Plasma Research Express

The traveling-wave tube (TWT), also known as the traveling-wave amplifier (TWA) or traveling-wave tube amplifier (TWTA), is a widely used amplifier in satellite communications and radar. An electromagnetic signal is inputted on one end of the device and is amplified over a distance until it is extracted downstream at the output. The physics behind this spatial amplification of an electromagnetic wave is predicated on the interaction of a linear DC electron beam with the surrounding circuit structure. Pierce, known as the 'father of communications satellites,' was the first to formulate the theory for this beam-circuit interaction, the basis of which has since been used to model other vacuum electronic devices such as free-electron lasers, gyrotrons, and Smith-Purcell radiators, just to name a few. In this paper, the traditional Pierce theory will first be briefly reviewed; the classic Pierce theory will then be extended in several directions: harmonic generation and the effect of high beam current on both the beam mode and circuit mode as well as 'discrete effects', giving a brief tutorial of recent theories of TWTs.

This tutorial is intended to provide a basic overview of plasma catalysis, which is considered an emerging branch of plasma processing. This highly versatile technique can provide not only a route to produce highly specialized materials such as semiconductors and nanostructures at mild conditions, but it can open new pathways towards the decentralized production of several specialty chemicals such as ammonia, by pairing this technology with renewable electricity sources. Moreover, plasma catalysis offers the advantages of one pot ultra-fast reactions with minimal waste production as compared to traditional wet chemistry synthesis techniques. However, in order to completely exploit the full potential of plasma catalysis, a strong fundamental understanding of the effects of plasma on catalyst, catalyst on plasma and its synergism should be gained. This is a prospect that can be achieved by a multidisciplinary knowledge of the phenomena occurring at the plasma gas phase and at the interphase plasma-catalyst. Here in, first principles of plasma catalysis are presented. The main goal of this brief tutorial is to transmit to the scientists willing to explore this research area, the main characteristics that make this plasma research field so promising as a sustainable route to solve current energy and environmental challenges.

Fundamental processes for electric breakdown, i.e., electrode emission and bulk ionization, as well as the resultant Paschen's law, are reviewed under various conditions. The effect of the ramping rate of applied voltage on breakdown is first introduced for macroscopic gaps, followed by showing the significant impact of the electric field nonuniformity due to gap geometry. The classical Paschen's law assumes uniform electric field; a more general breakdown scaling law is illustrated for both DC and RF fields in geometrically similar gaps, based on the Townsend similarity theory. For a submillimeter gap, effects of electrode surface morphology with local field enhancement and electric shielding on the breakdown curve are discussed, including the most recent efforts. Breakdown characteristics and scaling laws in microgaps with both metallic and non-metallic (e.g., semiconductor) materials are detailed. For gap distance down to micro/nano scales, the breakdown characteristics and the breakdown mode transition from the secondary electron emission to the electric field emission or thermionic emission dominant regime. Additionally, the combined thermo-field emission regime is also reviewed. Previous efforts, including key simulations and experiments, have been devoted to diagnosing breakdown path evolution, measuring breakdown fields, and quantifying breakdown dependence on frequencies for gaps down to micro/nano scales. By summarizing and analyzing fundamental theories, recent progress, and on-going challenges, this tutorial review seeks to provide basic understanding and the state of the art of electric breakdown, which aids in advancing discoveries and promoting application prospects for discharge devices engineered in a wide range of regimes.

High-density reactive species plasmas uniformly covering large surface areas are required for semi-conductor processing. Novel, self-matched plasma sources using microwave solid state generators have been developed for this purpose. The technology applied, based on automatic frequency tuning, allowed to eliminate the impedance matching system. Large surface plasmas have been achieved by using a distribution of elementary sources. A big campaign of plasma density measurement using a Langmuir probe has allowed to create a database for different plasma conditions for a single source. Thanks to an internally developed software, the density obtained with several sources in various distribution configurations has been simulated. The position and the power of each source have been optimized and the calculations have been validated by experimental measurements. High plasma densities >10¹¹ cm⁻³ over large areas >400 mm in diameter with only 13 plasma sources have been achieved with all tested gases. An increase of compactness i.e., increasing the sources number over the same area, allows to have the same plasma surface while increasing the plasma density up to 5 × 10¹¹ cm⁻³.

