Table of contents

Atmospheric pressure plasmas, and streamers in particular, sustained in air often encounter dust or aerosol particles having sizes of a few to tens of micrometres. The dynamics of streamers intersecting such particles are of interest due to their possible use for functionalizing the surfaces of the particles. Using a 2-dimensional plasma hydrodynamics model having an unstructured mesh, the consequences of dust particles on streamer dynamics were investigated while varying the particle size, shape and material properties. We found that while small dielectric particles (< tens of micrometres) are enveloped by the streamer, larger particles can intercept and reinitiate streamers. By increasing the permittivity and capacitance of the particles, streamer interception and re-initiation may also occur on smaller particles. The presence of multiple particles in the path of a streamer can increase the speed of the avalanche front due to synergistic polarization of the particles.

An atmospheric pressure glow discharge plume (APGD-p) using a dielectric barrier discharge reactor with one conductive liquid electrode was designed in our study. The preliminary characteristics of the plume and application in the degradation of a dye, methyl violet 5BN (MV-5BN), were presented in this paper. The APGD reactor produced a cold plasma plume with temperature not higher than 320 K at power 5–50 W. The MV-5BN solution as a probe for dye wastewater was treated by the downstream gases of the plasma plume. The results indicated that the active argon (Ar) and nitrogen (N₂) gases had little effect on the MV-5BN degradation, but the air and oxygen (O₂) gas depleted the organic molecules effectively. In particular, the downstream O₂ gas degraded the dye molecules entirely.

The decomposition of carbon dioxide in a plasma reactor was investigated experimentally, using capillary discharge tubes with a diameter of 0.5 or 3.0 mm and a length of 25, 50, 75, 100 or 150 mm. The chemical composition of the reaction products and the current–voltage characteristics were measured over a pressure range of 3.33–120 Torr, and the CO₂ conversion rates and reduced electric fields were calculated. The results show that the influence of downscaling on the reduced electric fields can be well evaluated by adjusting both the current density, i, and the products of the pressure and the tube diameter, pd. However, the characteristics of CO₂ decomposition cannot be determined based on i and pd; they are better characterized by i and p. It can be deduced from our experimental results that the CO₂ conversion rate is predominated by the electron impact CO₂ dissociation and gas phase reverse reactions even in a capillary plasma reactor.

We report the observations of pinching in a miniature plasma focus (PF) (58—160 J) operated in repetitive mode using fast pseudospark switch (PSS). The size of the device, which includes the capacitor bank, PSS and the focus chamber, is of the order of 22 cm × 22 cm × 38 cm. Several diagnostic tools, the gated imager, streak camera, current and voltage probe, are employed simultaneously to confirm the occurrence of pinching in this fast miniature PF device. The device is optimized for operation in neon and hydrogen as the working gas. The best focus formation was obtained at pressures between 0.5 to 8.0 mbar for neon and between 7.0 to 15.0 mbar for hydrogen. When the system was operated at 100 J with hydrogen as the filling gas, the typical dip in the current derivative signal and the typical peak in the voltage signal associated with pinch compression, are observed to be most intense indicating efficient pinching in the miniature PF device.

The knowledge of absolute concentrations of radicals in molecular discharges, such as the density of atomic hydrogen in H₂ plasmas, is crucial for understanding processes at the surface and is, therefore, of great interest in a variety of plasma applications. Reliable spectroscopic methods are indispensable for the determination of the degree of dissociation in processing plasmas. In this paper, we describe a novel optical emission spectroscopy method called two-gas actinometry (TGA). It is based on using a second actinometer gas to take into account dissociative excitation, which is of particular importance at comparatively low degrees of dissociation. TGA is employed for measuring the characteristic dependence of the degree of dissociation, in a wide range of plasma parameters, in an inductively coupled radio-frequency hydrogen plasma. Absolute densities with high accuracy are obtained using two-photon absorption laser-induced fluorescence spectroscopy.

Dielectric barrier discharges (DBDs) are investigated in helium and nitrogen as a function of pressure from 5 to 1000 mbar. Different regimes are observed: glow, Townsend, multi-peak and filamentary, depending on pressure, power and electrode gap. In helium, DBD is a glow-like discharge with a transition to multi-peak or Townsend discharge at high power. In nitrogen, the discharge is Townsend-like and shows a transition to multi-peak mode below 300 mbar. Transition to filamentary mode is observed for large gaps. Fast exposure imaging is used to investigate multi-peak mode in nitrogen. Electrical measurements and time-resolved optical emission spectroscopy are used to characterize the discharge, to study the evolution of metastable species as a function of the pressure and to analyse the discharge startup. These results offer new perspectives for the operation of DBDs in low vacuum.

