An experimental study of the effect of nonuniform axisymmetric magnetic field on the breaking of the current of a vacuum-arc discharge

An experimental investigation is made of the effect of breaking of current in a vacuum-arc discharge as a result of superposition of a pulsed axisymmetric magnetic field with longitudinal and transverse components. A study is made of the dependences of the probability of breaking of current on the current magnitude, the pulse amplitude of the magnetic field, and the value of emf of the electric circuit in the current range of 100 to 600 A. The main factors affecting the probability of breaking of current are analyzed.Translated from Teplofizika Vysokikh Temperatur, Vol. 42, No. 6, 2004, pp. 850–855.Original Russian Text Copyright © 2004 by E. F. Prozorov, K. N. Ulyanov, and V. A. Fedorov.     

The effect of cathode deuteration on the parameters of vacuum-arc plasma

We propose a model for determining the influence of the relative content of deuterium in a zirconium cathode on the properties of vacuum-arc plasma. It is shown that the occlusion of deuterium in the cathode leads to an additional energy consumption for its ionization and to the related decrease in the average charge of cathode material ions in the discharge plasma. Deuterium in the cathode spot is fully ionized, and the drift velocity of deuterium ions almost coincides with that of ions of the cathode material.     

The effect of external magnetic field on plasma acceleration in electromagnetic railgun channel

Technical Physics Letters - We have studied the effect of an external magnetic field on the dynamics of a free plasma piston (PP) accelerated without solid striker armature in an electromagnetic...     

The effect of magnetic field configuration and propellant supply rate on insulator erosion in a hall thruster

Dependence of the rate of insulator erosion on the walls of discharge chamber of a Hall thruster on the propellant supply rate and magnetic field configuration at a constant discharge voltage has been studied. The regime of thruster operation was controlled by varying the propellant mass flow rate. The magnetic field configuration was optimized by monitoring the intensity of the spectral line of sputtered boron atoms. It is established that the rate of insulator erosion in the discharge chamber significantly decreases upon optimization of the magnetic field configuration, while the integral characteristics of the thruster change rather insignificantly. With the optimum magnetic field configuration, the rate of erosion of discharge chamber walls depends rather insignificantly on the propellant supply rate.     

DC vacuum arc in a nonuniform axisymmetric magnetic field

An experimental investigation is performed of the characteristics of DC vacuum arc during the opening of contacts in an axisymmetric magnetic field with different ratios between the axial and radial components of magnetic field induction. A study is made of the main features of the dynamics of plasma glow in the contact gap during the stable and unstable stages of arcing until the arc extinction in the current range of 50 to 150 A with the voltage limited at the instant of breaking of current to a level of 8 kV. Possible mechanisms of disturbance of the vacuum arc stability in an axisymmetric magnetic field are discussed.     

A theoretical study of the impact of magnetic field of Hall current on the parameters of a high-current vacuum-arc discharge

It is demonstrated that the magnetic field of Hall current in a short high-current vacuum-arc discharge significantly distorts the external axial magnetic field and affects the distribution of current density in the discharge gap. This effect decreases with increasing external magnetic field, with decreasing arc current, and with decreasing ratio of the length of discharge gap to its transverse dimension. A 2D magnetohydrodynamic mathematical model is used to calculate the discharge parameters for different values of induction of external magnetic field. The calculation results are compared with similar results obtained using a 1.5D model in which the impact made by magnetic field of Hall current is ignored. It is inferred that the simpler 1.5D model may be employed in calculations of parameters of vacuum arc in a wide range of variation of arc current and of induction of external magnetic field.     

