Abstract: A laser device provided with the function of predicting occurrence of condensation and preventing occurrence of condensation in advance. The laser device is provided with a controlling part calculating a reference temperature for judging whether a cooling water feed device may feed cooling water based on a temperature measured by a thermometer and a humidity measured by a hygrometer, and a comparing part comparing a reference temperature and a cooling water temperature. The cooling water feed device is configured to stop the feed of cooling water after a command for starting up the laser oscillator has been output and the cooling water temperature is lower than the reference temperature and to start or continue the feed of cooling water when the cooling water temperature is the reference temperature or more.

Abstract: Techniques and architecture are disclosed for managing alkali vapor concentration in a lasing gas at non-condensing levels. In some instances, the disclosed techniques/architecture can be used to control and/or stabilize the concentration of alkali vapor in a lasing gas volume to any desired fraction of its saturation value under dynamically changing thermal loads. In some such instances, the concentration of alkali vapor in a given lasing gas volume can be maintained at a value which is sufficiently far from the saturation point to prevent or otherwise reduce condensation of the alkali vapor, for example, upon accelerating the lasing gas through a pressure drop into an optical pumping cavity of an alkali vapor laser system (e.g., such as a diode-pumped alkali laser, or DPAL, system). In some instances, the disclosed techniques/architecture can be used to establish a temperature gradient and/or an alkali vapor concentration gradient in the flowing lasing gas volume.

Abstract: A slab laser includes first and second slabs defining an ionizing chamber intermediate the first slab and the second slab. A Radio Frequency Power Amplifier (RFPA) generates pulses to the ionizing chamber. The laser has a viewing window with access to the ionizing chamber and an optical sensor mounted to access the ionizing chamber through the viewing window. A controller is in communication with the optical sensor, and varies RFPA pulse power in response to the detection of glowing plasma by the optical sensor.

Abstract: A liquid supply device includes a liquid cartridge, which has a liquid chamber that stores liquid, a cartridge mounting portion, and a surface detector. The liquid chamber has a first portion, a second portion, and a third portion. The liquid cartridge removably attaches to the cartridge mounting portion. The surface detector detects a surface of the liquid stored in the liquid chamber. A horizontal cross-sectional area of the first portion of the liquid chamber is less than each of a horizontal cross-sectional area of the second portion and the third portion of the liquid chamber, and the first portion of the liquid chamber is positioned between the second portion and the third portion of the liquid chamber in a direction orthogonal to the horizontal cross-sectional area of the first portion of the liquid chamber.

Abstract: A laser-sustained plasma light source with a bulb for enclosing a relatively cool gas environment, and an electrode disposed at least partially within the gas environment. A power supply applies a potential to the electrode, where the power supply is sufficient to create a corona discharge at the electrode within the gas environment, and the power supply is not sufficient to produce an arc discharge within the gas environment. The corona discharge thereby produces a relatively heated gas environment. A pump laser source focuses a laser beam within the gas environment, where the laser beam is sufficient to ignite a plasma in the relatively heated gas environment, but is not sufficient to ignite a plasma in the relatively cool gas environment.

Abstract: Arcing is minimized in a discharge chamber of a gas laser system by utilizing an electrode which comprises a surface portion capable of functioning as one of an anode and a cathode in order to energize a gas mixture in a discharge chamber of the gas discharge laser system, a shoulder portion being positioned on either side of the surface portion and being exposed to the gas mixture, and a coating layer made of electrically insulating material, wherein the coating layer is attached to the shoulder portion by a cold spraying method.

Abstract: Controlled avalanche driver circuits and apparatuses for gas lasers. One embodiment typically delivers short, rapid, high voltage ionizing pulses in combination with an electric field whose magnitude is too low to sustain a normal glow discharge. The plasma is typically impedance matched with the pulse-forming network. Pre-ionization pulses may be generated. The circuits enable very high power, stable lasers.

Abstract: A laser oscillator comprises a discharge tube for exciting laser medium, at least a pair of mirrors disposed along an optical axis of laser light emitted by the laser gas excited inside the discharge tube, a laser gas passage connected with the discharge tube, laser gas circulation means for circulating the laser gas inside the laser gas passage, and heat control means for controlling heat generated in at least one of the mirrors and the laser gas circulation means.

