Hot Cathode Arc Research Articles

Plasma mass separation in configuration with potential well

The details of the charged particle separation by mass in the configuration with axial magnetic and radial electric fields are studied. The radial electric field, oriented to the discharge axis, is induced in a background reflex discharge with a hot cathode (−550 V, 8–14 A). The plasma source is based on a hot cathode arc discharge with independent metal vapor injection (18–21 V, 30 A) was situated at 18 cm from the axis. It was shown that the separated Ag + Pb mixture is transported across the magnetic field under the background discharge electric field. Effective separation is possible in such a system, while the separation coefficient increases from 4.9 to 6.2–8.4 when the mixture injection point is moved away from the background discharge axis from 18 to 23 cm. The effect of mixture injection on the plasma potential distribution is examined. It was shown that the presence of a plasma source of separated substances can cause a local (1–2 cm) distortion of the background plasma potential profile. Such distortion, as well as fluctuations of the background plasma potential, can significantly affect the width of the deposited spots of separated substances.

Surface Alloying of SUS 321 Chromium-Nickel Steel by an Electron-Plasma Process

The mechanisms of forming nanostructured, nanophase layers are revealed and analyzed in austenitic steel subjected to surface alloying using an electron-plasma process. Nanostructured, nanophase layers up to 30 μm in thickness were formed by melting of the film/substrate system with an electron beam generated by a SOLO facility (Institute of High Current Electronics, SB RAS), Tomsk), which ensured crystallization and subsequent quenching at the cooling rates within the range 105–108 K/s. The surface was modified with structural stainless steel specimens (SUS 321 steel). The film/substrate system (film thickness 0.5 μm) was formed by a plasma-assisted vacuum-arc process by evaporating a cathode made from a sintered pseudoalloy of the following composition: Zr – 6 at.% Ti – 6 at.% Cu. The film deposition was performed in a QUINTA facility equipped with a PINK hot-cathode plasma source and DI-100 arc evaporators with accelerated cooling of the process cathode, which allowed reducing the size and fraction of the droplet phase in the deposited film. It is found that melting of the film/substrate system (Zr–Ti–Cu)/(SUS 321 steel) using a high-intensity pulsed electron beam followed by the high-rate crystallization is accompanied by the formation of α-iron cellular crystallization structure and precipitation of Cr2Zr, Cr3С2 and TiC particles on the cell boundaries, which as a whole allowed increasing microhardness by a factor of 1.3, Young’s modulus – by a factor of 1.2, wear resistance – by a factor of 2.7, while achieving a three-fold reduction in the friction coefficient.

Influence of negative bias voltage on structural and mechanical properties of nanocrystalline TiNx thin films treated in hot cathode arc discharge plasma system

Ti thin films were grown by DC sputtering on a glass substrate and then nitrided in a hot cathode arc discharge plasma system, which is an effective approach to independently monitoring the plasma and nitriding parameters. The hardness of pristine Ti thin film is found to be ~3.06GPa, which increases upto ~16.08GPa with an increase in negative bias voltage to −140V and then decreases to ~15.05GPa for higher of −240V bias voltage. Similar kind of variation has been observed in crystallite size and surface roughness. Crystallite size is found to increase from 11.1nm (pristine Ti) to 14.8nm (for −140V) and then reduces to 11.9nm for –240V. Surface roughness increases from 2.78nm (pristine) to 6.84nm (for –140V), which is found to be 4.14nm for –240V. Optical and electrical measurements also reveal the strong impact of negative bias voltage on the bandgap and resistivity of the films. Above results are understood on the basis of diffusion of nitrogen ions for lower voltages and saturation of nitrogen ions in the host lattice for high voltages.

