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Impact of the driver beam charge on the wakefield formation and evolution in a particle-driven plasma accelerator
No full textParticle accelerators are important instruments in contemporary scientific research, with applications extending to industry and medicine. One application is the generation of light pulses with distinctive properties, as exemplified by free electron lasers (FELs). These machines are of significant interest, particularly those that provide radiation in the X-ray regime, which necessitates the use of electron bunches with an energy in the multi-GeV range. The accelerating field strength in conventional radio-frequency (RF) machines is constrained by material limitations, which necessitates the construction of X-ray FELs as facilities with a size of hundreds of meters or even kilometers. Plasma wakefield accelerators, which are employed for electron acceleration and driven by either intense laser beams (LWFA) or relativistic particle bunches (PWFA), have the potential to provide accelerating field strengths that exceed the limit of conventional RF-accelerators by multiple orders of magnitude.
Current state-of-the-art LWFAs can produce electron bunches at application-relevant energies over acceleration stages of tens of centimeters length. However, they often struggle with stability, reliability, and beam quality. PWFA offers a promising alternative but requires a relativistic electron bunch as a driver, which restricts the potential for downsizing. The hybrid laser-plasma wakefield accelerator (LPWFA) merges these two plasma acceleration techniques by using an LWFA-generated beam to drive a subsequent PWFA stage, leveraging the benefits of PWFA without requiring a preceding RF accelerator.
This thesis covers the evolution of LPWFA from initial experimental demonstrations to controlled and tunable injection using a hydrodynamic shock. The study compares the operation in the self- and pre-ionized regime, observing reduced field strengths within the cavity in the case of self-ionization. A few-cycle optical probe shadowgraphy technique is employed, revealing significant differences in the morphology of plasma waves in both regimes. Another aspect identified by this diagnostic is the driver-charge-dependent elongation of the first cavity. This correlation is employed to examine the evolution of the driver beam charge within the PWFA stage. A controllable witness beam acceleration via injection at a sharp density downramp is achieved and the results are presented in this work. This study reveals that the observed elongation has an impact on the witness beam acceleration, demonstrating the significance of a comprehensive understanding of the wakefield dynamics for further optimization of the acceleration process. The findings are primarily based on experimental observations supported by simulations, showcasing the potential for a stable and efficient LPWFA design
European Workshop on Photocathodes for Particle Accelerator Applications 2024 – Summary of Oral Contributions
Full text linkThe European Workshop on Photocathodes for (particle) Accelerator Applications (EWPAA) brings together experts in the field of photocathode electron sources for use in particle accelerators with the aim of sharing their knowledge and latest research and development progress in this crucial field of particle accelerator science.
The workshop is convened every other year, and is thus complementary to the P3 workshop (Photocathode Physics for Particle accelerators) run in the USA. Consequently, there is a workshop focusing on photocathodes for particle accelerator applications convened every year, either in Europe or the USA.
The EWPAA 2024 is the 5th meeting in this workshop series. The event was hosted by the ELBE Department at the HZDR Helmholtz–Zentrum Dresden–Rossendorf in Dresden between September 17th and 19th. Photocathodes have been developed, studied and utilized in SRF
photoinjectors at the ELBE center for more than 20 years.
The programme was organised with 7 working groups, with each oral contribution assigned to the most appropriate group. Details of the event and the scientific programme can be found at the website https://events.hifis.net/event/1255/overview. The proceedings present the main points raised by each of the speakers in their oral presentations.
The Local Organizer Committee acknowledges the EWPAA Scientific Programme Members for their support in drafting and delivering the agenda and thanks them for their help in organizing and achieving such a successful event.
The organizers also gratefully acknowledge the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) for their part-funding of the workshop cost under DFG Project No. 545151564.
