Hollow Cathode Source Research Articles

The E × B magnetized plasma device (EMPD).

A plasma device has been created to study dynamic plasma coupling in an E × B-drifting magnetized plasma. The E × B magnetized plasma device is a 1.2m diameter by 2m long cylindrical chamber with two sets of Helmholtz coils in a mirror configuration. A steady-state axial hollow cathode source injects a plasma discharge in electrical contact with a floating conductor at a range that forms a unique axisymmetric equipotential surface or Virtual Cathode Lightsaber (VCL). The VCL generates two plasma populations streaming relative to one another providing a suitable environment for the investigation of dynamic plasma coupling. The plasma density, radial electric field, and plasma rotational velocity outside the VCL are shown to be influenced by the current-voltage relationship of the cathode and applied magnetic field strength. A basic characterization of the device and plasma environment is presented with an emphasis on diagnostics systems and the analytical techniques utilized.

A substrate constituent Na-catalyzed growth of carbon nanotubes on glass substrate by atmospheric pressure PECVD

A growth mechanism of carbon nanotubes (CNTs) without any externally added catalyst is reported in this study. Instead of any externally added catalyst, the constituents of the used soda lime glass substrates seem to play the pivotal role in the growth of CNTs. XPS analysis of the synthesized CNTs reveal that among the various constituents of soda lime glass, sodium (Na) emerges as the primary catalyst for initiating CNT growth. The adopted PECVD technique involving an especially designed spiral-shaped fused hollow cathode source for generating the required atmospheric pressure plasma makes such synthesis easily feasible. The important key factors influencing CNT growth include substrate temperature and plasma pre-treatment of the substrate. Plasma pre-treatment of the substrate at an elevated temperature leads to the formation of catalyst nanoparticles on the surface of the substrate. This report features a detailed CNT growth mechanism proposed on the basis of optical emission spectroscopy and XPS analyses. To be precise, this study demonstrates a novel Na-catalysed synthetic approach for achieving uniform CNT growth on glass substrates without using any externally added catalyst, facilitating the preparation of clean CNTs.

Study of nonlinear characteristics in hollow cathode discharge in unmagnetized plasmas

AbstractParametric study and nonlinear dynamical analysis of the discharge parameter variations are presented here for a hollow cathode source in the glow discharge regime and later in the radio frequency (RF) discharge regime. A plasma source consisting of a semi‐transparent hollow cathode leads to the generation of nonthermal energetic charged particles and the formation of multiple potential regimes in the plasma column during both the glow discharge as well as the RF discharge regimes. The hollow cathode discharge obtained using this single plasma source exhibits significant mixed‐mode oscillations (MMOs) during the glow discharge regime. Various regular and irregular sequences of MMOs evolved during the progressive change of discharge voltage in the glow discharge regime. During the RF power application across the hollow cathode source, the charged particles oscillate and appear in bursts in the time series. The present study investigates energy distribution among the coherent modes of discharge through the application of the Empirical Mode Decomposition technique. Multiple coherent modes are identified during both discharge regimes that carry most of the discharge energy.

Sputter hot filament hollow cathode ion source and its application to ultra-low energy ion implantation in 2D materials

We describe the design of a new ion source that combines a hot filament hollow cathode source with a sputtering source. This combination makes it possible to provide ion beams of a wider range that previously could not be used due to respective high melting points and low vapor pressure of the needed elements. We demonstrate the sources viability for molybdenum, cobalt, niobium and the rare-earth element gadolinium. An implantation current of 20–900nA on the sample, depending on the element, could be achieved. Moreover, we experimentally prove that these ion beams are suitable for ultra-low energy implantation into 2D materials like graphene and transition metal dichalcogenides (TMDs). Furthermore, computational studies were conducted to investigate the ion trajectories within the source and ion implantation into 2D materials. RBS and PIXE measurements were performed to quantitative investigate the implanted samples.

