Hollow Anode Research Articles

Spectroscopic investigation of the plasma in a hollow anode with an incorporated ferroelectric plasma source

Spectroscopic measurements are reported of the plasma formed inside a hollow anode (HA) with a ferroelectric plasma source (FPS) incorporated in it. The HA was used as a cathode in a diode supplied by an accelerating pulse (≤300kV, ≤400ns). It was found that the HA discharge (1.2kA, 10μs) is accompanied by the formation of a dense (≈8×1014cm−3) plasma layer at the surface of the FPS. This surface plasma serves as a practically unlimited source of electrons. In the bulk of the HA plasma the density is ≈3×1013cm−3 and it remains the same during the accelerating pulse whereas the plasma electron temperature increases from 4 to 11eV.

Grid-controlled electron emission from a hollow-anode electron source

We describe the operation of a hollow-anode electron source with a biased output grid in a diode powered by a 200 kV 400 ns pulse. The hollow anode had a ferroelectric plasma source incorporated in it. Three electrical schemes for the hollow-anode output grid bias were tested and compared. It is shown that the use of an autobias grid allows electron-beam generation with a current amplitude up to 1.2 kA in a plasma emission-limited mode and with insignificant plasma prefilling of the accelerating gap. The use of an externally biased output grid (either with a positive or negative potential) showed the possibility to control the emission properties of the hollow-anode plasma without changing the amplitude of the discharge current. Electron beams with an amplitude up to 2 kA and insignificant plasma prefilling of the accelerating gap were obtained. It was found that the application of the accelerating pulse leads to a drastic increase in the potential of the plasma up to several kV. It is shown that, in spite of the large positive plasma potential, electron emission occurs due to the dynamics of ions inside the sheath near the hollow-anode grid.

Glow discharge pretreatment tools for vacuum web coating

In the last few years plasma pre-treatment has been established as a powerful tool to increase the quality in vacuum web coating whereas, the effect of web pre-treatment under atmospheric conditions is declining due to several reasons, glow discharge assisted in line–in vacuo pre-treatment is much more reliable. Two tools for plasma pre-treatment are presented here. Both are easily scalable as to comply with the needs of large area web coating with a typical coating width of over 2 m, and they operate in a pressure range that is compatible with sputtering and evaporation processes taking place in the same vacuum system. The effect of the glow discharge on polymeric web depends on electron temperature (typically a few electron volts), electron density (ranging typically from 10 −9 to 10 −11 cm −3), ion energy, and chemical composition. The mentioned electron density range is indispensable to meet the demands of satisfactory production speeds, in particular with evaporation. By means of the so-called Treatmag ®, an abnormal glow discharge enhanced by a closed loop tunnel shaped magnetic field is generated in the 10 −2 mbar pressure range. This tool is widely used for the improvement of metallic coatings on polymeric web. The ion energies typically range well below 70 eV. Indeed, water vapor and oxygen permeation rates through OPP have been quartered respectively, third. The so-called RF hollow anode described herein next is comprising a capacitively coupled, asymmetric 13.56 MHz radio frequency glow discharge driven in a hollow life electrode, operated in the 10 −2 mbar pressure range. The easily scaleable RF hollow anode is dedicated to the dynamic pre-treatment or coating of either dielectric or metal web (or rigid sheet), and can be used in conjunction either with sputtering or, at line speeds of typical 5–10 m/s, with evaporation processes. The RF hollow anode renders ion fluxes of up to 1 mA/cm 2 at energies between 100 and several hundred electron volts. So far it complements the Treatmag ®, which yields ions with considerably lower energies. The adhesion improvement by the RF hollow anode we attribute to a pronounced increase of the cross-link density (amorphization) in the near surface region of in-plane oriented polymeric web commonly used. Ex situ XPS spectra taken 3 days after venting from PET samples treated at high web speeds are given. It is mentioned that the industrial application of the RF hollow anode is based on the surface modification as yielded in-situ/in-vacuo almost immediately after treatment. In case the RF hollow anode is operated with hydrocarbon, silane or other gases, it can also be employed for thin base-coatings or top-coatings on web material.