The next workshop in 2026 will be hosted by the Irène Joliet-Curie Laboratory (IJCLAb) at Orsay in Paris
Annual Report 2024 - Institute of Resource Ecology
No full textThe Institute of Resource Ecology presents selected works accomplished in 2024
Entwicklung von SiPM-basierter Auslese für Detektoren an R³B/FAIR und Untersuchung astrophysikalisch relevanter Kernreaktionen an R³B
No full textThe NeuLAND (New Large-Area Neutron Detector) plastic-scintillator-based time-of-flight detector for 0.1 to 1.6 GeV neutrons is currently under construction at the Facility for Antiproton and Ion Research (FAIR), Darmstadt, Germany. In its nal conguration, NeuLAND will consist of 3,000 plastic scintillator bars with a size of 2.7 m ×5 cm ×5 cm that are read out on each end by fast timing photomultipliers. Here, data from a comprehensive study of an alternative light readout scheme using silicon photomultipliers (SiPM) are reported. For this purpose, a NeuLAND bar was instrumented on each end with a SiPM-based prototype of the same geometry as a 1 photomultiplier tube, including four 6×6 mm2 SiPMs, ampliers, high voltage supply, and microcontroller. Tests were done using the 35 MeV electron beam of the superconducting Electron Linac for beams with high Brilliance and low Emittance (ELBE) with its picosecond-level time jitter in two dierent modes of operation, namely parasitic mode with one electron per bunch and single-user mode with 1 to 60 electrons per bunch. Acqiris fast digitizers were used for data acquisition. In addition, o-beam tests using cosmic rays and the NeuLAND data acquisition scheme have been carried out. Typical time resolutions of sigma≤120 ps were found for ≥95% eciency for minimum ionizing particles, improving on previous work at ELBE and exceeding the NeuLAND timing goal of sigma < 150 ps. Over a range of 10 to 300 MeV deposited energy in the NeuLAND bar, the gain was found to deviate by ≤10% (≤20%) from linearity for 35 µm (75 µm) SiPM pitch, respectively, satisfactory for calorimetric use of the full NeuLAND detector. The dark rate of the prototype studied was found to be lower than the expected cosmic-ray induced background in NeuLAND. In addition, simulations in Geant4 were developed to understand electron scattering and the propagation of scintillation light as well as the time behavior of SiPMs.
Additionally, collaboration and data evaluation of experiments on astrophysically interesting reactions in the form of the coulomb breakup reaction 16O(gamma, alpha)12C at R³B/GSI were part of this work and methods for data quality analysis of large scale detectors were developed
Annual Report 2024 - Institute of Ion Beam Physics and Materials Research
Full text linkThe year 2024 has been another remarkable and highly successful one for our institute. We are proud to report the publication of 187 scientific papers, achieving an impressive average impact factor of 8. This accounts for approximately 30% of the total impact generated at HZDR, maintaining the high standard set in 2023. Given the ongoing constraints on our personnel budget, we are optimistic that we can sustain this level of excellence in the years ahead through strategic efforts and continued dedication.
In addition to our publication success, we have secured 15 new third-party grants, amounting to a total funding volume of 6.4 million euros. This external support is greatly valued, as it alleviates some of the budgetary challenges we face. Notably, we take immense pride in the achievement of Dr. Denys Makarov, head of the Department of Intelligent Materials and Systems, who has been awarded a prestigious ERC Advanced Grant for his groundbreaking project on Curvilinear Multiferroics. This significant accomplishment underscores the excellence of our researchers and the global recognition of their contributions. Congratulations to Dr. Makarov on this well-deserved honor!
We are also thrilled to welcome Prof. Sebastian Mährlein as the new head of the Department of High-Field THz-Driven Phenomena at the Institute of Radiation Physics. His leadership and expertise will undoubtedly enhance our collaborative efforts to explore novel material phenomena under THz radiation, further strengthening our research profile in this exciting field.
We bid farewell to our esteemed technical staff members Bernd Scheumann, Gabi Schnabel, and Andrea Scholz, and extend our sincere gratitude for their many years of dedicated service at the X-ray laboratory and the cleanroom, and wish them all the best for the future.
A particular highlight of 2024 was the revival of our annual Institute Workshop after a four-year break due to the pandemic and its aftermath. Held in Schmochtitz, the workshop provided a valuable platform for scientific exchange, stimulating discussions, and fostering connections across departments and hierarchical levels in a relaxed and cooperative atmosphere. We look forward to reestablishing this tradition as a regular event in the future.
