Comparison of Spectra Excited in HF and DC Hollow Cathode Discharges

Spectra excited in hollow cathode discharges operating at high frequency (27.2 MHz) and direct currents have been compared. The cathodes made of copper, brass and steel and argon as a carrier gas were used. Line intensity ratios (I_hf/I_dc) for species excited at different pressures have been investigated and discussed.     

Fluorine Determination and Matrix Effects in DC and HF Hollow Cathode Discharges

Abstract

The InF bands excited in a hollow cathode discharge have been used for fluorine determination in solid samples (containing from 10^?6 to 10^?1% F) and solutions (at the F^? concentrations from 1 μg/ml to 1 mg/ml). The discharge operated at direct current (dc) or high frequency current (hf). A dependence of the InF band intensities on the fluorine concentration has been investigated. Matrix effects caused by some metals and halides have been studied and discussed.     

Theory of Optogalvanic Signals Originating from Metastable States in Hollow Cathode Neon Discharges

A previous theoretical model is enlarged to elucidate some features of the optogalvanic signals originating from the metastable states in hollow cathode neon discharges. Numerical experiments were performed on the basis of this model to obtain the time evolution of the optogalvanic signals in pulsed and chopped cw experiments at 588.2 nm for different discharge currents and different laser intensities. The predictions of the numerical experiments were found to be in qualitative agreement with real experimental results.     

Comparison of Radial Helium Emission Line Profiles in Transverse and Longitudinal Hollow Cathode Discharges

Results of measurements of the radial distributions of intensities of the He I and He II spectral lines emitted by the transverse and longitudinal hollow cathode discharges direct current excited are presented. The results show that both hollow cathode discharges exhibit different excitation efficiency of the spectral lines. The metastable level 2s³S seems to be important for excitation of He I emission lines.     

Generation of Plasma with Increased Ionization Degree in a Pulsed High-Current Low-Pressure Hollow Cathode Discharge

Russian Physics Journal - The paper presents the results of research of the processes of generation of pulsed beam-plasma formations in a high-current non-self-sustained glow discharge with a...     

Application of Diode Lasers to Determine Excitation Temperature in Hollow Cathode Discharges by Optogalvanic Spectroscopy

The excitation temperatures of sputtered gadolinium and uranium atoms in an argon hollow cathode discharge have been determined by diode laser-excited optogalvanic spectroscopy. These results have been compared to those determined by conventional emission spectroscopy. It was found that the temperatures derived from each method do not differ very much, but the optogalvanic method revealed a better standard deviation uncertainty due to the good signal-to-background ratios and excellent spectral resolutions. Temperature variations with discharge currents ranging from 15 to 50 mA have been examined.     

Some Investigations of the Ignition and Development of Breakdown in Cylindrical Hollow Cathode Glow Discharges

The breakdown behaviour of a hollow cathode glow discharge is investigated in a cylindrical, hollow cathode structure having an internal diameter of 2 cm. The anode is a plane electrode across one end of the cathode cylinder. Pressures of argon between 20 and 107 Pa were used (0.15 to 0.80 torr), and applied voltages between 800 and 2500 V. It is shown that the statistical time lag for breakdown is in the range of ～ 1 ms and depends on the applied voltage, the gas pressure, and the history of operation of the discharge tube. The rise time of the discharge current ranges from about 10 ns at high pressure and voltage to about 200 ns at the lowest pressure and voltage used. The discharge propagates along the cathode axis at a speed of about 10⁸ cm s^?1. From the obtained data, a qualitative model of the first stage of the discharge is derived. Based on this model, a simple calculation gives values of Townsend modified first coefficient η at high values of E/N, 10⁴ < E/N < 8 · 10⁴ Td which fit well at the lowest E/N, where they approach the data of PENNING and KRUITHOF in argon. In contrast to the extremely short initial current-rise times, in the submicrosecond range, the discharge currents reach steady-state values only after about 300 μs.     

Experimental Measurements on the Current Balance at the Cathode of a Cylindrical Hollow Cathode Glow Discharge

The contribution of positive ions, photons and metastable particles to the secondary emission of electrons from the cathode of an argon glow discharge with cylindrical cathode is measured by sampling the plasma species through a small orifice in the cathode wall and analyzing them in a high vacuum region. Additional experiments are made with a second apparatus which enables the sampling fo plasma species from the negative glow and the dark space. The paper describes the experimental techniques used in both cases and presents estimates on the validity of the results obtained. The positive ions are found to be the dominant contribution to the discharge current at the cathode. The secondary emission of electrons is — in decreasing order of importance — due to impact fo singly charged ions, doubly charged ions and metastable atoms.     

Emission Characteristics of the D.C., 100 kHz and 13.5 MHz Hollow Cathode Discharges

Hollow cathode discharges in argon at various pressures and currents have been studied by optical emission spectroscopy. The cathodes were made of copper, bronze and brass. The discharges were supplied by direct, 100 kHz and 13.5 MHz currents. Atomic and ionic spectra of plasma gas and elements of cathode materials and molecular bands of ZnH and PN formed due chemical reactions between plasma components have been excited and measured. Relations between emission intensities, excitation temperatures and discharge conditions have been analysed and discussed.     

