Hollow Cathode Glow Discharge Research Articles

Special Features of Parasitic Current Formation in a Sealed-Off Cold-Cathode Thyratron with Trigger Unit Based On an Auxiliary Glow Discharge

Results of investigation of the glow discharge with hollow cathode and ring anode in the trigger unit of a coldcathode thyratron TPI1-10k/50 are presented. A specific feature of the discharge sustainment is that a highly emissive tablet containing cesium carbonate is placed in the cathode cavity. The current-voltage characteristics of the discharge in the trigger unit are obtained for different tablet compositions together with the measured parasitic current to the main cathode cavity. Stepwise transitions to the regime with decreased discharge burning voltage accompanied by an increase in the parasitic current are observed. A model of current sustainment in a hollow-cathode glow discharge is used to interpret the characteristics obtained. Instead of the conventional secondary emission yield, the model uses a generalized emission yield that takes into account not only the ion bombardment of the cathode, but also the emission current from an external source. Based on estimations of the discharge parameters in the trigger unit, a reason for a parasitic current increase is revealed.

Influence of the hole diameter in the perforated electrode on the parameters of electron beam generated by a forevacuum plasma electron source

We present experimental results on geometry optimization of the emission electrode in a plasma cathode electron source operating in the forevacuum range of pressure. For the 2-mm thick emission electrode, we have determined an optimal diameter of the emission aperture that provides the most efficient electron extraction from a hollow cathode glow discharge plasma in helium. At the working pressure of helium in the vacuum chamber 30 Pa, the beam power during emission from a single aperture can vary from 2 to 6 kW, while the beam diameter does not exceed 0.5 mm.

Influence of the Anode of a Non-Self-Sustained Glow Discharge with a Hollow Cathode on the Spatial Distribution of Plasma Concentration

The results of investigation of the influence of geometrical dimensions, shape and position of the anode of a high-current non-self-sustained glow discharge with a hollow cathode at low (≈1 Pa) pressure with the current up to 100 A on the degree of inhomogeneity of azimuthal plasma-concentration distributions are presented. The azimuthal measurements demonstrate that upon injection of an electron flow with the current exceeding that of the electrons, formed as a result of the secondary ion-electron emission, the value of the average path length L of electrons before their escape to the anode is much lower than that in a self-sustained discharge burning mode. It is determined that in the case of injection of an electron flow into the hollow-cathode glow discharge the anode position considerably affects the degree of plasma concentration inhomogeneity. It is shown that placing the annular anode in the site preventing the line-of-site between the electron injection and anode surface directions allows achieving the minimum inhomogeneity coefficient value.

Non-Self-Sustained Hollow-Cathode Glow Discharge at Low Burning Voltages

The results of investigations of low-voltage burning modes of a non-self-sustained glow discharge with a ~0.2 m3 hollow cathode at low (≈1 Pa) pressure, which is assisted by an external injection of electrons from the electric-arc plasma. The current-voltage characteristics recorded at low burning voltages 20–80 V demonstrate that there is a threshold glow-discharge burning voltage, at which a stepwise transition takes place from the burning conditions with high plasma inhomogeneity to the conditions of homogeneous plasma glow in the entire volume of the hollow cathode. This transition, accompanied by an enhanced hollow-cathode effect, is characterized by a 20–40% increase in the main discharge current. The glow discharge burning voltage, at which this current jump takes place lies within the range 45–60 V and depends on the value of the auxiliary discharge current and working pressure.

Effect of the Geometric of (Al) Hollow Cathode on Paschen Curves in Nitrogen

In this paper, an experimental study of DC hollow cathode glow discharge plasma at different nitrogen pressures ranged from (0.065 to 0.75Torr) has been proposed. Investigated was carried out under the influence of the hollow cathode geometry such as diameter and depth of hollow cathode on the breakdown voltage of the nitrogen gas, the discharge system consists of two electrodes, the cathode forms various geometrical shapes and anode as a disc- shaped with diameter (8.8cm). The electrodes are enclosed in a large cylindrical glass chamber of pyrex filled with nitrogen gas. Three important physical parameters affecting the condition of the discharge are the gas pressure, constant inter-electrode distance and the cathode geometry. We used the hollow cathode with geometric shapes such as Cylindrical, conical, oppressive and variable dimensions. The cylindrical and conical shapes have inner diameters (3 & 6) cm and repressive shapes have inner diameter (1 & 2) cm. The breakdown voltage Vb is shown to depend on the product (p.d), for lower values of pressure, p or gap, d. This work represents the investigation of the dependence of the breakdown voltage on the gas pressure and on the distance between electrodes and the cathode geometry. The minimum value of breakdown voltage increases with increases gap d or increase the diameter of the hollow cathode with the length of the cavity is fixed.