Investigation of a hollow anode with an incorporated ferroelectric plasma source for generation of high-current electron beams

We report experimental results of operation of a high-current hollow anode (HA) with a BaTi ferroelectric plasma source (FPS) incorporated in it. It is shown that the application of the FPS allows one to significantly decrease the HA surface area, thus providing a compact electron source. Use of this HA as an electron source in a high-voltage diode for generation of high-current electron beams is described as well. It was found that the FPS allows reliable ignition and sustaining of the HA discharge with current amplitude ⩽1.2 kA and pulse duration ⩽2×10−5 s at N2 gas pressure of (1–3)×10−4 Torr. Also, it was found that the operation of the HA is characterized by plasma formation with density of ∼4×1012 cm−3, electron temperature of ∼5 eV, and that the plasma acquires a positive potential of ∼10 V with respect to the anode and of 50–70 V with respect to the autobiased HA output grid. It is shown that the autobiased HA output grid prevents plasma penetration towards the accelerating gap if the grid half-cell size has approximately the same value as the thickness of the double layer formed between the plasma and the grid wires. Generation and characterization of a high-current electron beam with current amplitude of ∼1.2 kA was achieved under an accelerating pulse amplitude ⩽300 kV and ∼400 ns pulse duration.

Electron beam generation in a diode with a gaseous plasma electron source II: Plasma source based on a hollow anode ignited by a hollow-cathode source

We describe the operation of a hollow plasma anode (HPA) with a hollow cathode incorporated in it for the production of preliminary plasma. The operation of the hollow anode was studied with a discharge current amplitude up to 1 kA. It was shown that the gaseous discharge is realized without formation of plasma spots at the anode wall and the output grid. The plasma parameters inside the HPA were measured for different N2 gas pressures and discharge current amplitudes. It was found that the plasma acquires a positive potential with respect to the anode and that the plasma density and temperature are ⩽5×1012 cm−3 and ⩽10 eV, respectively. This plasma source was used as a cathode in a diode for the generation of high-current electron beams under an accelerating-voltage ⩽250 kV and 400 ns pulse duration. The characteristics of the diode and the generated electron beam as a function of the HPA parameters are presented. It was found that at the beginning of the accelerating pulse the diode operates in a plasma prefilled mode, and further in the accelerating pulse the diode current is determined by the emission capability of the HPA. It was shown that this source allows reliable generation of a uniform electron beam with a cross-sectional area of 100 cm2 and a current amplitude up to 1 kA without the formation of explosive plasma at the HPA output grid.

Electron beam generation in a diode with a gaseous plasma electron source I: Plasma source based on a hollow anode ignited by a multi-arc system

We report on the operation of an electron diode with a cathode based on a hollow plasma anode (HPA) design. Six arc sources placed inside the anode cavity were used to produce a preliminary plasma. The latter was used to produce a high-current (up to 4 kA) gaseous discharge without formation of plasma spots at the anode wall and output grid. The plasma parameters inside the HPA were measured for different N2 and Xe gas pressures and discharge current amplitudes. It was found that the HPA operation is characterized by a negative anode potential fall and that the plasma density and temperature inside the anode are ≈6×1012 cm−3 and ≈9 eV, respectively. The characteristics of an electron diode and the generated electron beam were studied under an accelerating voltage amplitude ⩽250 kV and 400 ns pulse duration for different parameters of the HPA. It was found that in the beginning of the accelerating pulse the diode operates in a plasma prefilled mode while later the diode current is determined by the emission capability of the HPA plasma. It was shown that this source allows generation of an electron beam with a cross-sectional area of 100 cm2 and a current amplitude up to 1.2 kA, without the formation of explosive plasma at the surface of the HPA output grid.

