Lightning bolt underwater 

© RUB, Kramer

A plasma tears through the water within a few nanoseconds. It may possibly regenerate catalytic surfaces at the push of a button.

Electrochemical cells help recycle CO2. However, the catalytic surfaces get worn down in the process. Researchers at the Collaborative Research Centre 1316 “Transient atmospheric plasmas: from plasmas to liquids to solids” at Ruhr-Universität Bochum (RUB) are exploring how they might be regenerated at the push of a button using extreme plasmas in water. In a first, they deployed optical spectroscopy and modelling to analyse such underwater plasmas in detail, which exist only for a few nanoseconds, and to theoretically describe the conditions during plasma ignition. They published their report in the journal Plasma Sources Science and Technology on 4 June 2019.

A plasma tears through the water within a few nanoseconds. Following plasma ignition, there is a high negative pressure difference at the tip of the electrode, which results in ruptures forming in the liquid. Plasma then spreads across those ruptures.

Video: Experimentalphysik II

Plasmas are ionised gases: they are formed when a gas is energised that then contains free electrons. In nature, plasmas occur inside stars or take the shape of polar lights on Earth. In engineering, plasmas are utilised for example to generate light in fluorescent lamps, or to manufacture new materials in the field of microelectronics. “Typically, plasmas are generated in the gas phase, for example in the air or in noble gases,” explains Katharina Grosse from the Institute for Experimental Physics II at RUB.

Ruptures in the water

In the current study, the researchers have generated plasmas directly in a liquid. To this end, they applied a high voltage to a submerged hairline electrode for the range of several billionth seconds. Following plasma ignition, there is a high negative pressure difference at the tip of the electrode, which results in ruptures forming in the liquid. Plasma then spreads across those ruptures. “Plasma can be compared with a lightning bolt – only in this case it happens underwater,” says Katharina Grosse.

Hotter than the sun

Using fast optical spectroscopy in combination with a fluid dynamics model, the research team identified the variations of power, pressure, and temperature in these plasmas. “In the process, we observed that the consumption inside these plasmas briefly amounts to up to 100 kilowatt. This corresponds with the connected load of several single-family homes,” points out Professor Achim von Keudell from the Institute for Experimental Physics II. In addition, pressures exceeding several thousand bars are generated – corresponding with or even exceeding the pressure at the deepest part of the Pacific Ocean. Finally, there are short bursts of temperatures of several thousand degrees, which roughly equal and even surpass the surface temperature of the sun.

Water is broken down into its components

Such extreme conditions last only for a very short time. “Studies to date had primarily focused on underwater plasmas in the microsecond range,” explains Katharina Grosse. “In that space of time, water molecules have the chance to compensate for the pressure of the plasma.” The extreme plasmas that have been the subject of the current study feature much faster processes. The water can’t compensate for the pressure and the molecules are broken down into their components. “The oxygen that is thus released plays a vital role for catalytic surfaces in electrochemical cells,” explains Katharina Grosse.  “By re-oxidating such surfaces, it helps them regenerate and take up their full catalytic activity again. Moreover, reagents dissolved in water can also be activated, thus facilitating catalysis processes.”

By Meike Drießen, Translated by Donata Zuber
Recent research achievement

How bacteria protect themselves from plasma treatment 

© Daniel Sadrowski

Plasmas are applied in the treatment of wounds to combat pathogens that are resistant against antibiotics. But bacteria know how to defend themselves.

Considering the ever-growing percentage of bacteria that are resistant to antibiotics, interest in medical use of plasma is increasing. In collaboration with colleagues from Kiel, researchers at Ruhr-Universität Bochum (RUB) investigated if bacteria may become impervious to plasmas, too. They identified 87 genes of the bacterium Escherichia coli, which potentially protect against effective components of plasma. “These genes provide insights into the antibacterial mechanisms of plasmas,” says Marco Krewing. He is the lead author of two articles that were published in the Journal of the Royal Society Interface this year.

A cocktail of harmful components stresses pathogens

Plasmas are created from gas that is pumped with energy. Today, plasmas are already used against multi-resistant pathogens in clinical applications, for example to treat chronic wounds. “Plasmas provide a complex cocktail of components, many of which act as disinfectants in their own right,” explains Professor Julia Bandow, Head of the RUB research group Applied Microbiology. UV radiation, electric fields, atomic oxygen, superoxide, nitric oxides, ozone, and excited oxygen or nitrogen affect the pathogens simultaneously, generating considerable stress. Typically, the pathogens survive merely several seconds or minutes.