Atmospheric non-thermal plasma is gaining increasing attention for various applications including food, medical and healthcare technologies because of its unique capability in producing reactive species. In spite of its promising potential, generating non-thermal plasma over large and complex geometries such as the human body or a narrow channel is still challenging and is limiting the use of atmospheric non-thermal plasma. In this study, we propose two new electrode systems, printed and knitted electrodes, to enhance scalability and flexibility of a conventional atmospheric non-thermal plasma source. The flexibilities of both electrode systems are quantified for varying curvatures to generate non-thermal plasma over complex geometries. Moreover, both electrode systems are assessed for varying system size to assess the ability of large scale plasma geometries. Electrical and optical diagnostics including Optical Emission Spectroscopy (OES), are used to monitor the property of plasma generated by these systems. The present study shows that both printed and knitted electrodes can produce non-thermal plasma, however both have certain limitations. Concluding from these findings, a schematic of new hybrid electrode system for the treatment of large surfaces or narrow long channels is proposed to eradicate these limitations.

Decolorization of Acid Orange 142 (AO142) as important water pollutant was observed on the exposure of the dye solutions to an atmospheric non-thermal gas plasma. A response surface methodology (RSM) combined with a central composite design (CCD) was utilized to optimize the main factors (variables) affecting the degradation efficiency (response) of AO142, such as the applied voltage, the gap distance between the high voltage electrode and the surface of the solution. The regression analysis showed that a first-order polynomial model well fits the experimental data with a coefficient of determination R² = 0.96. FT-IR, UV-vis, TOC and GC-MS measurements were used to investigate the decolorization of the dye on exposure to the plasma discharges. A possible degradation pathway was postulated. Additionally, the conductivity and pH changes during the treatment were also evaluated. The plasma treatment combined with Fe²⁺ (plasma Fenton reaction) exhibited a higher degradation efficiency, higher energy yield connected with lower energy consumption in comparison to the plasma treatment without Fe²⁺ addition.

The SMall Aspect Ratio Tokamak (SMART) device is a novel, compact (R_geo = 0.42 m, a = 0.22 m, A ≥ 1.70) spherical tokamak, currently under development at the University of Seville. The SMART device is being developed over 3 phases, with target on-axis toroidal magnetic fields between 0.1 ≤ B_ϕ ≤ 1.0 T, and target plasma currents of between 35 ≤ I_p ≤ 400 kA; with phases 2 and 3 enabling access to a wide range of elongations (κ ≤ 2.30) and triangularities ( − 0.50 ≤ δ ≤ 0.50). SMART employs four internal divertor coils with two internal and two external poloidal field coils, enabling operation in lower-single, upper-single and double-null configurations. This work examines phase 3 of the SMART device, presenting a prospective L-mode discharge scenario without external heating, before examining five highly-shaped equilibria, including: two double null triangular configurations, two single null triangular configurations and a baseline double null configuration. All equilibria are obtained via an axisymmetric Grad-Shafranov force balance solver (Fiesta), in combination with a circuit equation rigid current displacement model (RZIp) to obtain time-resolved vessel and plasma currents.

The growth rate of bump on tail instability propagating in unmagnetized plasma has been derived. The dispersion relation has been characterized for (r, q) distribution function with spectral indices r and q which ultimately contributes towards tails and shoulder of distribution function. The growth rate of the bump on tail instability has been estimated numerically for different ratios of temperature and number density using solar wind data and also by varying values of indices r and q . The higher value of q play the role towards decreasing the growth rate where the instability has the higher value when the number density of the superthermal electrons in the bump is higher and the temperature is low. The maximum growth rate increases with the increase in number density of electrons and decreases with the increasing temperature in the bump.

Fundamental knowledge of the electric arc properties is important for the development of process control of electric arc furnaces. In this work, a pilot-scale AC electric arc has been studied with optical emission spectroscopy together with filtered camera footage. The properties of the arcs were determined with plasma diagnostics and image analysis in order to obtain both the characteristic plasma parameters and the physical form of the arc. The plasma temperatures, ranging from 4500 to 9000 K, were derived individually for three elements. The electron densities of the plasma were between 10¹⁸ and 10²⁰ cm⁻³ and fulfilled the local thermal equilibrium criterion, but the plasma temperatures derived from atomic emission lines for different elements had high and unpredictable differences. The properties of the electric arcs have been studied with respect to the arc length derived from the image analysis. The slag composition, especially the relative FeO content of over 30%, was observed to have a notable effect on the brightness of the arc on slag and thus also on the radiative heat transfer.

