Neon Glow Discharge Research Articles

Inexpensive THz Focal Plane Array Imaging Using Miniature Neon Indicator Lamps as Detectors

Development of focal plane arrays (FPAs) for mm wavelength and THz radiation is presented in this paper. The FPA is based upon inexpensive neon indicator lamp Glow Discharge Detectors (GDDs) that serve as pixels in the FPA. It was shown in previous investigations that inexpensive neon indicator lamp GDDs are quite sensitive to mm wavelength and THz radiation. The diameters of GDD lamps are typically 3-6 mm and thus the FPA can be diffraction limited. Development of an FPA using such devices as detectors is advantageous since the costs of such a lamp is around 30-50 cents per lamp, and it is a room temperature detector sufficiently fast for video frame rates. Recently, a new 8 × 8 GDD FPA VLSI control board was designed, constructed, and experimentally tested. First, THz images using this GDD FPA are given in this paper. By moving around the 8 × 8 pixel board appropriately in the image plane, 32 × 32 pixel images are also obtained and shown here, with much improved image quality because of much reduced pixelization distortion.

Disalignment rates of the neon 2p5 and 2p10 atoms due to helium atom collisions measured at temperatures between 77 and 294 K

Using a positive column of helium–neon glow discharge plasma at several temperatures between 77 and 294 K, the disalignment rates of excited neon atoms in the 2p5 and 2p10 (in Paschen notation) levels are measured by a polarization-resolved laser-induced fluorescence technique. For the 2p10 case, the disalignment rate due to radiation reabsorption is evaluated from the optical thickness of the plasma measured by a self-absorption method, and then is subtracted from the disalignment rate measured. From the slope of the obtained disalignment rate plotted against the helium atom density we determine the rate coefficients due to helium atom collisions. These rate coefficients are compared with the results of quantum multi-channel close-coupling calculations using the modified long-range potentials proposed by Bahrim and Khadilkar (2009 Phys. Rev. A 79 042715) from the original potentials of Hennecart and Masnou-Seeuws (1985 J. Phys. B: At. Mol. Phys. 18 657). Our present experiment agrees excellently with the theory for the 2p5 level at any temperatures between 77 and 294 K, and for the 2p10 state only at 294 K. Below 294 K, the experimental rate coefficients for the 2p10 state show a more rapid decrease with the decrease in temperature than the theory predicts.

Temperature effects on the width, shift and asymmetry of 748.8 nm self-broadened neon line

The influence of temperature on the shape of the self-broadened 748.8 nm Ne line emitted from the low pressure glow discharge of neon was investigated with a Fabry-Perot interferometer. Detailed analysis showed departures of the registered line shapes from the ordinary Voigt profile. These departures were consistent with fits of the speed-dependent asymmetric Voigt profile to experimental profiles. The values of the pressure broadening, shifting and collision-time asymmetry were determined and compared with those calculated in the adiabatic approximation for the van der Waals and Lennard-Jones potentials.

Wall Conditioning in LHD

Wall conditioning in the Large Helical Device (LHD) has been conducted successively since the first experimental campaign in 1998. The effects of wall conditioning on the vacuum condition, the plasma performance, and the surface modification of the plasma-facing components have been analyzed by both macroscopic and microscopic observations such as residual gas analysis and transmission electron microscope observation, respectively. The main tools for the conditioning are mild baking (95°C); glow discharges with hydrogen, helium, and neon; and wall coating with titanium and boron. Though the baking temperature is lower than in other fusion devices, it reduces impurity gases well just after the start of vacuum pumping, and it reduces retained hydrogen in plasma-facing components during the experimental campaign. Helium glow discharge was revealed to cause heavy damage on the surfaces of metallic components and the contamination of the hydrogen discharges with helium released from wall. Neon glow discharge has been conducted since it causes much less damage and hastens the conditioning of the wall. Boronization is very effective to reduce oxygen impurity in plasma, and the effects last for the whole experimental campaign in LHD.

