News

Awards

Rahel Buschhaus from SFB TR 87 project C7 wins a poster prize at DPG conference 2022

Rahel Buschhaus won the poster prize in the category 'Phd students in low-temperature plasma physics'. During the annual DPG spring meeting, she presented a poster entitled 'Ion-induced secondary electron emission of metal surfaces analyzed in an ion beam experiment'.

Publications

Achim von Keudell new Editor in Chief for Plasma Processes and Polymers

Achim von Keudell became with the beginning of March one of the four Editors in Chief of Plasma Processes and Polymers

Awards

Dissertation Award of the Faculty of Physics and Astronomy for Dr. Katharina Grosse.

The generation of plasmas in liquids is important for applications such as electrolysis, water purification or medicine, but also opens up a number of very fundamental questions. These plasmas are generated by short voltage pulses in the range of many kilovolts and a few nanoseconds in duration applied to a tungsten tip submerged in water. There is a lively debate around understanding the ignition of these plasmas, as electron multiplication during plasma ignition is postulated to occur either within small nanovoids, small fractures in the water, or as an electron avalanche in the water itself. In both cases, field emission at interfaces or field ionization of water molecules plays a crucial role. Dr. Grosse studied the whole dynamics of these plasmas from ignition to afterglow using time-resolved emission spectroscopy and compared it with modeling of emission and fluid dynamics. It showed that the broad continuum is produced by blackbody radiation, with a temperature of 7000 K, exactly equal to that of boiling tungsten. Electron densities of several 1025 m-3 can be derived from the strong broadening of the Balmer lines of the hydrogen atoms. Furthermore, a strong self-absorption of light from the region of the plasma channel is observed while light from the running ionization front shows no self-absorption. From this it can be deduced that the plasma runs directly through water and is not formed within nanovoids. Thus, field emission and field ionization dominate. After this first plasma pulse, the high power density leads to the phase transition from water to water vapor and bubble formation within the first microsecond. The high pressure in the range of GPa causes an expansion of the cavitation bubble and the generation of a sound wave propagating in the liquid. This could be directly observed using shadowgraphs. In particular, the speed of sound reaches several 1000 meters per second, indicating the very high pressure at the beginning of the discharge. Based on this measurement, Dr. Grosse has very significantly extended the understanding of these plasmas.

Funding

DFG approves second funding period of the CRC 1316

Plasmas for the Systems for material conversion are an important component in the utilization and storage of decentrally generated renewable energies. The Collaborative Research Center 1316 (CRC 1316) "Transient Atmospheric Pressure Plasmas - from Plasma to Liquids to Solids" is dedicated to combining atmospheric pressure plasmas with catalysis to develop the most flexible solutions possible for this material conversion. "They should be scalable, controllable and robust against external influences, such as impurities in the starting materials," explains Prof. Dr. Achim von Keudell, spokesman of the CRC.

The first funding period of the CRC 1316 was dedicated to the elucidation of transient phenomena in atmospheric pressure plasmas as well as interfacial processes at the surface of catalysts. Here, the focus was on three systems: the plasma-catalytic conversion of gases, the combination of plasmas with electrolysis at the interface between liquid and solid, and plasma-assisted biocatalysis, in which enzymes very selectively produce new molecules. The researchers were able to make great progress in these areas: For example, they achieved precise control of the formation of reactive particles in these plasmas. They were also able to gain a deeper understanding of the atomic and molecular surface processes in these systems.

In the second funding period, these findings will be brought together to make the best possible use of the interplay between a plasma with its reactive particles and a catalytically active surface. There are many further questions in this regard, since in traditional catalysis, for example, stable molecules are essentially reaction partners, whereas in plasma catalysis, reactive particles or highly excited species can accelerate or suppress a specific reaction path. On this basis, the first prototype plants for plasma catalysis, plasma electrolysis and plasma biocatalysis are to be developed.

In addition to the RUB as the host university, researchers from the University of Ulm, the Jülich Research Center and the Fritz Haber Institute in Berlin are involved in the CRC.

Funded Workshop

Hereaus Seminar in "Non-thermal plasmas for sustainable chemistry" on April 23-27, 2023

The Herause Foundation just funded a workshop on Non-thermal plasmas for sustainable chemistry organized by Yiguang Ju (Princeton), Tomohiro Nozaki (Tokyo Inst. technol.), Annemie Bogaerts (univ. Antwerp), and Achim von Keudell (RUB) to be held in Bad Honnef in April 2023.

Teaching

Hands-on Writing course

On 11st June, 18 EP2 members, students, PhDs, and PostDocs, participated in an online hands-on writing workshop provided by A. von Keudell. During the day, we learned language and structure tips and tricks for clearly delivering our research results and messages. We applied what we have learned directly by writing our own texts and based on them discussed typical mistakes. All in all, it was a motivating and fruitful workshop day.