A Nd:Yag laser operating at 1064 nm, 900 mJ maximum pulse energy and 9 ns pulse duration, is employed to irradiate solid tin targets placed in a high vacuum (10⁻⁷ mbar). The Sn plasma produced on the target surface is investigated with different analysis techniques, such as ion collectors, mass quadrupole spectrometry, electron microscopy and surface profilers. Measurements of ablation threshold, ablation yield, atomic and molecular emission, ion and neutral emission are reported. A time-of-flight technique is employed to calculate the velocity and the kinetic energy of the ion emission from the plasma. The angular distributions of the ejected ion species and of their kinetic energy are strongly peaked along the normal to the target surface. A valuation of the electric field generated inside the non-equilibrium plasma is given and discussed.

The theoretical values of the numerical evaluation of the electron and ion diffusion coefficients in plasmas from mixtures of argon and fluorine are presented. The temperature dependence of the diffusion coefficients for low-pressure (from 0.1 to 1.0 kPa) and low-temperature (from 500 to 5000 K) argon plasmas with 20% and 30% of added fluorine are investigated. These values are results of the applications of the specific numerical model to the evaluation plasma composition and transport coefficients in argon plasma with fluorine as additive. It is assumed that the system is kept under constant pressure and that a corresponding state of local thermodynamical equilibrium (LTE) is attained. Since the LTE can be assumed, a Maxwellian electron distribution function will be adopted. The hypothesis of LTE, which is commonly used in most of the numerical evaluations, is analysed with the modified Debye radius .

The binary electron and ion diffusion coefficients are calculated with the equilibrium plasma composition and with the collision frequencies. Strictly speaking, Maxwellian distribution function (in the state LTE) is not valid for low pressure, but in this case with the aid of the modified Debye radius, a Maxwellian is assumed correctly. It is shown that the electron diffusion coefficients are about four orders of magnitude larger than the corresponding overall diffusion coefficients of ions. Both diffusion coefficients are lower in argon plasma with 30% than with 20% of fluorine additives, in the whole temperature range examined.

In the simulation of streamer discharge propagation, classical integral methods used to calculate the photoionization source term are computationally very expensive. In this work, a new approach based on the direct solution of an approximate radiative transfer equation is developed. Different approximations of the radiative transfer equation are discussed and tested for typical conditions encountered in streamer discharges. An improved Eddington approximation is shown to be very accurate to calculate the photoionization term for a Gaussian emission source term with a half-width length of the order of 0.02 cm when the absorption coefficient of the gas is higher than or equal to 50 cm⁻¹. For steeper gradients of the source term, good agreement is obtained for higher values of the absorption coefficient. Furthermore, the computation time of the improved Eddington method is four orders of magnitude less than with the usual integral method. For streamer propagation in air at atmospheric pressure, the absorption coefficient is shown to be of the order of 130 cm⁻¹ which validates the use of the improved Eddington approximation to calculate the photoionization term. Finally, two-dimensional calculations of a positive streamer discharge in air at atmospheric pressure in plane–plane geometry with the improved Eddington approximation are presented.

This paper deals with the diagnostics of a high power pulsed magnetron sputtering device (HPPMS). The HPPMS plasma was spatially and temporally characterized in the post-discharge using optical absorption spectroscopy and Langmuir probe time resolved measurements. A circular titanium target was used, the buffer gas was argon and the pressure was fixed at 4 Pa. The titanium densities (neutrals and ions) were measured by a pulsed resonant absorption spectroscopy technique. We found an ionization degree higher than 0.5. Comparison beetween the experimental results and a simple one-dimensional model of diffusion shows that in these conditions, the transport of neutral and ionized sputtered atoms is mainly controlled by diffusion (ambipolar diffusion for ions).

It is shown that a presheath near a wall in fully ionized collisional plasma is unstable due to resistive excitation of electrostatic drift waves. The instability depends on the plasma inhomogeneity and resistivity but is independent of the particle flows to the wall. The wave spectrum and growth rate were calculated using a fluid model of the plasma and the Wentzel–Kramers–Brillouin approximation. The electron-wave collision frequency and the additional diffusion flux of the particles were calculated. The resistive instability may be a cause of the fluctuations in plasma parameters observed in transporting vacuum arc plasma beams through magnetized ducts.