Furthermore, in November, we had the honor of hosting the Helmholtz Program Workshop on Quantum Materials at HZDR. With approximately 70 Helmholtz scientists in attendance, the workshop facilitated in-depth discussions on recent advancements in the field, leveraging the unique capabilities of Helmholtz large-scale research infrastructures. This event underscored the importance of collaboration within the Helmholtz community and highlighted the cutting-edge research being conducted in quantum materials.
Finally, we extend our deepest gratitude to all our partners, colleagues, and supporting organizations for their invaluable contributions to our progress in 2024. We are especially grateful to the Executive Board of the Helmholtz-Zentrum Dresden-Rossendorf, the Ministry of Science, Culture, and Tourism of the Free State of Saxony, as well as the Federal Ministries of Education and Research, and of Economic Affairs and Climate Action. Their unwavering support has been instrumental in enabling our research and innovation.
We also acknowledge the vital role played by our collaborators from universities, industry, and research institutions worldwide, whose expertise and cooperation have significantly contributed to our advancements. Most importantly, the directors would like to express their sincere appreciation to all members of our institute for their outstanding dedication, hard work, and resilience during these extraordinary times. Your commitment continues to drive our success, and we look forward to another year of groundbreaking achievements together
TRIGUS - Tribologisch induzierte Grenzflächen- und Strukturveränderungsprozesse in Trockenschmiersystemen unter definierten Atmosphären: Abschlussbericht an die Deutsche Forschungsgemeinschaft, Projektnummer 415726702
No full textIm Projekt TRIGUS wurden durch Reibung verursachte Strukturveränderungen von 2 Trockenreibungs-Modellsystemen, wasserstofffreiem amorphem Kohlenstoff (ta-C) und Molybdändisulfid (MoS₂), in Abhängigkeit von Atmosphäre, Gegenkörper und Fremdatomen untersucht. Dazu wurden mehr als 150 Reibexperimente unter definierter Atmosphäre durchgeführt. Die Ausgangsschichten, Reibspuren und Gegenkörperkontaktflächen wurden lateral und tiefenaufgelöst mittels Ionenstrahl-Mikroanalyse, Ramanspektroskopie, Rasterelektronenmikroskopie und in Einzelfällen durch Querschnitts-Transmissionselektronenmikroskopie charakterisiert.
Die Weiterentwicklung und neue Ansätze zu triboskopischen Methoden erlaubten eine quantitative Auswertung des zeitlichen und lateralen tribologischen Verhaltens. Die unseres Wissens nach erstmals zur Analyse von Trockenreibsystemen eingesetzte Ionenstrahl-Mikroanalyse lieferte detaillierte Informationen zu Elementübertrag, -verteilung und -konzentration in der Reibspur und auf dem Gegenkörper, die mit dem Reibmechanismus korreliert werden konnten. Durch Implantation mit Si und Ta in ta-C sowie Ko-Abscheidung von C und Si konnte die Umgebungsabhängigkeit des Reibwertes des ta-C signifikant verringert werden. Die ta-C:Ta-Schicht wies zudem eine nahezu unverändert hohe Härte und einen ähnlich hohen E-Modul wie ta-C auf, was auf strukturelle Besonderheiten dieses Systems zurückgeführt wurde. Im Reibkontakt von ta-C gegenüber 4 metallischen und 2 keramischen Gegenkörpern zeichnete sich die Paarung ta C/Messing durch einen Kurzzeit-Reibwert von 0.05 ≤ µ ≤ 0.13 sowohl unter Umgebungsbedingungen als auch im Vor- und Hochvakuum aus.
Im Reibsystem MoS₂/100Cr6 Stahl wurde der atmosphärenabhänge Reibwert mit Strukturveränderungen von Reibschicht und Gegenkörperoberfläche korreliert. Nach Reibexperimenten in trockener Luft wurde entgegen dem aktuellen Stand der Erkenntnis keine Oxidation der MoS₂-Schicht gefunden. Andererseits zeigte sich eine heterogene Element- und Strukturverteilung auf dem Gegenkörper. Diese wurde einer Reihe von komplexen Zwischenstufen der allgemeinen Zusammensetzung [(Fe_n)(Mo_x)(O_y)(S_z)] zugeordnet. Als Reibmechanismus wurde der Übertrag von MoS₂ auf den Gegenkörper vorgeschlagen, das unter dem Reibdruck und möglicher Mitwirkung des Gegenkörpermaterials unvollständig oxidiert. Des Weiteren wurde die Wechselwirkung von ta-C und MoS₂-Schichten mithilfe mikrostrukurierter Substrate untersucht und eine erhöhte mechanische Belastbarkeit an Luft und in Vakuum aufgezeigt.
