EPJD Topical review - Plasma potential probes for hot plasmas

Plasma probes are well-established diagnostic tools, being relatively simple to construct and easy to handle. The most easily accessible parameter is the floating potential, but the floating potential of a cold probe is not very significant; much more important and relevant is the plasma potential. However, in most types of plasmas, consisting mainly of electrons and only positive ions, the higher mobility of the electrons means that the floating potential is more negative than the plasma potential by a factor proportional to the electron temperature.

In a new Topical Review in EPJD co-authored by teams from Austria, Slovenia, Denmark and Italy, the authors present a review of probes whose floating potential is close or ideally equal to the plasma potential. Such probes are known as Plasma Potential Probes (PPP), and they can either be Electron Emissive Probes (EEPs) or so-called Electron Screening Probes (ESPs). These probes make it possible to measure the plasma potential directly and thus with high temporal resolution.


EPJ D Highlight - Inner electrons behave differently in aromatic hydrocarbons

Coincidence spectrum for benzene and other hydrocarbons

A new study explores how the characteristics of aromaticity affect the process of Auger decay

When an electron from one of the lower energy levels in an atom is knocked out of the atom, it creates a space which can be filled by one of the higher-energy electrons, also releasing excess energy. This energy is released in an electron called an Auger electron - and produces an effect known as Auger decay. Now, Guoke Zhao from Tsinghua University in Beijing, China and colleagues at Sorbonne University in Paris, France have studied the Auger effect in four hydrocarbon molecules: benzene, cyclohexane, hexatriene and hexadiene. These molecules were chosen because they exhibit different characteristics of aromaticity. The authors found that molecules containing pi bonds have a lower threshold for Auger decay.


EPJ D Highlight - Optimising proton beam therapy with mathematical models

The MEVION S250™, Romina.cialdella, Mevions250.jpg (CC BY-SA)

New model improves our understanding of energy transfer in radiotherapy treatment plans by replacing 50-year-old parameters with more complex ones

Particle beam therapy is increasingly being used to treat many types of cancer. It consists in subjecting tumours to beams of high-energy charged particles such as protons. Although more targeted than conventional radiotherapy using X-rays, this approach still damages surrounding normal tissue. To design the optimum treatment plan for each patient, it is essential to know the energy of the beam and its effect on tumour and normal tissue alike. In a recent study published in EPJ D, a group of researchers led by Ramin Abolfath at the University of Texas MD Anderson Cancer Center, Houston, Texas, USA, put forward a new mathematical model outlining the effects of these beam therapies on patients' tissues, based on new, more complex, parameters. Using these new models, clinicians should be able to predict the effect of proton beams on normal and tumour tissue more precisely, allowing them to prepare more effective treatment plans.


EPJ D Highlight - Electron-gun simulations explain the mechanisms of high-energy cosmic rays

The chance of photodetachment of hydrogen ions depends on the speed of the surface motion.

Model explains the mechanisms of scraping negative ions from moving surfaces under a strong electric field

When cosmic rays collide with planets or debris, they lose energy. Scientists use the collision of electrons with a moving surface to simulate this process. A new study published in EPJ D provides a rudimentary model for simulating cosmic rays’ collisions with planets by looking at the model of electrons detached from a negative ion by photons. In this work, Chinese physicists have for the first time demonstrated that they can control the dynamics of negative ion detachment via photons, or photodetachment, on a moving surface.


EPJ D Highlight - Better safeguards for sensitive information

Schema of the encryption channel.

Study improves the lower boundary and secret key capacity of an encryption channel

The secure encryption of information units based on a method called quantum key distribution (QKD) involves distributing secret keys between two parties - namely, Alice, the sender, and Bob, the receiver - by using quantum systems as information carriers. However, the most advanced quantum technology, QKD, is currently limited by the channel's capacity to send or share secret bits. In a recent study published in EPJ D, Gan Wang, who is affiliated with both Peking University, Bejing, China, and the University of York, UK, and colleagues show how to better approach the secret key capacity by improving the channel's lower boundary.


EPJ D Highlight - Quantifying how much quantum information can be eavesdropped

Eavesdropping. Credit: Photo by Dmitry Ratushny on Unsplash

New study yields more precise characterisation of monogamous and polygamous entanglement of quantum information units

Encrypted communication is achieved by sending quantum information in basic units called quantum bits, or qubits. The most basic type of quantum information processing is quantum entanglement. However, this process remains poorly understood. Better controlling quantum entanglement could help to improve quantum teleportation, the development of quantum computers, and quantum cryptography. Now, a team of Chinese physicists have focused on finding ways to enhance the reliability of quantum secret sharing. In a new study published in EPJ D, Zhaonan Zhang from Shaanxi Normal University, Xi'an, China, and colleagues provide a much finer characterisation of the distributions of entanglement in multi-qubit systems than previously available. In the context of quantum cryptography, these findings can be used to estimate the quantity of information an eavesdropper can capture regarding the secret encryption key.


