limit of the porous layer through a circuit that comprises the plasma flow and the tissue.

Abstract: A plasma source includes a structure made up of two hollow cathode shapes connected to a bipolar AC power supply. The bipolar power supply alternately drives one hollow cathode to a negative voltage while the opposite hollow cathode is driven to a positive voltage. As one of the two hollow cathode shapes is driven negative, the hollow cathode discharge forms within the corresponding cavity. The other cathode then forms an anode, causing electrons to escape the plasma and travel to the other side, completing the electric circuit. The plasma generator thus formed may be used as a heat source for an effusion cell to form a plasma from a reactant gas, or to increase the reactivity of gas situated between a vacuum deposition source and a substrate to be coated.

Abstract: A method and apparatus for simultaneously cleaning and bonding a wire to a bonding surface is presented. In accordance with the invention, a gas is energized to form a plasma, which is then directed in a directional pressurized flow at the wire and bonding surface to form a dynamic plasma cleaning chamber bubble around the portion of the wire and bonding surface that are to be bonded together, and then the respective portions of the wire and bonding surface are bonded together within the plasma cleaning chamber bubble.

Abstract: A contact start plasma torch and method of starting the torch includes a negatively charged cathode body and a positively charged anode body. A conductive element in the torch is constructed of an electrically conductive material and is free from fixed connection with the cathode body and the anode body. The torch is operable between an idle mode wherein the conductive element provides an electrically conductive path between the cathode body and the anode body and an pilot mode wherein a pilot arc is formed between the conductive element and at least one of the cathode body and the anode body. The pilot arc is blown by working gas flowing through the torch toward an exit orifice of the torch whereby 10) the working gas is exhausted from the torch in the form of an ionized plasma.

Abstract: An apparatus, system and related method are disclosed for sensing a characteristic of a workpiece, such as the location of a welding seam, using a sensor that is independent of another device for performing an operation on the workpiece, such as a welding torch for welding a seam. The sensor preferably takes the form of a plasma arc torch. This plasma arc torch travels along the workpiece, preferably just ahead of the welder for welding the workpiece or other implement and simultaneously moves to and fro in a direction transverse to the direction of travel of the welder. A non-transferred electrical arc serves to ionize a plasma gas issuing from the plasma arc torch to create a concentrated plasma jet directed towards the workpiece.

Abstract: A plasma processing apparatus having a process chamber to process specimens, further comprising a status detecting means for detecting the internal processing status of said process chamber and outputting a plurality of signals and signal converting means for extracting an arbitrary number of signal processing filters from a signal filter database by a signal filter selecting means and creating arbitrary number of device status signals; wherein said signal converting means create a fewer effective device status signals of a time series from said output signals.

Abstract: A method and apparatus for plasma cutting is disclosed. A regulated flow of gas is provided to the torch. Power is also provides to the torch. A controller controls the system and includes a delay circuit. A gas pressure sensor is connected to the torch and/or the gas flow control, and/or the controller. A user indicator is connected to the delay circuit, and the user indicator is activated upon low pressure being detected, and maintained even if the pressure rises.

Abstract: A plasma processing apparatus has a plasma processing chamber, a radiofrequency generator, and an matching circuit. The plasma processing chamber includes a plasma excitation electrode and a susceptor electrode for exciting a plasma. The radiofrequency generator is connected to plasma excitation electrode. The matching circuit matches the impedance between the plasma processing chamber and the radiofrequency generator. A capacitance which is 26 times a plasma electrode capacitance Ce between the plasma excitation electrode and the susceptor electrode is greater than a loss capacitance CX between the plasma excitation electrode and ground potential positions which are DC-grounded.

Abstract: A method and apparatus produce short-wave radiation from a gas-discharge plasma, comprising pre-ionization of the gas in the discharge region between coaxial electrodes achieved through an axial aperture formed in one of the electrodes and initiation of a pinch-type discharge. In order to increase the efficiency, energy, average power and stability of the radiation of the gas-discharge plasma, pre-ionization is achieved by a flux of radiation having wavelengths from the UV to X-ray range and by a flux of accelerated electrons from the plasma of a pulsed sliding discharge initiated in a region not optically communicating with the axis of the pinch-type discharge, with a rate of growth of the discharge voltage across the region of more than 1011 V/s, the fluxes of radiation and electrons being formed axially symmetrically and directed into the part of the discharge region outside the axis.

Abstract: The invention concerns a device for high frequency treatment of a liquid, solid or gaseous product comprising at least one treatment inductance (2) enclosing a tubular conduit (1) designed to be passed through by a stream of the product to be treated, said inductance (2) being powered by a high-frequency generator (3) via coupling means (22, 24).

Abstract: A device to place an incision into matter with a harmonious plasma cloud. A radiofrequency generator system produces pulsed or continuous electromagnetic waveform which is transmitted by an active transmitter incising electrode tip. This generated electromagnetic wave is utilized to initiate a plasma cloud with processes such as thermal ionization and a photoelectric effect which then trigger an Avalanche Effect for charged atomic particles at the surface of the active transmitter incising electrode tip. This electromagnetic wave is impedance matched, frequency matched, power matched and tuned to the plasma cloud in order to sustain and control a harmonious plasma cloud with reduced atomic particle turbulence and chaos. This harmonious plasma cloud forms a coating over the surface of the active transmitter electrode tip as well as acts to reduce the energy needed from the power amplifier of our plasma cutting device.