Die Ergebnisse präzisieren und erweitern das Mechanismusverständnis zu den untersuchen Trockenreibungs-Modellsystemen und erlauben zukünftig durch geeignete Anpassung der Oberflächen in der Raumfahrt, Medizintechnik und Vakuumtechnik verbesserte tribologische Eigenschaften zu erzielen.In the TRIGUS project, structural changes caused by friction in two dry friction model systems, hydrogen-free amorphous carbon (ta-C) and molybdenum disulfide (MoS₂), were investigated as a function of atmosphere, counter body, and foreign atoms. More than 150 friction experiments were conducted under controlled atmospheric conditions. The initial layers, friction tracks, and counter body imprints were characterized laterally and in-depth using ion beam microanalysis, Raman spectroscopy, scanning electron microscopy, and, in some cases, cross-sectional transmission electron microscopy.
The advancement of triboscopic methods and new approaches enabled a quantitative evaluation of the temporal and lateral tribological behavior. Ion beam microanalysis, which to our knowledge was used for the first time to analyze dry friction systems, provided detailed information on element transfer, distribution and concentration in the friction track and on the counter body, which could be correlated with the friction mechanism. By implanting Si and Ta in ta-C and co-deposition of C and Si, the environmental dependence of the friction coefficient of ta-C could be significantly reduced. The ta-C:Ta layer also had an almost unchanged high hardness and a similarly high modulus of elasticity as ta-C, which was attributed to structural peculiarities of this system. In the frictional contact of ta-C with 4 metallic and 2 ceramic counter bodies, the ta C/brass pairing was characterized by a short-term friction coefficient of 0.05 ≤ µ ≤ 0.13 both under ambient conditions and in pre-vacuum and high vacuum.
For the MoS₂/100Cr6 steel friction system, the atmosphere-dependent friction coefficient was correlated with structural changes in the friction layer and counterbody surface. Contrary to current knowledge, no oxidation of the MoS₂ layer was found after friction experiments in dry air. However, a heterogeneous element and structural distribution, including oxygen, was observed on the counterbody. This was attributed to a series of complex intermediate compounds with the general composition [(Fe_n)(Mo_x)(O_y)(S_z)]. The proposed friction mechanism involved the transfer of MoS₂ onto the counterbody, where it underwent incomplete oxidation under friction pressure and possible interaction with the counterbody material. Furthermore, the interaction between ta-C and MoS₂ layers was studied using microstructured substrates, demonstrating increased mechanical durability in both air and vacuum conditions.
The results clarify and expand the understanding of friction mechanisms and will allow improved tribological properties to be achieved in the future through suitable adaptation of surfaces in aerospace, medical technology and vacuum technology
BMBF-Verbundprojekt RADEKOR: Speziation und Transfer von Radionukliden im Menschen unter besonderer Berücksichtigung von Dekorporationsmitteln: Teilprojekt A
No full textGelangen Radionuklide (RN) über den Nahrungspfad zum Menschen, können sie eine radio- und chemotoxische Gefahr darstellen. Um die Gesundheitsrisiken bei einer oralen Aufnahme von RN mit der Nahrung präzise abschätzen und wirksame Dekontaminationsverfahren anwenden zu können, ist ein Prozessverständnis der Biokinetik der RN auf zellulärer und molekularer Ebene zwingend notwendig. In dem Verbundprojekt wurden für die orale Inkorporation ausgewählter RN neben quantitativen Ausscheidungsanalysen und biokinetischen Modellierungen die molekulare Speziation der RN im Verdauungstrakt und ihre Wechselwirkungen mit Zellen des Verdauungs- und Ausscheidungssystems in An- und Abwesenheit gängiger und neuer potentieller Dekorporationsmittel untersucht. Ziel dieser Arbeiten war es, mit einem tieferen Prozessverständnis der RN-Wechselwirkungen im Verdauungstrakt auf molekularer und zellulärer Ebene zur Erstellung eines präzisen biokinetischen Modells und zur Entwicklung bzw. Verbesserung von nuklidspezifischen Dekontaminationsstrategien beizutragen
Plasma dynamics between laser-induced breakdown and relativistically induced transparency: An investigation of high-intensity laser-solid interactions by time-resolved off-harmonic optical shadowgraphy
Full text linkLaser-plasma-based ion accelerators are becoming a versatile platform to drive different fields of applied research and life sciences, for example translational research in radiation oncology. To ensure stable accelerator performance, complete control over the ion source, i.e., the high-intensity laser-solid interaction, is required. However, idealized interaction conditions are almost impossible to reach, as the utilized high-power lasers always feature a non-negligible amount of light preceding the laser peak. This leading edge of the laser pulse usually exceeds the ionization potential of bound electrons much earlier than the arrival of the high-power laser peak and the solid-density target undergoes significant modifications even before the actual high-intensity laser-plasma interaction starts. Control over this so-called target pre-expansion is a key requirement to achieve quantitative agreement between numerical simulations and experiments of high-intensity laser-solid interactions.