Режимы поддержания тлеющего разряда с полым катодом и нитью накала внутри полости

Режимы поддержания тлеющего разряда с полым катодом и нитью накала внутри полости

Distinctive features of the high-current glow discharge with the hollow cathode at low gas pressures

A pulsed hollow cathode glow discharge with current up to 200 A, with the pulse width amounting to a few milliseconds, is studied in a wide range of the gas pressure p from 0.01 to 10 Pa. The high current discharge is established due to the application of a high-voltage pulse with amplitude Uo up to 5 kV between the anode and the hollow cathode of a continuous discharge with a current of Io = 0.5 A. The establishing time τ ranges from 10 to 300 μs, diminishes with the pulse amplitude growth, increases in the gas pressure, and decreases in the output orifice area of the hollow cathode. At Uo > 2.5 kV, an abnormal mode of the discharge establishing process is observed with intensive oscillations of the discharge current and voltage in the frequency range from 1 to 10 MHz. In the abnormal mode, the high current establishing time τ can be reduced by hundred times down to τ ∼ 1 μs. At a low gas pressure p < 0.1 Pa, the high current can be reached only in the abnormal mode. Without oscillations at the pulse front, only low-current high-voltage discharge is established.

Hollow-cathode glow discharge in a trigger unit of pseudospark switch

This paper deals with the investigation of the sealed-off cold-cathode thyratron (pseudospark switch) with a trigger unit that uses a low-current auxiliary glow discharge. As distinct from the commercially produced thyratron TPI1-10k/50, the trigger system of the device under investigation is modernized so that it is able to operate in the absence of the so-called high-emissivity tablet. The data on the principal features of the discharge sustainment in the novel trigger system are obtained. The interpretation of the data is carried out based on the model of the discharge with a hollow cathode, which has been developed as applied to the conditions of the low current densities. It is shown that the regimes of the auxiliary discharge have an impact on the trigger characteristics of the switch. The ability of the switch operation with nanosecond stability with respect to a trigger pulse at high anode voltages is demonstrated.

Generation of an electron beam by the forevacuum plasma source with a single emission channel

We present the results of our investigation on the influence of the geometry of a discharge-emission system on the parameters of the electron beam generated by the forevacuum plasma electron source based on the hollow-cathode glow discharge. The extraction of electrons was implemented through a single emission channel. We have determined the optimal geometric dimensions of the hollow cathode, yielding a maximum efficiency of the electron extraction at the beam power density level of 6⋅105 W/cm2.

Ion-beam chemical-thermal treatment of aluminum

The paper reports on a study of A7 aluminum alloy exposed to thermochemical treatment with a nitrogen ion beam produced in a source based on a non-self-sustained hollow-cathode glow discharge. The material was placed in a plasma generated by a source with a thermionic and hollow cathodes and simultaneously treated by accelerated ions and neutrals of the working gas. No negative bias was used, allowing dielectric surface treatment with no cathode spots. The ion charge at the treated surface was compensated by electrons from the plasma. The specimen temperature was maintained independent of the ion beam energy and current using an active screen whose temperature was controlled by applying a negative bias. The method provides the formation of a nitride film on the Al surface.

Structure and properties of titanium after nitriding in a plasma of pulsed hollow cathode glow discharge

The paper reports on a study of the structure, phase composition and mechanical characteristics of a modified surface layer of VT1-0 titanium after nitriding in the plasma of pulsed and stationary non-self-sustained glow discharge. It was revealed that after nitriding in a pulsed glow discharge, the volume fraction of nitride phase (Ti2N, TiN) in the surface layer of VT1-0 titanium is higher than that in the nitrited layer obtained by exposure to a plasma of steady glow discharge at the same nitriding temperatures, average ion current density at the surface and ion energy. As a result, the hardness of the surface layer of samples obtained by nitriding in pulsed discharge mode exceeds that of samples treated in steady glow discharge mode. Wear resistance of titanium after nitriding in the plasma of a pulsed glow discharge is approximately four times higher than that of titanium without treatment and 1.5 times higher than that achieved by nitriding in a steady glow discharge plasma.