Argon and hydrogen plasmas were produced by a Compact ECR Plasma Source (CEPS) attached coaxially to a large chamber. This paper presents characterization results of the two plasmas using a newly designed Langmuir Probe. Experiments in argon were conducted to benchmark the plasma parameters and to determine the efficacy of the CEPS for thruster applications, recommended by recent results (Ganguli et al 2019 Plasma Sources Sci. Technol. 28 035014), while the hydrogen experiments were undertaken to determine the typical range of plasma parameters for assessing the usefulness of CEPS for different applications. In argon plasma, high densities (≈10¹² cm⁻³), high electron temperatures and plasma potentials are obtained at fairly low pressures ≈0.3–0.5 mTorr. The plasma potential drops substantially (≈65 V) within the CEPS itself, demonstrating its suitability as a plasma thruster. On the other hand, plasma densities are lower for hydrogen in front of the CEPS, and the electron temperatures and plasma potentials, higher. The hydrogen experiments have helped establish an important aspect of such plasmas. At low pressures (≈0.5 mTorr) plasma density is relatively low with a single, high temperature electron population; on the other hand, at higher pressures (≈6 mTorr), the plasma has two electron populations, a low temperature, high density population and another low density, high temperature warm population. For hydrogen this transition from the former (with single electron population) to the latter state (with two electron populations) occurs at a pressure, ≈3 mTorr while similar transition for argon occurs at ≈0.3 mTorr. Apart from the observed two states of plasma, each state with its own distinctive properties, another important feature of the hydrogen plasma is that the axial density profiles obey approximately n/B = constant although no such scaling is observed for argon.

This tutorial is intended to provide a basic overview of non-equilibrium phenomena for thermal plasmas. Thermal plasmas (TPs) mainly issued from electrical discharges are often assumed to be in ≪ equilibrium ≫ as opposed to ≪ non-equilibrium plasmas ≫ where non-equilibrium phenomena are more pronounced. As a first approximation it can be shown that TPs are close to a local thermodynamic equilibrium (LTE) which is often taken as their reference state. However, in many situations, deviations from LTE can clearly exist. The main goal of this brief tutorial is to explain to interested scientists the main phenomena, mechanisms and characteristics associated to TPs or quasi-TPs. Then we introduce the different laws of the thermodynamic equilibrium applied to these plasmas and show that not all of them are valid in TPs, which lead us to define the LTE. However, even if the transport phenomena are non-equilibrium mechanisms, we show with illustrations that they are studied and estimated within the framework of the LTE. The next sections focus on phenomena named 'departures from equilibrium' for thermal plasmas. For convenience and educational reasons, we split them into the departures from the chemical and the thermal equilibria respectively. In each case we present and clearly define the mechanisms that promote equilibrium and those that tend to create departures. We present not only experimental setups that highlight these deviations but also the basis for the mathematical models that allow them to be simulated, before concluding the tutorial with the outlooks and challenges currently under research.

A compact microwave plasma has been employed as an ion source for focused ion beam applications, that can provide non-toxic ions and facilitate rapid processing of materials without introducing any metallic contamination. A variety of microstructures with high aspect ratio (line width/depth) (∼100–1000) relevant to the energy and current regimes, are created on copper thin films using 26 keV Ne, Ar and Kr ion beams. A mathematical formulation is developed to calculate the impact of the ion beams, which act as energetic projectiles falling onto the target sample, by defining a new parameter called 'current normalized force' which is the total momentum transferred per unit time, normalized with the beam current. Capillary guiding of the plasma ion beams has demonstrated beam self-focusing which can be employed to further reduce the beam source size (plasma electrode aperture) for demagnification. Particle-in-cell (PIC) simulations are performed to interpret the experimental results of self-focusing. Hysteresis in beam current with extraction voltage (ion energy) is observed and the hysteresis area is used to calculate the dissipated charge from the beam during capillary transmission. The effect of plasma and beam parameters on focal dimensions has been investigated, and a unique feature of enhanced nonlinear demagnification is observed when the aperture size of the plasma electrode is reduced to below the Debye length. Submicron focusing of plasma ion beams is observed by minimizing the space charge effects and reducing the plasma electrode aperture (source size).

