Radiation Efficiency and Kinetic Calculations for the Positive Column in Hg/Ar Mixtures. I. Thg Variation

Properties of the positive column of low pressure Hg/Ar discharge have been investigated from the point of view of its application in fluorescent lamps. The results obtained are based on experimental methods to determine both UV resonance radiation fluxes of the 6³ P₁ and 6¹P₁ Hg levels and to measure the electron distribution function by probes; in addition a kinetic model is applied for the theoretical interpretation of the experimental results and to give a deeper insight into the particle and energy budget. In the present first part of the paper the effects of recently determined τ_eff-values on radiation, net collision rates, power transfer and the electron energy distribution for extended parameter values are investigated especially in dependence on mercury partial pressure.     

Distribution Radiale de la Densité des Atomes Métastables dans les Plasmas Produits par un Champ Electrique Continu ou de Haute-Fréquence

The radial density distribution of metastable Ar(³P₂) and resonant Ar(¹P₁) atoms is determined experimentally in two types of electrical discharges of cylindrical shape: the positive column plasma of a DC discharge and the plasma produced by an electromagnetic surface wave. The exitation and deexcitation rates for Ar(³P₂) by electron collisions are determined as a function of radius from the measured radial population density profile using a population density balance equation. These rate coefficients are obtained for various electron density values on the axis. The published values for these coefficients in the positive column plasma assume that they are independent of the discharge current. In this work, it is shown that these coefficients actually decrease as the electron density increases. In a more general way, the results obtained indicate that the examination of the radial density distributions of exited atoms is a powerful method for determining the kinetics of their creation and destruction.     

Estimation of the pressure in a “slow” spark discharge in a cylindrical water-filled chamber

On the assumption that a spark discharge in water is quasi-steady, its pressure and channel radius are calculated. It is shown that the key discharge parameter is the action integral S=∫ ₀ ^t i ² dt, where i is the current in the channel. The conductivity only slightly affects the computational results and thus can be assumed to be constant. The formulas obtained can be applied to a discharge along the axis of a cylindrical water-filled chamber if the deformation of its walls over the discharge time is negligibly small and the pulse duration is several times greater than the time of sound propagation in water from the axis of the chamber to its wall. At relatively low pressures (P≤10⁸ Pa), P∼R ^−4/3, where R is the chamber radius.     

Ionenschallinstabilitäten in Edelgas-Gleichstromentladungen bei niedrigen Drücken. I. Meßanordnung und experimentelle Ergebnisse

An experimental study of self-excited ion acoustic waves with wavelengths greater than the radius of the discharge tube in a de-low pressure column is presented. The propagation of this type of waves was observed over a pressure range of 5 · 10^?4 torr ≦ p ≦ 10^?1 torr and currents of 0,02 A ≦ i ≦ 0,6 A in various gases (argon, neon, helium, and hydrogen) in cylindrical glass tubes with diameters of d = 2;4 and 6 cm. The Dispersion behaviour and the existence range were measured in dependence of the internal parameters of the discharge (characteristic velocities and collision frequencies) and the geometry of the discharge tube. It is shown, that the existence range depends not only on gas pressure and current but is influenced also by the geometry of the discharge tube. The minimum wavelengths which belong to the upper cut-off frequencies correlate with the radius of the discharge tube at currents higher than i ～ 0,2 A and increasing pressure.     

Temperaturen in Ionenlaserplasmen

Plasma temperatures of the wall-stabilized low pressure Ar-arc, which has been optimized for maximum inversion density of the Ar II 4p- 4s laser transitions (i.e.kT _e?4 eV), have been determined experimentally and compared with literature data. Ion temperature is obtained from the Doppler linewidths of Ar II transitions, which have been measured both spectroscopically and indirectly by measuring the gain of the 4880 å laser line. Neutral temperature is obtained from the Doppler linewidths of Ar-I-transitions and by relating fill pressure and calculated values of the corresponding gas density. Ion- and neutral temperature are reported to reach values ofT _i? 30000 K andT _a? 25 000 K, respectively. In the range under present concern (kT _e?4 eV, 15≦jR [A cm^?1]≦150)T _i as well asT _a is a function of the characteristic parameterjR alone (j=current density,R=tube radius).     