Energy spectra measurements of X-ray emission from electron interaction in a dense plasma focus device

Electrons generated during a pinch implosion in a hollow anode Mather-like plasma focus device (PF) are considered as a possible X-ray source via the impinging of those particles on medium and high- Z targets. A usual PF device has been slightly modified to optimise the X-ray production and their measurements by means of a suitable and non-invasive spectrometer. This ensemble allows measurements of X-rays generated booth by electrons turning back to the anode and by target collision of the so-called relativistic electron beam. The spectrum of the emitted photons is evaluated by using a differential absorption based technique. The X-ray spectrometer consists of a stack of LiF dosimeters which act both as detectors and filters to give curves of attenuated intensities. Finally, the energy distribution is calculated from such attenuation curves using an iterative procedure based on spectral algebra formalism.

Deposition of titanium nitride thin films on stainless steel—AISI 304 substrates using a plasma focus device

A 3.3 kJ pulsed plasma focus device was used to deposit thin films of titanium nitride (TiN) at room temperature onto the stainless steel—AISI 304 substrates. The small plasma focus device, fitted with solid titanium anode instead of the usual hollow copper anode, was operated with nitrogen as the filling gas for deposition of TiN thin films. Films were deposited with different numbers of focus shots, at different distances from the top of the anode, and at different angular positions with respect to the anode axis. Deposited films have been characterized for their structure by X-ray diffractometry (XRD), surface morphology by scanning electron microscopy (SEM), elemental composition and distribution mapping by energy dispersive X-ray (EDX) analysis and hardness using a nanoindenter. XRD patterns show the growth of as-deposited polycrystalline TiN thin film. Diffraction patterns for films deposited along the anode axis show induction of a phase corresponding to iron chromium nickel on the film–substrate interface. SEM pictures confirm uniformly distributed TiN grains with hardly any crack over the film surface. Conglomeration of smaller TiN grains, to form bigger size grains, is seen to occur at the films deposited with higher total ion flux. The EDX spectra show the presence of expected constituent elements. EDX mapping confirms the uniform distribution of TiN on the film surface. The variation in structure, morphology, thickness and hardness of the deposited films with the variation of film deposition parameters is explained, qualitatively, on the basis of ion emission characteristics of the focus device. Polycrystalline, smooth and hard thin films of TiN are successfully deposited at room temperature stainless steel—AISI 304 substrates using the plasma focus device.

Operational features and air plasma characteristics of a thermal plasma torch with hollow electrodes

The operational features and thermal plasma characteristics of a plasma torch with hollow electrodes are investigated based on their dependence on input current, gas flow rate and electrode diameter when air is used as a plasma gas. A plasma torch with a hollow cathode and anode has been designed and fabricated, and the arc voltages and thermal efficiencies are measured from its discharge. The newly modified similarity criteria are derived from the measured data related to torch performances. From the fact that these criteria successfully describe both the arc voltage and thermal efficiency behaviour of the torch, depending on its operating and geometrical parameters, it is proved that they can be usefully applied to the design and operation of high power torches. For the numerical modelling of the interior region of the torch, a cold flow analysis is employed along with a simplified balance equation of the Lorentz and gas dynamic drag forces in order to determine a cathode spot position on the cathode surface. The validity of this method is confirmed by comparison of the calculated and measured net powers. As a practically useful result of this analysis, carried out through this numerical and experimental work, it is suggested that low input current, high gas flow rate and relatively large electrode diameter are more favourable as appropriate operating conditions of the torch for the efficient treatment of hazardous organic wastes.

Relativistic electron beams detection in a dense plasma focus

Fast electron beams into a hollow anode of a small plasma focus machine (2 kJ, 4 μF) were measured. The diagnostic method designed for this purpose is founded in a small Rogowski coil introduced into a cavity performed in the anode. By means of this, electron beam pulses of about 10 ns width generated in the plasma focus are detected. Simultaneously, hard X-ray signals obtained from a scintillator-photomultiplier system are registered. The electron beam energy was measured through the time-of-flight of the electrons between probe and anode top. The beams are found to be relativistic and its energy is into the range of hard X-rays energy. An analysis of signal intensities and relative delays for three hundred shots are here presented.

