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Johannes Gruenwald

Johannes Gruenwald
Gruenwald Laboratories GmbH · www.g-labs.eu

Dr.

About

58
Publications
217,083
Reads
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415
Citations
Citations since 2017
28 Research Items
277 Citations
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Introduction
I am professionally interested in plasma physics (but I like all other fields of physics as well) and in history, philosophy and mathematics as hobbies. At the moment I am working on a project which deals with the development of new deposition techniques for industrial applications and the fundamental understanding of the physical mechanisms involved therein.
Additional affiliations
January 2018 - present
Gruenwald Laboratories
Position
  • CEO
Description
  • We at Gruenwald Laboratories provide technical and scientific consulting in plasma science and nearly all other fields of science and engineering as well.
July 2016 - June 2017
Extreme Light Infrastructure
Position
  • Senior Researcher
March 2015 - present
Leibniz Institute for Plasma Science and Technology
Position
  • Senior Researcher
Education
August 2009 - December 2012
University of Innsbruck
Field of study
  • Experimental Physics
October 2003 - December 2008
Karl-Franzens-Universität Graz
Field of study
  • Experimental and theoretical Physics

Publications

Publications (58)
Article
The aim of this work is to propose a novel scheme for a small scale aneutronic fusion reactor. This new reactor type makes use of the advantages of combining laser driven plasma acceleration and electrostatic confinement fusion. An intense laser beam is used to create a lithium–proton plasma with high density, which is then collimated and focused i...
Article
Metal oxide coatings have a variety of applications in industrial processes. As some of them have bio-sensitive properties there is growing interest for their use in medical applications as well. Thus, the development of suitable deposition techniques is of major importance for these purposes. From these techniques plasma deposition at atmospheric...
Article
As there is a growing interest in conducting human missions to Mars, the need for suitable life support systems becomes more and more important. The reliability of such systems has to increase with the duration of manned missions. Furthermore the maintenance requirements have to be low in order to ensure their efficient use over a long period of ti...
Article
Full-text available
This paper describes the derivation of a simple engineering equation to calculate the minimal necessary bias voltage for the onset of an inverted fireball. The calculation uses the electron density in the absence of an inverted fireball as well as the grid constant and the working gas species as input parameters. It will be shown that the interplay...
Article
Full-text available
The surface of carbon films deposited with inverted plasma fireballs is analysed in this paper. Measurements were conducted with Raman spectroscopy, atomic force microscopy and nanoindentation. The latter was used to obtain Young's modulus as well as Martens and Vickers hardness. The roughness of the film was measured by atomic force microscopy and...
Article
Full-text available
In this paper we present for the first time the measurement of inverted fireballs in a low-pressure Ar/n-hexane plasma by using a Multipole Resonance Probe. The basic plasma parameters such as electron density, electron temperature and Debye length as well as the particle collision frequency have been obtained for different experimental settings. T...
Article
Full-text available
The work presented in this letter suggests that it is possible to enhance the yield in laser driven aneutronic fusion devices by fusion chain reactions. This mechanism will be described using the example of aneutronic fusion between an incoming high-energy proton beam and a 11 B target.
Article
In this paper the results of a first attempt to ignite an inverted fireball with a magnetron sputter source are presented. The conducted measurements show that there is no inverted fireball visible to the naked eye present during the experiments. However, some features are observed that indicate at least an initial onset of such an inverted firebal...
Article
Full-text available
The properties of sheaths and associated potential structures and instabilities cover a broad field which even a review cannot cover everything. Thus, the focus will be on about a dozen examples, describe their observations and focus on the basic physical explanations for the effects, while further details are found in the references. Due to famili...
Article
Full-text available
In this study the charging efficiency of a radioactive and a non-radioactive plasma bipolar diffusion charger (Gilbert Mark I plasma charger) for sub-12 nm particles has been investigated at various aerosol flow rates. The results were compared to classic theoretical approaches. In addition, the chemical composition and electrical mobilities of the...
Article
Full-text available
