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Thin films were deposited using a vacuum arc with a refractory anode. The arc was sustained between a water cooled Zr cathode and a graphite anode. Both electrodes with diameter 32 mm and 30 mm length, with a gap of 10 mm between them. The distance from the arc axis to the substrate was 110 mm. The arc was operated either 40 or 60 s before a glass substrate was exposed to the plasma for 15 s. The film thickness was measured by profilometry. The deposition rate was obtained from the film thickness and exposition time. The visual radiation emitted by the plasma plume was photographed with a digital camera. The highest measured deposition rate was 0.71 μm/min, for an arc current of 225 A and time before exposure of 60 s.

A physical model of spot operation on film cathodes was developed and a system of equations was derived to understand Kesaev’s measurements of spot parameters on Cu films of 0.017 to 0.14 μm thickness deposited on glass substrates. Kinetics model of cathode vaporization was used to describe the spot phenomena. The plasma velocity normalized by the plasma sound speed is determined by the rate of film evaporation, dependent on the spot action. The power losses due to film heat conduction was calculated comparable with that power losses by vaporization. The calculations and measurements were comparable, in particular, for low cathode potential drop (~ 12 V).

The hot refractory anode vacuum arc (HRAVA) plasma source was previously developed with a consumed cathode and a refractory anode to reduce the macroparticle (MP) contamination in vacuum arc deposited films. The HRAVA had open cylindrical electrodes and demonstrated that it not only reduced MP sizes and numbers but also converted MP material to plasma, and thus increased the deposition rate. This paper presents a new HRAVA configuration with a double arc between a common water-cooled Cu cathode with two active surfaces and two refractory graphite or tungsten anodes, with the aim of depositing film over a wider area. The arc current in each of the two arcs was 125 A for graphite and 150 A for tungsten. The radially expanding plasma plumes from each of the cathode–anode gaps merged, forming a wider common plasma. Cu films were deposited and over a 150 mm length parallel to the arc axis, while the corresponding length from a single-HRAVA source was only 75 mm.

The anode in a vacuum arc with a blackbody assembly was measured as a function of time. A 30-mm-diameter Cu cathode and a hollow Ta anode, 50 mm in diameter, were used for a plasma cavity. Cu plasma was ejected through an array of 250 holes of 0.6 mm diameter in the anode. The arc currents were $I = 175$ , 200, and 225 A and the arc duration was 160 s. The anode temperature was measured using high-temperature thermocouples in the top and side of the anode. The anode temperature increased sharply during a transient time of ~70–90 s and then, it slightly increased with time up to 160 s reaching at 1650 K ( $I = 175$ A) and 1850 K ( $I = 225$ A) at the top, and 150–200 K less in the side.

Analysis of the experimental works published previously shows the presence of relatively large forces and as result generation of the high-velocity jet. These works mainly investigated the electrode material loss as vapor flow and some separate works considered also the presence of the ions. On other hand, the electrode material flow is a highly ionized complicated structure, which consists of a multi-charged and represented a supersonic plasma flux.

Different aspects of experimental investigation of cathode spot motion in a vacuum arc under transverse- and oblique-oriented magnetic fields will be reviewed and analyzed.

According to the considered analysis in above chapters, the cathode spot is a complicated subject that is difficult to investigate not only experimentally, but also hardly studied theoretically. Therefore, the previously involved approaches used arbitrary parameters that are preferable to calculate. The main problem consists in perception for long time by the researches that the cathode spot is completely non-equilibrium formation and of extremely material state, which cannot be considered by traditional approaches [1]. The goal of any complete spot theory is to indicate mechanism that can determine the difference between non-equilibrium and equilibrium regions and to understand the charge particles’ motion near the surface.

For long time, traditionally, the anode mechanism of an electrical arc commonly was accepted to be less complicated than the processes in cathode region. Nevertheless, in the second half of the twentieth century and, especially, in the last few decades, the experimental investigations showed different important forms of existence of vacuum arcs at the anode. A discussion of the importance for anode phenomena study is presented in this chapter.

Limited number of publications was presented concerning to the theoretical study of the anode region of vacuum arcs up to 70–80 years of the twentieth century. The most of arcs were operated with relatively small arc current, and therefore, without or at small contraction of the electrical current at the anode surface. This provokes for long time an opinion that the anode plays only a passive role as electron collector, while the cathode mechanism was traditionally studied as a complicated object supporting a source of electrons. The further arc applications were connected with development plasma accelerators, high-current electro-commutation apparatus, plasma jet generators, and welding plasma devices.