Abstract: A metal vapor laser has a discharge tube with electrodes at opposite ends. A power source is electronically connected to the electrodes and generates a discharge in a discharge region within the discharge tube. The discharge generates laser light which emerges from the tube via windows. In order to cool the apparatus, the discharge tube is surrounded by a cooling jacket in the form of a hollow cooling vessel. A liquid flows in the cooling vessel and removes heat. The space between the cooling vessel and the discharge tube is evacuated. The cooling vessel is conductive and, since it is connected between one of the electrodes and the power supply, its inner and outer walls provide two potential paths for return current. The fact that the inner and outer walls have different diameters means that the inductance of the return paths is large. Therefore, the outer wall has a gap in it filled with insulating material.

Abstract: A discharge exciting pulse laser device such as an exima laser device. The laser device is capable of accelerating the timing of rise of the voltage between an auxiliary electrode and one of main electrodes without decreasing a discharge start voltage between the main electrodes, so that the laser output power is increased and the laser oscillation efficiency is improved.

Abstract: An excitation circuit for TE lasers serves to generate a homogeneous high pressure glow discharge between laser electrodes within a gas space of a laser chamber. A fast acting high voltage switch of a pulse forming network is a multi-channel pseudo-spark switch and is preferably integrated with the laser. The switch is formed of a parallel circuit including a number of individual pseudo-spark switches with gaps. The total multi-channel pseudo-spark switch is filled with an ionizable low pressure gas filling at a given pressure. Voltage is applied to the anode and the cathode in such a way that the resulting gas discharge is located on the left-hand branch of the Paschen curve. The switch of the excitation circuit can also be used as a separate structural element for triggering an electrical high voltage switch circuit, and also for so-called flat plane laser systems.

Abstract: The invention relates to a process to electrically excite a laser gas, especially a CO.sub.2 --He--N.sub.2 mixture, which is admitted at an angle, preferably perpendicular, to the axial laser gas discharge gap, and which is ignited by means of bunched microwaves. In order to avoid the formation of wall boundary layers during the microwave excitation of a laser gas and in order to achieve a homogeneous, large-volume glow discharge, the microwaves are axially bunched into the laser gas discharge gap in the area of the laser gas inlet so that the microwaves and the ignited laser gas spread over the axial laser gas discharge gap.

Abstract: A control circuit for a laser system having a first and second power supply connected in parallel. A mode selector is available to the laser operator to change the operational mode of the laser system from continuous to pulse mode or vice versa, and any combination of the modes. In the pulse mode, a series of short-time voltage pulses is superimposed on a low power level laser mode by using the circuit control characteristic of the thyratron tube and shunting the ballast resistors to sharply increase the laser output power for the duration of the individual pulses.

Abstract: In a gas laser, an anode of discharge electrodes is formed from stainless steel. Alternatively, the anode is formed from a metallic base material and chromium coating is applied on the surface of the metallic base material. A cathode is formed from titanium as a base material and the surface thereof is oxidized. Alternatively, the cathode is formed from molybdenum as a base material and titanium coating is applied on the surface of the molybdenum base material. The surface of the cathode is oxidized.

Abstract: In a gas laser, the surface of either or both of discharge electrodes are formed from titanium oxide which provides fine sputtering proof. The discharge electrodes are formed from titanium as a base material having an oxidized surface. Alternatively, the discharge electrodes are formed from molybdenum as a base material with titanium coated and the surfaces are oxidized. In the gas laser of the direct current discharge type, the cathode is formed as described above. Both of cathode and anode are formed as described above in the gas laser of the alternate current discharge type.

Abstract: A metal vapor laser intended to be excited by an electrical discharge pulsed through a metal vapor, consisting of a tubular chamber terminated at each end by a terminating flange, the terminating flange (1) having formed integrally with it a cold cathode structure having associated with it a multiplicity of electron generating devices (10, 11, 12) for non-thermionic generation of electrons. The electron generating devices (10, 11, 12) consist preferably of a series of annular grooves (10) formed in the surface of a bore of the terminating flange (1) and a circular groove or grooves (11) coaxial with the axis of the laser and cut in to a face of the terminating flange (1) facing directly into the discharge volume (8). Additionally, to increase carrying capability and facility for easily striking the discharge there is provide a ring of refractory metal pins (12) fixed into that surface of the terminating flange (1).