In this work, we present a copper oxide nanostructured analysed as a gas sensor, but the focus of the paper is on the temperature dependence of the sensor sensing properties. As a case study, temperature dependent diethylamine sensing is presented. The CuO nanoflakes were deposited and evenly distributed on intercalated electrodes by an atmospheric...
Preprint
Full-text available
Abstract. In this study the charging efficiency of a radioactive and a non-radioactive plasma neutralizer (Gilbert Mark I plasma charger) have been investigated at various aerosol flow rates. The results were compared to classic theoretical approaches. In addition, the chemical composition and electrical mobilities of the charger ions have been exa...
Article
Full-text available
Measurements regarding the plasma-sheath instability have been described in a recent paper [Phys. Plasmas 26, 113502 (2019)] by the authors Paul and Chakraborty. They measured low frequency oscillations in a cylindrical, highly transparent grid electrode by using Langmuir probes and magnetic field sensors. This topic is very interesting for low tem...
Conference Paper
Full-text available
Rogowski coils have been used to diagnose high energetic electron or proton beams since the seventies of the last century but usually these measurements were restricted to a single point on the beam axis. A new experimental concept is presented to measure the axial and radial density profiles of the laser-accelerated proton beam. We propose to use...
Article
Full-text available
The influence of the electron emission current on the beam-generated plasma is analyzed using the self-consistent one-dimensional Particle-in-Cell Monte Carlo collision model. It is established that the emission current can be used to control both the ion current and the ion energy at the anode. It is also found that for the values of the emission...
Article
In this paper an analytically derived dispersion relation for the Buneman instability in spherically confined plasmas is presented. The calculations are based on plasmas with spherical symmetry in which the dependence of the dispersion relation is, thus, only radial. This article is supposed to give a solution for said dispersion relation as this h...
Article
Full-text available
In this paper the possibility of utilising a plasma centrifuge for oxygen generation in outer space is discussed. It is proposed that a plasma centrifuge can not only create oxygen for human consumption very efficiently but is also able to produce useful by-products. Special emphasis is given to life support systems working in the atmosphere of Mar...
Article
Full-text available
As discovered in recent work, plasma fireballs have the ability to exert considerable force onto ions and neutrals and, hence, induce macroscopic gas flows. This property makes them interesting objects for fundamental scientific research. Furthermore, there are also the possibilities for applications in the field space propulsion. As there is a lac...
Article
The metal-oxides have raised significant scientific interest in recent years, due to their sensing properties. In is notable that the gas sensing properties can be enhanced by structural and morphological manipulation of the sensor. Previously was demonstrated that increasing the sensor surface to volume ratio during synthesis with formation of she...
Article
Full-text available
In this letter we present measurements of the influence on inhomogeneous electrode biasing on the basic plasma parameters of inverted fireballs in a hydrogen plasma. The measurements were performed in hydrogen because it is often used in many reactive plasmas, which are very important for technical or industrial applications. The dependence of the...
Article
Full-text available
An easy method to obtain the digestive index as a benchmark number for measuring the digestion capabilities of Apis mellifera is developed and presented in this paper. The aim of this method is to provide an entity that allows to quantifying digestion efficiency of the western honey bee. This will enable a fundamental understanding of digestive ill...
Article
Full-text available
It was highlighted in a very recent article by Guerra et al (2017 Plasma Sources Sci. Technol. 26 11LT01) the creation of oxygen out of the Mars atmosphere is viable. As this idea is not entirely new, this work aims at closing the gaps between this new article and some former work done by the author of this comment.
Article
In this paper, we present systematic measurements of the basic plasma parameters of inverted fireballs (FBs) in a helium plasma for the first time. Inverted FBs in helium with a diameter of 10 cm are generated in a highly transparent hollow electrode via impact ionisation of accelerated electrons from an existing background plasma. The measured qua...
Article
In order to introduce spatially resolved measurements of the plasma density in a plasma accelerated by a laser, a novel concept is proposed in this work. We suggest the usage of an array of miniaturized Rogowski coils to measure the current contributions parallel to the laser beam with a spatial resolution in the sub-mm range. The principle of the...
