Cold Hollow Cathode Research Articles

Effect of thermal cyclic nitriding modes on microstructure and chemical composition of titanium alloy surface layers

A method has been developed for cyclic low-temperature ion nitriding using a plasma source with an integrally cold hollow cathode, which is superior in performance to a source with an incandescent cathode. The results of the effectiveness of the developed method are presented. It has been established that the greatest influence on the microhardness of titanium alloys is exerted by the bias voltage and the l ocation of the surface with respect to the plasma flow. Microstructural studies have shown that the α-phase is stabilized in the near-surface layer due to nitrogen diffusion, grain growth is not observed. Alloy VT8M1 retains a two-phase structure. The possibility of controlling nitriding by changing the duration and direction of surface saturation is also shown.

Генерация плазмы в сильноточном тлеющем разряде с полым цилиндрическим катодом с использованием двух источников электронов

Experimental distributions of plasma parameters in the volume of a hollow cathode of a high-current non-self-sustaining low-pressure glow discharge supported by electron injection from one and two electron sources located on the upper and lower bases of the cylindrical hollow cathode are obtained. A plasma source based on an arc discharge with an integrally cold hollow cathode is used as an electron source. The possibility of applying the superposition principle to predict the distribution of plasma concentration in the hollow cathode of a high-current, low-pressure glow discharge with two electron sources is investigated. The distributions of plasma parameters were measured at arc discharge currents of 20 and 45 A and at glow discharge currents up to 200 A. With an increase in arc discharge currents by about 2 times, from 20 to 45 A, the accuracy of the superposition principle decreases. The maximum degree of inhomogeneity of the plasma concentration when two sources of electrons with currents of 20 A were turned on in the longitudinal direction was 25%, in the radial direction - 52%, the maximum discrepancy between the inhomogeneity coefficients for the experimental distribution and the distribution obtained as a result of summing the data obtained with separate operation of electron sources, amounted to 8%. When two sources of electrons with currents of 45 A were switched on, the maximum inhomogeneity in the longitudinal direction was 8%, in the radial direction 34%, and the maximum mismatch of the inhomogeneity coefficients was 25%.

Influence of cold hollow cathode geometry on the radial characteristics of downstream magnetized plasma column

In this paper, the effect of cathode geometry on the radial characteristics of a downstream plasma column is presented for a cold cathode type of hollow cathode (HC) system. It is observed that when an axial magnetic field is applied to a cylindrical cathode, the downstream plasma exhibits an off-centered peak in the plasma density. However, as the magnetic field increases, the discharge extinguishes rapidly above a critical value, due to the suppression in secondary electron emission from the cylindrical cathode surface. On the other hand, by replacing the hollow cylinder with a cone-shaped cathode an oblique sheath is formed with respect to the axial magnetic field. This configuration helps in sustaining the discharge at twice the magnetic field than in the cylindrical case. It is also found that the downstream plasma exhibits a peak plasma density at the center for the case of the conical cathode. The above experimental observations for each HC setup has been qualitatively explained with the help of a phenomenological model.

Surface Modification of Corundum Ceramics by Argon Ion Beam

The mechanical properties of near-surface layers of aluminum oxide ceramic treated with a continuous ion beam of argon are investigated. The phase and structural changes of the modified near-surface layers were analyzed by X-ray diffraction analysis and scanning electron microscopy, respectively. Samples for research were made from corundum plates used in microelectronics. Ion processing was carried out using an ILM-1 ion implanter equipped with a Pulsar-1M ion source based on a low-pressure glow discharge with a cold hollow cathode. Argon ions with energy of 30 keV and ion current density j = 300 μA/cm2 were used for the irradiation. Two irradiation modes with the fluences of 1016 and 1017 cm–2 were implemented. It was established that the ion treatment promotes the manifestation of the initial grain structure of a sample and increases the mechanical characteristics (modulus of elasticity and nanohardness) of near-surface layers of samples. According to the X-ray diffraction data, after the action of an ion beam, there is a decrease in the size of the coherent scattering region with respect to the initial state. The irradiation leads to an increase in the values of crystal lattice microstrains. Possible mechanisms of modifying the ceramic surface are discussed.