In order to find out if bacteria, may develop resistance against the effects of plasmas, like they do against antibiotics, the researchers analysed the entire genome of the model bacterium Escherichia coli, short E. coli, to identify existing protective mechanisms. “Resistance means that a genetic change causes organisms to be better adapted to certain environmental conditions. Such a trait can be passed on from one generation to the next,” explains Julia Bandow.

Mutants missing single genes

For their study, the researchers made use of so-called knockout strains of E. coli. These are bacteria that are missing one specific gene in their genome, which contains approximately 4,000 genes. The researchers exposed each mutant to the plasma and monitored if the cells kept proliferating following the exposure.

“We demonstrated that 87 of the knockout strains were more sensitive to plasma treatment than the wild type that has a complete genome,” says Marco Krewing. Subsequently, the researchers analysed the genes missing in these 87 strains and determined that most of those genes protected bacteria against the effects of hydrogen peroxide, superoxide, and/or nitric oxide. “This means that these plasma components are particularly effective against bacteria,” elaborates Julia Bandow. However, it also means that genetic changes that result in an increase in the number or activity of the respective gene products are more capable of protecting bacteria from the effects of plasma treatment.

Heat shock protein boosts plasma resistance

The research team, in collaboration with a group headed by Professor Ursula Jakob from the University of Michigan in Ann Arbor (USA), demonstrated that this is indeed the case: the heat shock protein Hsp33, encoded by the hslO gene, protects E. coli proteins from aggregation when exposed to oxidative stress. “During plasma treatment, this protein is activated and protects the other E. coliproteins – and consequently the bacterial cell,” Bandow points out. An increased volume of this protein alone results in a slightly increased plasma resistance. Considerably stronger plasma resistance can be expected when the levels of several protective proteins are increased simultaneously.

By Meike Drießen, Translated by Donata Zuber
Press releases

New class of catalysts for energy conversion

© RUB, Marquard

The research group of Prof. Ludwig and his colleagues recently published their new results in the catalyst production. “At our department, we have unique methods at our disposal to manufacture these complex materials from five source elements in different compositions in form of thin film or nanoparticle libraries,” explains Professor Alfred Ludwig from the Chair of Materials for Microtechnology at RUB. The atoms of the source elements blend in plasma and form nanoparticles in a substrate of ionic liquid. If the nanoparticles are located in the vicinity of the respective atom source, the percentage of atoms from that source is higher in the respective particle. “Very limited research has as yet been conducted into the usage of such materials in electrocatalysis,” says Ludwig.

The full press releas can be found here.


New PIs within the Research Department

During the last general meeting of the Research Department Plasmas with Complex Interactions, new Senior PIs were elected to join the collaboration of different scientists over the campus. Due to changed cooperations, the group was enlarged by four new Senior PIs: Prof. Dr. Martin Muhler from the chair for technical chemistry, Jun.-Prof. Dr. Dirk Tischler from the chair for microbial biotechnology, and Dr. Julian Schulze as well as Jun.-Prof. Andrew Gibson from the chair for electrical engineering and plasma technology.

With the coming into force of the new by-laws, the Research Department Plasmas with Complex Interactions now includes Associated PIs from other universitites, who work together with the scientists on campus. Here, the new memebers are: Prof. Dr. Jan Benedikt from the chair for plasma physics at the CAU Kiel, Prof. Dr. Guido Grundmeier from the chair for technichal and macomolecular chemistry at the university of Paderborn, Prof. Dr. Timo Jacob from the Insitute for Electrochemistry at the Uni Ulm, Prof. Dr. Thomas Mussenbrock from the chair for theoretical electrical engineering at the BTU Cottbus Senftenberg, Prof. Dr.-Ing. Jens Oberrath from the institute for product and prozess innovation at the Leuphana Universität Lüneburg, Prof. Dr. Beatriz Roldán Cuenya from the institute for Interface Science at the Fritz-Haber-Institut Berlin, Prof. Dr. Jochen M. Schneider from the chair for material chemistry at the RWTH Aachen, and finally Dr.-Ing. Jan Trieschmann from the chair for theoretical electrical engineering at the BTU Cottbus.