A hybrid model was used to simulate a dc argon micro glow-discharge at atmospheric pressure. The simulations were carried out for a pin-plate electrode configuration with inter-electrode gap spacing of 200 µm together with an external circuit. The predicted voltage–current characteristics and current density profiles identify the discharge to be a normal glow-discharge. The neutral gas temperature predictions indicate that the discharge forms a non-thermal, non-equilibrium plasma. Experimental studies were conducted to validate the numerical model. Predictions from the numerical model compare favourably with the experimental measurements.

Currently, research on accelerator driven subcritical systems (ADSS) is gaining significance due to their high safety levels and extremely attractive potential in terms of both thorium utilization and nuclear waste transmutation. While high energy and high current proton beams are being built worldwide, intensive efforts are being undertaken in parallel towards the development of complex lead bismuth eutectic target systems. The major focus is directed towards understanding of the material compatibility and detailed thermohydraulic simulation of the liquid metal flow. The requisite heat flux is being deposited using innovative and easily controllable heat sources. This paper presents an experimental and simulation study to explore the potential of using dc arc plasma torches as a tailored heat source for thermohydraulic simulation of proton beam–target interaction in such systems.

Molecular dynamic simulations are performed to investigate SiF₃ continuously bombarding the amorphous silicon surface with energies of 10, 25, 50 and 100 eV at normal incidence and room temperature. Saturation of the uptake of F atoms on the surface is observed. At above 10 eV, the transition from deposition to etching occurs. Accompanying the saturation of F atom deposition on the surfaces, balance between etching of Si atoms from the substrate and deposition of Si atoms from incident SiF₃ is established. This behaviour is in good agreement with the experimental data. The Si_xF_y interfacial layer through which Si atoms in the initial substrate are carried to the surface to form volatile products is formed, whose thickness increases with incident energy. The composition of the interfacial layer is discussed.

This paper investigates the validity of the similarity law in cases of dc and pulse breakdown of gases. Geometrically similar systems insulated with SF₆ gas were used during experiments. It is shown that the similarity law is valid for dc breakdown voltage if the electron mean free path is included in geometrical parameters of the system, but not for pulse breakdown voltages. The explanation for this is the mechanism of the pulse discharge. The similarity law was expanded to take into account mechanisms of pulse breakdown initiation. Thus, the general similarity law is obtained, the validity of which in case of a pulse breakdown is established experimentally.

Gas-phase and surface analysis techniques were utilized to investigate the effects of gas-phase species on plasma deposited diamond-like carbon (DLC) thin films. A vacuum system was built to perform Langmuir probe and energy analysis-based mass spectrometry measurements to characterize the gas-phase of low pressure, 13.56 MHz inductively coupled plasma molecular beams. Low-energy peaks contributed significantly to the total area of the ion energy distributions (IEDs) measured for Ar⁺ in Ar and CH₄/Ar plasmas. In contrast, for all other ions in these systems, the low-energy peaks had a lower contribution to the IEDs as a result of the low probability of energy exchange via ion–neutral collisions. Hydrogenated DLC films were deposited on silicon wafers at different substrate potentials to determine the effect of ion bombardment on film properties. Films were characterized via Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy and nanoindentation measurements. The hydrogen content, surface roughness and deposition rate decreased, whereas the hardness of the films increased when a negative bias voltage was applied. These results demonstrate that ion energy has a significant effect on the composition and morphology of plasma deposited DLC films.

One of the modern trends in the development of electron cyclotron resonance (ECR) sources of multicharged ions is enhancement of the power and frequency of microwave pumping. Therefore, gyrotrons—powerful sources of radiation in the millimetre wavelength range—are now used for the creation and heating of plasma. These generators of microwave radiation are capable of producing and confining plasma of very high density (10¹³ cm⁻³ and higher), thus providing conditions for a substantial increase in the extracted ion beam current. Most ECR sources use for plasma confinement mirror magnetic traps with 'min B' configuration, which suppress MHD plasma instabilities. However, it is extremely difficult to construct such systems for pumping frequencies higher than 30 GHz because strong magnetic fields of complicated configuration are needed. All this makes the search for simpler axisymmetric MHD-stable systems for plasma confinement very topical.