Influence of ion-plasma nitriding on wear-resistance of Cr6VW die steel

The paper presents research data on the surface structure, phase state, microhardness, and tribological properties (wear resistance, friction coefficient) of Cr6VW steel nitrided in the plasma of a non-self-sustained low-pressure hollow-cathode glow discharge at a bias of -200 V and temperature of 460 and 520°C for 3 and 8 h.

Effect of electron injection on the parameters of a pulsed planar magnetron

We have explored the influence of supplementary electron injection on the operational parameters of a planar magnetron operating in repetitively pulsed mode (repetition rate 300 Hz, pulse duration 50–100 μs). The supplementary electron flux was provided from the plasma of an auxiliary hollow-cathode glow discharge and was accelerated directly into the magnetron cathode layer. We show that this supplementary electron injection eliminates magnetron ignition delay and increases the sputtered ion current from the magnetron plasma.

Electron sheath evolution controlled by a magnetic field in modified hollow cathode glow discharge

The electron sheath formation in a DC magnetised plasma of modified hollow cathode source is studied. The discharge consists of two plane parallel cathodes and a small cubical anode placed off axis at the center. The argon plasma is produced, and the properties of the plasma in response to the sheath formation near the anode are studied using electrical and optical diagnostics. In particular, the effect of pressure and magnetic field on the discharge parameters, such as discharge current, plasma potential, plasma density, and electron temperature, is studied. The discharge showed an onset of anode glow at a critical applied magnetic field, indicating the formation of electron sheath and a double layer. The discharge current initially decreases; however, it starts to rise again as the anode spot appears on the anode. The critical magnetic field at which the anode glow formation takes place is dependent upon operating pressure and discharge voltage. The transition from ion sheath to electron sheath is investigated in detail by Langmuir probe and spectroscopy diagnostics. The plasma potential near the anode decreases during the transition from ion sheath to electron sheath. The plasma potential locks to the ionization potential of argon gas when anode spot is completely formed. A systematic study showed that during the transition, the electron temperature increases and plasma density decreases in the bulk plasma. The spectroscopy of the discharge showed the presence of strong atomic and ionic lines of argon. The intensity of these spectral lines showed a dip during the transition between two sheaths. After the formation of the anode spot, oscillations of the order of 5–20 kHz are observed in the discharge current and floating potential due to the enhanced ionisation and excitation processes in the electron sheath. The reason for the electron sheath formation at particular magnetic field is attributed to the reduction of the electron flux reaching to the anode in the direction perpendicular to the magnetic field.

Influence of the cathode material in the cathode fall characteristics of a hydrogen hollow cathode glow-discharge

In this work, we present Doppler free two photon optogalvanic measurements to determine the local electric field strength (E-field) in the cathode fall region of a hollow cathode discharge, operated in pure hydrogen, via the Stark splitting of the 2S level of hydrogen. The main aim of this article is the comparison of the measurements made with different cathode materials, stainless steel, and tungsten; both of them are widely used in the low-pressure discharges. Sputtering of stainless steel is the principle cause of the differences observed for the E-field variation, and the differences are analyzed in the frame of the sputtered material in a wide range of discharge conditions. Complementary images of the discharge luminosity allow for the conclusion; the cathode dark zone corresponds in good approximation to the cathode fall length.

Non-self-sustained low-pressure glow discharge for nitriding steels and alloys

Structural steel 40Cr and die steels 8Cr4W2MoVSi2 and Cr12Mo were nitrided in the plasma of a non-self-sustained hollow-cathode glow discharge at a pressure of 1 Pa, negative bias of 300 V, and temperature of 520 °C and 400 °C. The method has been shown promising for low-temperature nitriding of steels to a depth of several tens of micrometers with minimum tempering.

Direct determination of oxygen and other elements in non-conducting crystal materials by pulsed glow discharge time-of-flight mass spectrometry with potassium titanyl phosphate as an example

Direct quantification of oxygen in dielectric materials using non-destructive or nearly non-destructive techniques still remains a nontrivial task. Simultaneous assessment of oxygen with other elements in a single analytical procedure is even more challenging. In the current study, a method of direct determination of oxygen and other matrix elements in solid samples, based on time-of-flight mass spectrometry with pulsed glow discharge in combined hollow cathode (CHC) is designed and tested. The possibility to effectively ionise oxygen owing to the electron impact mechanism under short repelling pulse delays has been shown. Stable sputtering and ionisation of dielectric samples were obtained via sample coating with thin conducting layer of silver. The parameters of oxygen quantification were optimised: duration and voltage of the discharge pulse, cell pressure, repelling pulse delay and material of the auxiliary cathode. The calibrations of oxygen, phosphorus and potassium are presented. The intensity of 16O+ was shown to be highly dependent on discharge cell pressure. The limits of detection were 0.001, 0.001, and 0.002 mass% for oxygen, phosphorus and potassium respectively. The designed approach enables direct, fast and accurate quantitative and in depth analysis of oxygen-containing samples.