Investigation of parameters and uninterrupted service of a generator of gas-discharge plasma based on a nonsustained hot-cathode arc discharge in gas

The design of an electrode system and the characteristics of a gas-discharge plasma source (generator) based on an arc discharge in gas sustained by thermionic emission are presented. The results of an experimental investigation of the service life of a thermionic (hot) cathode of the plasma generator are reported as a function of the discharge current and voltage and the cathode filament power. It is shown that an increase in the burning voltage from 28 to 60 V considerably reduces the service life of the hot cathode, while the discharge current and the cathode filament power exert a less critical effect on its lifetime. The conditions necessary for achieving long-term service life parameters and high efficiency of plasma generation are found out.

Study on a negative hydrogen ion source with hot cathode arc discharge

A negative hydrogen (H(-)) ion source with hot cathode arc discharge was designed and fabricated as a primary injector for a 10 MeV PET cyclotron at IMP. 1 mA dc H(-) beam with ɛ N, RMS = 0.08 π mm mrad was extracted at 25 kV. Halbach hexapole was adopted to confine the plasma. The state of arc discharge, the parameters including filament current, arc current, gas pressure, plasma electrode bias, and the ratio of I(e(-))/I(H(-)) were experimentally studied. The discussion on the result, and opinions to improve the source were given.

The current-voltage characteristic of a hot-cathode electric arc at low pressures

It has been shown that in a hot-cathode electric arc operating at low pressures of the working gas, a positive anode voltage drop arises that results in an increase in discharge voltage with current even before the transition of the discharge into a constrained arc.

Influence of Highly Energetic Electrons on Probe Measurements in A Hot Cathode Arc Discharge Plasma

AbstractInfluences of highly energetic electrons on probe measurements has been investigated in a vacuum arc discharge plasma. Double and triple probe measurements clearly show these probe method is very sensitive for the small amount of hot electron component. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High-rate hot hollow cathode arc deposition of chromium and chromium nitride films

The hollow cathode in the diffuse arc regime (hot cathode arc) was used for deposition of chromium (Cr) and chromium nitride (CrN) films. The chromium hollow cathode serving as a gas inlet was connected to a radio frequency (rf) generator with the rf power up to 300 W. The temperature of the hollow cathode outlet reached 1400 °C. The microcrystalline structure and properties of both Cr and CrN films deposited at different rf powers were studied in more detail. Films were deposited on unheated silicon and steel substrates. Hard, highly textured crystalline CrN films with thickness of 45 μm were deposited at rates as high as 2.5 μm/min. These deposition rates exceed rates of TiN films deposited at comparable conditions. The process parameters and film properties are very promising for industrial applications of the hot hollow cathode arcs (HCAs) generated by the linear magnetized hollow cathodes.

Plasma-assisted deposition of a three-layer structure by vacuum and gas arcs

The durability and adhesion of thin coatings often depends on the structure and properties of the layer intermediate between the coating and the substrate, especially in the case where the layer and the substrate are highly different in microhardness. With a vacuum arc and a hot-cathode arc, a process has been arranged which involves cleaning of the surface, nitration of the article, and deposition of a coating. As a result, a three-layer composition has been produced which consists of a TiN layer of thickness up to 5 /spl mu/m and microhardness 20 GPa, an intermediate Fe/sub 4/N layer of thickness up to 8 /spl mu/m and microhardness 7.5 GPa, and a nitrated layer of thickness up to 100 /spl mu/m with a gradually varying microhardness. With the TiN layer showing high adhesion, the coating has a durability three of four times greater than that of a coating produced with the use of a conventional technology.

Thin film processing by radio frequency hollow cathodes

Abstract The main features of the radio frequency (RF) hollow cathodes for thin film processing are summarized. The utilization of cylindrical RF hollow cathodes in both the plasma-enhanced chemical vapour deposition (PECVD) and the physical vapour deposition (PVD) of films is reviewed. An example of the high rate PECVD of Si–N films is described in more detail. Gas metastables excited inside the cathode can act as a source of additional heat, thereby enhancing the thermionic electron emission and ionization of the gas. Transition from the glow into a hot cathode arc regime is characterized by changes in the plasma parameters and consequently in the growth of films. Examples for PVD of TiN films are shown. Magnetic focusing in the linear arc discharge source leads to the formation of linear hot zones at the outlet of the parallel-plate cathode and enables the hollow cathode discharges to be scaled up for large area applications.