Numerous applications indicate that laser–matter interaction is technologically important (Hoffmann et al. in Laser Part Beams 23:47–53, 2005, [1]). In particular, the interaction of intense laser beams with plasmas is highly relevant to laser fusion (Miller et al. in Nucl. Fusion 44:S228–S238 (2004), [2]), material science and medicine (Gamaly et al. in Phys Plasmas 9:949–957, 2002, [3]), and nanoparticles generation (Eliezer et al. in Laser Part Beams 23:15–19, 2005, [4]).

Before an electrical discharge occurs, two electrodes are insulated by the vacuum from each other. In a vacuum, an arc can ignited when a conducting material will be appeared in the electrode gap, to which a voltage is applied.

Igor Tamm and Andrei Sakharov in 1950 are the first physicists who proposed an idea to use toroidal camera for high-temperature plasma confinement named then as Tokamak. The first tokamak, the T-1, began operation in 1958. Also in 1958, the model of the Harwell controlled Zero Energy Thermonuclear Assembly (ZETA) was demonstrated in London. High-temperature plasma exposes a high heat load the facing a divertor material and first wall in fusion reactors. Different materials were used for tokamak construction. One of these materials, tungsten, was used as a metal with high durability against the high heat load and low sputtering yield. When the sprayed tungsten was exposed to the helium plasma, the surface was covered with arborescent nanostructured tungsten containing many helium bubbles inside the structure.

Two important phenomena at electrode surfaces occurred during the plasma formation in the arcs. These processes will be described in this chapter. When the electrode is heated, the neutral atoms evaporate from the hot surface, a vapor plume is generated, and due to its expansion, it has a pressure lower than saturated pressure. The rarefied collisions determine the kinetics of the plume flow immediately near the surface. Vaporization of the heated electrode material will be analyzed using the kinetic approach. Simultaneously, the electrons are also emitted from the hot electrode surface. The current of electron emission is enhanced by the electric field produced at the surface in case of cathode plasma generation. In this Chapter, we will describe the electron emission caused by different mechanisms due to high body temperature and electric field at the surface as well as the influence of an individual field and explosive phenomena.

In this chapter, the arc definition and the experimental data characterizing the cathode spot including arc voltage, cathode voltage, threshold (minimal) arc current, spot definition, and problem of spot dynamics and the current density are described.

The near-cathode phenomena in electrical arcs such as spot motion and spot dynamics, especially in a magnetic field, determine the arc performance and playing an important role in different applications. The current per spot and spot motion depend on the arc current, gap length, interelectrode pressure

Since the cathode is negatively charged with respect to the adjacent dense plasma, the electrons were repelled from the cathode, while a high-density ion flux toward the cathode is produced. As a result, a relatively large positive space charge in the vicinity of the cathode arises leading to cathode potential drop uc formation and to occurrence of a strong electric field E at the cathode surface.

Most of published works (Chap. 15) used a system of equation, in which the number of unknown not equal to the number of equations. In this case, a number of arbitrary parameters, characterizing the cathode plasma, the cathode surface, and the spot current structure, added to the mathematical description. The cathode potential drop uc was used as input parameter traditionally referred to its measurement with high accuracy. Another parameter is the cathode erosion rate G was calculated by evaporation rate using Langmuir–Dushman (or Frenkel) formula that is incorrect not only by describing the mass loss in vacuum (with rarefied collisions), but also, it does not account the returned mass flux to the surface in the cathode dense plasma. Nevertheless, the study of transient spot parameters by gasdynamic model (GDM, Chap. 16, [1]) shows that the values uc and G can influence the spot parameters during its transient development. The presence of two values in solution when these parameters are fixed requested a physical reason to choose the correct data. In addition, the observed voltage oscillations indicate that there is more complicated behavior of cathode spot at low arc current. Thus, an investigation of the cathode spot behavior requires use of mathematical formulation in a physical closed approach.

One of the important issues is the electrical arc initiation and development in devices with flowing plasmas or in high-pressure systems. Such arcing occurred in generators of low-temperature plasmas, in plasma accelerators, in plasma of products of combustion, and in a rail gun [1, 2, 3, 4, 5, 6, 7, 8]. The plasma devices consist of complicated designs and different types of electrode assemblies. In this case, different problems arise by the projection of the assemblies and their optimization

The near-cathode plasma is relatively dense and hot. The plasma generation supported by thermal phenomena in the cathode body and in region of the plasma cathode transition. The conductive plasma expanding up to the anode executes the electrical contact needed for vacuum arc burning. As result, a large heat fluxes outputted by the both cathode and anode bodies. The ratio of the heat power (in Watt) to the arc current is named as equivalent or effective voltage for cathode ucef and for anode uaef. The measurements of electrode heat losses and the effective voltages were conducted by different methods. One of them is a calorimetric approach measuring the maximal temperature of water and its mass flux in systems of water cooling electrode or measuring the temperature of electrode having a high thermal resistance lead. The energy input in the electrode was obtained using the mass and heat capacity of the water flux or electrode. Another approach involved calculating the heat conduction flux using an analytical expression for the temperature distribution in one-dimensional approximation and corresponding electrode temperature distribution measured by thermocouples. Let us consider the measuring effective electrode voltages by different approaches and conditions.

