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An inductively coupled radio-frequency plasma in chlorine is investigated via a global (volume-averaged) model, both in continuous and square wave modulated power input modes. After the power is switched off (in a pulsed mode) an ion–ion plasma appears. In order to model this phenomenon, a novel quasi-neutrality implementation is proposed. Several distinct Cl wall recombination probability measurements exist in the literature, and their effect on the simulation data is compared. We also investigated the effect of the gas temperature that was imposed over the range 300–1500 K, not calculated self-consistently. Comparison with published experimental data from several sources for both continuous and pulsed modes shows good agreement with the simulation results.

Collisional Radiative Models (CRM) are widely used for the determination of plasma parameters such as the electron temperature and density. In combination with other techniques, they have also been used to investigate departure of the electron energy distribution from Maxwell [1]. Two of the main building blocks of a CRM are the electron and heavy particle kinetics, and accurate data describing these processes is of vital importance. Usually, comparison and validation of CRMs is performed in steady state. Here, Laser Collisional Induced Fluorescence (LCIF) is employed to study the various particle kinetics. To this end, a time dependent CRM of argon has been developed in the Plasimo plasma modeling platform [2] that can model a LIF experiment. The model allows for the different processes to be studied in detail, including the changes of the escape factors. The results of the model are compared to measurements performed on a low pressure microwave plasma with known characteristics [3-4]. [1] E. A. D. Carbone et al. (2012) J. Phys. D: Appl. Phys. 45 475202 [2] J. van Dijk et al (2009) J. Phys. D: Appl. Phys. 42 194012 [3] J.M. Palomares et al. (2010) Spectrochim. Acta B 65 225 [4] E. A. D. Carbone et al. (2012) J. Phys. D: Appl. Phys. 45 345203

Strong deviations from Maxwellian equilibrium of the electron energy distribution function (EEDF) are very often encountered in (relatively) high pressure, non-equilibrium plasmas. The shape of the EEDF will strong affect all electron induced excitation processes and consequently excited species net effluxes. In this contribution, we will present an experimental investigation of the EEDF of an intermediate pressure (argon) microwave plasma by a combination of experimental and modelling techniques.

Microwave induced plasmas are applied in many fabrication processes such as the deposition of SiO2 for the production of optical fibers and the deposition of Si to make solar cells. To control these deposition processes a good understanding of the plasma kinetics is required. Experimental investigation and modelling are two complementary strategies for the investigation of plasmas. In this thesis, the surfatron source is chosen as a model system for the validation of different diagnostic techniques and models. One of its main advantages is its flexible operation range and stability when operated in complex gases. Various experimental techniques, such as Thomson scattering, laser (collisional) induced fluorescence and optical emission spectrometry, are used to investigate the plasma properties as a function of external parameters (e.g. the pressure and the gas composition). For pure argon, the results are compared with two-dimensional simulations of the plasma source, a time dependent global plasma model and a collisional radiative model. The validity and limitations of the various techniques and models are discussed case by case. The radial electron density and temperature profiles are measured by Thomson scattering for various pressures. Radial contraction is observed for pure argon plasmas above 20 mbar. Molecular ions are found to be partially responsible for that trend but other effects such as Maxwell deviations cannot be neglected either. Deviations from maxwellian equilibrium are investigated as well along the plasma column by a combination of experimental and modelling methods. It is found that the tail of the electron energy distribution function is increasingly depleted for lower ionization degrees. Electron and heavy particles kinetics are an important part of plasma dynamics and need to be included in any plasma model. In combination with different diagnostic techniques, plasma sources can be used for the determination of rate coefficients as well. Electron transfer rate coefficients between the metastable and resonant 4s states of argon are measured using laser diode absorption spectroscopy and pulsed dye laser perturbation of the plasma in steady state. Pulsed laser collisional induced fluorescence (LCIF) can be used as well for studying electron and heavy particles kinetics. The method is applied, for the first time, to a pure argon plasma. The results are compared with a time-dependent collisional radiative model (CRM) simulating the LCIF experiment. The argon CRM is found to give relatively good results for steady state but significant discrepancies are found in the case of fast relaxation processes. Based on the experimental results, a path for improvements of the CRM is given. LCIF is used to probe quenching mechanisms in the case of an argon-hydrogen plasma. Significant quenching by atomic hydrogen of argon 4p states is demonstrated. Power modulation is a commonly used method to tune time-averaged plasma properties. The ignition and decay of the plasma are studied using different experimental techniques. The results are compared with a zero-dimensional plasma model and a relatively good agreement is found. It is shown that power interruption has a very small influence on the plasma properties when normalized to time averaged power density. The reasons for this behavior are finally discussed. The criterion to avoid perturbation of the plasma during scattering measurements is revised in the case of high pressure, low electron densities plasmas. It is shown that electron-atom inverse bremsstrahlung contributes predominantly to laser heating of the electron gas for low ionization degree plasmas. In resumé, advanced (time-resolved) diagnostic techniques and modelling tools are combined to obtain a complete picture of the plasma dynamics. The surfatron source is shown to be a flexible and relatively simple tool for the investigation of plasma chemistry. Although argon plasmas are usually considered to be rather simple, if not trivial, the extensive comparison between experimental results and state-of-the-art modelling shows that significant improvements can still be achieved in our understanding of (microwave) argon plasmas.