The traveling-wave tube (TWT), also known as the traveling-wave amplifier (TWA) or traveling-wave tube amplifier (TWTA), is a widely used amplifier in satellite communications and radar. An electromagnetic signal is inputted on one end of the device and is amplified over a distance until it is extracted downstream at the output. The physics behind this spatial amplification of an electromagnetic wave is predicated on the interaction of a linear DC electron beam with the surrounding circuit structure. Pierce, known as the 'father of communications satellites,' was the first to formulate the theory for this beam-circuit interaction, the basis of which has since been used to model other vacuum electronic devices such as free-electron lasers, gyrotrons, and Smith-Purcell radiators, just to name a few. In this paper, the traditional Pierce theory will first be briefly reviewed; the classic Pierce theory will then be extended in several directions: harmonic generation and the effect of high beam current on both the beam mode and circuit mode as well as 'discrete effects', giving a brief tutorial of recent theories of TWTs.

Fundamental processes for electric breakdown, i.e., electrode emission and bulk ionization, as well as the resultant Paschen's law, are reviewed under various conditions. The effect of the ramping rate of applied voltage on breakdown is first introduced for macroscopic gaps, followed by showing the significant impact of the electric field nonuniformity due to gap geometry. The classical Paschen's law assumes uniform electric field; a more general breakdown scaling law is illustrated for both DC and RF fields in geometrically similar gaps, based on the Townsend similarity theory. For a submillimeter gap, effects of electrode surface morphology with local field enhancement and electric shielding on the breakdown curve are discussed, including the most recent efforts. Breakdown characteristics and scaling laws in microgaps with both metallic and non-metallic (e.g., semiconductor) materials are detailed. For gap distance down to micro/nano scales, the breakdown characteristics and the breakdown mode transition from the secondary electron emission to the electric field emission or thermionic emission dominant regime. Additionally, the combined thermo-field emission regime is also reviewed. Previous efforts, including key simulations and experiments, have been devoted to diagnosing breakdown path evolution, measuring breakdown fields, and quantifying breakdown dependence on frequencies for gaps down to micro/nano scales. By summarizing and analyzing fundamental theories, recent progress, and on-going challenges, this tutorial review seeks to provide basic understanding and the state of the art of electric breakdown, which aids in advancing discoveries and promoting application prospects for discharge devices engineered in a wide range of regimes.

This tutorial is intended to provide a basic overview of plasma catalysis, which is considered an emerging branch of plasma processing. This highly versatile technique can provide not only a route to produce highly specialized materials such as semiconductors and nanostructures at mild conditions, but it can open new pathways towards the decentralized production of several specialty chemicals such as ammonia, by pairing this technology with renewable electricity sources. Moreover, plasma catalysis offers the advantages of one pot ultra-fast reactions with minimal waste production as compared to traditional wet chemistry synthesis techniques. However, in order to completely exploit the full potential of plasma catalysis, a strong fundamental understanding of the effects of plasma on catalyst, catalyst on plasma and its synergism should be gained. This is a prospect that can be achieved by a multidisciplinary knowledge of the phenomena occurring at the plasma gas phase and at the interphase plasma-catalyst. Here in, first principles of plasma catalysis are presented. The main goal of this brief tutorial is to transmit to the scientists willing to explore this research area, the main characteristics that make this plasma research field so promising as a sustainable route to solve current energy and environmental challenges.

Plasma discharges can be transient and randomly distributed where a few investigations have been carried out using laser-induced fluorescence to capture snapshots of plasma-produced radicals in the near vicinity of the discharge. Radical distribution dynamics, however, are challenging to study in situ with high spatial and temporal resolution to fully capture the interactions between the discharge and the gas. We here demonstrate a planar laser-induced fluorescence method that can capture molecular distributions of ground state hydroxyl radicals in a discharge plasma and follow how the distribution develops in time with a repetition rate of 27 kHz. The technique is demonstrated by monitoring, in real-time, how the tube-like distribution of ground state OH radicals, surrounding a gliding arc plasma, is affected by flow dynamics and how it develops as the high voltage is turned off at atmospheric pressure. The method presented here is an essential tool for capturing radical-distribution dynamics in situ of chemically active environments which is the active region of the plasma induced chemistry.

An atmospheric-pressure argon plasma jet featuring a novel integrated resonator-based multi-frequency impedance matching is presented and briefly characterized. Two narrow RF frequency bands can be chosen for operation or used simultaneously. This includes a mode with the higher frequency value being exactly five times the lower one. Phase-resolved optical emission spectroscopy measurements show a distinct influence of the input frequency combination on the discharge dynamics. Measurements of the dissipated electrical power and the emission spectrum for each operating mode complete the basic characterization of the device. Although it is constructively much simpler and more compact than dual-frequency discharges using a conventional impedance matching system, the presented device shows an excellent performance in dual-frequency operation.

