Abstract: A plasma arc torch system, a circuit, and a method for controlling a pilot arc is disclosed. A rate of change sensor, such as a dv/dt sensor, monitors an output current signal or an output voltage signal 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. A power supply preferably regulates the output current or voltage to a first level when a pilot arc is present, and to a second mode when a transferred arc is present.

Abstract: The present invention is directed to a method and apparatus for coordinating the idle mode of a plasma cutter with the idle mode of a power supply so as to prevent lock-out of the plasma cutter when the power supply is in an idle operating state. By putting the plasma cutter in a non-lock-out or “sleep” mode, fuel consumption as well as noise generated by the power supply are reduced. Additionally, by placing the plasma cutter in sleep mode, the user need not turn the power switch of the plasma cutter on and off in order to save power. User input to the plasma cutter kicks the power supply out of idle. The power supply will remain at a non-idle, full operating run mode during the cutting process. However, once the cut is complete and the current draw of the plasma cutter is at a level lower than the power supply idle mode, the plasma cutter will return to sleep mode.

Abstract: There are provided a plasma arc torch and associated methods for selectively switching between a working mode and a standby mode. An electric arc is established between an electrode and a workpiece, and the torch is operated selectively in the working and standby modes. In the working mode, the arc extends between the electrode and the workpiece, the arc has a working arc current, and a plasma gas flows through a nozzle at a working flow rate. In the subsequent standby mode, the arc extends between the electrode and the nozzle and has a current less than the working arc current. The gas flow rate in the standby mode can be reduced to less than the working flow rate, and the plasma gas can be switched from an oxidizing gas to a non-oxidizing gas.

Abstract: Method and an apparatus for igniting plasma in a semiconductor manufacturing apparatus are disclosed. An example plasma ignition method and apparatus sets a predetermined pressure, source power and bias power of a chamber and flows a predetermined flow rate of CHF3 and Ar gases into the chamber, introduces a predetermined flow rate of Cl2 gas into the chamber, completes the supply of Cl2 gas, and ignites plasma.

Abstract: A dual mode plasma arc torch is provided that preferably comprises a start cartridge disposed between an electrode and a tip. In one form, the start cartridge comprises an initiator that is in electrical contact with the electrode and that is resiliently biased into contact with the tip, such that when the plasma arc torch is in a contact start mode, the initiator is movable against the resilient bias to separate from the tip and establish a pilot arc between the initiator and the tip. Further, when the plasma arc torch is in a high frequency start mode, the start cartridge spaces the tip from the electrode such that a pilot arc is established between the electrode and the tip. In other forms, a contact start torch is provided that is operable under high frequency, and conversely, a high frequency start torch is provided that is operable under low voltage.

Abstract: Methods and apparatus are provided for igniting, modulating, and sustaining a plasma for various plasma processes and treatments. In one embodiment, a plasma is ignited by subjecting a gas in a multi-mode processing cavity to electromagnetic radiation having a frequency between about 1 MHz and about 333 GHz in the presence of a plasma catalyst, which may be passive or active. A passive plasma catalyst may include, for example, any object capable of inducing a plasma by deforming a local electric field. An active plasma catalyst can include any particle or high energy wave packet capable of transferring a sufficient amount of energy to a gaseous atom or molecule to remove at least one electron from the gaseous atom or molecule, in the presence of electromagnetic radiation.

Abstract: Methods and apparatus for initiating a welding arc by directing a plasma jet into the space between the tip of the welding electrode and the workpiece. This is done while an electrical potential is applied between the electrode and the workpiece. The ionized plasma gas renders the space between the electrode and the workpiece more conductive, thereby reducing the voltage threshold needed to initiate an arc between the electrode and the workpiece. When the voltage threshold reaches the level of the applied electrical potential, the arc will be initiated.

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 and method are disclosed whereby if the arc in a DC or long-pulse AC vacuum arc plasma process (eg in vacuum deposition) starts to extinguish, this is automatically detected and a re-ignition process is activated. Detection of a tendency for the arc to extinguish is detected by monitoring the main power supply voltage, which will increase if the arc is extinguished.

Abstract: A plasma torch including at least two electrodes separated by an insulating cylindrical case having a void, wherein the electrodes are separated by a distance (D) for forming an igniting arc therebetween when the electrodes are connected to a voltage, the distance (D) and the voltage being selected to form substantially a 1 Megavolt/meter electrical field between the electrodes, for forming an arc and causing plasma to be generated from the plasma generating material.