Mechanism of lithium insertion in hollow carbon fibers-based anode

This paper presents the cyclic voltammetry (CV) characteristics concerning the reversibility of lithium insertion into hollow carbon fibers heat-treated at various temperatures (900, 1600, 2200 and 2800 °C). To approach the elucidation of the influence of heat treatment temperature (HTT) on the mechanism of the insertion/extraction process occurring with carbon-based anodes, the electrochemical data were supported by the results of both the X-ray diffraction (XRD) analysis and the BET surface area measurements.

Deuterium plasma focus measurements using solid state nuclear track detectors

A camera obscura technique was used to investigate the spatial distribution of fusion protons emitted from a small deuterium plasma focus device operated in its neutron-optimized regime (14 kV, 3 kJ, and 400 Pa D2 gas). An indium-foil activation detector was employed simultaneously to measure the shot-to-shot neutron yield. The camera obscura was positioned on the forward axis of the plasma focus, 12 cm from the tip of the hollow copper anode, covering a conical field-of-view of half-angle slightly less than 20 degrees. The nuclear track detector material PM-355 was used in the camera focal plane to register protons from the 2H(d, p)3H reaction, hence imaging the spatial distribution of fusion occurring in the plasma focus. A kapton film covering the camera entrance pupil served to protect the detector from the hot plasma jet; it also stopped completely all energetic charged particles other than the ( 3 MeV) fusion protons. Following chemical etching of the detector plates, the track parameters - size, circularity, average-grey-value and (x-y) position - |were measured by an automated scanning system comprising an optical microscope equiped with a CCD camera, motorized stage and focus-adjust, and interfaced to a PC computer. From the accumulated track data, representing 119 plasma focus shots, the imaged fusion density profile was obtained. A detailed Monte Carlo simulation program was used to interpret this profile. The results indicate that the beam-target mechanism, in which energetic deuterons emitted in a forwardly directed cone from the plasma focus pinch interact with the cold deuterium gas, accounts for 90 to 96% of the fusion production for our device. There is however clear evidence for a non-zero (4 to 10%) contribution emitted directly from the pinch region.

Cylindrical hollow anode ion source

The hollow anode ion-electron source is based on the hollow anode discharge, a kind of plasma utilizing a cold cathode and a tiny bore or slot in the anode that simultaneously serves as exit aperture of the ion (or electron) source. These sources are particularly suitable, for example, for deposition of films on large flat surfaces. The length of the slot-shaped hollow anode aperture can be sufficient so that, together with sweeping of either source or substrate, large area substrates can be processed, thereby simulating the function of large area plasma sources.

Room temperature deposition of titanium carbide thin films using dense plasma focus device

Thin films of titanium carbide (TiC) were deposited on 304-stainless steel substrates using a dense plasma focus device. The conventional hollow copper anode of the 3.3 kJ Mather type plasma focus device was replaced by solid titanium anode for deposition of TiC thin films. The argon–acetylene admixture (in 7:3 ratio) was used as the filling gas at a pressure of 1.5 mbar. Substrates were placed along the anode axis at a distance of 11.5 cm from the top of the anode. Thin films of TiC were deposited using different numbers of focus shots, like 10, 20 and 30, at room temperature substrates. Deposited films were analyzed for their structure, surface morphology, surface profile, elemental composition and distribution using X-ray diffraction (XRD), scanning electron microscopy (SEM), surface profiling and energy dispersive X-ray spectroscopy (EDX). XRD patterns in all three cases are found to have diffraction peaks for (111), (200), (220), (311) and (222) TiC crystalline planes. Scanning electron micrographs show a smooth film surface with increasing clustering of TiC grains with the increase in number of focus deposition shots. EDX spectra confirm the presence of expected constituent elements with the gradual increase in TiK α peak (of the TiC thin film) relative to FeK α peak (of the substrate) with increasing numbers of focus deposition shots due to increasing film thickness. EDX mapping reveals a uniform distribution of TiC over the substrate surface. These results confirm the first ever deposition of TiC thin films using a dense plasma focus device.