A set of soft x-ray cameras provided measurements of high frequency instabilities as well as steady-state emission in the Mega Amp Spherical Tokamak (MAST). It is shown that Abel inversion can be readily applied to fluctuating soft x-ray emission from the MAST midplane associated with fast particle-driven 'fishbone' instabilities, characterised by toroidal mode number n = 1. Each fishbone burst had an early phase in which high amplitude fluctuating soft x-ray signals from the plasma core were close to being in phase with each other, and there was a region close to the outboard plasma edge in which the fluctuations were relatively weak and in antiphase with those in the core. The major radius of the 'phase axis' at which the mode amplitude changed sign R_p was initially outboard of the tokamak magnetic axis at R₀, but moved inboard during the burst, eventually becoming close to R₀, at which time the oscillations were of similar amplitude inboard and outboard of R_p. The fishbone radial structure early in the burst can be understood in part by recognising that the mode is supported by energetic ions with a high average toroidal rotation rate: in a co-rotating frame, the effective magnetic axis is shifted outboard by a distance that is comparable to the difference between the major radii of the phase axis early in the burst and the laboratory frame magnetic axis. It is conjectured that the transition to a mode with R_p ≃ R₀ occurred because most of the energetic ions were expelled from the plasma core region where the mode amplitude peaked, so that the instability could no longer be characterised as an energetic particle mode. Abel inversion of fishbone soft x-ray emission thus provides useful insights into the nature of energetic particle modes in tokamak plasmas and their relationship with MHD modes.

High-density reactive species plasmas uniformly covering large surface areas are required for semi-conductor processing. Novel, self-matched plasma sources using microwave solid state generators have been developed for this purpose. The technology applied, based on automatic frequency tuning, allowed to eliminate the impedance matching system. Large surface plasmas have been achieved by using a distribution of elementary sources. A big campaign of plasma density measurement using a Langmuir probe has allowed to create a database for different plasma conditions for a single source. Thanks to an internally developed software, the density obtained with several sources in various distribution configurations has been simulated. The position and the power of each source have been optimized and the calculations have been validated by experimental measurements. High plasma densities >10¹¹ cm⁻³ over large areas >400 mm in diameter with only 13 plasma sources have been achieved with all tested gases. An increase of compactness i.e., increasing the sources number over the same area, allows to have the same plasma surface while increasing the plasma density up to 5 × 10¹¹ cm⁻³.

Cyanide, among with NO_x, CO₂, and CO, is one of the adverse compounds that form in the ironmaking and steelmaking industry. High-temperature processes are suitable environments for cyanide formation, and cyanide can form as a result of recombination in electric arc plasma. Even though the cyanides might not survive e.g. the post-combustion process, understanding the formation mechanisms of hazardous materials in the steelmaking industry is important. In this work, the recombination of cyanide in a pilot-scale AC electric arc furnace is studied with optical emissions from the CN molecule. The results show how the optical emissions from the cyanide change in different process steps. Electric input, plasma temperature, and interaction of the arc with solid charge material were observed to have an impact on the CN signal. Additionally, equilibrium composition computation highlights how different sources of carbon change the recombination rate and that the highest recombination occurs at 6821 K.

Atmospheric non-thermal plasma is gaining increasing attention for various applications including food, medical and healthcare technologies because of its unique capability in producing reactive species. In spite of its promising potential, generating non-thermal plasma over large and complex geometries such as the human body or a narrow channel is still challenging and is limiting the use of atmospheric non-thermal plasma. In this study, we propose two new electrode systems, printed and knitted electrodes, to enhance scalability and flexibility of a conventional atmospheric non-thermal plasma source. The flexibilities of both electrode systems are quantified for varying curvatures to generate non-thermal plasma over complex geometries. Moreover, both electrode systems are assessed for varying system size to assess the ability of large scale plasma geometries. Electrical and optical diagnostics including Optical Emission Spectroscopy (OES), are used to monitor the property of plasma generated by these systems. The present study shows that both printed and knitted electrodes can produce non-thermal plasma, however both have certain limitations. Concluding from these findings, a schematic of new hybrid electrode system for the treatment of large surfaces or narrow long channels is proposed to eradicate these limitations.

