Determination of the gas temperature in high-pressure microwave discharges in hydrogen

Abstract

Results of experimental determinations of the gas temperature and plasma parameters in a microwave discharge not at thermal equilibrium are presented. The investigation is concerned with high-pressure hydrogen under conditions such that radiation is emitted both by atomic and by molecular components of the plasma are primarily governed by the interaction of the excited atoms and molecules with heavy particles. Because this takes place the approximate models which are successfully applied to analyse data from spectroscopic diagnostics cannot be used to describe the radiative properties of the discharge. One of the main objectives of research consists of making headway in spectral methods of gas-temperature determination in the high pressure range by invoking for interpretation of experimental data calculations performed in the framework of the kinetic scheme of thermal non-equilibrium discharge in hydrogen as well as general physical reasoning relating to the role of interactions between heavy particles in non-equilibrium plasma radiation. The following measurement techniques have been used: spectral measurements of Balmer-series radiation; spectral measurement of the gas temperature by recording the Doppler broadening of the ; and spectral measurements of by recording the Fulcher band. In addition the electron concentration has been measured with the help of a microwave interferometer and pyrometric measurements of the temperature of a test solid body placed in a microwave-discharge plasma have been performed. Measurements of the gas temperature agree satisfactorily under the assumption that collisions of excited particles with heavy components of a gas-discharge medium are of considerable importance. Conclusions regarding the ion composition and degree of dissociation of hydrogen molecules can be drawn.

Time-resolved measurements of the gas temperature in a H2/CH4 medium pressure microwave 915 MHz pulsed plasma

“…Ovtchinnikov et al [5] measured, in a dc discharge, the rotational temperature corresponding to the population densities of the d 3 u substates involved in the emission of the Q-band of the Fülcher system, and showed that this temperature is in good agreement with the translational temperature obtained from the Doppler broadening of Hα and Dα spectral lines. The same conclusions were obtained by Gritsinin et al [6] in a high-pressure hydrogen discharge sustained in a cylindrical chamber using a microwave excitation device. Concerning the use of the rotational temperature of the H 2 (G 1 + g ) state for the determination of the gas temperature, the results are controversial.…”

Spatially Resolved Optical Emission and Modeling Studies of Microwave-Activated Hydrogen Plasmas Operating under Conditions Relevant for Diamond Chemical Vapor Deposition

“…H 2 shows a wealth of rovibrational structures in the visible and near-infrared (IR) spectral regions associated with transitions between bound excited electronic states. − Most prior experimental studies of MW-activated hydrogen-containing plasmas have focused on the d 3 Π u –a 3 Σ g + (Fulcher) system, − ,− though lines within the G 1 Σ g + –B 1 Σ u + origin band − and a 3 Σ g + –b 3 Σ u + continuum emission , have been used for plasma diagnostics, and limited studies have been undertaken using the e 3 Σ u + –a 3 Σ g + system . As Figure shows, the structured emissions are from excited states that lie at energies > 13 eV above the ground (X 1 Σ g + ) state of H 2 .…”

Kinetics of populations of singlet and triplet states in non-equilibrium hydrogen plasma

“…The studies reported in [207,[214][215][216] were devoted to developing models that describe the kinetics of collisionalradiative processes involving excited neutral atoms and ions of a hydrogen plasma. The dependence of the rate of neutralization of atomic ions H − and H + (processes 36.0, 41.0, and 41.1) on the electron concentration N e and temperature T e in the nearcathode layer, where negative hydrogenatom ions H − are dominant (N = 10 16 cm −3 ; in the nearelectrode layer, T e ⩾ 1.5 eV, N e = 10 12 -10 14 cm −3 , and H − = 10 11 -10 12 cm −3 ), was theor etically analyzed in [207].…”

“…A model is developed in [216] to describe the excitation of electron states of hydrogen atoms in the flow of recombin ing hydrogen plasma. In contrast to models known in the lit erature, this model takes into account inelastic interactions of excited atoms with heavy particles.…”

“…Since the model in question is semiempirical, experimental data are required in solving the equations for EEDF and the bal ance equations for the concentrations of excited particles. A detailed analysis of a vast amount of experimental data was performed in [69-77, 210, 211, 217, 218], and this analysis was used there as a basis for choosing the studies reported in [38,78,79,201,210,211,218,[220][221][222][223][224][225][226][227][228][229][230][231][232][233][234][235][236] and devoted to exploring lowpressure gas discharges at a thermalemission cathode in a magnetic field [201,[220][221][222][223][224], a pulsed glow discharge [225], RF [210,211,218] and microwave [78,79,[226][227][228] discharges, PC of DCGD [38,[229][230][231], a hollow cathode discharge [...…”