Abstract: An automated hardfacing system useful for hardfacing roller cones is disclosed. The automated system includes a robot with an arm, a positioner, and a controller which co-ordinates the alignment of the robot and the positioner. The robot holds a hardfacing torch and is capable of movement in three axes of movement. These axes are the x, y, and z axes of the Cartesian co-ordinate system. The positioner holds a roller cone and is capable of movement in at least two axes of movement. The movement includes tilting and rotation about a Cartesian axis. The hardfacing coating produced by the automated system has improved quality and consistency as compared to the one obtained by a manual process.

Abstract: A variable frequency RF power delivery system is used with a control system that adjusts the output frequency of the RF power delivery system. Frequency adjustments are made so as to maintain the required input current and input voltage within the capabilities of the input current and input voltage source.

Abstract: An improved toroidal low-field plasma source allows plasma ignition within a wider range of gas conditions than permitted by prior art plasma sources. Power efficiency of the plasma source is improved by automatically adjusting the power delivered to the plasma based on the load to the power supply. The plasma source can be operated over a wider pressure range than allowed by prior art plasma sources. The plasma source can be operated so as to increase the output of atomic species from the source. The plasma source can be operated to increase the etch rate of organic materials. The plasma source can efficiently remove hazardous gas compounds from effluent gas streams by converting them into scrubbable products.

Abstract: An improved toroidal low-field plasma source allows plasma ignition within a wider range of gas conditions than permitted by prior art plasma sources. Power efficiency of the plasma source is improved by automatically adjusting the power delivered to the plasma based on the load to the power supply. The plasma source can be operated over a wider pressure range than allowed by prior art plasma sources. The plasma source can be operated so as to increase the output of atomic species from the source. The plasma source can be operated to increase the etch rate of organic materials. The plasma source can efficiently remove hazardous gas compounds from effluent gas streams by converting them into scrubbable products.

Abstract: A radio frequency generated plasma is provided to a skin surface in a controlled manner, in order to heat and selectively damage a thin superficial layer, thereby inducing a renewal process of the epidermis. The plasma is generated by providing a vacuum to the probe, and also providing an rf pulse to an electrode within the probe, thereby creating a glow discharge that includes gas ions that contact the skin and cause the skin to heat up.

Abstract: A plasm-arc torch system, a circuit, and a method for controlling a pilot arc. A rate of change sensor, such as a dv/dt sensor, monitors the output of an error amplifier to determine whether to close a switch to re-attach a pilot arc before a transferred arc becomes extinguished. The switch selectively connects a tip into a circuit path with an electrode and a power supply to allow the pilot arc to form between the tip and the electrode. The error amplifier preferably provides an error signal for use by a pulse-width modulator for providing a current regulated power supply capability. The power supply preferably regulates the output current to a first level when a pilot arc is present, and to a second mode when a transferred arc is present. The pilot arc may also be re-attached between the tip and the electrode by use of a pilot regulator that attempts to maintain the current flowing through the tip at an intermediate level between the first level and the second level.

Abstract: This invention relates to methods and apparatus for controlling a power supply of a plasma arc system. According to the method, any AC input voltage within a range of input voltages is provided into the input stage and a rectified output voltage is thereby generated. The rectified output voltage is provided into the power factor corrected boost stage and a DC signal is thereby generated. The DC signal is provided into an auxiliary power supply and a regulated power signal is thereby generated. The regulated power signal is provided into a digital signal processor module and an output control signal is thereby generated. The output control signal is provided into the inverter stage and a plasma arc current is thereby generated.

Abstract: An apparatus and method for producing an exhaust processor comprising: a clamping device for applying a predetermined clamping pressure to clamp a case or other component of the exhaust processor about a substrate or other component of the exhaust processor to define a gap between the case and substrate; a measuring device for measuring a size of the gap during application of the predetermined clamping pressure, the measuring device including a clamping pressure control system for adjusting the predetermined clamping pressure of the clamping device in response to the gap measurement so that the gap size is within a predetermined range; and a welder for welding a portion of the case component to an other portion of the caset when the gap size is within the predetermined range. The measuring device also includes a camera for measuring the gap size.

Abstract: Multiple plasma jet path sensing positions and multiple localized steering magnetic fields for each plasma jet leg in an atmospheric plasma jet control system are described for a precise control over positions of plasma jet legs as well as their directions in a vertex zone, where a hot gas stream is generated for treatment of a semiconductor device. With a plasma jet generator system in accordance with the invention precise control over the plasma jet legs enables one to virtually eliminate plasma jet path instability at the vertex region.