A cusp trap produced by two coils with opposite currents is the simplest MHD-stable magnetic trap. Magnetic lines at any point of plasma in such a trap have a curvature that suppresses MHD perturbation in the plasma. In the present work the possibility of creation of an effective ECR source of multicharged ions based on a cusp magnetic trap was investigated numerically and in experiments. The pioneer result is the realization of the quasi-gasdynamic regime of plasma confinement in the trap of the multicharged ion ECR source of multicharged ions with cusp configuration of the magnetic field. Experiments were made with a small cusp trap which was designed for plasma creation by 37.5 GHz gyrotron radiation under ECR conditions. The total current and ion charge state distribution in the extracted ion beam were studied. The results of experiments with the simplest kind of cusp trap have demonstrated good correspondence with theoretical calculations, and therefore the adequacy of the developed approach and the possibility to build more effective source on this basis. Two ways of possible evolution of ECR ion sources based on a cusp magnetic trap are proposed.

Separation mitigation using asymmetric dielectric barrier discharges is studied by considering the neutral gas flow past a flat plate at an angle of attack. A self-consistent plasma actuator model is employed to couple the electric force field to the momentum of the neutral gas. The equations governing the motion of electrons, ions and neutrals are solved with Poisson's equation to study effective control of flow separation. The impact of select parameters such as amplitude of the excitation, dielectric constants, the initial ionization level and the electrode shape is elucidated. It is found that the dielectric surface just downstream of the exposed electrode becomes negatively charged during part of the cycle for the chosen work parameters and a time averaged force acts on the plasma predominantly downstream, with a transverse component towards the wall. The momentum of the plasma couples to neutral gas through collisions, which results in the enhancement of near-wall momentum yielding a wall-jet feature that effectively eliminates the separation bubble.

A fluid-plasma model of diffusion-controlled cylindrical inductive discharges in an argon gas is presented. The plasma-field structure of the discharge obtained is completed by the interrelated behaviour of concentrations of charged particles, electron temperature, power absorbed on average by an electron, radial distribution of the components of the high-frequency field, of the Joule heating and of the high-frequency current density in the plasma. The self-consistency of the model and its validity over a wide pressure range (p = (0.05–5) Torr) is reached by involving detailed treatment of the electron energy balance, of the nonlinear processes in the charged particle balance and of the momentum equations. By accounting for the velocity dependence of the elastic electron–neutral collision frequency, concepts from the kinetic plasma theory are introduced in a fluid-plasma description of the discharge. The analysis of the results is in terms of changing gas pressure, power and frequency of the maintenance field. The changes of the parameters of the external coil due to the plasma loading in the coil are also discussed.

The exit velocity of singly-charged xenon ions is determined by means of Fabry–Pérot interferometry at the exhaust of a high-power PPSX000 Hall effect thruster by analysing the Doppler shifted spectral profile of the 541.91 nm Xe⁺ ion line. A technique combining numerical simulations and CCD imaging is used to re-adjust the obtained velocity profiles in space, as this information is lost due to the accumulation of light along the line of sight. The applied voltage is varied from 200 to 900 V, and the xenon mass flow rate is varied from 5 mg s⁻¹ to 15 mg s⁻¹ to investigate the evolution of both the ion speed and the distribution of the accelerating potential over a broad power range. The goal of these measurements is twofold, namely, collecting reliable and extensive data and looking for a simple correlation between thruster parameters and corresponding accelerating potential distributions. Furthermore, this study reveals the presence of low velocity ions in the vicinity of the thruster channel exhaust.

A steady-state submerged arc discharge stabilized by a water stream is modelled as a plasma bubble water. On the upstream boundary of the bubble, the water is evaporated, and the water vapour is dissociated and ionized. With a directed water velocity of ∼ 1 m s⁻¹, the convective heat flux in the water stream direction is much more than the conducted flux. For a discharge power of ∼ 100 kW, the plasma bubble will have a length of ≈0.115 m and a radius of ≈0.018 m; the maximum plasma temperature will be ≈3800 K and the minimum plasma to water density ratio will be ≈5 × 10⁻⁵. The flow of plasma and water through a tube was considered using conservation laws. A criterion for tube chocking was obtained: pressure in the water upstream of the plasma bubble is determined by the discharge power and bubble cross-section. The plasma radiation is approximately black body in the core of the bubble, but on the boundary with the liquid water it is depressed in the ultraviolet region due to a strong absorption by the neutral hydrogen and oxygen atoms.