Thin film deposition using hot anode vacuum arcs developed in the last decade is described. Two configurations were used: (i) with an open gap—the hot refractory anode vacuum arc (HRAVA) and (ii) with a closed gap—the vacuum arc with black body assembly (VABBA). In both configurations, the anode was heated by the arc with current I = 145–340 A, and a relatively dense plasma plume of cathode material (Cu, Ti, Cr, Al, Sn, Mo, Nb), was formed by re-evaporation of cathode material from the hot (2000–2500 K) anode, which was fabricated from graphite, Mo, Ta, or W. A steady state mode was reached when the anode was sufficiently hot and a plasma plume expanded, either radially (HRAVA) or directly from the front hot anode surface. As an example, the deposition rate measured in 300 A HRAVAs at distances of 80 mm from the arc axis, to be 3.6; 1.4 and 1.8 μm/min for Cu, Cr and Ti cathodes respectively. Interconnector trenches (100 nm wide ×300 nm deep) on microelectronic wafers were filled using a Cu HRAVA at a rate of 0.5 µm/min.

Vacuum arc cathode spot theories are reviewed, beginning from the primary studies in second half of the 19th century up to the present. The evolution of the main ideas is presented, starting from those, which developed, for separate phenomena, up to systematic inclusive models. New spot type classifications are proposed based on observed characteristics, instead of the previous simple numbering. Different approaches were considered for generating plasma comprised of cathode material, based on cathode vaporization and local explosions. Models with closed systems of equations were developed. A kinetic model advantageously allows calculating the cathode potential drop. These closed models explain various phenomena and two base rules were derived: 1) impeded plasma flow enables cathode spot operation and 2) the heat loss in the cathode must be smaller than the energy input to the cathode spot. Based on these rules, mechanisms for the spot types were derived and observed spot behavior in transverse and oblique magnetic fields was described.

Vacuum arcs are used as metallic plasma sources to deposit thin films, but conventional arcs also produce macroparticles (MPs) which degrade film quality. To reduce the MPs, the Hot Refractory Anode Vacuum Arc (HRAVA) plasma source was developed with a consumed cathode, which supplies the coating material, and a refractory anode. To obtain a wider deposition area, this work presents a new configuration with a double-arc between a common cathode and two refractory anodes. Experiments were conducted using two anodes from graphite or tungsten and a water-cooled consumable Cu cathode with two active surfaces. Cu film depositions were obtained over a length of 150 mm, in contrast to the deposition from a single BRAVA that produced a deposition length of 75 mm.

Refractory metal plasma generated by a vacuum arc was used to deposit thin films with different arc currents $I$ . The deposition rate $V_{\rm dep}$ was measured for electrode configurations including a planar Zr cathode and a planar W anode; cylindrical W or Mo electrode pairs and a cylindrical Nb cathode closed by a BN plate and a W or Nb shower-head cup anode or with one-hole Ta cup anode. $V_{\rm dep}$ for a Mo electrode pair with $I=275$ A at a distance $L=110$ mm from the electrode axis reached 2.2 $\mu \text{m}$ /min, 60 s after arc ignition. For the W electrode pair $V_{\rm dep}$ was $\sim 1\mu \text{m}$ /min at 80 s ( $I=200$ A and $L=110$ mm), while for W film deposition with shower-head anode $V_{\rm dep}$ was $\sim 0.6\mu \text{m}$ /min ( $I=200$ A and $L=60$ mm). For Nb films deposited with the closed electrode configuration, $V_{\rm dep}$ was 0.3 $\mu \text{m}$ /min at 30 s after arc ignition ( $I=275$ A and $L=80$ mm from the anode front).

This Chapter describes main mechanisms of different types of electrical discharges. After a brief introduction into electrical breakdown based on the Townsend mechanism, the Chapter deals with the broad range of discharges including sparks, streamers, glow and atmospheric and vacuum arcs. The physics of gas breakdown and the Paschen law are detailed. Towards the end, simulation of the cathode phenomena of the vacuum arc is presented.

The local cathode heating, vaporization, electron emission, cathode sheath, and so on were considered taking into account the kinetics of mass flow at the vaporized cathode surface. A self-consistent model was developed and simulation was conducted for given spot current $I$ to obtain the cathode erosion rate $G$ and jet velocity $V$ determined the force on the cathode. The time-dependent cathode and plasma characteristics were calculated for Cu, Ag, Al, and W cathodes. The primary plasma needed to initiate the spot was taken into account. Various primary plasma parameters were defined by different spot ignition time $\tau$ at which then the spot can be developed. The model shows that the time-dependent range of $G$ agrees well with the measured data and the jet velocity $V$ calculated from the experimental data of cathode force also close to that velocity obtained experimentally in a literature. The trust performance was obtained larger for W cathode than that for Cu and Ag cathodes and this and other results were discussed.