Corrosion Behavior of W-Mo Co-Penetrated Layer Produced by Glow Discharge Plasma Technique in Acid Solution

Abstract To improve the corrosion resistance of Ti6Al4V alloys in acid solution, a W-Mo co-penetrated top layer was prepared by hollow-cathode glow discharge plasma technique below the β phase transition point. The surface morphology, chemical composition and crystal structure of the coatings were determined by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray power diffraction (XRD), respectively. Results indicate that a dense co-penetrated layer is produced with maximum thickness of approximately 23 μm. The layer is composed of AlMoTi2 and TixW1-x phases. The static corrosion test is conducted in acid (H2SO4 and HCl, separately) at room temperature (RT) by the electrochemical workstation. The results show that the W-Mo co-penetrated layer could achieve relatively stable corrosion potential in reducing acid and the Icorr of co-penetrated layers occupy merely 1/10 and 1/6 of that of Ti6Al4V substrates. In addition, there is barely any corroded product and crack on the corroded surface of co-penetrated layers, indicating no corroded shedding phenomenon occurs. So the corrosion resistance are obviously improved in the premise of keeping the basic properties of the substrate.

Hydrogen-Free Carburization on the Surface of Commercial Purity Titanium by Equipotential Hollow-Cathode Glow Discharge

The treatment of hydrogen-free carburization was applied on commercial purity titanium by the technology of equipotential hollow-cathode glow discharge at the commercial purity titanium phase transition temperature. The morphology, distribution of composition and phase composition were analyzed by the scanning electron microscope, the energy dispersive spectrometer, the X-ray diffraction, respectively; the tribology capability of the sample was studied by the friction and wear tester; the corrosion resistance of the samples in 3.5% NaCl solution was studied under the room temperature static condition by the electrochemical workstation. The results show that the high hardness alloy layer forms on the commercial purity titanium surface by the treatment of hydrogen-free carburization, and the maximum thickness of the carburized layer is 7.5 μm; and the maximum HV 0.2 hardness is 12.98 GPa, which is 5.43 times of that of the substrate. Due to the improved surface hardness, the wear resistance on the surface of the sample increases significantly, and the average friction coefficient is only 0.312, which obviously decreases compared with 0.746 of the original sample. The minimum annual corrosion rate of the samples is 1/11 of the original sample in 3.5% NaCl solution. So the wear resistance and corrosion resistance obviously improve in the premise of keeping the mechanical properties of the substrate.

Emission Spectrometric Evaluation of a Hollow-Cathode Glow Discharge Plasma with Helium–Oxygen Mixed Gas for Surface Modification of Co–Cr–Mo Alloy

This paper represents emission spectrometric analysis of a hollow-cathode glow discharge plasma with helium–oxygen mixed gas for surface treatment of a cobalt-based alloy, together with surface analysis of the resulting oxide layer. A Co–28Cr–6Mo alloy was employed as a specimen. The objective of this work is to obtain plasma information for the operating conditions to be optimized for producing a stoichiometric oxide layer on the alloy surface. Helium atomic lines, atomic and ionic lines of oxygen atom, and band heads of oxygen molecule ion were observed in the emission spectra. These intensities drastically changed depending on a mixing ratio of helium–oxygen mixed gas; particularly, the emission intensity of the molecular bands was largely enhanced in the mixed gas plasma compared to the pure oxygen plasma. This band spectrum is assigned to an electronic transition from the 4 Σ g to 4 Π u states of oxygen molecule ion, whose excitation energies are 18–19 eV from the ground state of oxygen molecule. It is thus suggested that a Penning-type ionization process with metastables of helium atom (1s2s 1 S 0, 20.6 eV and 3 S 1, 19.8 eV) is an excitation mechanism how the number density of the corresponding excited state can be elevated in the helium–oxygen mixed gas plasma. This effect, which more populated the excited oxygen species in the plasma, also exerted influence on the resultant oxide layer, such as the chemical composition and the layer thickness. Surface analysis by X-ray photoelectron spectroscopy indicated that an oxide layer consisting of iron and chromium oxides was formed by this plasma treatment, and that chromium atom was enriched in it. The thickness of the oxide layer varied with a mixing ratio of the plasma gas.