Langmuir probes used in radiofrequency (rf) discharges usually include compensation elements that minimize the effect of high frequency oscillations in plasma potential. The design of these elements requires knowledge of the capacitance of the sheath on the probe tip, a quantity which varies nonlinearly during the rf cycle. Sheath capacitance has been studied previously for capacitively coupled discharges, where the rf is applied to the electrodes. Here the problem is treated from the standpoint of a small probe in a fluctuating discharge. This work differs from existing literature in that (a) no step model is used and the Debye sheath is treated exactly, (b) the treatment is simple and analytic, (c) the time-variation of the capacitance is explicitly shown, (d) the results are applied to probe design and (e) cylindrical geometry is considered. The rf frequency is assumed low enough that electron transit times can be ignored. We find that when the rf excursions bring the sheath from the Child–Langmuir region into the Debye sheath or electron saturation region, its capacitance has a strongly non-linear behaviour.

The gas temperature in plasma enhanced chemical-vapour-deposition is a key parameter to determine the properties of deposited films because it influences gas-phase reactions of radicals and surface reactions of precursors. In this paper, we report the measurement results of the gas temperature determined from optical emission spectroscopy of molecular spectra and discuss heating of the growing surface of the film. It is found that the gas temperature linearly increases with the plasma density and the surrounding wall temperature. The surface heating is dominated by collisions with high-temperature gas molecules in a plasma generated at a high gas pressure condition. The measurements are performed in a hydrogen diluted silane plasma generated by very-high-frequency discharge under a high-rate growth condition of hydrogenated micro-crystalline silicon for photovoltaic applications.

We present experimental results of the spatial distribution of Ar and Ti optical emission and absorption lines in Ar–Ti plasma during sputtering of Ti. Measurements were performed in a dc magnetron reactor with movable planar magnetron using optical emission/absorption spectroscopy. A study was made for two different working pressures: 0.5 and 4 Pa. The results show that the intensity of emission lines decay exponentially with the increase in the distance from the target with two different decrements which correspond to the different parts of the discharge, namely the plasma region with a steep decay (up to about 1.5 cm from the target) and the 'far' region with a slow decay (more than 2 cm away from the target). Ti absorption data reveal similar behaviour. The emission decrement values which correspond to the steep decay of intensity lie in the range 1.4–3 cm⁻¹, whereas those for slow decay group around 0.3 cm⁻¹.

The large gas reservoir surrounding the H-1NF plasma leads to difficulties in achieving the density control required to maximize the plasma temperature. We have designed and tested an alternative fuelling system which uses a double conical nozzle to generate a directed flow of particles into the plasma without adding to the gas inventory in the rest of the vacuum vessel. By using a closed plenum at a programmable pressure and a piezo-electric valve, the particle flux can be dynamically changed in a controlled and quantitative manner. Measurements of the gas jet using constant temperature hot wire anemometry show that, for plenum pressures between 500 and 1000 Torr, the particle injection rate (helium) ranges between 2 × 10²⁰ and 4 × 10²⁰ s⁻¹ with half-cone angles between 5° and 20°. The system has been installed on the H-1NF device and first plasma results indicate localized gas injection consistent with test tank anemometry measurements.

The present developments of Hall thrusters for satellite control and space mission technologies represent a new step towards their routine use in place of conventional thermal thrusters. In spite of their long R and D history, the complex physics of the E × B discharge at work in these structures has prevented, up to now, the availability of predictive simulations. The electron transport in the accelerating layers of these thrusters is one of the remaining challenges in this direction. From the experimental point of view, any diagnostics of electron transport and electric field in this critical layer would be welcome for comparison with code predictions. Appropriate diagnostics are difficult, due to the very aggressive local plasma conditions. This paper presents the first step in the development of a new tool for characterization of the plasma electric field in the very near exhaust thruster plume and comparison with simulation code predictions.

The main idea is to use very short bursts of electrons, probing local electron dynamics in this critical plume area. Such bursts can be obtained through photoelectric emission induced by a UV pulsed laser beam on a convenient target. A specific study, devoted to the characterization of the electron burst emission, is presented in the first section of the paper; the implementation and testing of the injection of electrons in the critical layer of Hall thruster plasma is described in the second section. The design and testing of a fast and sensitive system for characterizing the transport of injected bursts will be the next step of this program. It requires a preliminary evaluation of electron trajectories which was achieved by using simulation code. Simulation data are presented in the last section of the paper, with the full diagnostic design to be tested in the near future, when runs will be available in the renewed PIVOINE facility. The same electron burst injection could also be a valuable input in the present discussion on the physics of the 5–10 MHz instability observed in almost all Hall thrusters.