Abstract: A high pressure self-sustained gas laser operating at a high specific energy loading and long pulselength. The laser comprises an endless duct for circulating a laser generating gaseous medium and two discharge electrodes for exciting the molecules of the gaseous medium. Behind the discharge cathode electrode is an electron-beam transmitter for transmitting a beam of preionizing electrons into the gaseous medium to preionize the region near the cathode discharge electrode. The region unpreionized by the electron beam is ionized by drifting electrons from the cathode region and avalanche ionization. The applied discharge voltage never exceeds the glow voltage allowing low discharge flush factors under repetitive operation with flowing laser gas.

Abstract: The present invention provides a ring laser gyro which utilizes a gas impervious block containing at least three tunnels which meet to form a closed-loop, gas containing, cavity, and allow passage of laser beams therethrough. A pair of electrodes are positioned in alignment with one of the tunnels, and positioned relative to each other to support a current through the gas and establish a glow discharge region within a portion of one of the tunnels to induce a pair of counter-propogating laser beams to propogate through the established glow discharge region in a direction transverse to the direction of the discharge current.

Abstract: A CO.sub.2 gas laser device comprises a plurality of divided cathode electrodes disposed in a linear row extending transversely across a high-speed flow of a gas containing CO.sub.2, and parts of the cathode electrodes producing negative glow are disposed at the same height as anodes at a downstream position. Additionally, a device for controlling the distribution of gas flow velocity, which functions doubly as means for creating turbulent flow, and a preliminary discharge electrode are disposed on the upstream side of the cathode electrodes, the former being set at a height position corresponding substantially to that of the middle portions of the cathode electrodes.

Abstract: A gas laser arrangement includes a discharge tube arranged between a cathode and anode and including a central discharge channel and at least one gas return channel. An auxiliary electrode for pre-discharge is allocated to the cathode, the auxiliary electrode being connected to an operating voltage source through a resistor.

Abstract: A ring laser angular rate sensor construction utilizes an anode-cathode configuration which generates a glow discharge region in the propagation path of the laser beams. The anode-cathode construction provides a hollow cathode and effect for a ring laser. Specifically the ring laser block incorporates a tubular cavity which forms in part a cathode. A slot is provided into the block to provide an electrically insulated anode to produce the hollow cathode effect and the generation of counter-propagating laser beams.

Abstract: A laser transmitter is comprised of a power converter connected to a power conditioner for converting the preregulated dc power to high voltage dc required for laser discharge. A pulse forming network is connected to the power converter, for generating short, high voltage high current pulses. A laser cavity is connected to the PFN for generating laser pulse beams in response to the PFN output. The laser cavity includes a housing with two thermal-expansion-matched metal electrodes sandwiched between opposing preionization electrodes mounted in wells formed in the ceramic housing. The ends of the wells are ceramic to form dielectric between the cavity electrodes and the preionization electrodes for capacitively coupling the preionization electrodes for cavity chamber and producing coronas in the laser cavity which produce UV radiation in the cavity without arcing.

Abstract: In a method and apparatus for amplifying and/or generating electromagnetic wave radiation, a gas plasma region having a non-Maxwellian electron distribution is produced by effecting collisions between scattering particles in the gas with free electrons which have been accelerated to an energy level which is greater than that providing maximum probability of collision of the electrons with scattering particles in said gas; and the electromagnetic wave radiation is subjected to the plasma region such as to produce amplification of the radiation by stimulated emission of Bremstrahlung from scattered free electrons in the plasma region.

Abstract: In laser apparatus, an amplification section of a laser apparatus, including a cavity bounded by first and second opposing surfaces, closely spaced relative to the dimensions of the surfaces, electrodes for generating an electric field within the cavity and magnetic devices for creating a magnetic field in a direction perpendicular to the surfaces, with provision for shaping the electric field so that the electric field is relatively narrow in the dimension parallel to the magnetic field compared to the dimension perpendicular to both the magnetic field vector and the electric field vector established between electrodes within the cavity. The electrodes extend over a distance greater than the spacing between electrodes. An electrical discharge is established with the magnetic field exerting a force on the discharge to move the discharge parallel to the surfaces with the predetermined magnetic field strength causing the discharge to become uniform and stable.

Abstract: A silent discharge type laser device which comprises a detector for detecting the amount of electric charges passed between electrodes and controlling means for controlling an output current or voltage of a power supply so that a charge amount detected by the detector is equal to a target level, thereby keeping the passage charge amount always constant.