Article
Full-text available
Energy deposition into a plasma for an inverted fireball geometry is studied using a self-consistent two-dimensional Particle-in-Cell Monte Carlo collision model. In this model, the cathode is a pin which injects the fixed electron current and the anode is a hollow metal tube covered with the metal grid. We obtain an almost constant ratio between t...
Article
The article of Chauhan et al. [“Plasma fireball: A unique tool to fabricate patterned nanodots,” Rev. Sci. Instrum. 88(6), 063507 (2017)] describes the very interesting idea of utilising the plasma phenomenon of fireballs for the creation of patterned nanodots on a GaSb substrate. For this purpose, the authors obtained a large plasma fireball in a...
Article
Full-text available
A novel approach that employs the plasma phenomenon of inverted fireballs (FBs) was used to deposit chromium containing diamond like carbon (DLC) films on various substrates. The DLC films were obtained with a H2/CH4 feed-gas mixture. Three different types of substrates - graphite, SiC and stainless steel (SS) were coated with 4 – 12μm thick DLC fi...
Article
Front Cover: Nanostructured copper oxide films can be used in a large variety of technical applications such as bioactive surface coatings, low cost solar cells, gas sensors or pseudocapacitors. This paper demonstrates the successful deposition of such films with a non-thermal atmospheric pressure plasma source. The maximum temperature remained wel...
Article
Copper oxide films have been deposited successfully on borosilicate glass substrates with a copper containing nitrogen plasma at atmospheric pressure. This was done by using a nonthermal DC jet with a sacrificial electrode as copper source. The produced films have been systematically investigated by different methods, including scanning electron mi...
Article
This comment aims at clarifying some points in the very recent work of Chauhan et al. who presented an experimental study of a fireball (FB) configuration in a magnetized plasma, similar to R. L. Stenzel et al., Plasma Sources Sci. Technol. 21, 015012 (2012).
Article
Full-text available
A model of the behavior of transit time instabilities in an electrostatic confinement fusion reactor is presented in this letter. It is demonstrated that different modes are excited within the spherical cathode of a Farnsworth fusor. Each of these modes is dependent on the fusion products as well as the acceleration voltage applied between the two...
Article
The recent progress in plasma medicine as well as biomedical aspects of plasma physics over the last years have enhanced the need for experimental plasma devices which are capable of producing non-thermal atmospheric pressure plasmas. These plasma sources are used for studying the effect of non-thermal plasmas on biological samples of different nat...
Article
Full-text available
Inverted fireballs (FBs) are plasma phenomena, which develop inside a highly transparent, positively biased grid electrode through electron impact ionization. The ionizing electrons are accelerated into the grid by the high potential on the wires. This leads to an enhanced plasma density inside the hollow anode as well as a strong light emission. F...
Article
Full-text available
Recently discovered inverted fireballs are non-linear plasma phenomena, which are formed in hollow grid anodes with high transparency in an existing background plasma. If a sufficiently large potential is applied, accelerated electrons from the bulk start to oscillate through the grid. Experimental investigations have shown that they produce differ...
Article
Full-text available
As plans for human expeditions to the planet Mars become more numerous and ambitious, the need for reliable life support systems increases. These systems have to be light, robust and as simple as possible in terms of maintenance. Furthermore, they should rely on resupplies from earth as little because possible, since the necessary logistics to the...
Article
Full-text available
In this paper we present Langmuir probe measurements of inverted fireballs (FBs) in hydrogen plasma. Spatial profiles of the plasma potential and the electron densities were taken inside as well as outside an inverted FB. It was demonstrated that the plasma potential inside the FB is homogeneous and exhibits a strongly enhanced electron density. Fu...
Article
Full-text available
There are several planned projects that aim to send humans to Mars which are currently developed by the ESA, the NASA or by initiatives from the private sector (e.g. The Mars One Project). Some of these projects include long-term stays or even permanent human outposts on the red planet. To achieve the necessary habitats on Mars, a vast amount of di...
Article
Full-text available
Knowledge of the electron energy distribution function (EEDF) is of great interest in different branches of plasma physics ranging from laboratory to fusion plasmas. In the frame of this work systematic measurements of the EEDF in low temperature helium plasmas ( T e ≈ 2 eV) at different working gas pressures and discharge currents ( I dis between...