Asymmetry and speed-dependent effects on the 748.8 nm self-broadened neon line

Using an interferometric method, detailed analysis of the self-broadened 748.8 nm Ne line shapes emitted from the glow discharge of neon was performed, where departures from the ordinary Voigt profile were observed. These departures are shown to be consistent with fits of the speed-dependent asymmetric Voigt profile to experimental profiles. It was shown that neglecting the correlation between Doppler and collisional broadening may cause errors in determined line shape parameter values. Coefficients of the pressure broadening, shift and collision-time asymmetry are determined and compared with those calculated in the adiabatic approximation for the van der Waals and Lennard-Jones potentials.

Advances in Boltzmann equation based modelling of discharge plasmas

The paper reports on advances in numerical modelling of gas discharge plasmas with the focus on hybrid methods which combine a fluid description of the plasma species with the solution of the Boltzmann equation of the electrons. The time- and space-dependent treatment of the kinetic equation of the electrons is based on the two-term approximation of the velocity distribution function and the quasi-stationary description of the anisotropic part of the velocity distribution. Basic aspects of the hybrid approach are given and the integration of the kinetic equation of the electrons into the self-consistent description of non-isothermal plasmas is represented. New hybrid methods have been applied to analyse the spatiotemporal evolution of one-dimensional glow discharge plasmas in inert gases. In particular, the relaxation behaviour of a neon glow discharge disturbed by a short laser pulse and the periodic evolution of the radially inhomogeneous column plasma of a He–Xe lamp discharge are discussed.

Hydrogen and helium removal retained in stainless steel by neon glow discharge

In order to examine the effect of neon glow discharge on hydrogen or helium removal, neon glow discharge was conducted for the stainless steel after the exposure to hydrogen or helium glow discharge, and then the amount of desorbed hydrogen or helium and retained neon were evaluated. Large hydrogen desorption was observed at the initial period of the neon discharge following the hydrogen discharge. The removal ratio of retained hydrogen by the neon discharge with 2 h was 1.3 times larger than that by the argon discharge, and a half of that by the helium discharge. In the case of the neon discharge following the helium discharge, the removal ratio of retained helium was 4 times larger than that by the argon discharge. The amount of retained neon was an order of magnitude smaller than that of helium retained in the stainless steel.

Response of an Isolated Particulate Subjected to Lateral Electric Fields in a DC Glow Discharge

Isolated spheres of borosilicate glass are suspended in a dc glow discharge in neon. The isolated sphere is laterally displaced by applying a transient voltage across a pair of electrodes mounted on the wall of the discharge tube. By monitoring the response of the particulate when subjected to a step change in the voltage and to sinusoidally varying voltages of different frequencies, the charge on the suspended sphere is inferred. Unlike most previous studies, this paper considers heavier (from 16 to 42 times heavier) particulates and heavily damped conditions. Measurements are reported for 20.3- and 4.9-mum -diameter borosilicate glass spheres. It is found that lateral excitation of an isolated particulate in a dc glow discharge cannot drive the motion to classical resonance as has been observed in previous work involving axial displacements in RF plasmas. The classical forced damped oscillator model used successfully in previous work to explain experimental observations is found to be inadequate for the conditions of this paper. Rather, the base excitation (BE) model is found to exhibit good agreement with the present experimental results at frequencies exceeding the frequency at which the displacement is a maximum. Sheath polarization, neglected in previous work, is included in this paper. It is found that drag due to collisions with neutrals is insufficient to account for the total drag on the particulate under heavily damped conditions. A new means of estimating the charge from the frequency response of the particulate motion using the BE model is described. Based on this method, charge numbers of Z = 9.2 times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> and Z = 1.5 times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> are inferred for the 20.3- and 4.9-mum spheres, respectively.

Imaging of Dielectric-Barrier Glow Discharge in Neon

In this paper, we present images of light emission by the plasma in a planar dielectric-barrier glow discharge in pure neon. The images have been obtained using an intensified charge-coupled device digital camera at nanosecond exposure time. The time-dependence discharge images for lower and higher frequency at a constant voltage are presented.

