de Jm Hans Regt

A combined Thomson-Rayleigh scattering diagnostic using an intensified photodiode array

A combined Thomson–Rayleigh scattering device is discussed. It consists of a Nd:YAG laser as a light source in combination with a multichannel detection technique consisting of a gated light amplifier in combination with an optical multichannel analyzer. Special attention is focused on the analysis of the measured spectra. Including convolution methods and taking into account weak coherent effects increases the dynamic range and the accuracy of the measured electron density ne and temperature Te and neutral particle density n0. Accuracies of 1%–4% for ne, 2%–6% for Te, and 10%–50% for n0 depending on the plasma condition are obtained. The dynamic range for ne is 7×1017–1021 m−3, for n0 is 1020–1023 m−3 and for Te is 1000–50 000 K.

The behaviour of heavy particles in the expanding plasma jet in argon

This paper concerns the behaviour of heavy particles in an argon plasma expanding from a cascaded arc. The plasma is characterized using high-accuracy spatially resolved Thomson-Rayleigh measurements. It is shown that the expansion of the heavy particles, neutral particles and ions, is close to adiabatic and that three-particle recombination has a small effect on the ion density. The measurements are compared with an adiabatic model and are found to be in good agreement. The behaviour of the neutral particles in the shock front is independent from that of the ions. The neutral particle shock front is identical to the shock front found in neutral gases and is accordingly characterized by the neutral particle Mach number. It is experimentally confirmed that the shape of the shock front is of the Mott-Smith type. The motion of the ions in the shock front is influenced by the presence of the electrons in such a way that the electrons are compressed by the ions. The shape of the ion shock front is of the Mott-Smith type, however, with a different Mach number which includes the electron temperature.

On the electron temperatures and densities in plasmas produced by the “torche à injection axiale”

Abstract The electron temperature and the electron density of plasmas created by the “Torche a Injection Axiale” (TIA) are determined using Thomson scattering. In the plasma with helium as the main gas, temperatures of around 25 000 K and densities of between 0.64 and 5.1 × 1020m−3 are found. In an argon plasma the electron temperature is lower and the electron density is higher: 17 000 K and around 1021 m−3 respectively. From these results it can be established that the ionisation rates of both plasmas are much larger than the recombination rates, which means that the plasmas are far from Saha equilibrium. However, deviations from a Maxwell electron energy distribution function, as reported for the “Microwave Plasma Torch” (MPT), are not found in the TIA. The excitation and ionisation power of the TIA appears to be stronger than that of the MPT.

Thomson scattering experiments on a 100 MHz inductively coupled plasma calibrated by Raman scattering

A new calibration method to obtain the electron density from Thomson scattering on an inductively coupled plasma is discussed. Raman scattering of nitrogen is used for recovering the Rayleigh scattering signal. This has the advantage that no corrections are necessary for stray light, like with other calibration methods, using the direct measured Rayleigh scattering signal on a well‐known gas. It is shown that electron densities and electron temperatures can be measured with an accuracy of about 15% in density and of about 150 K in temperature.

A diode laser absorption study on a 100 MHz argon ICP

Diode laser absorption on the - argon transition is used to measure heavy particle temperatures in a 100 MHz argon inductively coupled plasma. Radial profiles of this temperature are obtained from the Gaussian part of the absorption profile with an accuracy of about 500 K, for four different input powers and at two different heights. The integrated profile is used to calculate the 4s level density and to trace the ionizing and recombining plasma parts. The measurements also show that the method of attributing the Lorentzian width only to Stark broadening for calculating electron densities is not correct for this argon transition in atmospheric plasmas. A second broadening process with Lorentzian shape, Van der Waals broadening, has to be taken into account. Under the measured conditions at the hottest positions in the plasma about 50% of the Lorentz component is due to Van der Waals broadening and this increases to almost 100% at the edges of the plasma.

Comparison of active and passive spectroscopic methods to investigate atmospheric inductively coupled plasmas

A comparison of Thomson and Rayleigh scattering, diode laser absorption and line emission measurements is performed on a 100 MHz atmospheric argon-flowing inductively coupled plasma. The parameters, which are measured in two or more ways, are the electron density, the electron temperature and the heavy particle temperature. The optimized diagnostics show the same behavior for the electron density and temperature. Nevertheless, the Thomson scattering diagnostic is the best at retrieving the radial profile. The heavy particle temperature, as measured by using both Rayleigh scattering and diode laser absorption, is identical within the estimated errors. The technique of measuring the temperature during power interruption, with both Thomson scattering and emission spectroscopy, shows that the electron and heavy particle temperatures are not equal during the period of power interruption.

Components of continuum radiation in an inductively coupled plasma

Measurements of the continuum emission of an inductively coupled plasma in argon have been carried out. The mechanisms responsible for this radiation show different electron-density-dependences. By interrupting the power that is followed by a decay of the electron density, it is possible to unravel these different mechanisms. From the measurements it is concluded that the electron-atom interactions are in general of equal importance to the electron-ion interactions in creating continuum radiation. The relative contribution of the electron-atom interactions depends on the conditions of the plasma. Furthermore, the measurements show that the cross section for electron-atom momentum transfer deduced from our experiment using the formula for electron-atom free-free continuum radiation is not in agreement with the literature.

A closed inductively coupled plasma for lighting purposes mapped by spectroscopical techniques

A closed 13.6 MHz inductively coupled argon plasma with a volume of is investigated by active and passive diagnostics. The study considers the influence of varying argon filling pressures in the range 10 - 100 mbar and different input powers in the range 50 - 125 W. The combination of the applied techniques of absolute line emission intensities, Thomson scattering and diode laser absorption measurements reveals the typical behaviour of temperature and electron density of the plasma. One of the observed characteristics is that, upon increasing the filling pressure, the ring-shaped radial distribution of the electron density becomes more pronounced, while the electron temperature decreases over the whole radial profile. Furthermore, the influence of input power on the electron temperature and density depends strongly on the filling pressure. It is to be expected that insight into plasma processes and parameters for argon filling will lead to a better understanding of future light sources as well.

The effect of evaporation on the analyte emission intensities during power interruption in an inductively coupled plasma

Abstract A power interruption technique is used to study the population balances of excited states of analytes in an inductively coupled plasma (ICP). Measurements on Li analyte emission show that the Boltzmann balance of excitation of and de-excitation to the ground state is the dominant population process for the lower excited levels. During the power interruption, changes in the excitation and de-excitation flows are visible and it turns out that the ionization degree of Li depends strongly on position, central flow and plasma power. The results cannot be explained unless evaporation of analyte is assumed to have an important impact on the excitation flow in the Li system.

Air entrainment in an inductively coupled plasma measured by Raman and Rayleigh scattering

A new technique to study the entrainment of air into the inductively coupled argon plasma is presented. The combination of vibrational Raman scattering and Rayleigh scattering enables measuring absolute particle densities of air and argon. The measurements show the entrainment of air into the plasma. At an axial position of 2 mm above the end of the quartz torch it is found that at 90% of the plasma radius 55% of the particles originate from air and by exponential extrapolation towards 70% of the radius about 1% entrainment of air is predicted to be present. Furthermore, a comparison with a cold argon flow shows that due to the higher viscosity the entrainment in the plasma is lower than in the cold argon flow.