The large effluxes generated by high-tech plasmas force plasmas to non-equilibrium conditions. This implies that plasma features are decoupled from each other and that therefore different methods have to be used quasi-simultaneously to characterize the plasma. Even more insight in plasmas and methods is obtained if polydiagnostics is applied to a series of plasma conditions that gradually differ in equilibrium departure. After discussing methods of passive and active spectroscopy, we apply polydiagnostics on an argon plasma operated in open air. By introducing H2 and reducing the power we approach conditions of cool atmospheric plasmas (CAPs). It is seen that especially the passive methods for the electron temperature determination are very sensitive to the degree of equilibrium departure suggesting that active spectroscopy is preferable. However, one should realize that lasers can easily heat cool plasmas.This is due to the fact that the ionization degree of (semi-) CAPs is small.

The reaction kinetics in the excitation space of Ar and the conversion space of Ar-molecule mixtures is explored using the combination of high rep-rate YAG-Dye laser systems with a well defined and easily controllable Surfatron Induced Plasma set-up. Applying the method of Saturation Time Resolved Laser Induced Fluorescence (SaTiRe-LIF) we could trace excitation and conversion channels and determine rates of electron and heavy particles excitation kinetics. The time resolved density disturbances initiated by the laser, observed in the Ar excitation space, reveal excitation channels and corresponding rates; responses of molecular radiation in argon-molecule mixtures point to the presence of conversion processes induced by heavy particle excitation kinetics.

The determination of the main excitation kinetics channels in the production of active species in a plasma is of main importance for the understanding and control of plasmas. In this contribution we will present the combination of two diagnostics methods, namely Laser (Collisional) Induced Fluorescence (LCIF) and Thomson scattering. The latter allows to measure locally the electron temperature and density meanwhile LCIF probes the excitation channels of selected atomic/molecular species with nanosecond time resolution after perturbation of the steady-state plasma with a nanosecond pulse tuned to an atomic transition.

A large panel of diagnostic techniques for the determination of effective electron temperatures Te exists and they rely on different hypothesis/physical phenomena for its measurement. Due to the different underlying assumptions and physical mechanisms used for the calculation of Te, different values of Te may be expected while measuring a plasma in the same conditions, particularly in the case of a non-Maxwellian plasma. To each of these definitions of effective Te, a different effective Te can be defined using the EEDF of the plasma. In this study, we take a low pressure Argon microwave plasma as test case and compare Thomson scattering with line intensity measurements corrected by a collisional radiative model. The results are compared with those obtained from the electron particle balance (ePB).

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The plasma properties of a capacitively coupled atmospheric pressure plasma in Argon as a function of the driving frequency fd is studied for a number of frequencies in the range 4–40 MHz by means of a 2D fluid model. It is observed that the increase of fd while keeping the applied voltage constant results into amplification of the chemical processes. More neutral active species are produced, which is mainly due to the increase of the electron density ne. However the increase of ne will also facilitate the destruction of excited species Ar* so that the increase of excited species density n(Ar*) will lag behind that of ne.

The radial and axial profiles of a cylindrical surfatron plasma created at intermediate pressure in argon were mapped by Thomson scattering. This technique provides accurate, non-perturbing access. The direct imaging capacity of a triple-grating spectrometer equipped with an iCCD camera allows investigating radial and axial profiles. The obtained radial ne(r) values match a Bessel function, even if the plasma column is strongly contracted. The axial profile is linear, depending on the pressure. However, the end of the plasma column shows a discontinuity.

Lasers are commonly used nowadays to investigate the plasma properties (laser-aided plasma diagnostics LAPD). However, in using LAPD, one should always be careful in tuning the laser power density to avoid perturbation of the plasma during the diagnostic. A general formula was given by Kunze [1] to determine the heating of electrons during laser diagnostics via electron-ion inverse bremsstrahlung (IB). In this contribution, it is shown that for low ionization degree and high pressure plasmas, electron-ion IB is a negligible heating process and that electron-atom IB becomes dominant. The criterion for non-invasive LAPD needs then to be revised consequently.

Various methods have been used to investigate the excitation kinetics as well as neutral species chemistry for mozaic of different plasmas conditions in the last decades and past century. In this contribution we will present a direct method to probe the interplay between various species in a low pressure microwave plasma. Short monochromatic photons pulse of 5-10 ns are focused in the plasma and used to selectively populate one Ar 4p state from an Ar 4s metastable state. The cascade kinetics response through the Argon excitation space (as well as for analytes present in the plasma phase) is then observed in real time while looking at selected atomic or molecular transitions. Experiments were carried on for pure Ar plasmas as well as Ar with small admixture of N2.