Increased Power Concentration and its Effects on the Discharge Parameters of the Low Pressure Hg-rare Gas Positive Column. II. Variation of Tube Radius

The reduction of the tube radius is an effective technique for enhancing power concentration. The increased wall losses are compensated by larger field strengths, which counteract the decrease in radiation efficiency with rising current density. The causal relationships are investigated for tube radii of 18-4 mm at constant discharge current i = 200 mA and constant current density j = 1.2 mA/mm² and for parameter variation of the field strength only. The measured efficiencies of the Hg-resonance lines 254 and 185 nm and the electron energy distribution functions agree well with the calculated values. Moreover, the results of the model calculations provide information on the elementary processes involved, such as elastic losses, collisions of second kind, stepwise processes and Coulomb interaction. The results show that Hg-rare gas discharge with tube radii R = 5–10 mm are no less suitable for light production than those with radii between 13 and 18 mm.     

Repetitive low-pressure volume discharge induced by attachment instability in an Ar/Cl<Subscript>2</Subscript> mixture

Ignition conditions and the characteristics of a repetitive volume discharge with a spherical anode and plane cathode are investigated. The discharge was ignited in Ar/Cl₂ mixtures (P≤2.0 kPa) used in excimer halogen lamps operating on the ArCl (B-X) 175-nm, Cl₂(D′-A′) 257-nm, and Cl ₂ ^** 195-to 200-nm molecular bands. At an interelectrode distance of 3 cm and a dc anode voltage of U _ch ≤1 kV, a stable repetitive pulsed discharge with a repetition rate of 1–50 kHz was ignited in chlorine or (0.1–2.0)/(0.04–0.12)-kPa Ar/Cl₂ mixtures. The development of attachment instability in the discharge plasma, in which the processes of the formation, decay, and diffusion of the Cl ₂ ⁻ and Cl⁻ negative ions play an important role, leads to the formation of a solitary pearlike plasma domain with an average diameter of 0.2–3.5 cm.     

感应磁场压缩下氢等离子体中巴耳末系谱线的斯塔克加宽

本工作研究感应磁场压缩下,氢等离子体中的巴耳末系谱线的斯塔克加宽。电容器对围绕在放电管外部的线圈放电,产生交变轴向磁场,使放电管中氢气离化、压缩与加热。放电周期14微秒,放电电压20千伏,最大电流165千安,初始工作气压2.0×10^-1毫米汞高。用照相方法研究H_β和H_γ的轮廓。这些谱线有显著的加宽。在整个发光阶段中,H_β的平均半宽度为14—16(埃),H_γ为18—19(埃),相应的离子密度为1.7—2.5×10¹⁶厘米^-3。实验轮廓与Griem,Kolb和Shen的理论较为接近,与Holtsmark理论相差较远。光电测量进一步表明:H_β的轮廓随着时间而改变,相应的离子密度亦在改变。在放电的第三半周期初级电流极大时,离子密度最大,达到3.2×1O¹⁶厘米^-3,为初始氢原子密度的2.2倍。     

Density of fast electrons on the Axis of a Zylindrical Hollow-Cathode Discharge

Fast electrons leaving a hollow cathode discharge axially through the orifice of a hole probe undergo ionizing collisions with the discharge gas in and behind the orifice. Ar⁺⁺ ions produced in this way are used as a monitor for the density of fast electrons, N_ef, on the axis of the negative glow of a cylindrical hollow cathode discharge. Data on N_ef as dependent on the pressure of the Ar discharge gas and on the discharge current are obtained and an analytical expression for these dependences is found and discussed.     

Space resolved density measurements of argon and helium metastable atoms in radio-frequency generated He-Ar micro-plasmas

Space resolved concentrations of helium He* (³S₁) and argon Ar* (³P₂) metastable atoms in an atmospheric pressure radio frequency micro-plasma jet were measured using tunable diode laser absorption spectroscopy. Even small absorptions down to 10^-4 could be measured using lock-in technique. The absolute density of metastable atoms densities at different rf-power, flow rate and gas mixture was deduced from measured absorption rates. Metastable concentrations range from 10⁹ to 10¹¹ cm^-3. Analysis of spectral profiles provided the pressure broadening coefficients of both metastable atoms by helium. The spatial distribution of metastable atoms in the plasma volume was obtained for various discharge conditions. Density profiles between the electrodes reveal the sheath structure and reflect the plasma excitation distributions in the discharge volume. It reveals the dominance of the α-mode discharge.     