Pulsed non-self-sustained glow discharge with a large-area hollow cathode for nitriding of iron-based alloys

The paper reports on a study of a pulsed non-self-sustained glow discharge with a hollow cathode area of 2.3 m2 and pulse current of up to 370 A. The ignition and operation of the discharge at low pressures (0.4-1 Pa) was sustained through electron injection from the plasma of an arc discharge based on a cold hollow cathode. The current-voltage characteristics of the pulsed glow discharge were measured. Specimens of 12 Cr18Ni10Ti, Cr12, and 40Cr steels were nitrided in the glow discharge plasma with double thermal shields at a temperature of 520 °C and pressure of 0.9 Pa for 4 h. The nitrided layer thickness for 40Cr, Cr12, and 12Cr18Ni10Ti steels was 240, 90, and 50 μm, respectively.

Low-energy dc ion source for low operating pressure.

We report on an experimental study of an ion source based on a Penning discharge with a cold hollow cathode in crossed electric and magnetic fields. The minimum vacuum chamber operating pressure was 3 × 10(-5) Torr for argon and 5 × 10(-5) Torr for hydrogen. The use of a hollow cathode allowed decreasing the discharge operating voltage down to 350 V at a discharge current of ~100 mA. At a discharge current of 100 mA and beam accelerating voltage of 2 kV, the ion current was 2.5 mA for argon and 8 mA for hydrogen, and the ion beam on-axis current density 170 and 450 μA/cm(2), respectively. The current-voltage characteristics of the discharge and the radial ion beam current density distribution were measured. The influence of pressure on the discharge parameters and their time stability was investigated.

Diamond-Like Carbon Film Deposition Using DC Ion Source with Cold Hollow Cathode

Carbon diamond-like thin films on a silicon substrate were deposited by direct reactive ion beam method with an ion source based on Penning direct-current discharge system with cold hollow cathode. Deposition was performed under various conditions. The pressure (12–200 mPa) and the plasma-forming gas composition consisting of different organic compounds and hydrogen (C3H8, CH4, Si(CH3)2Cl2, H2), the voltage of accelerating gap in the range 0.5–5 kV, and the substrate temperature in the range 20–850°C were varied. Synthesized films were researched using nanoindentation, Raman, and FTIR spectroscopy methods. Analysis of the experimental results was made in accordance with a developed model describing processes of growth of the amorphous and crystalline carbon materials.

Gas discharge source of metal vapor and fast gas atoms

A source of metal atom flow coinciding in time and space with a flow of fast gas atoms has been studied and the study results are presented. The fast particles are produced due to charge exchange collisions of ions accelerated by potential difference between a plasma emitter inside the source and secondary plasma inside a process vacuum chamber. The emitter is the glow discharge plasma, whose electrons are confined in an electrostatic trap formed by a cold hollow cathode and an emissive grid the latter being negative both to the cathode and the chamber. The metal atoms are produced due to sputtering a target placed at the hollow cathode bottom by ions from the plasma emitter with energy up to 3 keV. Sputtered atoms cross the emitter, together with accelerated ions enter the chamber through the emissive grid and deposit on pieces placed therein. When a mixture of argon and nitrogen is used, the metal nitride coatings are being synthesized and interruptedly bombarded during the synthesis by atoms and molecules with energy variable from ∼10 to ∼300 eV.

Source of metal atoms and fast gas molecules for coating deposition on complex shaped dielectric products

Beam-assisted deposition of wear-resistant coatings on complex shaped dielectric products is used as a source of slow metal atoms and fast gas molecules with coinciding trajectories of their movement from a common emissive grid to the products. This allows keeping the ratio of metal atom flow density to that of fast molecules constant as well as uniformity of deposited coating properties at the whole surface of the planetary rotating inside vacuum chamber products, including their cavities. The fast molecules are produced due to charge-exchange collisions of ions accelerated by potential difference between a plasma emitter inside the source and secondary plasma inside the chamber. The plasma emitter is produced by glow discharge with confinement of electrons in an electrostatic trap formed by a cold hollow cathode and an emissive grid the latter being negative to both the cathode and the chamber. Metal vapor is produced due to sputtering of a target placed at the bottom of the hollow cathode by ions from the plasma emitter accelerated by a negative bias voltage 2kV.