A vacuum arc with black body electrode configuration is used to deposit thin Cu films on glass substrates. In this configuration, a cup shaped anode, a refractory insulator, and a water cooled cathode form an enclosed volume from which dense plasma of cathode material was extracted through different types of apertures (one hole, frontal or radial shower-head) in the anode. All materials emitted from the cathode (including macroparticles) were re-evaporated from the hot anode producing in the enclosed volume a dense plasma which extracted through the anode aperture. The Cu deposition rate with the frontal shower anode was about 3.6 μm/min at a distance L s = 80 mm from the anode for current 200 A. Deposition with the radial shower anode produced a film which was azimuthally equal. The cathode erosion rate with this electrode configuration was a factor of 2–3 lower than that in a conventional cathodic arc indicating higher cathode material utilization.

The energy dissipated in the cathode in a vacuum arc black body assembly (VABBA) is investigated. A closed volume is formed by a water-cooled cylindrical Cu cathode and a cup-shaped W or Ta anode. Cu cathode material is emitted into the closed volume and the anode is heated by the arc. The VABBA confined and evaporated macroparticles while the plasma is extracted through small anode apertures. Arc currents are $I=175\hbox{--}250~{\rm A}$ and the arc time is 150 s. The effective cathode voltage $U_{\rm cef}$ is determined calorimetrically, using a thermocouple probe. It is observed that $U_{\rm cef}$ increases with time from ${\sim}{\rm 6.5}~{\rm V}$ for cold anodes (i.e., during conventional cathodic arcing) to a steady-state value of ${\sim}{\rm 11.2\hbox{--}12.0}~{\rm V}$ when the anode is sufficiently hot and the arc operated in the VABBA mode.

Anode temperature in a Vacuum Arc with a Black Body Assembly (VABBA) was measured as a function of time. The arc was ignited in an electrode assembly operated as a black body for the macroparticles (MPs). The cathode was a 30 mm diameter Cu rod and the refractory anode was 50 mm in diameter, and constructed from Ta. Plasma was ejected through an array of 250 holes of 0.6 mm diameter in the anode. The arc currents were I=175 & 225 A and the arc duration was 180 s. The anode temperature was measured using high-temperature thermocouples at two points (TC-top, TC-side) inside the anode body. The observed anode temperature increased sharply during a transient time of ∼90 s and then it slightly increased with time up to 180 s reaching at TC-top 1650K (I=175 A) and 1850K (I=225 A). The anode temperature at the top surface exceeded that at side surface by ∼150–200C.

The time-dependent anode temperature was measured in a hot refractory anode vacuum arc (HRAVA) sustained between a consumed water-cooled cylindrical Cu cathode and nonconsumed cylindrical W anodes with thicknesses of separated by gaps of 5, 10, 15, and 20 mm. Arc currents of were applied for periods up to 210 s. The anode temperature was measured using high-temperature thermocouples at different points in the anode body. The visual radiation emitted by the plasma plume was recorded with a digital camera. The anode temperature increased with time, reaching a steady-state value which slightly increased with arc current. The anode temperature decreased with the gap and was higher for thinner anodes. When was increased from 5 to 30 mm, the time for the anode front-surface temperature to reach the steady state increased from 45 to 140 s, while this temperature decreased from 2525 to 2325 K . Thus, minimizing advantageously minimizes the start-up transient when using the radially expanding HRAVA plasma plume for thin-film deposition.

Time-dependent cathode potential drop (CPD) is studied for a transient cathode spot on a Cu cathode protrusion when the spot operates continuously. A transient heat model was self-consistently developed, taking into account the kinetics of cathode vapor flow in a Knudsen layer, considering the momentum and energy conservation in the sheath, the electron relaxation zone, and the hydrodynamic region of the expanding plasma. The difference between evaporated and return fluxes of heavy particles determines the protrusion erosion rate and, hence, the decrease of its size during transient spot operation. It is shown that the spot parameters (e.g., CPD, temperature, and density) change from an initial to a steady-state value with time. Thus, for continuous spot operation on a Cu protrusion with a 5-μm radius, the CPD is about 90 V when the spot originates from initial plasma with a time duration of less than 50 ns and decreases to 13 V when spot operation continues up to 1 μs. This result explains the relatively large power supply voltage (~100 V) needed for arc ignition (after triggering the initial plasma at the cathode in a low-voltage electrode gap) compared to the low CPD appearing during steady-state arc operation. The calculated potential drop in the plasma expansion region at steady state is about 5 V, and the sum of this value with the CPD agrees well with the measured Cu arc voltage. The spot initiation and development can be consistently described as a vaporization mechanism by the gasdynamic model without involving any phenomena of explosion of irregularities at the cathode surface.