Recent research achievements

A new map of the sky with hundreds of thousands of galaxies

© RUB, Marquard

The group of Prof. Dettmar from the Astronomical Insitute contribute to the special issue of the journal "Astronomy & Astrophysics".

A team of astronomers from the Ruhr-Universität Bochum (RUB) has studied one of the discovered galaxies in detail and found a characteristic radiation distribution that suggests processes in the formation of galaxies and our Milky Way. 

The Lofar Telescope 

Lofar is a vast European network of radio telescopes linked together by a high-speed fibre-optic network, whose measurement signals are combined into a single signal. Powerful supercomputers convert 100,000 individual antennas into a virtual reception dish with a diameter of 1,900 kilometers. Lofar operates in the frequency ranges between about 10 to 80 megahertz and 110 to 240 megahertz, which have so far been largely unexplored. It is controlled by the Astron research facility in the Netherlands and is considered the world's leading telescope of its kind. There are six measuring stations in Germany which are operated by various scientific institutions.

Supernovae influence the evolution of galaxies

Dr. Arpad Miskolczi of the RUB Chair of Astronomy is one of the first authors of the collection of research results, all based on the analysis of a first phase of the multi-year project. In collaboration with international colleagues, he has investigated one of the many newly discovered galaxies in more detail. The object with the catalogue name NGC 3556 shows a characteristically different radiation distribution in the radio range than in visible light. "From this we conclude that the accumulation of numerous huge stellar explosions, so-called supernovae, releases so much energy that the gas between the stars, interspersed with magnetic fields and particles of cosmic rays, leaves the galaxy,"; explains Prof. Dr. Ralf-Jürgen Dettmar. These processes have influenced the evolution of Milky Way systems over billions of years. By comparing different such objects, the researchers hope to gain information about the origin of our own Milky Way.

Black holes, magnetic fields, galaxy clusters

With the help of Lofar, scientists have been able to create a new sky map. Many of the galaxies depicted were previously unknown because they are extremely far away and their radio signals have to travel billions of light years to reach Earth.

When scientists observe the sky with a radio telescope, they mainly see radiation from the vicinity of black holes, which are millions of times heavier than the sun. With Lofar, the researchers want to find out what influence the black holes have on the galaxies in which they are located and where they come from. Thanks to Lofar's sensitivity, the teams have already been able to show that black holes are present in all giant galaxies and that they are constantly growing. 

The radio radiation received by Lofar can also be used to measure cosmic magnetic fields. The researchers have also been able to detect magnetic structures between galaxies, thus proving theoretical assumptions for the first time. 

The fusion of two clusters of galaxies produces radio emissions - so-called radio halos - with a size of millions of light years. With Lofar they can be tracked down. The researchers learn a lot from this about the gas at the edge of the gigantic clusters of galaxies.

Gigantic amounts of data

The creation of low frequency radio sky maps requires both considerable telescope and computational time and requires analysis of the data by large teams. "Lofar produces gigantic amounts of data - we have to process the equivalent of ten million DVDs. This places the highest demands on software and hardware and is only possible through an international and interdisciplinary team,"; says Prof. Dr. Dominik Schwarz of Bielefeld University and representative of Germany to the Lofar steering committee. 

"In Germany, we worked together with Forschungszentrum Jülich to efficiently convert the huge amounts of data into high-quality images. These images are now public and will allow astronomers to study the evolution of galaxies in unprecedented detail,"; adds Prof. Dr. Ralf-Jürgen Dettmar. 

The Forschungszentrum Jülich accommodates around 15 petabytes of Lofar data. "This is almost half of all Lofar data, one of the largest astronomical data collections in the world. The processing of these gigantic data sets represents a great challenge. What would have taken centuries on conventional computers could have been reduced to one year by using innovative algorithms and extremely powerful computers,"; says Prof. Dr. Dr. Thomas Lippert, Director of the Jülich Supercomputing Centre. Jülich is one of the three data centres of the Lofar project. In addition, the Jülich Supercomputing Centre manages the data network traffic between the German Lofar stations and the central Lofar computer in Groningen.

15 million radio sources expected

The 26 papers now published in a special issue of Astronomy & Astrophysics are based on only about two percent of the observations planned with Lofar. The scientists now want to map the entire northern celestial sphere. After all, they expect to find around 15 million radio sources.

The original press releases can be found here.