PLASMA SOURCE WITH A COLD HOLLOW CATHODE BASED ON ARC DISCHARGE

PLASMA SOURCE WITH A COLD HOLLOW CATHODE BASED ON ARC DISCHARGE

Characteristics of a fast neutral atom source with electrons injected into the source through its emissive grid from the vacuum chamber

In order to increase the equivalent current of a fast neutral atom beam the cold hollow cathode of the beam source is bombarded with electrons extracted from the plasma produced in the vacuum chamber and accelerated in the sheath between the plasma emitter of the source and its emissive grid. The cold cathode bombardment by accelerated electrons raises its electron emission current by an order of magnitude and as a result voltage Uc between the anode and the cathode of the source diminishes more than two times. This allows of increasing several times the beam equivalent current or decreasing the working gas pressure. A slight decrease in the Uc with increasing the accelerating voltage U at an overall cutoff of the electrons from the chamber reveals the influence of secondary electrons emitted by the grid. Measurement of the beam current is discussed.

Broad beam sources of fast molecules with segmented cold cathodes and emissive grids

Experimental study of fast neutral atom and molecule beam sources with rectangular and circular cross-section of the beam up to 0.8 m2 is carried out and the study results are presented. The fast particles are produced as a result of charge exchange collisions between gas molecules and ions accelerated by potential drop between the plasma emitter of the beam source and the secondary plasma inside the processing vacuum chamber. As the emitter is used a glow discharge plasma, whose electrons are confined in an electrostatic trap formed by a cold hollow cathode and an emissive grid, which is negative both to the cathode and to the chamber. In order to prevent from breakdowns between the emitter and the cathode at a current in the cathode circuit up to 10 A as well as between the emitter and the grid at a voltage between them up to 10 kV the cathode and the grid are composed of isolated from each other segments, which are connected to power supplies through resistors. When resistance of the resistorR > U/I0, where U is the power supply voltage and I0 is the minimal current of stable vacuum arc for a given segment material, then transition from the glow discharge to the steady-state vacuum arc is totally excluded in spite of numerous breakdowns of microsecond duration due to contamination of the source electrodes during its operation with dielectric films and other stimulants of the arc.

Decrease in the operating gas pressure in an ion source

The results of use of a cold hollow cathode with a multipole magnetic field in a duoplasmatron-type ion source are described. The operating parameters of a duoplasmatron with the developed cathode and a duoplasmatron with a cold hollow two-cylinder cathode are compared. It is shown that the use of a cathode with a multipole magnetic field offers additional possibilities of reducing the operating gas pressure in an ion source and contributes to an increase in both the current and the phase density of the ion-beam current at the output of a charged-particle source and to a decrease in the phase volume of this beam.

Comparative Research of Efficiency of Water Decontamination by UV Radiation of Cold Hollow Cathode Discharge Plasma Versus That of Low- and Medium-Pressure Mercury Lamps

In this paper, the results of experimental studies of peculiarities of Escherichia coli water suspension inactivation by ultraviolet radiation of hollow cathode discharge plasma in different gaseous media are presented. It is shown that efficiency of the inactivation by the discharges on oxygen, mixtures of oxygen with deuterium, and water vapor is essentially higher than that by the discharge on air, as well as the discharges of low- and medium-pressure mercury lamps

Electron energy-dependent product state distributions in the dissociative recombination of O2+

We present product state distributions and quantum yields from the dissociative recombination reaction of O2+ in its electronic and vibrational ground states as a function of electron collision energy between 0 and 300 meV. The experiments have been performed in the heavy-ion storage ring, CRYRING, and use a cold hollow-cathode discharge source for the production of cold molecular oxygen ions. The branching fractions over the different dissociation limits show distinct oscillations while the resulting product quantum yields are largely independent of electron collision energy above 40 meV. The branching results are well reproduced assuming an isotropic dissociation process, in contrast with recent theoretical predictions.