Abstract: There are provided a plasma arc torch and associated methods for selectively switching between a working mode and a standby mode. An electric arc is established between an electrode and a workpiece, and the torch is operated selectively in the working and standby modes. In the working mode, the arc extends between the electrode and the workpiece, the arc has a working arc current, and a plasma gas flows through a nozzle at a working flow rate. In the subsequent standby mode, the arc extends between the electrode and the nozzle and has a current less than the working arc current. The gas flow rate in the standby mode can be reduced to less than the working flow rate, and the plasma gas can be switched from an oxidizing gas to a non-oxidizing gas.

Abstract: A dual mode plasma arc torch is provided that preferably comprises a start cartridge disposed between an electrode and a tip. In one form, the start cartridge comprises an initiator that is in electrical contact with the electrode and that is resiliently biased into contact with the tip, such that when the plasma arc torch is in a contact start mode, the initiator is movable against the resilient bias to separate from the tip and establish a pilot arc between the initiator and the tip. Further, when the plasma arc torch is in a high frequency start mode, the start cartridge spaces the tip from the electrode such that a pilot arc is established between the electrode and the tip. In other forms, a contact start torch is provided that is operable under high frequency, and conversely, a high frequency start torch is provided that is operable under low voltage.

Abstract: A plasma arc torch system, a circuit, and a method for controlling a pilot arc is disclosed. A rate of change sensor, such as a dv/dt sensor, monitors an output current signal or an output voltage signal 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. A power supply preferably regulates the output current or voltage to a first level when a pilot arc is present, and to a second mode when a transferred arc is present.

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 the working gas is exhausted from the torch in the form of an ionized plasma.

Abstract: An induction plasma torch comprises a tubular torch body, a gas distributor head located at the proximal end of the torch body for supplying at least one gaseous substance into the chamber within the torch body, a higher frequency power supply connected to a first induction coil mounted coaxial to the tubular torch body, a lower frequency solid state power supply connected to a plurality of second induction coils mounted coaxial to the tubular torch body between the first induction coil and the distal end of this torch body. The first induction coil provides the inductive energy necessary to ignite the gaseous substance to form a plasma. The second induction coils provide the working energy necessary to operate the plasma torch. The second induction coils can be connected to the solid state power supply in series and/or in parallel to match the impedance of this solid state power supply.

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 solenoid control and safety circuit suitable for use in connection with contact start, plasma-arc torches. The system monitors a voltage to determine when to open an air control solenoid as part of a contact starting process. If a proper voltage is sensed, a gas solenoid is opened to allow airflow to separate the contact starting elements. The system also includes a circuit that monitors a gas pressure switch to determine whether sufficient pressure exists to separate the contact start elements after a contact start process has been initiated. The circuit removes power if it senses insufficient pressure. Also disclosed is a circuit that monitors a differential voltage between the electrode and the tip to determine if the elements remain in contact after airflow has been provided to the torch head.

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: An apparatus and method are disclosed whereby if the arc in a DC or long-pulse AC vacuum arc plasma process (eg in vacuum deposition) starts to extinguish, this is automatically detected and a re-ignition process is activated. Detection of a tendency for the arc to extinguish is detected by monitoring the main power supply voltage, which will increase if the arc is extinguished.

Abstract: The present invention relates to novel heaters and methods of heating a vacuum chamber, such as a semiconductor wafer plasma processing chamber, using a ceramic igniter array consisting of a plurality of ceramic igniters positioned in a substrate.

Abstract: An improved system of igniting a plasma using a rapid voltage rise and thus causing ions that may be pre-existing to create secondary electron emission or the like is provided. In one embodiment, the voltage rise can be timed to be comparable to the transit time of the electrons across the plasma. It can also be arranged to achieve a voltage rise in less than 1000 microseconds, to result in a transition time that is less than one hundred times the transit time, to maximize the emission of secondary electrons, or even to merely result in collision energies ranging from 5 to 500 electron volts. The transition time can be controlled through an ignition control that may be programmable, may involve charging output storage devices, or may involve delayed switching to supply the increased voltage to the plasma after the storage elements have been more fully charged.

Abstract: A solenoid control and safety circuit suitable for use in connection with contact start, plasma-arc torches. The system monitors a voltage to determine when to open an air control solenoid as part of a contact starting process. If a proper voltage is sensed, a gas solenoid is opened to allow airflow to separate the contact starting elements. The system also includes a circuit that monitors a gas pressure switch to determine whether sufficient pressure exists to separate the contact start elements after a contact start process has been initiated. The circuit removes power if it senses insufficient pressure. Also disclosed is a circuit that monitors a differential voltage between the electrode and the tip to determine if the elements remain in contact after airflow has been provided to the torch head.