Low voltage-high current discharge of Ti vapour in high vacuum

A new type of discharge for ion plating has been investigated. A titanium vapour discharge is ignited on the electron beam evaporation source by applying a 22 V d.c. voltage to the anode which is located near the source. A dome-shaped plasma core is formed on the source and a strong blue light is emitted from the core. Changes in anode current (discharge current) ranging from ~ 2 A to over 100 A can be controlled by changing the anode voltage, electron beam gun power and electron-beam-scanning condition. Since the anode current immediately follows these changes, it is easy to control the discharge at will. Also, the ion collector current and ionization efficiency of titanium increase to ~ 20 A and over 100% respectively in keeping with the increase in anode current. This discharge is thus considered suitable for ion plating. This low voltage-high current discharge is closer to a vacuum arc discharge than to a glow discharge and this distributed discharge with no oscillation of the anode voltage and current is similar to the hot cathode arc but not the cold cathode arc. However, being a non-self-sustained discharge, it is not classified as a typical arc discharge.

Plasma Heating with Electrically Biased Plasma Guns

Electrically biased plasma guns firing across the magnetic field are an effective way to heat a magnetically confined plasma. INTRODUCTION AND THEORY It is well established that intense plasma beams can propagate across a magnetic field and refuel a plasma in a closed magnetic trap (Robertson et al., 1981; Demidenko et al., 1971; Demidenko, Lomino, and Padalka, 1971; Leonard, Dexter, and Sprott, 1987). A high-pressure plasma can push effectively the magnetic field lines aside and penetrate between them into the confinement core region (Tuck, 1959). When a lower pressure plasma stream is projected across a magnetic field the charged particles first experience Lorentz forces: FB = qVx B (1) where q is the electronic or ionic charge, B is the magnetic field strength, and V is the velocity of the plasma stream. The Lorentz forces deflect the positive ions to one side of the (bounded) stream and the negative electrons toward the other (Fig. 1). This charge separation produces space-charge boundary layers with a polarization electric field E between them. The charged surface layers in turn generate additional (electrical) forces FE = qE (2) which act on the particles in the interior of the plasma stream and E x B drift the plasma across the magnetic field at the speed: ExB v (3) B2 When the stream has reached the core of the confinement region the polarization charges can be drained off in various ways and the plasma beam is trapped. Specifically, two counterinjected beams (entering a magnetoplasma This content downloaded from 207.46.13.124 on Wed, 22 Jun 2016 05:35:21 UTC All use subject to http://about.jstor.org/terms VOLUME 97, NUMBERS 3-4 137 Sboundary -+--1-E layers 0 B out of page Figure 1. Polarization drift of bounded plasma stream across magnetic field. column radially from either side) can neutralize one another's polarization charges on contact and halt and trap both streams (Norem, 1978). EXPERIMENTAL METHOD AND RESULTS The experiments were conducted in a low-pressure, hot cathode arc plasma (Jones, 1988) confined in a simple magnetic mirror field (Fig. 2). A variety of diagnostics are employed. The plasma density n and electron temperature T are measured by Langmuir probe. A typical Langmuir probe consists simply of a metallic electrode which can be inserted into and electrically biased with respect to the plasma. As the probe is biased more and more negatively the (predominantly) electron current which is collected can be

Production of a large-volume plasma by a hot-cathode arc

Probe measurements reveal that the plasma produced by a hot-cathode arc contains two groups of electrons, with temperatures ≈4 and 10 eV, with a density of 1010–1011 cm−3. These electrons are distributed uniformly over a volume of 0.2 m3. The discharge voltage is found as a function of the gas pressure and the heater current. Low-temperature regimes of the deposition of TiN coatings on metals and insulators after a plasma processing of the articles are described. The design of the discharge system is discussed.

