Quantitative investigation of xenon consumption and recovery during low pressure ac discharges in rare gas mixtures

Abstract

Xe gas in low pressure discharge tubes (20 mm diameter, 800 mm length, commercial hollow electrodes at 650 mm distance, 50 Hz, 60 mA) was quantitatively determined using quadrupole mass spectrometry (QMS). The temporal Xe gas evolution over 5 to 20 h of gas discharge revealed the consumption and recovery of Xe gas to be dependent on the prevailing gas composition. The net consumption in the standard Xe/He(2.0/98) gas mixture was much faster than that in Xe/Kr/He(1.9/93/5). Xe recovery during discharges in ‘preloaded’ tubes refilled with pure gas revealed an increasing efficiency in the sequence He < Ne < Ar < Kr, being most efficient with the first refilling. The temporal evolution of Xe gas was simulated by a kinetic model based on two equilibria between Xe gas and Xe incorporated in the glass tube walls (1) and the electrodes (2). It is concluded that the experimental setup, the elaborated measurement procedures and the kinetic model provide a good basis for further quantitative investigations. The net Xe gas consumption during discharge, which is presently limiting the tube lifetime, may be reduced particularly by improving the discharge gas composition and the electrode materials.

Study of pulsed neon–xenon VUV radiating low pressure plasmas for mercury free fluorescent sign optimization

“…With AC excitation, the continuous operation of neon xenon signs results in a selective trapping of xenon in the glass tube and tube electrodes which induces strong limitation on the lifetime of the signs [10,22]. For AC excitation, there exists a strong trade off between the lifetime and the visible output of the signs.…”

“…The results of this section were obtained in sealed signs and hence include the potential cataphoresis, and any other longterm plasma phosphor, glass and electrode interaction effects. With ac excitation, the continuous operation of neon-xenon signs results in a selective trapping of xenon in the glass tube and the tube electrodes which induces a strong limitation on the lifetime of the signs [10,22]. For ac excitation, there exists a strong trade-off between the lifetime and the visible output of the signs.…”

Investigation of a low-pressure He–Xe discharge in spot mode

“…is solved, which includes the electron energy flux j eu and the energy loss rates P Xe and P He due to collisions with xenon and helium atoms. The particle and energy fluxes of charge carriers are described in the drift-diffusion approximation [16] j e = n e b e ∇V − ∇(D e n e ), (10) The electron transport and collision rate coefficients were determined from a kinetic treatment. The spatially homogeneous Boltzmann equation of the electrons was solved in two-term approximation with collision terms corresponding to elastic collisions, excitation and ionization from the ground and several excited states and second-kind collisions.…”

“…Therefore, experimental and theoretical investigations have been performed to study the discharge in the vicinity of the cathode. A new cathode has been used to prevent from the socalled 'gas clean-up' or gas consumption [10] usual for solid electrodes. The new cathode consists of an iron mesh with conventional Ba-Sr-Ca oxide coating and works in hot spot mode that corresponds to realistic lamp conditions.…”

Spot mode operation of a helium-xenon discharge for lighting

“…Lamps for advertisement are designed up to now by very expensive and time consuming empirical technological procedures using mostly cylindrical electrodes. An application of these electrodes in mercury-free fluorescent lamps, based on low pressure discharges in xenon, leads to the so called "gas cleanup or gas consumption" [1]. A proper design of the cathodes is of crucial importance for the efficiency and lifetime of lamps.…”