EPJ D Highlight - Fullerene compounds made simulation-ready

Color map of the pseudopotentials of C60.

New model helps understand compound nanomolecules made of football-shaped fullerenes

What in the smart nanomaterials world is widely available, highly symmetrical and inexpensive? Hollow carbon structures, shaped like a football, called fullerenes. Their applications range from artificial photosynthesis and nonlinear optics to the production of photoactive films and nanostructures. To make them even more flexible, fullerenes can be combined with added nanostructures. In a new study published in EPJ D, Kirill B. Agapev from ITMO University, St. Petersburg, Russia, and colleagues have developed a method that can be used for future simulations of fullerene complexes and thus help understand their characteristics.


EPJ D Highlight - Doubly-excited electrons reach new energy states

Novel energy levels of electrons at resonance in positronium ions.

New energy states reached by electrons entering resonance in three-particle systems may open the door to using similar calculations in atomic and nuclear physics

Positrons are short-lived subatomic particle with the same mass as electrons and a positive charge. They are used in medicine, e.g. in positron emission tomography (PET), a diagnostic imaging method for metabolic disorders. Positrons also exist as negatively charged ions, called positronium ions (Ps-), which are essentially a three-particle system consisting of two electrons bound to a positron.

Now, commercially available lasers are capable of producing photons that carry enough energy to bring the electrons of negatively charge ions, like Ps−, to doubly-excited states, referred to as D-wave resonance. Positronium ions are, however, very difficult to observe because they are unstable and often disappear before physicists get a chance to analyse them.

Sabyasachi Kar from the Harbin Institute of Technology, China, and Yew Kam Ho from the Academia Sinica, Taipei, Taiwan, have now characterised these higher energy levels reached by electrons in resonance in these three-particle systems, which are too complex to be described using simple equations. This theoretical model, recently published in EPJ D, is intended to offer guidance for experimentalists interested in observing these resonant structures. This model of a three-particle system can be adapted to problems in atomic physics, nuclear physics, and semiconductor quantum dots, as well as antimatter physics and cosmology.


EPJ D Highlight - Attosecond pulse leads to highest molecular level probe resolution

Attosecond pulse.

A team of Chinese physicists has published a study explaining how to turn low-intensity infra-red beams into high-intensity X-ray beams, opening the door to ultra-fast pulsed energy sources for ultra-high time resolution probes

Attosecond pulses enable physicists to probe dynamic processes in matter with unprecedented time resolution. This means such technology can provide better insights into the dynamics of electrons in molecules. Devising a source of ultra-fast X-ray pulsating in the attosecond range is no mean feat. Comparing an attosecond is to a second is the equivalent of comparing a second to about 31.71 billion years. Now, a team of physicists from China has exploited an optical phenomenon, opening the door to creating high-order oscillations in existing light sources. This makes it possible to shift the frequency of the original source into X-rays with a laser beam source pulsating in an ultra-fast manner, to reach the attosecond range. The trouble is that yield of such higher order oscillations decreases as the source laser wavelength increases. In a new study published in EPJ D, Liqiang Feng and Yi Li from Liaoning University of Technology, Jinzhou, China, have developed a method to select, enhance and extend the higher order emission peak from a laser beam changing from ultraviolet to a mid-infrared.


EPJD Editor-in-Chief Tommaso Calarco appointed Director of Institute of Quantum Control at Peter Grünberg Institute

Tommaso Calarco
Prof Dr Tommaso Calarco, Editor-in-Chief of EPJ D, has recently been appointed Director of the Institute of Quantum Control at the Peter Grünberg Institute (PGI), Forschungszentrum Jülich. The PGI is dedicated to fundamental research on novel physical concepts and emerging materials in information technology and related fields. It also provides a state-of-the-art platform for the development of process technologies, devices and innovative nanoelectronic material systems. The Institute of Quantum Control develops and applies theoretical methods to achieve optimal performance of quantum technological tasks in these and other systems.

In 2012 we organized the International Conference on Nuclear Structure and Related Topics (NSRT12). Among several offers for publishing the Proceedings we have chosen the open-access journal EPJ Web of Conferences and have not been disappointed. Since this was our first experience with the on-line publication we had many questions to the editorial staff and several times changed our mind. And always we got prompt, exhaustive and patient answers and instructions. We were fully satisfied with the final quality of publication when it has appeared on the website. So our experience in collaboration with the journal is encouraging without any doubts.

Prof. Andrej I. Vdovin, Joint Institute for Nuclear Research, Russia
Member of the Organizing Committee NSRT12, EPJ Web of Conferences vol.38, 2012

ISSN: 2100-014X (Electronic Edition)

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