Abstract: A laser flash lamp triggering circuit is connected in parallel with the flash lamp and between the flash lamp and the flash lamp power supply. A impedance element is connected between the parallel trigger circuit network and the pulse forming network in the power supply. The impedance element preferably in the form of a saturable reactor has a high impedance to the high voltage trigger pulse and a low impedance to the current flow from the storage capacitor forming part of the pulse forming network. This invention relates to a laser flash lamp power supply and, more particularly, a triggering circuit for the flash lamp which has low power dissipation.

Abstract: A helium-cadmium ion laser is disclosed which has a tubular housing hermetically closed at both ends by Brewster windows and having a hollow cathode mounted therein. Disposed outside the hollow cathode and open to its interior are a row of primary anodes and a row of metal chambers containing a metal material to be vaporized. A pair of secondary anodes are further disposed adjacent the opposite ends of the hollow cathode for protecting the Brewster windows from contamination by the metal vapor by sending it back into the hollow cathode. In order to prevent the metal vapor from depositing on the ends of the hollow cathode on being thus sent back, a pair of tubular insulators are coaxially mounted next to the opposite ends of the hollow cathode for the passage of the metal vapor therethrough. Each tubular insulator has a bore including a smaller diameter portion away from the hollow cathode, and a larger diameter portion closer to the hollow cathode.

Abstract: This application discloses light amplification apparatus in which population inversion is created in which energized particles collide with a lasing medium to create a population inversion. In the preferred embodiment the energized particles are atoms, ions, or molecules different than the lasing medium which are excited to a long-lived state above the ground state. Various materials usable in such light amplification apparatus are disclosed as well as means for passing light through an amplification region.

Abstract: To improve the power transfer of a glow discharge between a cathode (3) and an anode (4) in a glow discharge space (2), through which a laser-active is being passed (5) at high speed, the cathode is constructed to have a rotating surface, projecting through slits (8) of the walls (1) defining the discharge space into the discharge space, the tangential or surface speed of the cathode (3) being at least approximately equal to the flow speed of the gas, so that the gas will flow along the cathode in essentially laminar, linear flow, thereby avoiding turbulence at the surface and instabilities in the glow discharge.

Abstract: A gas ion laser employs two or more independently controlled electrical gas discharges including a longitudinal plasma arc created by a thermionic cathode and an anode and a transverse glow discharge electron beam created within a photocathode reflector. These separately controlled gas discharges are arranged in a unique topology that produces highly excited atomic ions on the optical axis of a laser cavity, giving rise to a beam of laser optical radiation characteristic of the gas ion species being excited. The longitudinal plasma arc on the optical axis is heavily populated with ground state thermal ions that are not sufficiently excited to the energetic states required for laser action. The additional energy to excite these ground state thermal ions to the upper laser states is provided by a second more energetic photo-electron and glow discharge electron beam generated by a negatively biased coaxial photocathode reflector.

Abstract: A highly efficient laser employs a glow discharge electron gun and includes a solid wall cathode that emits a beam of electrons resulting in a plasma that is a negative glow discharge having an electron distribution that has a larger number of high energy electrons than would be present in a Maxwellian distribution of the same electron density.

Abstract: A laser discharge tube comprises a discharge envelope and an anode and cathode both disposed within the envelope. The envelope includes a capillary tube having a hole. In this hole the tip portion of the anode is inserted. Outside the envelope there is provided a magnet generating a magnetic field which lies in the vicinity of the anode.

Abstract: A flowing gas laser of the kind normally operating in the glow discharge mode and having a glow discharge region through which the gas flows while the glow discharge occurs, employs one or an array of flow smoothing screens disposed in series in the gas flow path in a manner that enables the input power loading to be increased without causing arcing in the electric discharge of the lasing gas. The screens are disposed upstream of the glow discharge region and cause smoothing of small scale turbulence in the gas flow. The screen closest to the discharge region is spaced from the beginning of that region by a distance not less than ten times the distance between adjacent holes of the screen. Successive screens in the series array are spaced at intervals sufficient to enable the requisite flow smoothing by each screen to occur before the flow encounters the next screen of the array.