The Experimental Study of Novel Pseudospark Hollow Cathode Plasma Electron Gun

The high-power microwave devices with plasma-filled have unique properties. One of the major problems associated with plasma-filled microwave sources is that ions from the plasma drift toward the gun regions of the tube. This bombardment is particularly dangerous for the gun, where high-energy ion impacts can damage the cathode surface and degrade its electron emission capabilities. One of the techniques investigated to mitigate this issue is to replace the material cathode with plasma cathode. Now, we study the novel electron gun (E-gun) that can be suitable for high power microwave device applications, adopting two forms of discharge channel, 1: a single hole channel, the structure can produce a solid electron beam; 2: porous holes channel, the structure can generate multiple electronic injection which is similar to the annular electron beam.     

An Observation of Energetic Electron Beams in Low-Pressure Linear Discharges

Experimental observations of energetic axial electron beams in a linear Z pinch operating in the pseudospark mode are presented. The device is driven from a fast Marx generator and allows reproducible production of electron beams over a wide pressure range. Evidence of the importance of electrons generated in the cathode recess in the formation of the beams is presented. An electron beam of high energy which is not associated with formation of the discharge is identified. A second beam of high current density and lower energy associated with gas breakdown is also observed.     

Influence of Surface Contaminations on Cathode Processes of Vacuum Discharges

The influence of surface contaminations on the ignition and maintenance of vacuum discharges is discussed qualitatively. Surface analysis of the electrodes and gas analysis during the discharges demonstrate that fresh electrodes contain always impurities within the upper surface layers, which affect the behaviour of vacuum arcs and vacuum breakdowns. The most effective way for cleaning the surfaces are the discharges themselves, if they burn in UHV. During that cleaning the following variations have been found: Are cathodes spots change from rapid moving ones with small erosion (type 1) to slow ones with strong erosion (type 2). The ignition of nanosecond discharges needs higher field strength and field emission current density. Polishing effects by short discharges (< 5 ns) become more pronounced. Erosion craters in nanosecond discharges increase.     

The Harmonic Distortion Factor of the Current of Radio-Frequency Low-Pressure Discharges

In order to characterize an r.f. low-pressure discharge in diode systems which are capacitively coupled to the r.f. generator the content of harmonics in current and voltage is experimentally investigated. The discharge-conditioned content of harmonics in the voltage is practically negligible. The spectrum of the discharge current is qualitatively and quantitatively dependent on the whole reactor/generator arrangement producing the discharge. For an asymmetrical diode with a self-excited generator it is shown that the content of harmonics in the discharge current is highly dependent on the radio-frequency voltage, the d.c. self-bias of the r.f. electrode, the effective power and the pressure. Conclusions are discussed concerning a connection between the content of harmonics, on the one hand, and carrier-density modulation and power dissipation at the substrate electrode, on the other hand.     

Electrolyte Cathode Atmospheric Glow Discharges for Direct Solution Analysis

Abstract

The electrolyte cathode atmospheric glow discharge (ELCAD) invented in 1992 is a new optical emission source with upcoming application in the field of environmental protection as an outstanding instrument for monitoring the toxic heavy metal content of waters and wastewaters. The main operating parameters, mechanisms (secondary electron emission from the electrolyte cathode, self‐sustaining processes in the cathode dark space, dependence of the emitted line intensities on the discharge parameters, temperatures), and the analytical performance of this special discharge are presented through a critical review using the papers related to the ELCAD published from 1993 to 2006.     

Glow Discharge with an Extended Hollow Cathode

Russian Physics Journal - A low-voltage low-pressure glow discharge with a hollow cathode is discussed. The discharge is ignited in a reflective discharge system with two symmetric peripheral...     

Hollow-Cathode Low-Pressure Arc Discharges and Their Application in Plasma Generators and Charged-Particle Sources

This paper presents the results of a study of hollow-cathode arc discharges which generate gas-discharge plasmas of densities 10¹⁰–10¹² cm^–3 in large volumes (1 m³) at low pressures (10^–2–1 Pa) and at discharge currents of up to 200 A. Consideration is given to the design and peculiarities of hot-cathode and cold-cathode discharge systems. The parameters of plasma generators and charged-particle sources where use is made of arc discharges are cited and the problems of the most efficient application of such systems in technological processes of solid surface modification are discussed.     

Magneto-Galvanic Resonances in Hollow Cathode Discharge Lamps

The galvanic behavior of a hollow cathode discharge versus an external weak magnetic field is investigated. The application of this field leads to disordering of the self-aligned states, which is detected as a resonance in the discharge current, named the magneto-galvanic signal. A correlation magneto-galvanic signal–operating voltage-current point is established and attributed to Penning ionization. The contribution of the metastable Ne I 1 s₅ to the magneto-galvanic resonance is also verified.     

Plasma Parameters Near a Hollow Rectangular Cathode

Journal of Applied Spectroscopy - A single probe method is used to obtain the electron density and electron energy distribution function in a short discharge gap between a rectangular hollow...     

Pulsed Hollow Cathode Discharge with Nanosecond Risetime

This paper reports the operation of a cylindrical hollow cathode discharge with current risetimes of a few nanoseconds at current densities at the entrance of the cathode in the range of 50-560A · cm-2 and at voltages of 280-850 V. Time-dependent measurements of the impedance of the discharge are presented. They allow for the evaluation of discharge quantities such as risetime, delay time, discharge voltage, and current, depending on the operation parameters as applied voltage, pressure, and preionization. The power density in the active region of the hollow cathode exceeded 200 kW · cm-3.