Positive Column Of Discharge Research Articles

Allowed and forbidden transitions of singlet helium high Rydberg states

Allowed and forbidden transitions of singlet helium from 2s1S to ns1S, np1P, and nd1D states have been measured between n=8 and 31 by optogalvanic spectroscopy in a dc discharge positive column. The addition of neon in the discharge was found to increase the relative intensities of the forbidden transitions. For similar photon flux, the optogalvanic signal reaches a maximum at n=11 and decreases thereafter. Neutral collisional ionization of the excited states from n=13 and above was found to be responsible for the increased ionization efficiency of the high Rydberg states.

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Radial distributions of charged particles in an oxygen discharge depending on the relative concentration of negative ions are experimentally investigated. Corresponding change of the selfconsistent field along the radius of the discharge positive column at different pressures and currents are given.

Laser cooling of a direct-current atomic discharge

Light-induced heating and cooling of a positive column discharge are demonstrated by combining the optogalvanic and optoacoustic detection. The phenomena that we have observed for laser radiation resonant with several Ne and He transitions are compared with a simplified energy model.

Optogalvanic signals generated in a neon positive column discharge by resonant chopped cw radiation at 588.2 nm

The optogalvanic line profile for the 1s5-2p2 transition (Paschen notation) in a neon positive column discharge has been studied as a function of dye laser power (0–300 mW) and discharge conditions (2–20 mA, 1–2.5 Torr) for a variety of experimental arrangements, incorporating simultaneous absorption and emission studies. Under certain discharge conditions the sign of the optogalvanic signal changes as a function of dye laser power. A set of four rate equations describing the populations of the 1s5, 1s4, 1s3, and 2p2 levels in neon with and without resonant laser irradiation on the 1s5-2p2 transition at 588.2 nm are solved in the steady state. The steady-state values are used as initial values for numerical integration of the rate equations to show the time evolution of the various populations as the laser is switched on and off. A qualitative interpretation of the expected optogalvanic signal may be made from the results. In particular, it is seen that buildup in the 1s3 metastable density with laser irradiation on the 588.2-nm transition can explain the above observations of a sign reversal in a neon positive column discharge.

Optogalvanic signals generated in a neon positive column discharge by resonant chopped CW radiation at 588.2 nm

The optogalvanic line profile for the 1s 5−2p 2 transition (Paschen notation) in a neon positive column discharge has shown a change in sign as a function of dye laser power for a pressure of 1.5 Torr and small currents (2–20 mA). Rate equation analysis suggests this may be due to the increase in the 1s 3 metastable density.

An active filter for inert gas lines in a hollow cathode light source

The hollow cathode discharge tube has proved an excellent source for emission spectroscopy of metals, but in the red and near-infrared regions the limit of sensitivity for the detection of weak lines is set by scattered light or photon noise from the strong lines of the carrier gas, usually neon or argon. The paper describes an 'active filter' consisting of a long, low-current, positive column discharge in which an appreciable population of excited atoms is maintained in the lower levels of the lines in question, resulting in selective absorption of the hollow cathode radiation. Reduction factors of about 8 were achieved for lines starting from the two metastable levels. From subsidiary experiments on the reversal temperatures and equivalent widths of the filter discharge lines and on the widths and shifts of the hollow cathode lines, a simple radiative transfer model was constructed so that the effects of different discharge parameters on the reduction factors could be predicted. Of the various ways of increasing these, the most promising is to broaden the filter discharge lines by, for example, applying a magnetic field to the discharge.

Optogalvanic effects in the obstructed glow discharge

An anomalously strong 594.5-nm optogalvanic effect is observed in an obstructed glow discharge in 1.0 Torr of Ne occurring between plane parallel Al electrodes separated by 1.0 cm. The absolute size of a steady-state optogalvanic effect is characterized by a dimensionless ratio of the change in power delivered to the load resistor over the absorbed laser power. A ratio of −400 for the 594.5-nm effect is observed in the obstructed glow discharge, while ratios of −6 are typical for the 594.5-nm effect in the positive column discharge. The 594.5-nm effect in the obstructed glow discharge results from a laser induced depletion of metastable atoms which play an important role in electron emission from a cold cathode.

Light-induced drift of neon under optical excitation from a metastable state

A running light wave, resonant with the neon transition 1s 5-2p 2, has been found out to affect the spatial distribution of neon atoms in a positive discharge column. The effect has shown an antisymmetric dependence (typical of the light-induced drift) on the tuning out of the radiation frequency relatively the absorption line centre, as well as on the direction of the light wave vector.

Transient cataphoresis in a discharge tube with end volumes

A theoretical and experimental study has been made of time-dependent cataphoresis in a binary gas mixture when a dc discharge is initiated in a tube with end volumes behind the electrodes. The theoretical models as proposed by Shair et al. and Metze and Chanin are compared. Transient response curves of the impurity density, computed in accordance with the two models, are presented and discussed. The gas separation in the positive column of a dc discharge is also studied experimentally for a mixture of 0.025% argon in neon. The argon density is monitored at two locations within the positive column of the discharge using a mass spectrometer. The experimental data are compared with calculations based on the model formulated by Metze and Chanin. A good agreement between theory and experiment is obtained for the end-volume configuration under consideration.