Radiative lifetime of the v′1(3P2) states of the HgAr, HgKr, and HgXe molecules and the probabilities A(v′, v″) of the v′1(3P2?v″0+(1S0) transitions

A semiempirical method of analysis of quasi-molecular terms in conjunction with experimental potentials of interaction of Hg(6(³ P ₁)) atoms with Ar, Kr, and Xe atoms are used to obtain the Hg(6³ P ₂)-Ar, Kr, Xe interaction potential, which are applied to calculating the radiative lifetimes of the v′1(³ P ₂) states of the HgAr, HgKr, and HgXe molecules and the probabilities of the v′1(³ P ₂)−v″0⁺(¹ S ₀) transitions.     

Sheath and electron density dynamics in the normal and self-pulsing regime of a micro hollow cathode discharge in argon gas

A microplasma is generated in the microhole (400 μm diameter) of a molybdenum-alumina-molybdenum sandwich (MHCD type) at medium pressure (30–200 Torr) in pure argon. Imaging and emission spectroscopy have been used to study the sheath and electron density dynamics during the stationary normal regime and the self-pulsing regime. Firstly, the evolution of the microdischarge structure is studied by recording the emission intensity of the Ar (5p[3/2]₁–4s[3/2]₁)_{1}) line at 427.217 nm, and Ar⁺ (4p′ ²P_3/2–4s′ ²D_5/2)_{5/2}) line at 427.752 nm. The maximum of the Ar⁺ line is located in the vicinity of the sheath-plasma edge. In both regimes, the experimental observations are consistent with the position of the sheath edge calculated with an ionizing sheath model. Secondly, the electron density is recorded by monitoring the Stark broadening of the H_b_\beta-line. In the self-pulsing regime at 150 Torr, the electron density reaches its maximum value of 4 × 10¹⁵ cm^-3, a few tens of ns later than the discharge current maximum. The electron density then decays with a characteristic decay time of about 2 μs, while the discharge current vanishes twice faster. The electron density in the steady-state regime is two orders of magnitude lower, at about 6–8 × 10¹³ cm^-3.     

Multi-wavelength excimer ultraviolet sources from a mixture of krypton and iodine in a dielectric barrier discharge

New ultraviolet (UV) sources (excimer lamps) have been demonstrated using mixtures of krypton and iodine in a high-pressure dielectric barrier discharge to provide intense multi-wavelength radiation at λ=183 nm (atomic iodine line, ⁴ P _5/2?² P _3/2), 191 nm (KrI^*, B _1/2?X _1/2), 206 nm (atomic iodine line, ² P _3/2?² P _1/2), and 342 nm (I^* ₂, D _1/2?X _1/2). The characteristics of the optical emission spectra of the atomic species and the excited dimers (excimers) formed for different total gas pressures and in the presence of a buffer gas have been investigated. The highest intensity, at 183 nm, is obtained at pressures up to 1 bar while the overall emission spectra can be controlled by adjusting the total pressure. The results show that these strong multi-wavelength lamps offer an interesting alternative to conventional UV sources. Received: 1 March 2000 / Revised version: 5 April 2000 / Published online: 30 June 2000     

Striking and Running Voltages in a Glow Discharge for Combinations Fe/Ne + 1% Ar with and without Hg

Experimental investigations of striking U_s and running U_r voltages in a glow discharge for the combinations cathode material Fe gas filling 99% Ne + 1% Ar with and without Hg have been carried out. It is shown that Hg addings cause an increase of striking voltages U_s in the whole investigated range of Paschen curve as well as an increase of running voltage U_r in the whole pressure range p under investigation. The additional effects which occur in the discharge with Hg addings are discussed and a qualitative explanation of the obtained results is proposed.     

On distribution over the cathode surface of the current due to positive ions in discharge with oscillating electrons

The mechanisms of processes determining distribution of positive ions on the cathode surface in a discharge with oscillating electrons are studied. At low pressures P≤5×10⁻⁵ torr over the entire range of anode length variation l _a=0.5–11 cm, the ion current distribution over the cathode radius J _i(r) features a single maximum in the center and drops steeply with distance from the axis. At pressures P=1–4×10⁻⁴ torr, the distribution J _i(r) for short anodes (l _a<6 cm) is similar to the previous one but, for long anodes (l _a=6–10 cm), new maxima at higher J _i values have been detected. A physical explanation for the obtained results is proposed.     