Low-pressure hollow cathode plasma source carburizing technique at low temperature

A low-pressure hollow cathode plasma source carburizing was developed as a novel surface treatment technique based on the active screen plasma carburizing combined with hollow cathode sources. The cylindric cathodic cage with array holes was made of pure graphite, where the hollow cathode graphite tubes were inlaid on. A pulsed high voltage power with a peak voltage of 800 V and a pulse frequency of 30 kHz was supplied to ignite the hollow cathode discharge inside graphite tubes at a low pressure less than about 300 Pa using a gas mixture of CH 4 + 90%H 2 . The hollow cathode plasma source together with the pulsed high voltage power realized a high biasing current on the carburized samples at low pressure, and produced an enhanced heating except the thermal radiation by the cathodic cage. The graphite cathode as a carbon source besides the gas precursor provided an additional carbon potential. The AISI 304L austenitic stainless steel was carburized at a low temperature of 450 °C for a treatment time of 6 h with a bias of 200 V under the carburizing pressure of 50 Pa and 300 Pa, respectively. It was observed that the carburizing case at 50 Pa was about 13 μm with a higher surface carbon concentration of about 6.5 at.% and a higher hardness of about HV 0.25 N 8.5 GPa compared with that at 300 Pa. The carbon-expanded austenite (γ C ) phase was observed by the x-ray diffraction of both the carburizing cases. The metastable high carbon carbide Fe 5 C 2 only appeared at 50 Pa, which was attributed to high carbon potential at the lower pressure. Therefore, an increased carburizing efficiency at the low temperature was obtained by the low-pressure hollow cathode plasma source carburizing technique using a pulsed high voltage power. • Hollow cathode plasma source is utilized in low temperature plasma carburizing. • Pulsed high voltage is used in graphite hollow cathode discharge at low pressure. • High sample biasing current with enhanced heating is realized by plasma source. • Graphite cathode provides additional carbon potential besides the gas precursor. • Thick carburizing case with metastable carbide and high hardness is obtained.

One-Dimensional Model for Hollow Cathode Orifice Lifetime Prediction

Lifetime assessment of hollow cathode (HC) sources is an experimentally demanding process, due to the large amount of hours space qualification requires. In this Paper, we present a one-dimensional orifice model coupled to a global-averaged insert model, developed for lifetime prediction of a HC neutralizer in terms of orifice erosion; a modified sputtering yield curve is derived, similar to a previous literature work, and the role of anomalous resistivity is discussed in view of the erosion profile. Variations on the active length parameter, required for the insert modeling, are seen to affect the orifice plasma profiles and the erosion to a lesser degree, and the time evolution of the orifice channel confirms the expected asymptotic decrease of the erosion rate.

Mechanical and Wear Properties of 42CrMo Steel by Plasma Nitriding assisted Hollow Cathode Ion Source

Plasma nitriding is a plasma-activated thermochemical method widely used to increase the fatigue strength, hardness and wear resistance of low-alloy steels. In this work, a new structure consisting of a hollow cathode metal plate can produce a hollow cathode discharge and heat the workpiece by radiation. This principle is used to perform hollow cathode source plasma nitriding (HCSPN). Herein, 42CrMo steels were treated by conventional plasma nitriding (CPN) and HCSPN treatments. The 42CrMo steels were nitrided at 525 °C for 6 h in NH3 atmosphere. The mechanical and dry wear properties were measured by nano-indentation, Vickers micro-indentation and ball-on-disk tribometer, respectively. The H3/E⁎2 ratio was 0.0274 GPa (H=11.51 GPa and E⁎=235.84 GPa) for the CPN sample and 0.0276 GPa (H=10.87 GPa and E⁎=215.54 GPa) for the HCSPN sample. Compared with the untreated 42CrMn steel, all the nitrided samples possess increased fracture toughness. Because the workpiece was not used as a discharge cathode, this HCSPN treatment overcame the disadvantages of the conventional CPN treatment. Additionally, results showed that the surface of the HCSPN sample was smoother than that of the CPN sample, and its tribological performance was better.

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.

A high-flux-density hollow cathode plasma source for the studies on plasma surface interactions

A new type plasma generator based on hollow cathode discharge has been designed and installed on the linear magnetic device, for the researches on helium and hydrogen plasma interaction with plasma facing components. The hollow cathode plasmas for argon/helium/hydrogen discharges were realized. The performances of the hollow cathode source were analyzed based on argon discharges, such as the electron temperature and electron density with respect to radial position, gas flow rate and magnetic field. The plasma parameters have been measured with Langmuir probe on the linear magnetic device. It shown that this hollow cathode source could provide ion flux density up to 1022m−2s−1 with high gas efficiency and energy efficiency. Typically, for argon plasmas, it could reach an electron density of 2×1019m−3 and an electron temperature of 3.5eV in core region, with a power dissipation of 1kW and gas flow rate of 0.25 standard liters per minute. The plasma beam with a radius of 2.5cm was confined very well with a magnetic field around 0.05T. By the virtue of these properties, this plasma generator is a good candidate for the fusion related plasma-surface-interaction researches.