Abstract: A method for locally heating objects, in particular thin sheet metal, by charging the objects by means of a plasma ignited between two electrodes. In order to keep the thermal stress of a subject as low as possible outside of the zone to be heated it is provided that the machining such as spot welding or burning through a breakthrough occurs with merely one plasma pulse which is produced by applying a voltage pulse exceeding the arc-over voltage of the gap between the electrodes.

Abstract: A contact plasma-arc torch having a parts-in-place safety reset circuit and method. The torch includes an electrode and a tip. A safety reset circuit monitors parameters associated with the electrical relationship between the electrode and the tip to determine whether the tip and/or electrode are properly installed. The circuit also monitors an electrical relationship associated with the workpiece to detect when current is flowing in the workpiece when such current is not expected. The torch power supply and associated circuitry includes a soft start capability whereby the full power output of the power supply is supplied to the electrode over time due to the soft start characteristic of a soft start circuit. If the safety reset circuit detects that the tip and/or electrode arc not properly installed, or that current is flowing in the workpiece when such current is not expected, the safety reset circuit resets the soft start circuit.

Abstract: A plasma apparatus separately measures multiple plasma jets upstream of where the plasma jets converge into a combined plasma stream. The separate plasma jets can be separately adjusted to place the separate jets in a configuration that provides the combined stream with desired properties for a plasma treatment. The system can include an injector for a neutral jet that becomes part of the combined plasma stream. With an injector, the positions of the plasma jets can be measured relative to the injector so that the plasma jets and the neutral jet are properly aligned to form a combine plasma stream having the properties desired.

Abstract: A plasma apparatus separately measures multiple plasma jets upstream of where the plasma jets converge into a combined plasma stream. The separate plasma jets can be separately adjusted to place the separate jets in a configuration that provides the combined stream with desired properties for a plasma treatment. The system can include an injector for a neutral jet that becomes part of the combined plasma stream. With an injector, the positions of the plasma jets can be measured relative to the injector so that the plasma jets and the neutral jet are properly aligned to form a combine plasma stream having the properties desired.

Abstract: The invention relates to an automatic plant for cutting or welding by gas jet, especially by plasma jet, comprising a torch (T), a first pilot-gas line (L1), a second cutting- or welding-gas line (L2), control means (MP), first element (MR1) for adjusting the pressure of the pilot gas in the line (L1) and second element (MR2) for adjusting the pressure of the gas in the line (L2). The first adjustment element (MR1) are fitted in the line (L1) and controlled by control element (MP). A pneumatic control line (LP) pneumatically connects the line (L1) to the adjustment element (MR2) in order to enable the pressure of the cutting or welding gas to be adjusted in the second line (L2) on the basis of the pressure of the pilot gas in the line (L1), by acting on said second adjustment element (MR2).

Abstract: Process and unit for the arc working, particularly plasma cutting, of a workpiece, in which a plasma torch is supplied with an electric current and with a gas mixture containing hydrogen and nitrogen and/or argon, and a plasma jet obtained by the ionization of the gas mixture by the electric current is delivered by means of the plasma torch. The hydrogen concentration in the gas mixture containing hydrogen and nitrogen and/or argon is less than 50%. The gas mixture is obtained by adding a defined amount of hydrogen to nitrogen and/or argon, immediately before the gas mixture is introduced into said torch. The defined amount of hydrogen is defined according to the thickness of the workpiece, to the grade of the constituent material of the workpiece, to the desired work rate and/or to the intensity of the electric current.

Abstract: A modular system for constructing an atmospheric pressure plasma source. A plasma torch module may be constructed by reassembling the structural components of two (2) different models of spark plugs. Each module can produce a plasma torch having a radius of about 1 cm or more, a height of about 6 cm, and a peak density exceeding 1013 cm−3. A set of modules, each connected in series, may be used with a ballasting capacitor such that an array can be operated while sharing a common power supply to produce a plasma having a relatively large volume and a relatively high density. A system having a number of plasma torch modules may be used in applications for absorbing radiation, reducing air drag and igniting fuel.

Abstract: RF power is delivered to a load in an RF power processor for carrying out process operations. The RF power delivery is performed using a variable frequency RF power amplifier and a control system. The control system maintains RF power delivery using control signals derived from reference RF signals used by the RF power amplifier and measurements of a characteristic of the RF power. The magnitude of the delivered RF power is controlled using measurements of the power input to the RF power amplifier.

Abstract: An apparatus and process is provided for controlling the selection and supply pressure of gases used in a plasma arc torch. A plurality of pressurized feed gases are selectively routed by solenoid gas valves to one or more motorized pressure regulators. A separate regulator controls the pressurized output of a selected pre-flow gas, plasma gas, shield gas, and post flow gas. A microprocessor establishes recommended pressures for each type of gas and prevents operating pressures from being used which may damage a plasma arc torch.

Abstract: A plasma arc torch having new electronic circuit concepts wherein main current regulated power means regulates the pilot current prior to main arc transfer. Further, the circuit may contain two inductors to which DC current initially flows but is interrupted upon main arc transfer such that one inductor maintains the pilot arc while the current in the second inductor forces the establishment of the transferred arc. Also, advantages are presented in pulsing the cutting arc as well as pulsing the pilot arc.