Vacuum arc generated plasma was used to deposit metallic Al, Zn, and Sn coatings on glass substrates. An arc mode with a refractory anode and an expendable cathode (the “hot refractory anode vacuum arc”), overcomes macroparticle (MP) contamination experienced in other arc modes. I = 100–225 A arcs were sustained between a water-cooled coating source cathode and an anode, which was heated by the arc, separated from each other by a 10-mm gap, for times up to 150 s. The distance from the arc axis to the substrate (L) was 80–165 mm. Film thickness was measured with a profilometer. It was found that the deposition rate increased with time to a peak, and then decreased to a steady-state value. The peak occurred earlier when using short anode (9 mm long), e.g., with the Al cathode, L = 110 mm, and I = 200 A, the peak was at t p = 15 s after arc ignition while with the long anode t p = 45 s. t p decreased with I, from 45 s with I = 100 A, to 10 s with I = 225 A with the short anode. The peak is believed to appear due to initial condensation of cathode material (including MPs) on the cold anode, and its subsequent evaporation as the anode heated. In the later HRAVA steady state, a balance between condensation and evaporation on the anode is established. The deposition rate peak was significant with low melting temperature Al and Zn cathodes, which produce many MPs, and negligible with Cu and Ti cathodes.

A hot refractory anode vacuum arc (HRAVA) starts as a cathodic arc, which heats and deposits cathodic material on the anode. When the anode is hot, all the deposited cathode material is re-evaporated from the anode, forming a radially expanding plasma with reduced macroparticle (MP) contamination. This paper reports on the deposition of Sn films using this radially expanding arc plasma. The HRAVA current was I = 60–175 A and the duration was up to 180 s. Two electrode pairs were used. (1) A water-cooled Sn cathode with a diameter of D = 60 mm was used with a W anode having a thickness of d = 10 mm, diameter D = 60 mm and separated from the cathode by gaps of h = 10 and 15 mm. (2) A water-cooled Sn cathode with D = 30 mm was used with either of two graphite anodes, with d = 9 or 15 mm, D = 32 mm and h = 10 mm. The cathodes were recessed behind a boron nitride shield. A mechanical shutter controlled the deposition onset and exposure duration (15 s) on glass substrates. The distance from the arc axis to the substrate (L) was 80, 110, or 125 mm. Film thickness was measured with a profilometer. MPs on the coating surface were examined by optical microscopy. With D = 60 mm cathodes, L = 125 mm, and I = 175 A, the deposition rate Vdep monotonically increased with time from 0.5 initially to 3.0 μm/min after 120 s. With the D = 30 mm cathode, L = 110 mm, I = 175 A and d = 9 mm, Vdep increased with time to a peak of 0.84 μm/min at 20 s, and then decreased to a steady state of 0.69 μm/min at 45 s. The peak was due to re-evaporation from the hot anode of cathodic material, including MPs, which were deposited initially on the cold anode. The MP flux density decreased with I from 2.5 at I = 80 A to about 1 mm− 2 s− 1 at I = 175 A in case of D = 30 mm, L = 110 mm, d = 9 mm.

The axial force carried by the expanding plasma plume from 50-250-A copper and aluminum vacuum arcs was measured using a pendulum whose axle was equipped with a rotary optical encoder. It was found that the force was a linear function of current. The electrode geometry was varied to find the maximum force. At maximum, the average forces per unit current were 21.4 dyn/A for aluminum cathodes and 36.1 dyn/A for copper cathodes. The Cu ion current fraction was measured to be 8.6%.

The radially expanding plasma jet generated in a Hot Refractory Anode Vacuum Arc (HRAVA) was used to deposit thin chromium and titanium films on glass substrates. The arc was sustained between a water-cooled cylindrical cathode and a non-consumed cylindrical tungsten anode separated by a 10 mm gap, for time periods up to 120 s, operating with a current (I) of 200–300 A. The chromium cathode was 30 mm diameter and 20 mm height, and was used with 32 mm diameter, 30 mm height anode. The titanium cathode was 60 mm diameter, 25 mm height and was used with a 60 mm diameter, 15 mm height anode. Thin films were deposited on glass substrates exposed to the anodic plasma. A mechanical shutter controlled the deposition onset and exposure duration time. The distance from the arc axis to the substrate (L) was varied between 80 and 145 mm. The film thickness was measured by a profilometer, and macro-particles (MP) presence on the coating surface was examined by optical microscopy. It was found that the deposition rate of Cr films increased with arc current and reached ~ 1.4 µm/min at I = 300 A, L = 80 mm. The total MP flux was less than 1 mm− 2min− 1 for I = 300 A, L = 110 mm. The deposition rate of Ti films reached 1.8 µm/min at I = 300 A, L = 100 mm.