Initiation of hot cathode arc discharges by electron confinement in Penning and magnetron configurations

Initiation of hot cathode arc discharges by electron confinement in Penning and magnetron configurations

Initiation of hot cathode arc discharges by electron confinement in Penning and magnetron configurations

The paper describes a method to ignite hot cathode arc discharges by using ’’start-up’’ glow discharges in magnetron and Penning configuration. This method has been shown to provide the ignition of large, tantalum hollow cathode discharges even in a restricted space. It is simple, reliable, and requires lower voltages than some of the other methods.

Strong turbulence in low- plasmas

An investigation of the spectral structure of turbulence in a plasma confined by a strong homogeneous magnetic field was made by means of a fluid description. The turbulent spectrum is divided into subranges. Mean gradients of velocity and density excite turbulent motions, and govern the production subrange. The spectra of velocity and potential fluctuations interact in the coupling subrange, and the energy is transferred along the spectrum in the inertia subrange. Applying the method of cascade decomposition, the spectral laws k-3, k-3, k-2 are obtained for the velocity fluctuations, and k-3, k-5, k-3/2 for the potential fluctuations in the production, coupling and inertia subranges, respectively. The coefficient of Bohm diffusion is reproduced, and its role in electrostatic coupling is derived. Comparison is made with measured power laws reported in the literature, from Q-devices, hot-cathode reflex arc, Stellarator, Zeta discharge, ionospheric plasmas, and auroral plasma turbulence.

Operational Characteristics of Two-Stage Discharge Ion Source

A new type of ion source, which facilitates production of a source plasma, is described. The source plasma is produced through two stepwise discharges; the first stage is composed of a hot cathode arc discharge and the second stage is a type of hollow cathode discharge. The discharge current in the second stage easily exceeds that in the first, without damaging the filament cathode. A simple analysis shows that this higher current in the second stage is owing to electron emission from the anode mouth as well as high ion-pair production efficiency in the second stage.

Impedance probe and dc probe studies on a collisional plasma in an arc discharge

The collision-dominated plasma of a hot-cathode arc discharge in argon has been studied by a plane probe acting simultaneously as a rf impedance probe and a dc probe. Measurements carried out under different discharge conditions show that the electron temperatures, as given by the rf and dc methods, are in excellent agreement and that the corresponding electron densities agree fairly well, the agreement being better than that mentioned earlier for the plasma of a glow discharge. The thickness of the probe sheath as a function of the sheath voltage, as measured by the rf

Source for Negative Ions of Refractory Metal Oxides

A source is described for the production of negative ions of tungsten and rhenium oxides. Total negative ion currents of 4×10−8 and 1.5×10−8 A were obtained for rhenium and tungsten oxides, respectively, the dominant ions being ReO3− and ReO4− or WO3−, (WO3)2−, and (WO3)3−. Both thermionic emission and hot cathode arc discharges were used as the ion source with the oxides being produced by direct oxidation of the heated cathode.

Sustained Plasma Oscillations near the Crest of a Moving Striation

Plasma oscillations in the frequency range of 2 to 4 Gc/sec were observed with a radially directed probe in a tubular plasma column. The plasma oscillations, which are generated by application of a pulsed electric field at the plasma cathode or anode in an argon hot-cathode arc, are sustained for as long as 50 μsec after the pulsed field is removed. The oscillations occur near the crests of a moving striation. The plasma oscillations are associated with the striation and are most intense near the plasma anode. The frequency detected by the probe increases with increasing plasma density but is not related to the 300-G magnetic field which is applied parallel to the plasma column. The oscillations may be the result of the two-stream interaction of the plasma electrons with a group of high energy electrons associated with the striation.