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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2992-2992 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 2145-2154 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The penetration of a plasma jet into liquid water was observed at successive time intervals by means of x-ray shadowgraphy. The plasma jet was generated by producing in a polyethylene capillary tube a high-current pulsed discharge. The tube inner diameter and length were 0.64 and 22 cm, respectively. A pulse-forming network delivered 121–182 kJ of electrical energy in 500 μs. The plasma jet emerged from the open end of the tube and interacted with a column of water gel. Jet velocities around 250 m/s were measured by x-ray shadowgraphy. The water ablation rate, estimated by calculating the radiative energy flux emitted by the plasma and reaching the water surface, is approximately 0.0155 kg/s cm2. This rate is significantly lower than the measured average flux of mass lost by the water: 3.5 kg/s cm2. It is proposed, but not proven conclusively, that the main mechanism for water loss is in the form of droplets pulled apart by shear forces impressed by the plasma-water direct interaction. These droplets are entrained in the back-flowing part of the plasma jet, which streams out of the interaction chamber. Peak pressures up to 3.5×108 Pa were measured during the process.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 3068-3076 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The new mode of Vacuum arc-Hot Refractory Anode Vacuum Arc-was studied experimentally using a Langmuir probe, two types of thermal probes, and film collection substrates. The plasma density, electron temperature, plasma energy flux, cathode erosion, mass deposition rate on a substrate, and macroparticle contamination in the deposited films were measured. The arc initially operated as a usual vacuum arc sustained by cathode spots, i.e., and the vapor and plasma source located at the cathode spot. At a later stage the anode heated up and metal vapor originating at the cathode was re-evaporated from the nonconsumable hot graphite anode. Initially, plasma density was about (3–4)⋅1020 m−3 but it increased with time, reaching about 2⋅1021 m−3 after 60 s in a 340 A arc. The electron temperature initially was about 1.6 eV and decreased with time to a steady-state value of about 1.1 eV after 20 s. The radial plasma energy flux generated by 175 and 340 A arcs was about 1 and 2 MW/m2, respectively, at 1.6 cm from the electrode axis. The deposition rate on substrates placed 110–120 mm from the electrode axis reached about 2 μm/min. The density of macroparticles found on substrates exposed during the first 60 s of arcing was ∼103 macroparticles per mm2, however, this density was reduced to about 1 macroparticle per mm2 on substrates exposed to only the second 30 s period. © 2000 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3461-3468 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of magnetic field on the plasma-wall transition layer is investigated using the two-fluid formulation. The quasi-neutral, near-sheath plasma (presheath) is examined, with the presence of neutral particles, and a magnetic field parallel to the confining wall. A general approach is used which takes into account the electron momentum equation, including the electric field force, the magnetic force, the pressure gradient, and the drag force. The influence of the electron to ion current ratio on the potential and velocity distribution in the near-sheath plasma is investigated. It is shown that the electron density distribution in the presheath may deviate from the Boltzmann distribution normally used in previous presheath models. Even when the plasma density dependence on the potential corresponds to the Boltzmann distribution, the presheath thickness deviates from that calculated with a model based on this distribution. The potential in the presheath with respect to the plasma–presheath interface can be negative or positive depending on the electron to the ion flux ratio η and Hall parameter βi. In the case of magnetized ions (βi〉1) the potential distribution has a positive maximum and is always negative at the wall edge of the presheath. The value and position of the maximum depend on the parameter η. In the case of unmagnetized ions (βi(very-much-less-than)1) the potential is positive for large η and is negative for η〈100. With large βi the influence of the electrons is significant so that the presheath thickness decreases to the electron Larmor radius and has a strong dependence on the parameter η. © 1997 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 4355-4360 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A plasma beam formed by a stationary vacuum arc source with a copper cathode is considered as a supersonic hydrodynamic jet interacting by collisions with a neutral atmosphere of background gas (argon). The plasma jet propagation in the neutral atmosphere is calculated numerically using a one-dimensional approximation. The values assumed at the entrance cross section of the plasma jet were ion temperature 104 K, electron temperature 3×104 K, ion concentration ni=1019 m−3 plasma jet mass velocity 1.5×104 m/s, and neutral concentration of (0.1,1,2,5)×ni. Two cases were analyzed:(1) isothermal gas motion and (2) gas motion with energy transfer from the ions to the neutrals. It is found for the isothermal case that the plasma front expands with decreasing velocity, but it never decreases down to the speed of sound. A snowplow effect is found with respect to the neutral gas. The neutral gas is accelerated by the plasma jet up to supersonic velocity. With ion–neutral energy transfer the plasma jet deceleration leads to shock discontinuities for all studied neutral densities. © 2001 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6791-6802 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A two fluid magneto-hydrodynamic theory of vacuum arc plasma jet propagation in a magnetized toroidal duct is developed. The physical mechanisms of jet transverse displacement and plasma losses are analyzed and the centrifugal force on the ions is shown to play the principle role in these processes. Optimal conditions for jet propagation occur when the centrifugal