A model of generation of the plasma supported by the operation of a microscale vacuum arc was developed, considering the phenomena in the cathode and anode spots. The nonequilibrium layers produced by cathode and anode evaporation were studied, and the electrode erosion rates as well as the plasma parameters were calculated. The calculation for 50 A showed that the plasma is dense, with a degree of ionization of about 0.1, and consists of singly charged ions. The anode temperature and erosion rate exceed these parameters for the cathode. It was demonstrated that the relatively large anode erosion rate can cause the larger force in the short vacuum arc compared to the force generated in the long-gap arcs, and this effect should be taken into account when designing a microscale thruster.

First results of complete filling of 100nm widex300 nm deep trenches with Cu using the expanding plasma plume from a hot refractory anode vacuum arc (HRAVA) plasma source are presented. The arc was ignited between a consumed water-cooled cylindrical Cu cathode (30mm diameter) and a non-consumed W cylindrical anode (32mm diameter, 30mm height) that was heated by the arc. An arc current of 200A was applied for periods of 180s. The films were deposited on a Si substrate with a top SiO"2 layer. The substrates were exposed to the plasma plume for 120s, while a shutter was open. The distance to the substrate from the electrode axis was varied over the range of about 74-122mm. A pulsed bias voltage of -75 or -100V, with a 60kHz pulse repetition rate and a 50-80% duty cycle was applied to the substrate. The films were examined using a scanning electron microscope. The average film resistivity was measured with a four point probe. The deposition rate was as high as 425nm/min, and the minimum average resistivity was 5.5@m@Wcm.

Pulsed arc production of tungsten carbide (W-C) powders in deionized water and analytical (99.8%) ethanol was studied. The arc was ignited between two submerged electrodes: one of 99.99% graphite (C) and the other of 99.5% W. The pulse energy and duration were in the ranges of 7.7–192 mJ and 25–65 μs, respectively. The WC1−x production rate was maximized by configuring the C electrode as the anode and the W electrode as the cathode. The rate was greater in ethanol than in water. The rate of producing ∼10 nm particles in ethanol was two orders of magnitude greater when using W anode -C cathode configuration, than with the opposite polarity.

Copper films deposited by a radial expanding plasma plume from a tungsten hot refractory anode vacuum arc were investigated. The arc was sustained between a consumed water-cooled cylindrical copper cathode (30 mm diameter) and a cylindrical anode (32 mm diameter, 30 mm height) that was heated by the arc current. The anode temperature was measured at 2, 12 and 22 mm from its front side by high temperature W/5%Re–W/26%Re thermocouple probes ( T 1, T 2 and T 3 respectively). Coatings were deposited on glass substrates which were exposed to the plasma flux. Distances to substrate ( L ) were 80–165 mm and arc currents I = 150–300 A. The film thickness was measured by profilometry and macroparticle (MP) contamination was determined by the optical microscopy. It was found that the anode temperature increased with arc current ( T 1 ∼ 2300 K for I = 150 A and 2500 K for I = 250 A) and slightly decreases with gap distance. The number of MPs on portion of the substrate facing of the anode decreased as function of MP size, while total number of MPs was approximately 3 mm − 2 min − 1 (for I = 300 A, L = 110 mm, h = 10 mm). The MP size distribution had a similar shape as observed with a Mo anode, but the amount of MPs was about 15% less using the W anode. The deposition rate at L = 80 mm, h = 10 mm and I = 300 A was about 3.6 μm/min. The larger surface temperature was reached by using higher current with the W anode, due to its lower rate of vaporization in comparison to previously used Mo and graphite anodes.

Electrode erosion was studied in pulsed arcs ignited between two electrodes comprised of 99.99% C (graphite) and 99.5% W submerged in deionized water or analytical (99.8%) ethanol. In the both cases the erosion rate increased proportionally to the pulse energy, and the total electrode erosion per unit energy was inversely proportional to the discharge pulse duration. Fifteen and sixty-μF discharge capacitors were used for formation of the pulses in water. It was obtained that, respectively (a) erosion of the tungsten anode (Wa) was by factors of 5–6 and ∼10 greater than that of the carbon (Cc) cathode; (b) erosion of the carbon anode (Ca) was by a factor of 1.34 greater and by a factor of 2.65 less than that of the tungsten cathode (Wc); (c) the total erosion rate of both electrodes (anode and cathode) per unit pulse energy for the Wa–Cc pair was greater by factors of 11 and 12.5 than that for the Wc–Ca pair.