Generation of Gas Discharge Plasma by an Arc Source with a Cold Hollow Cathode

The results from a study of an arc plasma source with a cold hollow cathode are presented. The source generates plasma with a density of ∼1010 cm−3 in a volume of ∼0.2 m3 at discharge currents of up to 150 A, an arc discharge operating voltage of 30–40 V, and a low pressure of 0.1–1 Pa. The motion of the cathode spot in the crossed electric and magnetic fields inside the hollow cathode and the cathode’s special design make it possible to eliminate almost completely the penetration of the sputtered cathode material into the working vacuum chamber.

Hollow-Cathode Magnetron Discharge as a Generator of Charged Particles

A magnetron discharge with a cold hollow cathode and an uncooled rod cathode is studied. It is shown that such a discharge can be efficiently used to generate a plasma emitting charged particles. For a discharge current of 2 A and an accelerating voltage of 10 kV, ion and electron emission currents of 0.1–0.15 and 1 A, respectively, are achieved. The energy cost of ion extraction is 1–2 W/mA, which is two to five times less than for typical ion sources, and the energy efficiency is 15 mA/W, which is a factor of five or six higher than for electron emitters based on a hollow-cathode reflex discharge.

Spectroscopic and electrical study of rare-gas-based, hollow cathode luminescent discharges: Application to the lifetime and efficiency enhancement of mercury-free signs

Abstract This work deals with the potentialities of mercury-free mixtures for the efficient operation of luminous signs used for publicity lighting. The experimental study of rare-gas-based, cold hollow cathode, low-pressure luminescent discharges is reported. Electrical and spectroscopic measurements are presented with a special emphasis on the radiation properties of the positive column. The best mixtures for phosphor excitation are described in terms of composition and pressure together with their sensitivity to potential fluctuations of the operating conditions during sign lifetime. Aging studies are presented, showing evidence of a strong trade-off between the output power and the sign lifetime. The selective trapping of the heavier gas present in the gas mixture is presented and proven to be at present the main reason for the sign lifetime limitation. The limitation of commercial (sinusoidal or square waveform) ballasts for the excitation of such mercury-free discharge is presented. Finally, preliminary measurements, performed using a lab-developed short rise time and low duty-cycle driver, are reported, showing a significant increase of the illuminance and efficiency (up to a factor three) of mercury-free signs as compared to the values obtained with conventional excitation.

Beam-plasma mechanism for anode plasma generation in a low-pressure two-stage self-sustained discharge with a cold hollow cathode

Results are presented from experimental studies of the anode region of a low-pressure two-stage self-sustained discharge with a closed cold hollow cathode. It is shown that applying an external longitudinal magnetic field promotes the generation of a dense anode plasma, whereas the transverse field impedes this generation. It is established that the beam-plasma mechanism for plasma generation plays a dominant role in the anode region of the discharge. The geometry of the electrodes of the gas-discharge chamber is optimized.

Improvement of the efficiency of a glow discharge-based ion emitter with oscillating electrons

Ion emission from the plasma of a low-pressure (≈5×10−2 Pa) glow discharge with electrons oscillating in a weak (≈1 mT) magnetic field is studied in relation to the cold hollow cathode geometry. A hollow conic cathode used in the electrode system of a cylindrical inverted magnetron not only improves the extraction of plasma ions to ≈20% of the discharge current but also provides the near-uniform spatial distribution of the ion emission current density. The reason is the specific oscillations of electrons accelerated in the cathode sheath. They drift in the azimuth direction along a closed orbit and simultaneously move along the magnetic field toward the emitting surface of the plasma. A plasma emitter with a current density of ≈1 mA/cm2 over an area of ≈100 cm2 designed for an ion source with an operating voltage of several tens of kilovolts is described.