Teaching

 

Mikroplasma-Versuch Online

 

Der Praktikums-Versuch 401 "Mikroplasmen" wurde jetzt so weit überarbeitet, dass er weitgehend selbständig Online durchgeführt werden kann.

Steuerung des Onlineversuchs Mikroplasmen

Der Versuch erlaubt die emissionspektroskopische Untersuchung eines Atmosphärendruck-  Mikroplasmajets. Dabei wird per Frensteuerung sowohl die Entladung bedient und überwacht, als auch Spannung und Strom aufgenommen. Schrittmotoren erlauben eine Positionierung einer Lichtfaser im Bezug zum Entladungskanal. Die Spektren eines damit gekoppelten Spektrographs werden aufgenommen und können anschließend ausgewertet werden.

 

HOCHLEISTUNGSPLASMEN

Plasmastrukturen im Detail analysiert

Als auffiel, dass Plasmen inhomogen sind, gefiel das nicht jedem. Dabei bringt diese Eigenschaft Vorteile mit sich, zum Beispiel für die Industrie. Für das bloße Auge sind sie oft unsichtbar: die hauchdünnen Schichten, die mithilfe von Plasmen auf Oberflächen abgeschieden werden. Zum Beispiel auf Architekturglas, um das Reflexionsvermögen zu steuern, auf Werkzeuge, um sie vor Verschleiß zu schützen, oder auf Kunststoffe, um sie dichter gegen den Durchtritt von Gasen zu machen. Aus der Industrie sind Plasmen nicht mehr wegzudenken. Zwar kann man Oberflächen auch mithilfe von chemischen Prozessen beschichten, aber dafür sind teils so hohe Temperaturen erforderlich, dass die zu beschichtenden Objekte schmelzen würden. Plasmen hingegen bringen die erforderliche Energie nicht durch Wärme auf, sondern durch die darin enthaltenden reaktiven Teilchen.

Research

Unraveling ns plasma physics of streamers in water

The spectra are dominated by the black body continuum from the hot tungsten surface and line emissions from the hydrogen Balmer series. Typical temperatures from 6000K up to 8000K are reached for the tungsten surface corresponding to the boiling temperature of tungsten at varying tungsten vapor pressures. The analysis of the ignition process and the concurrent spectral features indicate that the plasma is initiated by field ionization of water molecules at the electrode surface. At the end of the pulse, field emission of electrons can occur. During the plasma pulse, it is postulated that the plasma contracts locally at the electrode surface forming a hot spot. This causes a characteristic contribution to the continuum emission at small wavelengths. The spectra also show pronounced emission lines of the hydrogen Balmer series.

Nanosecond plasmas in liquids are an important method to trigger the water chemistry for electrolysis or for biomedical applications in plasma medicine. The understanding of these chemical processes relies on knowing the variation of the temperatures in these dynamic plasmas. This is analyzed by monitoring nanosecond pulsed plasmas that are generated by high voltages (HV) at 20 kV and pulse lengths of 15 ns applied to a tungsten tip with 50 micrometer diameter immersed in water. Plasma emission is analyzed by optical emission spectroscopy (OES) ranging from UV wavelengths of 250nm to visible wavelengths of 850nm at a high temporal resolution of 2 ns.

The data indicate two contributions of the hydrogen line radiation that differ with respect to the degree of self-absorption. It is postulated that one contribution originates from a recombination region showing strong self absorption and one contribution from a ionization region showing very little self-absorption. The emission lines from the ionization region are evaluated assuming Stark broadening, that yielded electron densities up to 5 x 10^25 m^-3. The electron density evolution follows the same trend as the temporal evolution of the voltage applied to the tungsten tip. The propagation mechanism of the plasma is similar to that of a positive streamer in the gas phase, although in the liquid phase field effects such as electron transport by tunneling should play an important role.

It is striking that the electron density follows closely the voltage applied to the electrode during the rising and falling edge of the pulse. In nanosecond plasmas in gases at atmospheric pressures, the voltage and current exhibit usually a delay in between with the voltage rising first followed by the current due to the delayed build-up of the electron density in the ionization avalanche. During the plasma propagation in the liquid, however, the density of species is three orders of magnitudes higher, so that the build-up of charges is expected to be much faster compared to the variation of the voltage. The same also holds for recombination that should exhibit time constants of the order of ps at these densities. The actual electron density is then a balance between generation of free electrons in the high electric fields and their loss due to recombination. This is consistent with the observation that the electron density follows also the decrease of the voltage with a time constant of 8 ns. The decay of the electron density is not a free decay due to recombination, but rather follows a decreasing equilibrium value as a competition between ionization and recombination.

RUBIN Serie "Was ist ein Körper für mich..."

