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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 2020

Aufgrund der Coronakrise findet das Sommersemester 2020 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 20.4.2020. 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 & Interfaces Workshop

On November 2 & 3, 2020, the 7th International Plasma Science & Interfaces 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. 

Research

PLASNOW (Plasma generated Nitric Oxide in Wound healing)

The DFG granted research project PLASNOW (Plasma generated Nitric Oxide in Wound healing) is an interdisciplinary collaboration within the research field of plasma medicine. The project was approved in November 2019 for 36 months. It will start with the start of contract of the PhD student which is still in process at the moment. Two groups from electrical engineering (AEPT, Prof. Dr. P. Awakowicz) and plasma physics (Experimental physics II, Dr. V. Schulz-von der Gathen) are involved. It is a successor and continuation of projects that were beforehand bundled in the cooperation “Plasma2Cell“. In this cooperation, other groups participate e.g. from chemistry, medicine, and biology at the Ruhr-University, the Heinrich-Heine-University in Düsseldorf and the DLR in Cologne.

Outreach

Public Talk on Plasma in Liquids in the Blue Square

Prof. von Keudell presented an evening talk on plasmas in liquids from eletrolysis to plasma medicine in the series "Neue Fenster zum Universum" in the Blue Square in downtown Bochum.

Conferences

Bad Honnef Summer School 2019

The Bad Honnef summer school was again organized by the RD Plasma with the international chairpersons from Eindhoven. Prof. von Keudell contributed with the introductory lecture and and evening lecture on scientific writing. Dr. V. Schulz-von der Gathen gave lectures and an applied workshop on plasma (emission) spectroscopy.

Conferences

Plathinium 2019

The research of EP2 was presented at the Plathinium conference in Antibes with two poster contributions on HiPIMS systems and a plenary talk on plasma in liquids.

 

Lehre

Goldener Rotstift für Lehrteam EP2 für die Klausurkorrektur "Physik I für Chemiker"

Die Fachschaft Chemie verlieh den "goldenen Rotstift" für die schnellste Korrektur an das Lehrteam von EP2 für die Korrektur der Klausur Physik I für Chemiker, Biochemiker und Geowissenschaftler des Wintersemesters 2018/19.

Es fehlen die anderen Korrekteure Volker Schulz-von der Gathen, Wolfgang Breilmann, Mike Wilbert, Jannis Kostrzewa, Mathews George, Laura Chauvet, Beatrix Biskup, Julian Held, Sascha Monjé-Thiemann und Marc Böke, der das Team auch koordiniert hat.

Conferences

ISPC 24 in Naples

Between June 11th and 14th, the 24th International Symposium on Plasma Chemistry took place in Naples, Italy. A group of seven peole from the CRC 1316 as well as from the SFB-TR 87 joined the meeting. An honour was given to Achim von Keudell, who had a plenary talk on High power impulse magnetron sputtering – extreme plasmas for extreme materials. Further, Marc Böke had a talk on Separated effects of plasma species and post- treatment on the properties of barrier layers on polymers and Patrick Preissing presented his work on NO production in the COST Reference Microplasma Jet and a dielectric barrier discharge measured by means of Laser Induced Fluorescence (LIF). Moreover, five poster presentations were given by this group.

Conference

International Workshop on Microplasmas in Kyoto 5/2019

This year, the 10th edition of the International Workshop on Microplasmas took place in Kyoto. The scope of the workshop are the generation/sources of microplasmas, modelling, and applications (material processing, biomedical material treatments, environmental devices etc.). Around 70 participants from all over the world joined the meeting. A group of nine people from Bochum, especially from the CRC 1316 joined the conference. Finally, two oral presentations and six poster presentations were given by them.

An oral presentation was held by Sebastian Dzikowski from project A6 from the CRC 1316 with the title "Initial ignition behavior of a micro cavity plasma array (MCPA)". Moreover, an invited talk was given by Dr. Volker Schulz-von der Gathen from the CRC with the title "Micro cavity plasma array devices: From first ignition to continuous operation".

Conference

Frontiers conference in Bad Honnef

Between May 12th and May 16th, 2019, the 13th Frontiers in Low-Temperature in Plasma Diagnostics and 1st Frontiers in Low-Temperature Plasma Simulations was held in the Physikzentrum in Bad Honnef.

In detail, five poster presentations and four oral presentations were given by members of both SFBs.