DC normal glow (NG) discharges were created in atmospheric pressure air for a pin to plate type geometry. The rotational and vibrational temperatures of the discharge were measured by comparing modelled optical emission spectra with spectroscopic measurements from the discharge. The temperatures were measured as a function of discharge current, ranging from 50 µA to 30 mA, and discharge length, ranging from 50 µm to 1 mm. Rotational temperatures from 400 to 2000 K were measured over this range. Vibrational temperatures vary from 2000 K to as high as 5000 K indicating a non-equilibrium plasma discharge. Spectroscopic measurements were compared using several different vibrational bands of the 2nd positive system of N₂, the 1st negative system of and the UV transitions of NO. NO and transitions were also used to determine the electronic temperature and density. The discharge temperature appears to be controlled by two cooling mechanisms: (1) radial conductive cooling which results in an increase in temperature with increasing discharge current and (2) axial cooling to the electrodes which results in a temperature saturation with increase in discharge current. The measured discharge temperature initially increases rapidly with discharge current then becomes nearly constant at a higher discharge current. Thus, radial cooling appears to dominate at lower discharge currents and the axial cooling at higher discharge currents. The vibrational temperature decreases with increasing rotational temperature due to increased vibrational to translation relaxation but the discharge remains non-thermal and stable over the range studied. The discharge appears to have a maximum vibrational temperature at the low current limit of the NG regime.

The experimental work reported here is devoted to the electrical study of two atmospheric pressure dielectric barrier discharge (DBD) reactors operating at high gas flow, conceived for surface treatment applications in spatial afterglow conditions. Both reactors are of coaxial geometry with the dielectric covering the active electrode, and are driven by a power generator delivering quasi-sinusoidal voltage waveforms in the 100–160 kHz range. The influence of the gas flow value and of the input power on the electrical operation of these systems is investigated. The comparative study performed here, by means of electrical measurements, reveals the influence of parameters such as geometrical dimensions and dielectric material used on the operation of the DBD. Power factor measurements are used to quantify the reactors' electrical performance. Optical diagnostics and kinetic modelling reveal a high chemical activity of the systems appropriate for the treatment of surfaces at atmospheric pressure.

A rich variety of patterns including travelling hexagon, travelling square, quasi-crystal, static hexagon and stripe have been studied in a dielectric barrier discharge system. The phase diagram of pattern types as a function of air concentration and the applied voltage is given. The spatio-temporal correlations between discharge filaments in these patterns are measured in a nanosecond time scale by an optical method. It is found that the travelling pattern is an interleaving of two sub-patterns with a temporal sequence inversion in consecutive half-cycles.

A dielectric barrier discharge in a 2 mm air gap was studied. The experiments show that the mesh electrode and PET film really make the discharge looking homogeneous. The breakdown onset voltage in the case of a mesh electrode and PET film is 6.4 kV, considerably lower than 8 kV, the breakdown voltage in the usual case using two spherical electrodes. The field calculations show that even with this much lower voltage the gap field in the region very close to the PET film is enhanced to a value near the breakdown field in the usual case. It may be this field enhancement that initiates a corona discharge which provides seed electrons, leading to the breakdown of the whole air gap at a lower voltage. A lower voltage applied to the gap means a lower averaged field over the gap. Because the development of an electron avalanche is very sensitive to the electric field, a small decrease in the field will depress the avalanche significantly, preventing a homogeneous discharge from transiting to filament discharge. This may be the reason why a mesh electrode and PET film make the discharge look homogeneous.

In this paper we report on the optimization of an experimental arrangement of DBD type, aiming to work in a He + N₂ environment, applied to the surface treatment of polymers. Here the discharge was systematically investigated on an extended range of the gas mixture composition, using electric parameter measurement and emission spectroscopy. The effects of the He + N₂-DBD treatment on the surface of a test material are examined, compared with results obtained on the He-DBD treatment. The surface characterization was performed using contact angle measurement, AFM imaging and XPS analysis, so allowing the selection of treatment parameters for reproducible, efficient and stable surface modification.

Knowledge of the absolute densities of small radicals like CF, CF₂ and CF₃ in fluorocarbon plasmas is essential for a fundamental understanding of plasma chemical processes and plasma surface interaction. Infrared absorption spectroscopy by means of tunable diode lasers (IR-TDLAS) was established and widely used for density measurements in the last decade. The often unknown parameter in the calculation of absolute radical densities from a measured absorption of a single line is the rotational temperature. In particular, a strong dependence of the line strength on rotational temperature has a significant influence on density calculation. In this paper we report on measurements of the CF₂ rotational temperature in capacitively coupled CF₄/H₂ plasmas (CCP) with rf (13.56 MHz) powers up to 200 W. Rotational temperatures in continuous and pulsed modes of the discharge were found to be between 300 and 450 K. Furthermore, first measurements of the time dependence of the rotational temperature in pulsed rf plasma are presented. The rotational temperature rises in the plasma phase within 0.1 s and goes down again to the temperature of the background gas in the plasma pause within 0.5 s. It is also shown that accurate density measurements of the radicals by means of single line absorption need correct information about the rotational temperature and careful selection of a suitable absorption line.