A physical model and system of equations was formulated to describe transient cathode spot evolution at a single protrusion. The model considered the self-consistent processes including protrusion heating, kinetics of cathode vaporization, plasma generation, and current continuity. The time dependencies of spot current, current density, and protrusion size were calculated, taking into account the heat flux from the plasma (surface heat source) and Joule energy (volume source). The plasma density, temperature, degree of vapor ionization, electron current fraction, and cathode erosion rate were calculated as functions of the protrusion size, which reduced in time during the spot operation. It was shown that the spot operation on the protrusion was limited by the disappearance of the protrusion due to cathode erosion. The protrusion disappearance time determined the duration of the transient arc spot at a single protrusion. It was calculated that 1-5 mum protrusions reduce their size significantly due to evaporation in 0.5-10 mus, respectively. The smaller time of protrusion destruction occurs due to it relatively high heating, which was mostly by the heat flux from the surrounding plasma.

The model of plasma production by laser radiation onto a solid target was developed taking into account plasma heating by the emitted electrons and target heating by ion bombardment, as well as by the laser radiation. The near target plasma structure was analyzed. The space charge sheath was studied solving the Poisson equation and taking into account the volume charge of accelerated electrons and ions. The kinetics of atoms evaporated from the target and the back-flow of atoms and ions from the plasma towards the surface was analyzed. A system of equations, including equations for solid heat conduction, plasma generation and the plasma expansion was formulated. The calculation for Cu target, laser spot radius 100 μm, pulse duration 1 ms, 103, 10, 1ns and laser power density qL = 10−3–1 GW/cm2 was conducted. The ratio of net evaporation rate to the total evaporated mass flux was determined. It was shown that the plasma mainly generated in the electron emission beam relaxation region and there the plasma flow is subsonic. The electric field at the target surface is relatively large and therefore the ion current to the surface in the space region is large and comparable with the electron emission current. A large contribution of the plasma energy flux in the target heat regime was obtained, showing that the laser generated plasma significantly converts the absorbed laser energy to kinetic and potential energy of the plasma particles, which transport part of the energy through the electrostatic sheath to the solid surface.

Electric discharge utilized for electrosurgery is studied by means of a recently developed method for the diagnostics of small-size atmospheric plasma objects based on Rayleigh scattering of microwaves on the plasma volume. Evolution of the plasma parameters in the near-electrode sheaths and in the positive column is measured and analyzed. It is found that the electrosurgical system produces a glow discharge of alternating current with strongly contracted positive column with current densities reaching 103 A/cm2. The plasma electron density and electrical conductivities in the channel were found be 1016 cm−3 and (1-2) Ohm−1cm−1, respectively. The discharge interrupts every instance when the discharge-driving AC voltage crosses zero and re-ignites again every next half-wave at the moment when the instant voltage exceeds the breakdown threshold.

Two vacuum arc deposition techniques were compared for metal film deposition: 1) filtered vacuum arc deposition (FVAD), which applies a magnetic field to separate the plasma from macroparticles (MPs) generated in the cathode spots, and 2) hot refractory anode vacuum arc (HRAVA) deposition, in which anode plasma plume forms by re-evaporation of cathode material from the hot anode surface and MPs are vaporized in the hot interelectrode plasma. A Cu cathode and an arc current of 200 A were used in both systems. The FVAD film thickness was axially symmetric to within 10–20%. The focused plasma jet in the FVAD system covered a circular area, where the radius for half-thickness is ∼ 30 mm. The deposition rate was constant in time and maximal (about 0.25 μm/min) in the center of the circular area. The mass deposition rate was about 9.5 mg/min assuming bulk density. The HRAVA deposition rate initially increased with time and saturated at a maximum of ∼ 2.3 μm/min after 1 min. The plasma expanded radially, and was deposited on a cylindrical area of 100 cm 2 and height ∼ 20 mm, which was co-axial with the electrode axis. The thickness distribution was axially symmetric within 10%. The steady-state mass deposition rate was 400 mg/min. The HRAVA system produced an almost MP-free radially expanded mass throughput and cathode utilization efficiency ∼ 40 times greater than with the FVAD system.

The model of plasma generation by laser radiation and plasma interaction with a copper target was proposed. The target heating, ablation and electron emission from the hot surface and atom ionization were considered. The target is presented as a semi-infinite body solving the heat conduction equation. The kinetics of the target evaporation was analyzed taking into account the direct atom flux and plasma back flux. The plasma interaction with the target was due to ion and back electron fluxes bombardment. A space charge sheath at the target surface was considered where the charge particles acquired their energy. The electron and target temperatures, sheath potential drop, plasma and neutral densities were calculated as dependencies on laser pulse time and low power density (∼ 1 MW/cm2) and spot laser radius 100 µm. The solution shows that the plasma not only shields the laser radiation from the target, but also converts absorbed laser energy transported by the plasma particles through the electrostatic sheath to the matter. Critical power density of laser irradiance was found, consequently no plasma was formed.