Körper gibt es nicht

Verschiedene Disziplinen verstehen unterschiedliche Dinge unter dem Begriff „Körper“. Für die Physik stellt sich allerdings überhaupt nicht die Frage, was ein Körper ist.

Was ist ein Körper? Die Frage ist aus dem Blickwinkel der Physik falsch gestellt. Im Alltag nehmen wir die Körper in unserer Umgebung durch unsere Sinne wahr. Dabei findet eine Wechselwirkung von Teilchen mit diesem Körper statt, die uns Informationen über dessen räumliche Ausdehnung liefert: seien es die Lichtteilchen beim Sehen oder die Atome auf der Oberfläche unserer Hand beim Berühren. Die Art der Wechselwirkung bestimmt die Ausdehnung eines Körpers, die in der Atom- und Kernphysik in Streuexperimenten untersucht wird. Dabei beschießt man Atome oder Atomkerne mit bestimmten Teilchen und vermisst deren Ablenkung und Energieverlust. Als Projektile verwendet man Elektronen, Protonen, Neutronen oder Lichtteilchen – und je nach Art der Projektile und deren Energie unterscheiden sich die Ergebnisse deutlich. Mit Neutronen sieht man nur den Atomkern, mit Elektronen und Lichtteilchen eher die Atomhülle. Damit hat die Frage nach der Größe eines Atoms oder Atomkerns sehr viele Antworten. Diese Wechselwirkung hat auch im großen Maßstab Bedeutung. So ist die Größe eines Schwarzen Lochs eher durch die Grenze der Wechselwirkung von Licht mit der Gravitation definiert als durch die räumliche Ausdehnung des schweren Himmelskörpers in seinem Inneren.

Diese Arten der Wechselwirkung bestimmen unseren Umgang mit Körpern im täglichen Leben. So ist das Festhalten eines Buches mit Ihren Händen eigentlich die Wechselwirkung der Atome Ihrer Hand mit denen der Cellulose des Papiers, aus dem das Buch gemacht ist. Eines der wichtigsten Gesetze der Quantenphysik, das Pauli-Verbot, bestimmt, dass die Atome Ihrer Hände diejenigen des Papiers nicht so einfach durchdringen können. Deshalb liegt das Heft stabil in Ihren Händen und Sie können diesen Körper in seiner Größe wahrnehmen.

Foto: Damian Gorczany

Lehre

Online Lehre im Sommersemester 2021

Aufgrund der Coronakrise findet auch das Sommersemester 2021 als Online Semester statt. Dies stellt alle vor eine große Herausforderung, bietet aber auch die Chance sich mit digitalen Formen der synchronen oder asynchronen Lehre zu beschäftigen. Das Lehrteam von EP2 hat ein Konzept entwickelt bestehend aus Vorlesungsaufzeichnungen bzw. Vorlesungsstreaming, elektronischen Methoden zur Abgabe und Korrektur von Übungszetteln bis zu Videokonferenzlösungen für Sprechstunden und Übungsgruppen. 

Der reguläre Beginn der Veranstaltungen ist der 12.4.2021. Details zu den Veranstaltungen finden sie in den Moodlekursen

Bei jeglichen Fragen kontaktieren sie bitte die Dozenten direkt.

 

Research Visit

Visit at Masaryk University in Brno, Czech

J. Held, S. Monje, and A. von Keudell visited the plasma groups of Prof. P. Vasina and Dr. T. Hoder at Masaryk University in Brno from the 3rd to the 5th March 2020. They presented three lectures entitled ''Azimuthal Currents in HiPIMS plasmas - Hall current or spokes?'', ''Ns plasmas in liquids'', and a colloquium ''Plasma research in Bochum - from pascal to Gigapascal pressures".

Upcoming Workshop

7th International Plasma Science & Entrepreneurship Workshop

On November 2 & 3, 2020, the 7th International Plasma Science & Entrepreneurship Workshop takes place at the event centre of the Ruhr-Universität Bochum. The event is organized by Hugo de Haan (programme, Vision Dynamics), Guus Peemen (chair, TuE), and Achim von Keudell (host and chair, RUB).

  • Plasma medicine, medical and healthcare
  • Plasma Surface modification & thin films
  • Atmospheric pressure plasma @ Micro/Nano scale
  • Atmospheric pressure plasma jet (APPJ)
  • Nanoparticles generation and pariclesurface treatment
  • Surface diagnostics, energetics, analytics and –metrology
  • Plasma parameterization, diagnostics, simulation
  • Plasma for Emission Abatement & CO2
  • Plasma parameterization, diagnostics, simulation

The workshop will be a PhD (student) expert-level workshop focused on the achievements, challenges and opportunities for the scientific- and entrepreneurial  community working in the field.