Cold atmospheric plasmas (CAPs) are a topic of growing interest nowadays, especially due to their applicability in material processing and biomedical applications. The laser scattering techniques of Thomson, Rayleigh and Raman provide precise measurements of the electron temperature, electron density, and the gas temperature. These laser scattering diagnostic methods are advantageous due to the high spatial and temporal resolution that they can achieve. In this contribution we aim to address the possibilities of laser scattering techniques as well as the main complications that come into play when they are applied to cold atmospheric discharges. A classical problem for Thomson scattering experiments is the false stray light, which might deteriorate the detection limit. As a consequence of their low gas temperature and open air operation, CAPs present high concentrations of molecules. This implies that the Thomson and Raman spectra will overlap, and therefore the two signals must be precisely disentangled. Another characteristic of CAPs is the low ionization degree which can induce deviations in the electron energy distribution function (EEDF). These deviations mainly affect the tail of the EEDF. An energy region that is not easy to measure by Thomson scattering. Finally, the laser heating of the electron gas is another issue which has to be considered. In the case of CAPs the contribution to the laser-heating intermediated by electron-atom collisions cannot be neglected. To place the specific features of laser scattering techniques in a broader perspective we will compare the CAP results to those obtained on low pressure plasmas.

In this contribution we report the application of time resolved laser induced fluorescence (tr-LIF) experiments on low pressure surfatron plasmas with pure argon and argon mixed with molecules (O2, N2 and H2). In this technique a tuneable dye laser can be used to perturb one particular excited level, obtaining information from the response to the perturbation. In our experimental setup a high repetition rate Nd:YAG laser is used to induce the dye emission, increasing substantially the output intensity and reducing the measuring time. In this experimental study we pump different excited levels of the argon system, always from the argon metastable group. Studying the decay time of the fluorescence signal for different plasma conditions in combination with precise Thomson scattering measurements of the electron density, enable us to obtain the rates for the collisional processes that depopulate the levels, namely the heavy particle quenching and the inelastic electron-atom collisions rate. Simultaneously, trLIF measurements give information about the populations of the bottom level of the perturbed, providing spatial distributions of the argon metastable levels along the plasma. Finally, the response to the laser perturbation of different excited argon levels apart from the perturbed one, or even the response of different species (H, N, O radicals) can also give information about the interactions in the excitation space.

In this contribution we report the application of time resolved laser induced fluorescence (tr-LIF) experiments on low pressure argon surfatron plasmas to obtain insight in the argon excitation kinetics. In this experimental study we pump two excited levels of the argon system in the 4p and 5p group. Studying the decay time of the fluorescence signal for different plasma conditions in combination with precise Thomson scattering measurements of the electron density, enable us to obtain the rates for the collisional processes that depopulate the levels, namely the heavy particle quenching and the inelastic electron-atom collisions rate. We have measure depopulation rates one order of magnitude larger for the higher excited levels. We have also observed increase of the electron collision rates for lower gas pressures as well as indications of self-absorption of the studied 4p line under low pressure conditions (

In this study we investigate a pulsed microwave discharge at low pressure using time resolved Thomson scattering (TS). The plasma is surface wave induced, launched by a surfatron device. That provides a spatially extended plasma coloumn with well-known properties. A frequency doubled Nd:YAG laser is focused in the plasma detection volume. The scattered photons on free electrons were detected, using a sophisticated spectrometer setup to reject the laser wavelength. Due to the high temporal and spatial resolution of this laser scattering techniques we were able to measure the immediate response of the electron density and temperature on power pulsing for various pulse lengths and frequencies. Conclusions about the recombining nature of the decay process could be drawn.

Pulsed microwave discharges at low pressure were investigated using time resolved Thomson scattering. The response of the electron density and temperature on power pulsing is investigated for different working gases, such as pure Ar and Ar admixtures with N2, and O2.

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We show results of the characterization of an atmospheric argon plasma with the use of laser scattering. The plasma source that is used is a surfatron plasma with argon. We looked at Rayleigh scattering to de-termine the gas temperature, and at Thomson scattering to determine the electron temperature and den-sity. The Thomson scattering efficiency is very low (~10-15) and therefore care must be taken to filter un-wanted stray light. For this we used a triple grating spectrometer. The triple grating spectrometer has a mask to filter out the central wavelength, which consists of stray light and the Rayleigh signal. With the mask in place we can measure Thomson scattering and Raman scattering, the latter of which is used to calibrate the Thomson signal. With the mask removed we can measure Rayleigh scattering. Several pro-files of the gas temperature, electron temperature and electron density are presented.

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In the present work Stark broadening measurements have been carried out on low electron density (neb5·1019 m-3) and (relatively) low gas temperature (Tgb1100 K) argon–hydrogen plasma, under low-intermediate pressure conditions (3 mbar–40 mbar). A line fitting procedure is used to separate the effects of the different broadening mechanisms (e.g. Doppler and instrumental broadening) from the Stark broadening. A Stark broadening theory is extrapolated to lower electron density values, below its theoretical validity regime. Thomson scattering measurements are used to calibrate and validate the procedure. The results show in agreement within 20%, what validates the use of this Stark broadening method under such lowdensity conditions. It is also found that Stark broadened profiles cannot be assumed to be purely Lorentzian. Such an assumption would lead to an underestimation of the electron density. This implies that independent information on the gas temperature is needed to find the correct values of ne.