Electrostatic Tether Application for Scattering of Relativistic Particles in the Earth’s Radiation Belts

An electrostatic tether could be a recent technology application for removing energetic particles in the earth’s radiation belts. Both hollow cathode and high-voltage source will keep the conductive tether at high positive/negative bias. An effective Coulomb deflection of the particles into the loss cone will produce a high rate of atmospheric penetration, decreasing the amount of high-energy particles in the radiation belts. This paper focuses on the high positive-bias case with a sheath that is correctly modeled. For small radius and extremely high bias, the tether does collect the relativistic orbital motion limited current. Relativistic effects modify both potential and density profiles, decreasing the range of the sheath and, in turn, increasing tether current collection. The remediation time will increase if relativistic effects are considered. A remediation time of about six years is determined for 100 1-MV tethers moving in a circular equatorial orbit at an altitude of about 2000 km. In addition, the presence of both Coulomb and Lorentz forces may induce thrust or drag on the tether. Both forces are briefly studied with plasma condition characteristic of the inner radiation belt.

Novel experimental setup for time-of-flight mass spectrometry ion detection in collisions of anionic species with neutral gas-phase molecular targets.

We report a novel experimental setup for studying collision induced products resulting from the interaction of anionic beams with a neutral gas-phase molecular target. The precursor projectile was admitted into vacuum through a commercial pulsed valve, with the anionic beam produced in a hollow cathode discharge-induced plasma, and guided to the interaction region by a set of deflecting plates where it was made to interact with the target beam. Depending on the collision energy regime, negative and positive species can be formed in the collision region and ions were time-of-flight (TOF) mass-analysed. Here, we present data on O2 precursor projectile, where we show clear evidence of O– and O2– formation from the hollow cathode source as well as preliminary results on the interaction of these anions with nitromethane, CH3NO2. The negative ions formed in such collisions were analysed using time-of-flight mass spectrometry. The five most dominant product anions were assigned to H–, O–, NO–, CNO– and CH3NO2–.

Phase Resolved Imaging of a Repetitive Extrusion of Hydrogen Plasma From a Hollow Cathode Source

Hydrogen plasmas are useful in many areas of materials processing. In this paper, a hydrogen plasma is produced in a hollow cathode source and its expansion into a chamber over the course of an RF cycle (80 ns) is observed with an intensified CCD camera. The source is observed to launch plasma down into the expansion region once per RF cycle. The shape of the extrusion suggests a surface wave carries charge down the inside of the glass tube, before the plasma collapses back to the center of the tube downstream from the source. At the end of the RF cycle, the plasma in the tube is seen to completely detach from the source plasma.

Optical Emission Spectroscopy of Carbon Clusters Produced in a Hollow Cathode Sputter Source

ABSTRACT A hollow cathode sputter source is developed to trace the production of carbon clusters and study the influence of discharge current and argon gas pressure on cluster production using an optical emission spectroscopic technique. Optical emission spectra from the hollow cathode source reveal the production of the C2 Swan band. The sputter source is optimized for the maximum carbon cluster yield. The vibrational temperature analysis of the C2 cluster is carried out using the Boltzmann plot method. The dependence of vibrational temperature on argon gas pressure is discussed and the dominant method for C-C association in the glow discharge is suggested.

Interactions between arrayed hollow cathodes

An array of novel hollow cathode plasma sources of 4 mm diameter and driven by up to 500 W of 13.56 MHz rf power was constructed. It was investigated using spatially resolved Langmuir probe measurements in the plasma expansion region. Initial results suggest the plasma observed downstream is the combination of a diffusion from the exit orifice of the 30 mm long cylindrical source region and a uniform plasma created in the expansion region. By measuring the ion density of the plasma plumes produced by two or more active hollow cathode sources, their mutual interaction has been inferred with the aim of determining whether a much larger array of sources could be envisioned. The effectiveness of the plasma in dissociating reactive species was tested using SF6 and measuring etch rates on unbiased silicon wafers. The results have been modelled and show that it is possible to produce a uniform spread of ±5%.