Temperature dependence of the shift, width and asymmetry of the potassium (4p←7s) 5802 AA line perturbed by argon

The effects of temperature upon the Ar-perturbed K I 5802 AA emission line (4p 2P32/-7s 2S12/f) were measured with a Fabry-Perot interferometer. Low-pressure measurements were made between 443 and 760K in a positive-column discharge. Computer analyses of the line shapes are based upon the semiclassical theory in the impact approximation, and experimental values of shift, width and near-wing asymmetry are obtained. Empirically, the width varies approximately as T0.37+or-0.04. On the basis of an assumed potential form( Sigma nCn/Rn, the parameters C6 and C8 are adequate to yield shift and width values in close agreement with experiment. The experimental parameters set is C6 approximately=-8.3*10-56 erg cm6, C8 approximately=8.9*10-70 erg cm8 and C12 approximately=0. The importance of multitemperature measurements in reducing the ambiguity of C6 and C8 is demonstrated. The existence of the theoretically predicted near-wing red asymmetry is shown, and the experimental value is in quantitative agreement with the calculated value. The calculated K(7s)/Ar potential does not agree with the Baylis-type pseudopotential in which the effective noble-gas atom radius r0 corresponds to the ground state; however, a reduction in this radius yields moderately good agreement in the range R>or=19 AA, which is shown to be the approximate validity range for the potential derived from these low-pressure measurements.

Experimental measurements of time-dependent cataphoretic gas separation in a direct-current glow discharge when end volumes are present

A study has been made regarding the influence of end volumes on time-dependent cataphoretic gas separation in the positive column of a dc glow discharge containing 0.05% neon in helium. The neon 5400-Å-line intensity was monitored at several fixed points within the positive column of the discharge. The experimental data are compared with theoretical predictions based on the model formulated in the concurrent paper. The simplified model predicts the general features of time-dependent cataphoretic gas separation for the two end volume configurations considered.

Infrared optogalvanic spectroscopy in the helium positive column using an F-center laser

Using optogalvanic spectroscopy with a tunable cw F-center laser, we have detected helium transitions from the n=4 to the n=6 states between 2.61 μm and 2.7 μm. The observed sensitivity is in agreement with the predictions of a steady state model of the positive column discharge.

Study of density fluctuations in plasmas by small-angle CO2 laser scattering

Small-angle CO2 laser scattering techniques are described which provide detailed information about density fluctuations in plasmas. These techniques are nonperturbative and measure the frequencies, wave vectors, and amplitudes of the density fluctuations. The theories of the scattering and the heterodyne and homodyne detection processes are described in detail for the case of small-angle scattering. Several models are developed to describe recent experiments involving both coherent and stochastic fluctuations. The laser, detector, and physical arrangement used in the experiments are described in detail. Experimental studies of driven Bernstein waves, ion acoustic turbulence in a positive column discharge, and fluctuations in tokamaks are described to illustrate these techniques. It is demonstrated that CO2 laser scattering is useful in studying fluctuations with wavelengths between 0.01 and 1 cm and frequencies from 1 kHz to tens of giga-Hertz in plasmas with mean densities ranging from 1010 to 1017 cm−3.

A positive column discharge memory panel for color TV display

The dc gas-discharge display panel introduced combines internal memory characteristics with the positive column discharge, yielding high luminance and efficiency. The nature of the memory function is based on shifts in the discharge path between display and auxiliary discharge spaces. Because of this operating principle, the panel has a switching time as fast as 10 µs, enabling use of the panel for real-time color TV displays with 64 gray levels.

Population Densities of He Excited States in a Positive Column Discharge Used for the He–Cd+ Laser

The population densities of He excited states in a positive column discharge used for the He–Cd + laser were measured as functions of Cd atom density, initial He pressure, and discharge current with the modified absorption method. They were also calculated with the aid of the electron energy distribution function obtained from the Boltzmann equation. It has been shown that the variations of the population densities of the He(I) 2 3 S and 2 1 S states with the discharge current can be interpreted theoretically only when a new electronic collision process, He(2 3 S or 2 1 S)+ e →He(2 3 P or 2 1 P)+ e , is taken into account.

Scaling of positive-column Hg—Ar discharges towards display cells

Measurements are presented of the ultraviolet output and the electric field of Hg-Ar positive-column discharges with diameters 2R ranging from 0.5 to 5 mm. The UV exitance and efficiency remain constant (and equal to that of the standard fluorescent tube), provided the pressures are scaled in proportion to 1/R . From the existing models of the Hg-Ar column a parametric description is obtained. When full account is given of collisional line broadening in the transport of resonance radiation, comparison of measurements and model leads to the conclusion that they are not in agreement. The UV measurements suggest that the electron temperature remains constant at constant pR , which is also in disagreement with the models.

Measurements of gain in the hollow-cathode He—Zn laser

Small-signal gain measurements have been made for cw transitions of the hollow-cathode He—Zn laser using an oscillator-amplifier configuration. Maximum recorded gains at line-centre along the axis of the gain tube were 340%, 80%, 28% and 16% per metre respectively for the Zn + transitions at λ 7588, 4924, 7479 and 5894 Å. The results illustrate the superiority of the hollow-cathodeover the positive-column discharge for Duffendack (charge transfer)-excited laser transitions.

Effect of xenon on the electrical parameters of the positive discharge column of carbon dioxide gas with helium and xenon

Effect of xenon on the electrical parameters of the positive discharge column of carbon dioxide gas with helium and xenon

Investigation of the processes of neon excitation in the heliumneon mixture in the cathode region and in the positive discharge column

Investigation of the processes of neon excitation in the heliumneon mixture in the cathode region and in the positive discharge column

Experimental study on influence of cooling on glow discharge parameters

The influence of cooling of the discharge tube walls by the liquid nitrogen on some basic parameters of the neon glow discharge positive column is studied. By probe measurements, the longitudinal electrical fieldEz, the electron concentrationne and the electron temperatureTe are determined. The equation for determination of the radial profile of the relative electron concentration is derived and, on base of experimentally obtained quantities of the radial potentialV(r), this radial profile is computed.