Spatiotemporal Relaxation of a Disturbed Neon Glow Discharge

In this paper, spatiotemporal relaxation of a neon glow discharge plasma is theoretically investigated. The study concerns the positive column and the adjacent anode region. The relaxation is initiated by a short laser pulse that disturbs the column plasma by depopulating the metastable atoms near the cathode-sided boundary of the considered region. The resulting decrease of the ionization rate initiates a spatiotemporal relaxation of the plasma in the downstream region, which is similar to ionization waves. In accordance with the chosen discharge parameters, ionization waves of p-type are generated. After about 3-4 ms, relaxation is finished, and the undisturbed state is reached. The theoretical investigations are based on a self-consistent hybrid model comprising a fluid description of all relevant plasma components, the solution of the Poisson equation, and a spatially resolved kinetic treatment of the electrons.

Temperature dependence of the width and shift of the selfbroadened 748.8 nm neon line

Effect of temperature on the collision half-width and shift of the 748.8 nm neon line emitted from a low-pressure glow discharge in pure neon has been investigated with a Fabry-Perot interferometer.

Collisional–radiative model of neon discharge: determination of E/N in the positive column of low pressure discharge

A method for the determination of the reduced electric field strength (E/N) in a neon discharge from the optical emission spectra was developed. This method is based on a collisional–radiative model, which was used to calculate the emission spectra of the neon plasma. In the model, populations of 30 excited levels of the neon atom were studied. Various elementary collision processes were taken into account: electron impact excitation, de-excitation and ionization of neon atoms, emission and absorption of radiation, metastable–metastable collisions, metastable and radiative dimer production, Penning ionization, etc. To determine the rates of electron collisions, the Boltzmann kinetic equation for the electron distribution function (EDF) was solved for given E/N, and thus the dependence of the emission spectra on E/N could be determined. The EDF was expanded in terms of Legendre polynomials and the first two terms of this approximation were taken into account. The theoretical emission spectra were fitted by the non-linear least-squares method to the measured spectra with respect to the unknown parameter E/N.The method was applied to the study of low pressure dc glow discharge in neon. In such a discharge the calculated reduced electric field strength could be compared with the independent results of simultaneously performed electric probe measurements of E/N. Generally, close agreement of the calculated values with the experimental data was achieved.

Role of ions in the abnormal glow of the plasma–cathode interface of neon glow discharges

Experimental and theoretical studies of the luminescence of cathode zone of Ne/(Fe cathode) glow discharges are reported. The dependence of line intensity I( λ) on the discharge parameters (gas pressure p, current density j d and position x) was experimentally investigated by optical emission spectrometry (OES). The measured characteristics I( λ) =f( p, j d , p, x) were discussed based on complex modeling of the plasma–cathode interface. A few examples of Ne species excitation such as the electron–atom interaction and the participation of metastable Ne m atoms were considered. The fast Ne + ions interaction with Ne atoms and the cathode surface is concluded finally to be the dominating process affecting the line emission of all neon species occurring in the plasma–cathode interface.

Numerical Analysis and Simulation Analysis for Space‐Time Data

AbstractSpatio temporal dynamics of the positive column of a dc neon glow discharge is studied and investigated experimentally and theoretically. Spatio temporal analysis by means of biorthogonal decomposition method (BOD) gives insights into the mechanism of irregularity and can be employed for characterization of spatio‐ temporal complexity. In the weak nonlinear region, the wave dynamics is approximated by an amplitude equation of the Ginzburg‐Landau equation (CGLE) with complex coefficients and an additional integral term based on a fluid model. In the present work we deal with irregular spatio‐temporal data. A comparison between the numerical analysis of the experimental data and simulation results are studied. A good agreement between the dynamical behaviour for experimental space‐time data and theoretical simulation space‐time results was obtained. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Observation of intermittent states and nonlinear wave–wave interaction in neon glow discharges

In the plasma of a neon glow discharge under certain conditions two waves (s- and p-wave) are known to exist simultaneously. The transition region between these two kinds of waves is experimentally investigated in the space of plasma parameters. An intermittent behaviour of s- and p-waves dynamics is proved by the analysis of the recorded spatio-temporal patterns of light emitted by plasma. The experimental data are analyzed with the biorthogonal decomposition (BOD) and the empirical mode decomposition (EMD), respectively. The wave states can be described by means of a coupled system of amplitude equations resulting from a hydrodynamic plasma model. Comparison of experimental data and theoretical predictions shows satisfactory agreement. The discrepancies are discussed.