Abstract: An electric discharge apparatus, for example a gas laser or discharge lamp, includes first and second electrodes defining a first discharge path and third and fourth electrodes defining a second discharge path alongside the first. A respective impedance is associated with any electrical connection between electrodes. The electrodes are electrically arranged such that either the current flow of a discharge along the first path is so different from the current flow of a discharge along the second path that, overall, the discharges repel one another, or stable electric discharges which coalesce are generated between respective electrodes of the first and second sets.A multi-electrode plasma torch is also provided comprising an electrode holder from which a plurality of electrodes project and a pilot electrode common to more than one of the electrodes.

Abstract: A method and apparatus for transferring energy to a gas by means of a glow discharge. A transmission line is charged to a voltage of approximately twice that of the steady-state voltage of the glow discharge. A prepulse voltage source, having a higher voltage sufficient to initiate the glow discharge, is first connected to the discharge electrodes. After the discharge is initiated by the prepulse, the transmission line is connected and transfers its energy to the discharge. In a second embodiment, the transmission line is replaced by a capacitor.

Abstract: A lateral excitation type gas laser device having a small size and high output. An anode and a cathode are arranged opposite one another with a flow of laser gas therebetween. A high DC voltage is applied between the anode and cathode to cause a glow discharge therebetween. A dielectric electrode is disposed in the flow of laser gas upstream of the anode and cathode, and a high frequency high voltage is applied between the dielectric electrode on one hand and the anode and cathode on the other for causing a silent discharge therebetween. The dielectric electrode has a diameter of 3 mm<D<d/2, where D is the diameter of the dielectric electrode and d is the length of the gap between the anode and cathode. The dielectric electrode is disposed in a region defined by 0.ltorsim.l.sub.1 .ltorsim.2d and 0.ltorsim.l.sub.2 .ltorsim.d, where l.sub.1 is the distance in the direction of the laser gas flow between the dielectric electrode and the cathode and l.sub.

Abstract: The invention provides a novel means of stabilizing a glow discharge device against electrothermal instabilities and electrode induced instabilities comprising imposing a magnetic field on the discharge current to create a sheared flow system within the discharge volume. There is further provided an apparatus for producing a stable high power glow discharge comprising an anode and a cathode adapted to be connected to an electric power source and, when so connected, to establish an electric field and a glow discharge between said anode and cathode and an electromagnet adapted to be connected to an electric power source and, when so connected, to establish a magnetic field across said electric field. This application relates to high power glow discharge devices and to a means of stabilizing such devices against electro-thermal instabilities and electrode induced instabilities.

Abstract: A coaxial type laser oscillator to carry out excitation of laser medium gas by voiceless discharge with high performance.The laser oscillator is constructed in such a manner that at least a pair of ring-shaped electrodes are disposed on and around the outer peripheral surface of the discharge tube, and alternating current voltage is applied across the electrodes so as to enable the voiceless discharge to be generated in the discharge tube and to output laser beam outside the oscillator.

Abstract: A sealed structure laser apparatus is disclosed which utilizes corona discharge as a pre-ionizing means wherein the laser discharge space is defined by a dielectric material channel with C cross section and one of the two discharge main electrodes is located along the inner wall of the C channel opposite the C aperture while the other electrode confronts said aperture from the outside of the channel the latter being enveloped by a conducting material grid, two opposite slits being defined between the two edges of said C channel gap and a dielectric material wall located in front of said gap.

Abstract: An electrode assembly and a D.C. glow discharge system incorporating the electrode assembly. The system is stabilized by a lower pulse repetition rate (1 KHz-5 KHz) and power (<5% of sustainer power) than that required for pulse-sustained discharge. It operates with a self-sustained discharge at lower voltage than usual due to lowered work functions, increased secondary emission and effective ionization. The pulse-stabilized discharged provides an extended stable operation suitable for high power gas lasers. A water ballasted electrode unit used therein, having individually ballasted electrode elements with discrete water resistors so formed when water flows, eliminates temporally varying spatial current fluctuations and exhibits such unique characteristics as; providing capacitive coupling for a pulse, and resistive coupling for D.C., and self-optimizing current uniformity with the operating time.

Abstract: A CO.sub.2 laser has a cylindrical housing of vitreous or ceramic material enclosing two confronting main electrodes which are connected across a trigger circuit, one of these electrodes being in conductive contact with a metallic layer surrounding substantially the entire outer surface of the housing to serve as an excitation electrode generating a corona discharge inside the housing. The gas in the housing is under substantially atmospheric pressure.