Negative hydrogen ion sources for NBI systems at fusion devices rely on the surface conversion of hydrogen atoms and positive ions to negative hydrogen ions. In these sources the surface work function is decreased by adsorption of caesium (work function of 2.1 eV), enhancing consequently the negative ion yield. However, the performance of the ion source decreases during plasma pulses up to one hour, suggesting a deterioration of the work function. Fundamental investigations are performed in a laboratory experiment in order to study the impact of the plasma on the work function of a freshly caesiated stainless steel surface. A work function of 2.1 eV is achieved in the first 10 s of plasma, while further plasma exposure leads to the removal of Cs from the surface and to the change of the work function: a value of around 1.8–1.9 eV is measured after 10–15 min of plasma exposure and then the work function increases, approaching the work function of the substrate (≥4.2 eV) after 5 h. The Cs removal must be counteracted by continuous Cs evaporation, and investigations performed varying the Cs flux towards the surface have shown that a Cs flux of at least 1.5 × 10¹⁶ m⁻²s⁻¹ is required to maintain a work function of 2.1 eV during long plasma exposure at the laboratory experiment.

We report the design, fabrication, and experimental characterization of the first additively manufactured, miniature, metal multi-needle ionic wind pumps in the literature. The pumps are needle-ring corona diodes composed of a monolithic inkjet binder-printed active electrode, made in stainless steel 316L, with five sharp, conical needles, and a thin plate counter-electrode, made in copper, with electrochemically etched apertures aligned to the needle array; by applying a large bias voltage across the diode, electrohydrodynamically driven airflow is produced. The influence of tip multiplexing and tip sharpening on the ion current, airflow velocity, volumetric flow rate, and kinetic conversion efficiency of the pumps was characterized under different interelectrode separations, counter-electrode aperture diameters, and applied bias voltages, while triggering a negative corona discharge. At the optimal operating bias voltage (7.4 kV), the as-printed five-needle ionic wind pumps eject air at 2.66 m s⁻¹ and at a volumetric flow rate of 316 cm³ s⁻¹ –a twofold larger than the flow rate of an as-printed single-needle device and with 35% higher efficiency (i.e. 0.27%). Using a two-step electropolishing procedure, the needles of the active electrode can be uniformly sharpened down to 83.4 μm average tip diameter, i.e. about one quarter of their as-printed dimension (∼300 μm). Operated under the same conditions, the electropolished five-needle pumps eject air at 3.25 m s⁻¹, i.e. 22% higher speed compared to the as-printed devices, with the same kinetic conversion efficiency. A two-module model was built in COMSOL Multiphysics, consisting of a three-species corona discharge module and a gas dynamics module, to gain insights into the operation of the pumps and to determine trends for increasing device performance. The electrohydrodynamic (EHD) body force calculated using this model has the same periodic behaviour of the Trichel pulse current. A time-dependent EHD body force analysis was performed, and the stabilized forces averaged over a multiple of the Trichel pulse period were used to predict the large-timescale airflow. The EHD force from the corona simulation can be rescaled to calculate the flow at different bias voltages, greatly reducing the simulation time, and making possible to systematically study the relevant parameters and optimize the design of the air pump. The experimental data agree with the simulation results and the reduced-order modelling.

ITER as the next-level fusion device is intended to reliably produce more fusion power than required for sustainably heating its plasma. Modeling has been an essential part of the ITER design and for planning of future experimental campaigns. In a tokamak or stellarator plasma discharge, impurities play a significant role, especially in the edge region. Residual gases, eroded wall material, or even intentionally seeded gases all heavily influence the confinement and, thus, the overall fusion performance. Nitrogen is such a gas envisaged to be seeded into a discharge plasma. By modeling the impurities kinetically using the full three-dimensional Monte-Carlo code package EMC3-EIRENE, we analyze the distribution of nitrogen charge-state resolved in a seeded ITER baseline scenario and draw conclusions for the hydrogen background plasma density. Lastly, we compare the influence of a more refined kinetic ion transport in EIRENE including additional physical effects on the impurity density.

An increased low-energy positron flux is obtained from the reactor based NEPOMUC source when using its primary beam at energies as low as 20 eV. First experiments with this beam in a supported magnetic dipole trap resulted in the maximum current of injected positrons to date. According to single-particle simulations, remaining limitations in the injection efficiency, observed in the experiment, can be attributed to the spatial spread of the beam. In the first trapping measurements with this beam, top-down asymmetries in the electrostatic trapping potential are found to be detrimental to confinement.