Time series analysis of ionization waves in dc neon glow discharge

The dynamics of dc neon glow discharge is examined by calculating a Lyapunov exponent spectrum (LES) and correlation dimension (Dcorr) from experimental time series. The embedding theory is used to reconstruct an attractor with the delay coordinate method. The analysis refers to periodic, chaotic, and quasi-periodic attractors. The results obtained are confirmed by a comparison with other methods of time series analysis such as the Fourier power spectrum and autocorrelation function. The main object of the present work is the positive column of a dc neon glow discharge. The positive column is an excellent model for the study of a non-linearity plasma system because it is nonisothermal plasma far from equilibrium.

Equipment for measurements of radial profiles of excited species in DC glow discharge

The original experimental device for studying the radial dependences of emitted radiation, generated by the cylindrically symmetric positive column of the DC glow discharge, is proposed. Principle of detection of the radial intensity profiles of the spectral lines by means of the special scanner with two movable conic mirrors is described. The function of the scanner was verified experimentally and by the method of raytracing. As an example, the radial profiles of lines emitted by the positive column of the neon glow discharge are presented. No significant changes were found.

Study of the dark phase in the initial stage of the positive column formation in a neon glow discharge

The initial stage of the positive column formation in a neon glow discharge is investigated both experimentally and theoretically. A decrease in the plasma radiation intensity (the so-called “dark phase”) was observed experimentally over a time period of about 1 ms. A similar dip was also observed in the time dependence of the electric field strength. The measured population of the lower metastable states of Ne was found to have a maximum at the beginning of the dark phase. A relevant theoretical model has been developed and used to perform calculations for the actual experimental conditions. A comparison between the numerical and experimental results shows that the model adequately describes the processes that occur during the formation of the positive column in a neon glow discharge. Experimental and theoretical studies show that the dark-phase effect is related to the excessive amount of metastable Ne atoms at the beginning of a discharge and, accordingly, to the high rates of stepwise ionization and chemionization.

Ionization fronts and their velocities in a coupled Ginzburg-Landau model

The nonlinear dynamics within the transition region between p and s waves is studied for a neon glow discharge. Starting from a coupled set of complex Ginzburg-Landau equations, the coherent ionization waves are studied where we focus on a special subclass of uniformly translating front solutions. A stability analysis is performed to give necessary conditions for the existence of wave fronts and limits of their velocities. It is shown that the wave fronts that mark the transition between s and p waves, respectively, propagate with different velocities. The front velocities strongly depend on the chosen plasma parameters. The analytical results are supplemented by numerical simulations for selected values of the plasma parameters that have relevance to experimental results.

Temporal and spatial formation of the glow discharge in neon filled diode at 4 mbar pressure

The results of the investigation of the glow discharge time and space development in the neon-filled diode at 4 mbar are presented. The glow is of the diffusion type with saturation current value 0.2 mA. The temporal development of current and light intensity of the 585.2-nm line (originated from the negative glow) emitted perpendicularly on the diode axis from different parts of the diode, are registered. Electrically registered (by the oscilloscope), the total current through the diode reaches the saturation for 3 ms, which corresponds to the formative time delay. On the other hand, the value of the formative time delay estimated statistically from the series of 5000 breakdowns is 4.7 ms. The difference in formative time delays is associated with the pre-breakdown current growth in the gap. The prebreakdown current is registered measuring the emitted light from diode gap. The investigation of light shows the increase of excitation in the gap at least 1.25 ms before any significant current is registered (I<1 /spl mu/A). The negative glow appears in the diode gap and in the next a few milliseconds covers the cathode, which indicates the presence of the multiplication processes in diode. The stationary regime in the diode is established for about 10 ms. These results show the validity of the statistical approach in the breakdown time delay investigations and in the understanding the nature of the formative time delays.