In this work, we study a cascaded arc in argon that is used as a broadband light source for spectroscopic applications. In this arc, the arc channel is geometrically constricted. A numerical model is used to investigate the plasma parameters and light output of the arc. It is found that constricting leads to a higher electron density in the constricted area, which strongly enhances the local broadband emission of the plasma. A parameter study, in which the current is varied, is performed. The simulated arc voltages are compared with measured arc voltages, and excellent agreement is found. Furthermore, it is found that the emissivity increases strongly for increasing current, making the current a suitable control parameter to control the light output of the arc.

Plasma potential fluctuations are measured with an emissive probe in low-pressure CF₄ plasma produced by a 13.56 MHz rf source. The inflection point method in the limit of zero emission is employed to determine the plasma potential. The maximum and minimum values of the plasma potential are observed. The values of the potential fluctuations depend on the rf source power, the amplitude of the applied voltage and the plasma density. The variations in the plasma potential fluctuations with the source power show the plasma mode changes from a capacitively coupled to an inductively coupled and then to a helicon mode. Electron density, temperature and ion saturation currents measured with a double probe also exhibit the transition. A Langmuir probe is employed to measure the floating potential and its fluctuation and the result verifies the same transition.

Argon plasma characteristics in a dual-frequency, capacitively coupled, 300 mm-wafer plasma processing system were investigated for rf drive frequencies between 10 and 190 MHz. We report spatial and frequency dependent changes in plasma parameters such as line-integrated electron density, ion saturation current, optical emission and argon metastable density. For the conditions investigated, the line-integrated electron density was a nonlinear function of drive frequency at constant rf power. In addition, the spatial distribution of the positive ions changed from uniform to peaked in the centre as the frequency was increased. Spatially resolved optical emission increased with frequency and the relative optical emission at several spectral lines depended on frequency. Argon metastable density and spatial distribution were not a strong function of drive frequency. Metastable temperature was approximately 400 K.

There is much interest in scaling rf-excited capacitively coupled plasma reactors to larger sizes and to higher frequencies. As the size approaches operating wavelength, concerns arise about non-uniformity across the work piece, particularly in light of the well-documented slow-surface-wave phenomenon. We present measurements and calculations of spatial and frequency dependence of rf magnetic fields inside argon plasma in an industrially relevant, 300 mm plasma-processing chamber. The results show distinct differences in the spatial distributions and harmonic content of rf fields in the plasma at the three frequencies studied (13.56, 60 and 176 MHz). Evidence of a slow-wave structure was not apparent. The results suggest that interaction between the plasma and the rf excitation circuit may strongly influence the structures of these magnetic fields and that this interaction is frequency dependent. At the higher frequencies, wave propagation becomes extremely complex; it is controlled by the strong electrical nonlinearity of the sheath and is not explained simply by previous models.

The PDF file provided contains web links to all articles in this volume.

Low temperature plasma physics is the driving force of plasma technology which is considered to be one of the key technologies of the 21st century. Due to its central importance to many technologies there is a great demand for highly educated plasma scientists worldwide. Compared to its significance, education in low temperature plasma physics in Germany and other European countries is limited to a relatively small number of universities and institutions.

In the last decade research groups located in France, Germany, Ireland, Italy, The Netherlands, Portugal, Switzerland and the United Kingdom have enjoyed fruitful co-operation in founding a series of annual European summer schools with extraordinary success. These schools were organized by Daniel C Schram (Center for Plasma Physics and Radiation Technology (CPS), Eindhoven University of Technology, The Netherlands), Jörg Winter and Marc Böke (both CoE for Plasma Science and Technology (CPST), Ruhr-Universität Bochum, Germany). The purpose of the schools is to give new graduate students in Europe a solid introduction in and concise overview of low temperature plasma physics and to serve as a forum for providing coherent education in plasma science. The schools have become a part of the curriculum in participating universities. Our experiences have shown that contact between students and teachers forms the basis of enduring interaction. The emphasis has been on fundamental education and the in-depth treatment of subjects such as plasma sources and production, thermal and low pressure plasmas, atomic processes, plasma kinetics, diagnostics, modelling and plasma-surface interactions.