force is balanced by the electrical force on the ions. An analytical solution of the nonlinear problem of plasma beam transport through a toroidal duct is obtained for the two cases where ions are magnetized or not magnetized. The ion mass current decreases with the azimuthal distance along the torus as (1+cursive-phi/cursive-phi0)−1 where cursive-phi0 is a characteristic angular distance, for the case when ions are magnetized, and exponentially when the ions are not magnetized. Numerical calculations show that the decrease of plasma density leads to a longitudinal electric field and current. This current, together with the current due to the centrifugal drift, form a current loop which is closed through the plasma and structures outside the torus. Moreover if there are optimal conditions for jet propagation at the torus entrance, they are approximately conserved along the length of the torus. © 1996 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 4062-4066 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of imposing an electrical field parallel to the substrate of a growing metallic film was studied experimentally and analyzed theoretically. Ti films were deposited onto glass substrates using a filtered vacuum arc source while a voltage U of 0–300 V was applied between electrodes spaced 16 mm apart on the substrate surface. The current through the film was monitored during the deposition. Several characteristic stages of current evolution were observed after arc initiation: (1) an initial sharp jump of the current, (2) a stage of constant, relatively low current, (3) rapid current growth, (4) slower current growth, and (5) linear growth. Analyses showed that stages (1) and (2) are connected with current conduction through the plasma rather that through the sample while stages (3) and (4) are connected with tunneling and percolation during film formation. The tunneling stage could be distinguished only for U≤6 V; in other cases, conduction through the plasma obscured the observation. The percolative exponent increased from 1.0 to 2.68 and the critical thickness decreased by a factor of 4.3 with an increased U from 1 to 60 V. © 1997 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 709-717 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The low-density plasma flow in an axial magnetic field to a disk-shaped anode in a vacuum arc was studied theoretically using a two-dimensional model. The plasma expansion was modeled using the sourceless steady-state hydrodynamic equations, where the free boundary of the plasma was determined by a self-consistent solution of the gas-dynamic and electrical current equations. The anode was modeled as a current and plasma collector, which does not influence the plasma flow field. Magnetic forces from both the azimuthal self-magnetic field, and the imposed axial magnetic field were taken into account. It was found that the self-magnetic field does not substantially influence either the plasma jet shape, density, velocity, or the current density distribution for arc currents I≤200 A. On the other hand, the plasma jet angle (α0) at the starting plane and the radial plasma density gradient force in the expansion region do have a strong influence on the plasma and current flow. The mass and current flow in a 500 A arc are compressed in the near axis region, leading to an increase in the plasma and axial current density by a factor of 1.5 at a distance of about two plasma jet radii from the starting plane. The calculated arc current–voltage characteristics agree qualitatively with experiments on arc behavior in an axial magnetic field. © 1998 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 6224-6231 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron temperature, plasma density, and plasma potential were measured with a Langmuir probe in the radially expanding plasma streaming from the interelectrode gap of a hot refractory anode vacuum arc. Plasma parameters were measured when the anodic plume was formed, during the first 20 s after arc ignition, at points located 3 to 18 cm from the electrode edge. In addition, the ion energy distribution was determined using a retarding field analyzer. As a function of radial distance, the electron temperature decreased from 1.2 to 0.6 eV, the plasma potential decreased from 3.7 to 1.7 V, and the plasma density decreased from 2.1013 to 1.8.1011 cm−3. The measured mean ion energy per unit charge state increased from 8 eV at an axial distance of 3 cm to 20 eV at 18 cm. The electron temperature and plasma potential decreased with arc duration by about 0.4 and 2 eV, respectively, near the electrode region. The relatively small magnitude of the ion energy observed near the gap may be caused by nonelastic resonance charge exchange scattering of the cathode jet ions on atoms that are reevaporated from the anode. The observed ion acceleration at larger distances from the gap is caused by the gradient in the electron pressure caused by the plasma expansion from the interelectrode gap into the ambient vacuum. © 2000 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 114-119 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The free, steady state, two-dimensional radial plasma flow initiated between a pair of disk-shaped electrodes of a hot anode vacuum arc was analyzed in the hydrodynamic approximation. Studies include the influence of the self-magnetic field on the plasma density, velocity, radial spreading of the arc current and potential distribution. The free plasma boundary was calculated by solving the equations for the normal and tangential velocity components at the free boundary. It was found that the plasma significantly expands over a radial distance of about half of the interelectrode gap counted from the electrode edge and the plasma density in the center plane decreases by factor of 2, whereas the density of the fringe current decreases by a factor of 10. The self magnetic field does not influence the plasma flow and current spreading at radial distances larger than the interelectrode gap. The potential distribution is strongly nonsymmetric with respect to the central plane due to the influence of the plasma density gradients on the current spreading. © 1999 American Institute of Physics.
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