Development of a hollow cathode plasma source for microcrystalline silicon thin films deposition

The development of a hollow cathode plasma source and its implementation in an already existing plasma reactor used for the deposition of μc-Si:H thin films is presented. Electrical measurements of hydrogen discharges at 13.56 MHz were carried for two different in geometry hollow electrodes and the electrical parameters were compared with a previous Capacitively Coupled source installed in the same reactor. The results show a significant enhancement of discharge current and higher power dissipation for the same applied voltage. At reduced gas pressures that are necessary to minimize the dust formation, the hollow electrode with the larger cavity geometry showed better performance, achieving high electron densities of above 109 cm−3. Microcrystalline silicon thin films were deposited from SiH4/H2 discharges and an enhancement of the growth rate was found for the hollow cathode source as compared with the CCP source.

Stabilization of the spectrum position in the main stellar spectrograph of the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences

New results on the stability analysis study of the Main Stellar Spectrograph of the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences when it operated jointly with the CCD detection system on a laboratory source are reported. The spectrum is found to drift along the dispersion direction for several tenths of a pixel (several hundredths of angstrom) over a one-hour time scale. To prevent this drift (i.e., the spectrum shift)—a plane parallel glass plate is mounted; tilt angle of this plate varies as a function of the misalignment between the current and reference spectra of a hollow-cathode tube laboratory source. Operation of the spectrum stabilizer is described. The correction time is of about 1 minute, allowing the position of the spectrum to be maintained to within ±0.0006A.

Hollow cathode and hybrid atmospheric plasma sources

Abstract Generation and features of the radio frequency (RF) hollow cathode discharge (HCD) are compared for the atmospheric and moderate pressures. The atmospheric-pressure plasma systems, fused hollow cathode (FHC) and hybrid hollow electrode-activated discharge (H-HEAD), are described. Examples of applications where both FHC and H-HEAD have already been employed are given, and potentials for new processes are discussed.

Comment on "Argon I Lines Produced in a Hollow Cathode Source, 332 nm to 5865 nm".

Recent observations at the National Institute of Standards and Technology indicate that the Ar I wavenumbers reported by Whaling et al. [J. Res. Natl. Inst. Stand. Technol. 107, 149 (2002)] are systematically too large. To investigate the source of this problem, selected lines of Ar I and Ar II were remeasured in the same spectra used by Whaling et al. The measurements show that the Ar I wavenumbers of Whaling et al. are systematically shifted with respect to the Ar II wavenumbers previously reported by Whaling et al. [J. Quant. Spectrosc. Radiat. Transfer 53, 1 (1995)] based on the same spectra. The Ar I wavenumbers can be corrected by a constant multiplicative correction of 0.999 999 933.

Separation and Determination of Iron-Containing Proteins via Liquid Chromatography−Particle Beam/Hollow Cathode−Optical Emission Spectroscopy

Presented here is a method for the quantitative determination of iron-containing metalloproteins. Four iron-containing metalloproteins (transferrin, myoglobin, hemoglobin, and cytochrome c) were separated by high-performance liquid chromatography (HPLC) and determined through particle beam/hollow cathode-optical emission spectroscopy (PB/HC-OES) by the Fe (I) 371.9 nm optical emission. Parametric optimization of sample introduction, nebulization, and hollow cathode source conditions is performed for the suite of Fe-metalloproteins. Response curves for the Fe (I) emission were obtained under optimized conditions with detection limits for triplicate injections occurring on the nanogram level for iron ( approximately 24 ng) with variability of <7% RSD over the concentration range of 0.1-100 microg/mL iron in the metalloproteins. Response curves for S (I) emission yielded similar analytical characteristics. Optical emission detection of the liquid chromatography separations of the iron-containing metalloproteins demonstrates the feasibility of the PB/HC-OES system as a simple element-specific detector for liquid chromatography. The retention times of the four analytes are similar to those determined by UV absorbance (216 nm), demonstrating the ability of the PB interface to preserve the chromatographic integrity of the separation. Additionally, empirical formula calculations based on Fe (I) and S (I) emission response ratios provide a much higher level of specificity than single-element protein determination.

Isotope shifts and accurate wavelengths in Ne II and Ne III

Transition isotope shifts of 3s–3p transitions in Ne II and Ne III are measured in Fourier transform spectra from a hollow-cathode source. Accurate absolute line-center positions of the 20Ne isotope are derived for the purpose of tertiary wavelength standards in the region 2000–5000 A. A robust statistical treatment is applied, yielding line-position uncertainties that are lower than for the Ar II secondary standards used as references. The influence of Stark shifts on both the new Ne II standards and the Ar II standards is also investigated. In addition, improved wavenumbers of the 3p–3d and 3p–4s transitions are presented, of which 12 in Ne II have been measured for the first time.