Article
Indirectly heated emissive probes have advantages compared to conventional emissive wire probes. We have developed a laser-heated emissive probe consisting of a 1 mm diameter and 2 mm long pin of LaB6, heated by a focussed laser beam of 808 nm wavelength with a power up to 50 W. This probe is smaller and simpler than electrically heated emissive wi...
Article
Full-text available
Fireballs are luminous regions produced by double layers in front of positively biased electrodes in plasmas. Although fireballs have been investigated previously there are a great variety of unexplained nonlinear phenomena, some of which are addressed in this work. First, it is shown that a fireball is not an isolated local phenomenon but an integ...
Article
Full-text available
Electron inertia causes a delay between high-frequency currents and electric fields. When the transit time of a bunch of streaming electrons equals one RF period, the electrons can enhance the field and produce oscillations. Here, electron transit-time instabilities have been observed in magnetized sheaths and fireballs. Novel fireballs trapped in...
Article
Full-text available
The evolution of an electron-rich sheath on a plane electrode has been investigated experimentally. A rapidly rising voltage is applied to a plane gridded electrode in a weakly ionized, low temperature, and field-free discharge plasma. Transient currents during the transition from ion-rich to electron-rich sheath are explained including the current...
Article
Full-text available
Instabilities in an electron-rich sheath on a plane electrode in a discharge plasma have been investigated experimentally. The high-frequency sheath-plasma instability near the electron plasma frequency is observed. With increasing dc voltage, the instability exhibits bursty amplitude and frequency jumps. The electrode current shows spikes and jump...
Article
Full-text available
High-frequency instabilities are observed in connection with unstable fireballs. Fireballs are discharge phenomena near positively biased electrodes in discharge plasmas. They are bounded by a double layer whose potential is of order of the ionization potential. Fireballs become unstable when plasma losses and plasma production are not in balance,...
Article
Full-text available
Emissive probes offer the possibility for a direct determination of the plasma potential since for sufficient electron emission its floating potential is ideally equal to Phi(pl). By means of two such probes the true electric field can be derived. Emissive probes also deliver reliable results if there are electron drifts and beams in the plasma. A...
Article
Full-text available
A fireball is formed inside a highly transparent spherical grid immersed in a dc discharge plasma. The ambient plasma acts as a cathode and the positively biased grid as an anode. A strong nearly current-free double layer separates the two plasmas. Electrons are accelerated into the fireball, ionize, and establish a discharge plasma with plasma pot...
Article
Full-text available
A new fireball configuration has been developed which produces vircator-like instabilities. Electrons are injected through a transparent anode into a spherical plasma volume. Strong high-frequency oscillations with period corresponding to the electron transit time through the sphere are observed. The frequency is below the electron plasma frequency...
Conference Paper
Full-text available
Fireballs are luminous phenomena, which evolve if a positively biased electrode is inserted into a thin background plasma with a sufficiently high neutral pressure. These phenomena show a wide variety of instabilities and nonlinearities and are therefore an interesting topic of fundamental plasma research. Unstable as well as stable fireballs have...
Article
Direct measurements of the plasma potential with high temporal and spatial resolution are only possible with special probes whose floating potential becomes equal to the plasma potential. One of these probes is the emissive probe which can be heated to electron emission. This leads to the effect that the plasma electron current towards the probe is...

Questions

Questions (23)
Question
Dear colleagues,
I have some Raman spectra that puzzle me - we did some coating with a hexane-Ar plasma on glass. Thus, I think the films are surely (hydro)carbon films. The Raman spectra we took show only three peaks (so, the glass substrate is neatly covered). My problem now is that I have troubles identifying these peaks, except for the one at 1344 /cm, which is the first order D peak of graphite in my opinion. But there are two more peaks, a quite sharp one at 1541 /cm and a broad one at 2853 /cm. The only value I could find in the literature so far for the former one would be single carbon nano tubes but this is not supported by SEM microscopy and for the latter one I have no clue. Maybe some Raman expert could help me with the identifaction. I attached a spectrum to have a look. The parameters of the measurement were: 1.6 mW Laser power at 532 nm.

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