The effect of axial magnetic filed on the process of anode spot formation in a vacuum-arc discharge with CuCr50 electrodes

An experimental study is made of the effect of an external axial magnetic field on the process of anode spot formation in a pulsed vacuum-arc discharge in the range of currents from 5 to 12 kA in a discharge gap with CuCr50 electrodes. The times and currents, at which an anode spot is formed, are determined for each amplitude value of current depending on the magnitude of magnetic field. The minimal value of magnetic field preventing the anode spot formation is determined for each current. The measured values of diameters of the current channel are used to calculate the anode temperature. It is demonstrated that, under experimental conditions, the heating of anode is insufficient for marked evaporation, and the anode spot formation is associated with the critical flow of fast cathode ions.     

Charge distribution of ions in low-current vacuum-arc plasma

The charge distribution of vacuum-arc ions has been investigated for the arc between copper electrodes at currents varied from 8 to 60 A (with the arc voltage increased from 21 to 24 V). Plasma contains copper ions with charge states from +1 to +4. The mean ion charge state increases from 2.15 to 2.24 (i.e., by only 4%) due to a small increase in the fractions of multiply charged ions (Cu²⁺ and Cu³⁺) in the total ion flux. This conclusion does not contradict that of the ecton model of vacuum-arc cathode spot, according to which the number of cells in the spot that are due to microexplosions on the cathode increases proportionally to the arc current.     

The effect of pulsed vacuum-arc discharge on the surface of elements of a discharger

Regularities of erosion and transport of the material of discharger elements have been studied by the methods of surface structure visualization and X-ray fluorescence elemental microanalysis. Microrelief and oxide film on the surface of cathode material are found to affect the development of arc discharge in a commutator.     

The effect of vector field history on the remanence of magnetic tape

A method is described for simulating the recording process at various strata within a magnetic tape by duplicating the magnetic field intensity and direction in a sample tape volume. The method is flexible in that it requires only plots of field intensity and direction as a function of depth within the tape for any realizable head configuration. Several results are shown including remanence from sine wave recording wherein the phase shift vs. depth is pronounced. Demagnetization effects from adjacent layers are not measured by this method and corrections must be made for their existence.     

The effect of magnetic field on the performance of new design cyclone separators

In this paper it is attempted to improve the performance of the gas–solid new design cyclones with imposing magnetic fields. First, Eulerian-Lagrangian method is used to model the flow and to track the solid particles within the new design cyclones. The Reynolds averaged Navier–Stokes equations with Reynolds stress turbulence model (RSM) are solved by use of the finite volume method based on the SIMPLE pressure correction algorithm in the computational domain. The velocity fluctuations are simulated using the Discrete Random Walk (DRW). Then, to investigate the possible influence of the magnetic field, horizontal and vertical distances of the magnetic source from the coordinate origin as influential parameters are investigated. Solid particles with three different diameters and with different materials including polystyrene, ferrous and nickel are used. Results show that applying a magnetic field can improve the collection efficiency for all different particles’ materials. Analysis of results proves that there is a strong correlation between cyclone performances. It is observed that the collection efficiency is very sensitive to vertical distance of the magnetic source from the origin. Moreover, providing higher efficiency without imposing pressure drop is the advantage of implication of a magnetic field.     

The effect of reactor configuration on the oxygen plasma conversion of an organosilicon to SiO2

The plasma conversion of an organosilicon film to SiO₂ is inhibited in a parallel plate reactor compared to the conversion in a barrel reactor. The energetic ions present in a planar configuration inhibit the conversion of the film by modifying the surface and/or producing a chemical passivation.     

The effect of external cusp magnetic field on Ar ICP characteristics

In this paper, three permanent magnet rings, which were placed alternatively between the three antenna coils of a cylindrical inductively coupled radio frequency (rf) argon plasma for rf enhanced ionized magnetron sputtering system, were used to produce a closed magnetic field distribution with the magnetic field of the unbalanced magnetron sputtering to confine discharge plasma. Langmuir probe measurement was used to study the effect of the magnetic field on the plasma characteristics and their spatial distribution. The results show that the presence of the closed magnetic field leads to the increase of the ion density and the decrease of electron temperature and plasma potential. With the closed magnetic field, the plasma density distribution in radial direction will become more uniform.     