Velocity dependence of total Penning ionization cross sections

The velocity dependence of the total Penning ionization cross sections,σ(v), is measured in the thermal relative velocity region, using a time of flight method.σ(v) curves are reported for the collision systems He(2¹ S)/Ar, Kr, Xe, N₂, Hg, He(2³ S)/Ar, Kr, Xe, N₂, Hg, Ne(³ P _{2, 0})/Kr, Hg, and Ar(³ P _{2, 0})/Hg. In a qualitative discussion it is shown that all features of the measuredσ(v) curves may be explained within the frame of the theory of Penning ionization, allowing to extract information on the physical quantities governing the process: on the interaction potentialV(R) and on the transition probabilityW(R). A theoretical calculation for the He(2³ S)/Ar system shows good agreement with our experimentalσ(v) curve. On the basis of the present results earlier data onσ(v), and on absolute cross sections and rate constants obtained at certain relative velocity distributions are discussed.     

极板电压与间距对大气压射频氩等离子体放电参数的影响

 基于1维流体力学模型,对大气压射频裸露金属电极氩气放电过程进行了研究。模型中考虑了氩等离子体放电过程中主要发生的激发和电离等7个反应过程,对等离子体反应产生的主要粒子,包括电子、氩原子离子Ar⁺、氩分子离子Ar2⁺和氩激发态Ar^*等,建立连续性方程、动量方程和电流平衡方程。分析了极板电压、极板间距对上述粒子数密度分布的影响。给出了电子,Ar⁺,Ar^*和Ar₂⁺密度随极板电压及间距变化的时空演化过程。得出极板电压或极板间距的改变会使放电空间的电场发生改变,对应一定的极板间距,极板电压有一个最佳值,极板电压和间距的变化会使对应的极板间有一个最佳电场值,而对应最佳电场有一个等离子体气体间最佳反应系数,从而使放电空间粒子数密度发生改变。     

Continuous operation of a high power neon ion laser

A highly ionized neon low pressure discharge (p ≈ 1 torr) was operated in a 12 mm diameter segmented aluminium tube up to discharge currents i = 630 A. The threshold current of the isotope selective Ne II-line λ = 332.4 nm was lower than for the strongest Ar III-UV lines; the highest measured output power of this line was 6.3 W which is more than one order of magnitude higher than previously reported.     

Reaktionskinetik der Ozonbildung in der Sauerstoffglimmentladung

Hg-light absorption at λ = 2537 ǎ by O₃ has been used to measure the concentration of O₃ in the positive column of an oxygen glow discharge under the nonstationary conditions of the Q-form (tube diameter 3:4 cm). For all gas pressures investigated (p = 7 — 12 torr) the O₃ density (n₃) as a function of the current reaches a remarkable maximum at i ≈ 15 mA. n₃ ^max was found to increase almost linearly with the gas pressure. At i = 80 mA, on the other hand, n₃ increases according to a quadratic relation. In order to understand the dependence of n₃ on the pressure and on the current density (or equivalently on the electron density n_e) a kinetic model previously developed has been used involving the following particles . For example, it can be shown that in the region of the maximum of n₃ one main production process of ozone is the associative detachment reaction . The calculated maximum of the ozone density is higher than the measured one and appears at higher electron density.     

Buffer-gas pressure broadening for the 2ν3 band of methane measured with continuous-wave cavity ring-down spectroscopy

Buffer-gas pressure broadening for the P(1), Q(1), R(0) and R(1) transitions in the 2ν ₃ band of CH₄ was investigated in the 1660 nm region. The pressure broadening coefficients, γ(gas), were determined for a variety of buffer gases: N₂, O₂, He, Ne, Ar, Kr and Xe. The γ values generally increased with increasing polarizability of the buffer gases. γ(air) are 0.056(2) for P(1), 0.056(1) for R(0), 0.061(1) for R(1) and 0.059(1) for Q(1) in units of cm⁻¹ atm⁻¹ where numbers in parentheses are one standard deviation in units of the last digits quoted. The temperature dependent parameter (broadening exponent) for air is 0.84(7) for P(1) within the temperature range 233–298 K.