After the publication of eight lecture notes as a special section in Plasma Sources Science and Technology volume 9 issue 4 in 2000 we are now able to present four additional notes. Publishing the notes in 2000 was an experiment in itself and we found that the readers of Plasma Sources Science and Technology appreciated this type of presentation. The advantages were twofold: students were introduced to the journal and the content of the lectures could be flexible and change each year. The hope that the journal could profit and increase its readership community has been fulfilled with the great success of the first publication, proven by the huge download rates of most of the notes. However, some aspects could not be treated in the original publication. Now, both compilations serve as an introduction for readers to important subjects in plasma physics. They will be forwarded to the students of the 2007 school and could also serve as an introduction to future schools. The forthcoming schools will be held, as in the past 6 years, at the Physikzentrum Bad Honnef in Germany, organized jointly by the CPS and CPST.

We would like to thank all our colleagues for their continuous support and willingness to contribute to the education provided by the schools. Without their contributions and personal engagement the schools would not have been possible.

We would also like to thank the following school sponsors:

• The European Community • The WE Heraeus Foundation • The Center for Plasma Physics and Radiation Technology (CPS) • The CoE for Plasma Science and Technology (CPST) of Ruhr-Universität Bochum • Arbeitsgemeinschaft Plasmaphysik APP • Research Training Group GK 1051 • Collaborative Research Centre SFB 591.

Finally, we would like to thank the members of the local committees and also the management of the Physikzentrum.

These lecture notes are intended to give an introductory course on plasma spectroscopy. Focusing on emission spectroscopy, the underlying principles of atomic and molecular spectroscopy in low temperature plasmas are explained. This includes choice of the proper equipment and the calibration procedure. Based on population models, the evaluation of spectra and their information content is described. Several common diagnostic methods are presented, ready for direct application by the reader, to obtain a multitude of plasma parameters by plasma spectroscopy.

Within the last decade mid-infrared absorption spectroscopy over a region from 3 to 17µm and based on tuneable lead salt diode lasers, often called tuneable diode laser absorption spectroscopy or TDLAS, has progressed considerably as a powerful diagnostic technique for in situ studies of the fundamental physics and chemistry in molecular plasmas. The increasing interest in processing plasmas containing hydrocarbons, fluorocarbons, organo-silicon and boron compounds has led to further applications of TDLAS because most of these compounds and their decomposition products are infrared active. TDLAS provides a means of determining the absolute concentrations of the ground states of stable and transient molecular species, which is of particular importance for the investigation of reaction kinetic phenomena. Information about gas temperature and population densities can also be derived from TDLAS measurements. A variety of free radicals and molecular ions have been detected by TDLAS. Since plasmas with molecular feed gases are used in many applications such as thin film deposition, semiconductor processing, surface activation and cleaning, and materials and waste treatment, this has stimulated the adaptation of infrared spectroscopic techniques to industrial requirements. The recent development of quantum cascade lasers (QCLs) offers an attractive new option for the monitoring and control of industrial plasma processes. The aim of the present paper is threefold: (i) to review recent achievements in our understanding of molecular phenomena in plasmas, (ii) to report on selected studies of the spectroscopic properties and kinetic behaviour of radicals and (iii) to describe the current status of advanced instrumentation for TDLAS in the mid-infrared.

In this paper we describe the hitherto unravelled facts on the interactions of a cold atmospheric plasma with living cells and tissues. A specially designed source, plasma needle, is a low-power discharge, which operates under the threshold of tissue damage. When applied properly, the needle does not cause fatal cell injury which would result in cell death (necrosis). Instead, it allows precise and localized cell removal by means of the so-called cell detachment. In addition, plasma can be used for bacterial disinfection. Because of mild treatment conditions, plasma disinfection can be performed in vivo, e.g. on wounds and dental cavities. Presently, one strives to obtain a better control of the operating device. Therefore, plasma has been characterized using a variety of diagnostics, and a smart system has been designed for the positioning of the device with respect to the treated surface.

In this tutorial work, the Monte Carlo method to simulate the kinetics of charged particles in weakly ionized gases is explained. The method is collocated in the wider context of the general Monte Carlo and propagation methods. Besides providing the necessary background to develop basic models for the linear and the non-linear transport case, some more advanced topics are treated, e.g. the inclusion of the thermal distribution of neutral particles and the differential weighting technique.