Microhollow cathode discharge excimer lamps

Microhollow cathode discharges are high-pressure, nonequilibrium gas discharges between a hollow cathode and a planar or hollow anode with electrode dimensions in the 100 μm range. The large concentration of high-energy electrons, in combination with the high-gas density favors excimer formation. Excimer emission was observed in xenon and argon, at wavelengths of 128 and 172 nm, respectively, and in argon fluoride and xenon chloride, at 193 and 308 nm. The radiant emittance of the excimer radiation was found to increase monotonically with pressure. However, due to the decrease in source size with pressure, the efficiency (ratio of excimer radiant power to input electrical power), has for xenon and argon fluoride a maximum at ∼400 Torr. The maximum efficiency is between 6% and 9% for xenon, and ∼2% for argon fluoride.

Generation of homogeneous plasma in a low-pressure glow discharge

The possibility of producing homogeneous plasma in a low-pressure discharge with the use of a hollow anode or hollow cathode is analyzed. It is shown that, in contrast to the high-pressure discharge, where uniform ionization is needed to produce homogeneous plasma, in the low-pressure discharge, nearly uniform radial distribution of the plasma parameters can be achieved under nonuniform ionization conditions by increasing the ionization probability at the system periphery and reducing it near the system axis. It is shown that the magnetic field can facilitate generation of the homogeneous plasma instead of interfering with it.

A source of broad homogeneous beams of low-energy (∼0.5 keV) gas ions

A source of gas ions (argon, oxygen, nitrogen, etc.), the operating principle of which is based on the use of a glow discharge in an electrode system of a wide-aperture hollow cathode and anode in a magnetic field, is described. The exit aperture diameter of the hollow cathode, increased up to a size close to the ion beam diameter (10 cm), ensures the uniform ion emission of the plasma generated in the discharge region near the anode. A decreased angular divergence or increased ultimate ion-beam current density is achieved by a change in the potential drop in the space charge sheath between the plasma and the ion optics. The source generates broad (50 cm2) slightly diverging (ω/2∼3°–5°) ion beams with energies of 300–1000 eV at a beam current density of ∼0.5 mA/cm2.

Time-of-flight mass spectrometry studies of an ion beam generated by the titan source

The TITAN source generates wide-aperture beams of gas and metal ions of different materials. This is achieved because of two types of cold-cathode arc discharges, which operate simultaneously in the discharge system of the source. For metal ions to be obtained, use is made of the vacuum arc initiated between an ion-forming cathode and a hollow anode. To produce gas ions, a constricted low-pressure arc discharge is initiated with the same hollow anode. The constitution of ion beams generated by the TITAN source has been investigated using a homemade time-of-flight spectrometer. This paper describes the design of the latter and the principle of its operation, and discusses the physical peculiarities of the spectrometer operation, which affect the ion beam constitution.

Generation of a homogeneous plasma in a glow discharge with a hollow anode and a wide-aperture hollow cathode

The principles for designing electrode systems for sources of ion beams of large cross section on the basis of a glow discharge are considered, and a system with combined magnetic and electrostatic confinement of the fast electrons in a wide-aperture hollow cathode and the generation of an ion-emitting plasma in the anode cavity is proposed. It is shown that the system investigated generates a plasma with a nearly homogeneous distribution of the ion emission current density at low gas pressures and can be effectively used to obtain ion beams over a broad range of energies.

Compact glow discharge x-ray tube

We have developed a compact glow discharge x-ray tube (diameter: 10 mm, length: 20 mm), which is composed of a hollow anode tube, a cathode plate, and a thin film target. This glow discharge device was operated with an Al thin film target at a discharge voltage of 2.0 kV at a discharge current of 0.1 mA and at a He pressure of approximately 0.2 Torr, which was used as the discharge gas. The characteristic x rays of Al Kα are produced by bombardment of electrons emitted from the cathode surface. The strong x-ray emission intensity, which depended on the operating voltage and the gas pressure, was obtained throughout the discharge time of 1.5 h.