The paper reviews the vaporization phenomena at a target heated by heat flux from an adjacent plasma in vacuum and in low-pressure discharges. The kinetics of a nonequilibrium layer and the direct and returned mass fluxes formed in the vicinity of the target are described. The mechanism of cathode vaporization taking into account cathode electron emission in vacuum arcs is considered. It is shown that in vacuum arcs, the cathode electron beam relaxation region is an energetic zone which supports the generation of charged particles by atom ionization, balancing losses from ion motion towards the cathode and electron current. The mechanism of electron transport from the cathode to the plasma for cathode materials with strongly different thermal properties is considered. It is shown that the cathode electron current is controlled by a near-cathode space charge sheath whose structure depends on the thermo-physical properties of the cathode material. The potential structures has a large electric field at the cathode surface (like Cu), or a virtual cathode (W), or double plasma sheath (Hg), depending on the ratio of the electron emission flux to the vaporized atom flux, which in turn depends on the cathode material

A 200 A Hot Refractory Anode Vacuum Arc (HRAVA) was studied. The arc was sustained between a cylindrical Cu cathode and an Mo anode spaced ∼ 10 mm apart. In the HRAVA, metallic plasma (from cathode material) expands radially. He, N 2 or Ar gas was introduced into the arc chamber through an electrically controlled valve. Films were deposited onto glass microscope slide substrates. The angular film distribution and the influence of different background gases on films deposited by the HRAVA were measured. The film thickness was measured by profilometry. The ion current was measured by a circular flat probe. It was shown that the film thickness was uniform with respect to the azimuthal angle around the electrode axis within approximately 10%. The film thickness was independent of gas pressure p , below a critical value p cr . For p > p cr , the film thickness decreased with p , eventually reaching 0. The value of p cr was less for gases with larger molecular weight—60, 10 and 5 mTorr (0.67, 1.33 and 8 Pa) for He, N 2 and Ar, respectively. The ion current to a 78 mm 2 probe in vacuo increased with time and reached a saturation value of approximately 4.5 mA after about 60 s from arc ignition. The ion flux fraction in the total deposition mass flux was estimated to be about 60% in the fully developed HRAVA ( t = 60–90 s).

A model of plasma acceleration in a high-current short pulse vacuum arc was developed. The mathematical description includes equations for the cathode spot and the plasma jet, which were solved for rates of current rise dI/dt in the range of 0.01-10 GA/s. The multicharged ions in the cathode spot were taken in account. It was shown that the plasma could be accelerated to the measured energy by a gasdynamic mechanism. The ion energy, cathode erosion rate, and the ratio of the ion flux to the electron flux are linked by the equations. The calculated cathode erosion rate varies from 200 to 10 /spl mu/g/C when the ion energy increases from 0.1 to 10 keV. The ion current to the cathode mainly consists of singly- and doubly-charged ions. The singly-charged ion current fraction decreases with spot current decreasing and rate of current rise increasing.

The use of magnetic fields to control cathode spot location and motion and to collimate and direct the plasma flow in vacuum arc deposition apparatus is reviewed. Retrograde and acute angle motion are used to control the location and motion of cathode spots, in order to confine them to the cathode surface facing the substrates, to prevent local overheating, and to reduce macroparticle production. Axial fields are use to collimate cathode spot produced plasma jets and to bend them around macroparticle-occluding obstacles in filtered vacuum arc deposition. Advances have been made in understanding these phenomena, but theoretical models have not yet been formulated which can predict plasma behavior sufficiently well for apparatus design.

The temperature of an asymmetric anode was measured at three points in the anode body of a Hot Refractory Anode Vacuum Arc (HRAVA) using high temperature thermocouple probes placed near the front and rear surface. Different anode geometries with inclined front surfaces were used for arc currents in the range 125-225 A and for gaps with electrode separations of 5-18 mm. The measurements show that the transition period to the Hot Anode mode in the HRAVA decreased with arc current. Photographic study of the interelectrode region indicated that the plasma plume in the transition period expands from the anode toward the cathode and filled the gap. The plasma plume was asymmetrically distributed on the asymmetric anode surface, resulting in an asymmetric anode surface temperature distribution. Asymmetry of the anode surface temperature distribution increased for more asymmetric anodes and gap geometries. Molybdenum anode temperatures increased with arc current and decreased with electrode separation. The anode surface steady state temperature exceeded 2200/spl deg/K-2300/spl deg/K when the arc currents were larger than 145 A. The observed surface temperature variations were caused by fluctuations of the heat flux to the anode.