The positive column of low-pressure Hg/Ne and Hg/Ne/Ar discharges

Abstract

The electron density at the axis, the electron temperature and the electric field strength of the positive column of low-pressure Hg/Ne discharges have been measured using electrostatic probes. The measurements have been carried out for discharge currents between 0·1 and 0·8 A, noble gas pressures between 0·3 and 10 Torr, tube wall temperatures in the range of 13-70°C, and an inner tube radius of 18 mm. The addition of argon to neon as a filling gas has also been studied.By computing the volume and wall losses from the measured data, the authors have worked out the effect of the discharge conditions on the radiation efficiency of the column. These data have been compared with the results of a theoretical model of the positive column, showing a reasonable agreement. From this comparison it has been found that elastic collisions of electrons and of ions with neutral mercury atoms have a decisive influence on column properties at mercury pressures above similar 10−2 Torr. Furthermore a higher radiation efficiency of the column has been found in Hg/Ne discharges compared to Hg/Ar discharges for 3 Torr noble gas pressure, wall temperature 42°C, and discharge current 0·4 A.

Determination of electromagnetic properties of low-pressure electrodeless inductive discharges

“…A zero-order Bessel profile will be taken for f(F) as is usually found in low-pressure discharges (see e.g. Verbeek andDrop 1974, Cherrington 1979). In the case of skin depths smaller than R. the actual profile will deviate from a Bessel profile.…”

Application of similarity laws as a light source diagnostics

“…To check the efficiency of the proposed method, results of [25][26][27], where electrokinetic and optical characteristics of a positive column of a gas discharge in the mixture of mercury vapour and a rare gas were studied, were used. Figure 5(a) presents results of measurements and calculations of electron concentration n e , electron temperature kT e (kT e = (2/3) ε ) and efficiency η of a fluorescent lamp (bold and dashed lines) in dependence on the pressure of a rare gas for a dc discharge in the mixture of mercury vapour and neon [26]. The same figure also presents results of calculation of these characteristics with the help of similarity laws (solid lines) by using measured dependences of these characteristics on the mercury atom concentration N o and electric current i.…”

“…There is good coincidence between experimental and calculated data. The use of similarity laws made it possible to define also dependences of n e , kT e and η on the tube radius that were not measured in [26]. These data are in figure 5(b).…”

Electron mobility calculations for mercury-argon low pressure gas discharges

“…In order to obtain electron mobility in mercury we have followed the procedure of Verbeek and Drop (1974) in which case the cross-section can be expressed as (McCutchen 1958) Q m = 28000 (-) 2e 0.7 mu2 Using this expression in equation ( 1) and integrating gives where p~~ is the electron mobility in mercury vapour at reduced pressure PMO. Various publications (Nakamura andLucas 1978a, b, Elford 1980) concerningmomentum transfer cross-section of electrons in mercury vapour show discrepancies.…”

“…This is correct for low mercury concentration, but gives rise to a significant error at high mercury concentration as shown by Verweij (1961). Using similar values for p, for argon, and an equation for ye in mercury, Verbeek and Drop (1974) have calculated the mobility in the mixture using Blanc's law. Since the mobility data for argon and the use of Blanc's law are both approximate, their results are not so exact as those by Verweij. In this work, for the purposes of calculation, it has been convenient to describe the momentum transfer cross-section for argon by a simple algebraic expression.…”