Abstract: A main arc ignition method capable of extending lives of a plasma electrode and a nozzle. For this purpose, before or immediately after starting arc, a plasma torch is supplied with a plasma gas at least either at a lower flow rate or at lower gas pressure; the plasma gas is switched to a gas flow rate and gas pressure of a time of cutting a work, after pilot arc is ignited between an electrode and a nozzle, or after main arc is ignited between the electrode and the work; and when generation of the main arc between the electrode and the work is detected, a pilot current is interrupted promptly by a semiconductor switch which is interposed in series with a resistance, in a pilot current circuit that is connected to the nozzle and supplies the pilot current to the pilot arc.

Abstract: A high-frequency power supply apparatus for a plasma generation apparatus having a modulator for generating an intermittent high-frequency output on the basis of a modulation reference signal and a peak value setting signal, the high-frequency power supply apparatus having: a first control loop for comparing the peak value of the intermittent high-frequency output detected by a peak value detector with a preset peak value of the high-frequency output so that the output controller controls the peak value of the high-frequency output to be the preset peak value; and a second control loop for calculating an average value of the intermittent high-frequency output based on the preset peak setting value and a preset duty ratio setting value and generating a modulation reference signal for controlling the modulator on the basis of the average value of the high-frequency output detected by a monitor and the average value of the high-frequency output.

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: 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: 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: 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 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 valve includes a confinement channel and primary anode and cathode disposed therein. An ignition cathode is disposed adjacent the primary cathode. Power supplies are joined to the cathodes and anode for rapidly igniting and maintaining a plasma in the channel for preventing leakage of atmospheric pressure through the channel.

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: 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: 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: An plasma cutter, including a power supply, a cutting torch (with a nozzle), a source of air and a valve, is disclosed. The cutting torch is connected to the two power source outputs (cathode and anode). Air is supplied to the nozzle through the valve from the air supply. In one position the valve allows air to flow from the air source to the nozzle. In a second position the valve prevents air from flowing from the air supply to the nozzle and also vents the nozzle and torch. The torch has a movable electrode and the nozzle is in a fixed position. The nozzle and electrode are each electrically connected to a different one of the power outputs. The electrode is biased (preferably by a spring) to be in contact with the nozzle. However, air flowing into the torch and electrode overcomes the bias and moves the electrode away from the nozzle. If the arc is absent and the user desires current, then the valve is moved to prevent air from flowing into the torch and to vent the torch.

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 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: 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 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: A contact start plasma arc torch is provided that comprises an electrode, a tip, and an initiator that is resiliently biased into contact with the tip, the initiator being movable against the resilient bias to separate from the tip and establish a pilot arc between the initiator and the tip. The initiator is disposed within a start cartridge, which preferably comprises a coil spring that biases the initiator into contact with the tip. The plasma arc torch further comprises a plurality of head vent holes to vent gas from within the start cartridge during operation of the torch. Additionally, the tip defines a plurality of swirl holes and secondary gas holes to generate and control a plasma stream that is subsequently blown from a central exit orifice in the tip.

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 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: The invention features a centralized control architecture for a closely-coupled plasma arc system, in which the “intelligence” of the system is integrated into a single controller. The closely-coupled plasma arc system includes a power source, an automatic process controller and a torch-height controller, where each of these components individually has a closed-loop dynamic relationship with the controller.

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: An energy storage system for use in a magnetic pulse welding and forming apparatus includes a bank of capacitors and a very-low inductance conductive bus system interconnecting the capacitors. The energy storage system further includes an energy source connected to the capacitors, a discharge device, a charging control device, and a discharge control device for selectively initiating discharge of energy stored in the capacitors. The discharge device includes a central electrode placed coaxially inside a ring electrode with an adjustable concentric gap, and an ignition electrode designed as a coaxial ring surrounding the central electrode. The central electrode can be movable, i.e. either rotatable or slidable relative to the bus system. To control the direction of movement of the plasma jet, the central electrode is provided with a central air path and tangential jets opening adjacent to the ignition electrode for organizing air flow through the discharge gap.

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: A plasma arc torch that is capable of operating in a non-transferred arc mode and a transferred arc mode, and that is intended for use for use with a plasma arc treatment system. The plasma arc torch includes an electrode, a plasma gas ring and a nozzle. At least one power supply within the plasma arc treatment system is connected to the electrode, the nozzle and a workpiece. While the torch operates in a non-transferred arc mode, the non-transferred arc heats gas supplied by the plasma gas ring to create plasma gas that heats the workpiece to raise its conductivity. Once the workpiece is at an appropriately conductive level, the arc is automatically transferred since the ground point can now be found.

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.