Average current per vacuum-arc cathode spot and spot velocity in a magnetic field on a CuCr50/50 nanocomposite

It has been shown that such cathode spot characteristics as the average current per spot and its dependence on tangential magnetic-field induction B _t and the spot velocity and its dependence on B _t for two CuCr50/50 specimens with very different structures (nanocomposite and “solid-state sintered” composite) almost coincide if the surface of contacts has been totally remelted before measurements with the use of moderate arc currents in the process of conditioning.     

The effect of a magnetic field on the kinetics of melting of ionic crystals

The kinetics of melting of an ionic crystal treated in a pulsed magnetic field (H ∼ 10⁶ A/m) was studied by a computer-aided DTA technique. Significant changes in the nonequilibrium thermodynamic parameters of transient processes during melting and in the enthalpy of melting were observed for KCl crystals, which is evidence that the magnetic field induces a special nonequilibrium state in these nonmagnetic crystals.     

The effect of magnetic field on the shape of etch pits of paracetamol crystals

In the present study we investigate the effect of magnetic field on the shape of etch pits of the crystals of p-hydroxyacetanilide (paracetamol), which is widely used in pharmacy as antipyretic, antiphlogistic medicine. It was discovered that the magnetic field (H=0.5 T, τ=15 min) changes the morphology of etch pits and shifts dislocations in paracetamol crystal. Activation energy of the changes induced by the action of the magnetic field was determined to be 63 kJ/mol, which is comparable with the energy of hydrogen bonds in crystal lattice. Received: 29 October 2001 / Reviewed/Accepted: 3 November 2001 /     

Effect of pressure on plasma sheath in a magnetic field

The effects of collisions on plasma sheath in an external magnetic field have been investigated by considering the collisions between ions and neutral gas atoms. The ion fluid equations containing an external magnetic field and the collisions are solved numerically to study the ion dynamics under various pressures.     

The selective effect of a constant magnetic field on the crystallization of flexible-chain polymers

A weak constant magnetic field produces a selective action upon crystallization of a high-molecular-mass poly(ethylene oxide) which is a model crystallizable flexible-chain polymer with polar units.     

The effect of applied magnetic field on the growth mechanisms of liquid phase electroepitaxy

Binary (GaAs) and ternary (InGaAs) single crystals were grown by the growth process of liquid phase electroepitaxial (LPEE) under an applied static magnetic field. The effect of the applied magnetic field on two main growth mechanisms of the LPEE growth process, namely the “electromigration” and “natural convection” in the liquid zone, were examined numerically and experimentally. Numerical results show that the flow and concentration patterns exhibit three distinct stability characteristics: stable structures up to the magnetic field level of 2.0 kG, transitional structures between 2.0 and 3.0 kG, and unstable structures above 3.0 kG. In the stable region, the applied magnetic field suppresses the flow structures, and the intensities decrease with the increasing magnetic field level. In the transitional region, the flow intensity increases dramatically with the magnetic field strength, and concentrations show very different patterns leading to a wavy growth interface. Under strong magnetic field levels, the flows cells are confined to the vicinity of the vertical wall and exhibit significant non-uniformity near the growth interface.Experiments performed under various magnetic field levels show that the growth process at the 4.5 kG field level yields satisfactory growths. However, the growth experiments at higher field levels were unsatisfactory and unstable. Although the crystals were still grown, large wholes were observed in the grown crystals. This observation was attributed to the strong interaction of the applied electric and magnetic fields, making the convective flow in the solution very strong and unstable. However, lower magnetic field and electric current levels had very beneficial effects, namely flat growth interfaces and prolonged growth due to weak convection in the liquid zone, and a substantial increase in the growth rate (about 5–10 times higher) due to the effect of magnetic field on the mechanisms of “electromigration”. Such positive developments give the LPEE growth process the potential of becoming a commercial technique.