Abstract: A gas laser has an electrode of improved construction. The electrode, for example a cathode, comprises an inner cathode and at least an outer cathode spaced from the inner cathode and disposed on the side thereof away from to an anode. Each of the cathodes has a central hole from which glow discharge is formed, and the outer cathode further has a plurality of through-holes around the central hole. A gas medium flowing in a discharge tube passes through the central hole of the inner cathode via the central hole and through-holes of the outer cathode. The gas medium forcedly enters the glow discharge from the inner cathode thereby to cause it expand and a part of the gas medium having passed through the through-holes of the outer cathode squeeze the glow discharge from the outer cathode so that the glow discharge can enter the glow discharge from the inner cathode. Therefore, the current density of the glow discharge in the discharge tube is made information.

Abstract: This invention relates to a method and apparatus by which two series-connected glow discharge devices may be connected to a main power supply without interposing an output switch. The two series-connected glow discharge devices may be used within a single laser or in two different lasers which are pumped simultaneously. Both glow discharges may be initiated by a balanced main power supply, a single ended main power supply or a prepulse power supply in conjunction with a main power supply.

Abstract: A laser tube including an anode and a hollow cathode and adapted to obtain laser oscillation by utilizing a negative glow generated in a space within the hollow cathode. The laser tube has an elongate cylindrical member in which the anode and the hollow cathode are disposed opposite to each other, and the hollow cathode has formed therein a plurality of holes for communication between its internal space and the space outside thereof. The laser tube may further include a conducting grid provided in proximity to the anode and a conducting grid provided in a cathode dark space.

Abstract: A silent discharge type pulse laser device having a pair of opposing electrodes, at least one of which is an electrode covered by a dielectric, which is mounted opposite to a metallic electrode with a silent discharge space in between, a laser resonator consisting of a total reflection mirror and a partial reflection mirror mounted opposite to each other with the silent discharge section in between, a source of high frequency voltage for supplying to the pair of electrodes a high frequency voltage having a predetermined period for silent discharge, and a controller for controlling the high frequency voltage from the source with respect to a first interval and a second interval that form a period longer than the period for silent discharge.

Abstract: A silent discharge-type laser device in which silent discharge is established to produce a laser output by applying a high-frequency voltage across a set of opposing electrodes, at least one of the electrodes being a dielectric electrode; signals which are fed to the power source which produces a high-frequency voltage, used to modify the amplitude of the high-frequency output or to modify the frequency of the high-frequency output. According, the output voltage produced by the high-frequency power source can be increased or decreased at high speeds.

Abstract: A hollow cathode laser comprises a cathode body which constitutes a part of a discharge envelope. The cathode body has a cathode hole coaxial with the body. It further has three anode holes which are through holes extending parallel to the axis of the cathode body and communicating with the cathode hole through slits, respectively. Three cylindrical anodes extend respectively through the anode holes and are spaced by a given distance from the inner surfaces defining the respective anode holes. The anodes have portions which protrude through the respective slits and which are positioned flush with the inner surface defining the cathode hole in the circumferential direction thereof.

Abstract: A silent discharge gas laser apparatus has three or more electrodes arranged in axial symmetry with the laser radiation axis and supplied with voltage from a multi-phase high frequency power source to establish a continuous discharge and a higher discharge density at reduced frequencies, particularly in the central region of the discharge zone.

Abstract: This invention provides a laser or high voltage switch which has two spaced apart main discharge electrodes which define between them a main discharge gap, a discharge inducing member that is of an insulating material and which provides a planar or curved trigger discharge surface adjacent the electrodes and partially or completely bridging the main discharge gap, and an auxiliary conductor on the other side of the discharge inducing member to the main discharge electrodes and capacitively coupled to one of them by a distributed stray capacitance, such that when an excitation pulse is applied across the main discharge electrodes an initial capacitively initiated low order trigger discharge occurs onto the trigger discharge surface, and preferably across the surface from one main discharge electrode to the other. This trigger discharge photo-ionises a gas in the main discharge gap to cause a glow discharge between the main electrodes.

Abstract: A control device for a segmented anode gas discharge laser adapted to sense the onset of arcing in a region of the anode, switch off that portion of the anode and reenergize it when the arcing has ceased.