This thesis investigates several aspects that are relevant to improve the capability of simulations to model realistic experimental scenarios. The corresponding experiments are conducted with cryogenic hydrogen-jet targets and the DRACO-PW laser at peak intensities between 10^12 W/cm^2 and 10^21 W/cm^2 . The experimental implementation of time-resolved optical-probing diagnostics and technical innovations with respect to the technique of off-harmonic optical probing overcome the disturbances by parasitic plasma self-emission and allow for unprecedented observations of the target evolution during the laser-target interactions. The laser-induced breakdown of solids, i.e., the phase transition from the solid to the plasma state, can be considered as an heuristic starting point of high-intensity laser-solid interactions. As it is highly relevant to simulations of target pre-expansion, Chapter 3 of this thesis presents time-resolved measurements of laser-induced breakdown in laser-target interactions at peak intensities between 0.6 * 10^21 W/cm^2 and 5.7 * 10^21 W/cm^2 . By increasing the peak intensity, a lowering of the applicable threshold intensity of laser-induced breakdown well below the appearance intensity of barrier-suppression ionization occurs. The observation demonstrates the relevance of the pulse-duration dependence of laser-induced breakdown and laser-induced damage threshold to the starting point of high-intensity laser-solid interactions. To apply the results to other laser-target assemblies, we provide a detailed instruction of how to pinpoint the starting point by comparing measurements of the laser contrast with a characterization study of the target-specific thresholds of laser-induced breakdown at low laser intensity. Chapter 4 of this thesis presents an example of how optical-probing diagnostics are able to estimate target pre-expansion as a starting condition for particle-in-cell simulations. The measurement allows to restrict the surface gradient of the pre-expanded plasma density to an exponential scalelength between 0.06 um and 0.13 um. Furthermore, the plasma-expansion dynamics induced by the ultra-relativistic laser peak are computed and post-processed by ray-tracing simulations. A comparison to the experimental results yields that the formation of the measured shadowgrams is governed by refraction in the plasma-density gradients and that the observed volumetric transparency of the target at 1.4 ps after the laser peak is not caused by relativistically induced transparency but by plasma expansion into vacuum instead
Annual Report 2023 - Institute of Resource Ecology
Full text linkThe IRE is one of the ten institutes of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Our research ac-tivities are mainly integrated into the program “Nuclear Waste Management, Safety and Radiation Research (NUSAFE)” of the Helmholtz Association (HGF) and fo-cus on the topics “Safety of Nuclear Waste Disposal” and “Safety Research for Nuclear Reactors”. The program NUSAFE, and therefore all work which is done at IRE, belong to the research field “Energy” of the HGF
Annual Report 2023 - Institute of Ion Beam Physics and Materials Research
Full text linkThe year 2023 was highly successful, marked by significant high-level publications and the acquisition of new projects. The latter is increasingly crucial given the tight budget in 2023, which is expected to become even tighter in 2024 due to rising costs and well-deserved salary increases for our employees. As a result, we must reduce the number of our non-permanent scientific staff, which will impact future productivity.
Despite these challenges, our performance in 2023 remained outstanding with a total of 178 refereed publications and an average impact factor of 8.1. Notable publications include 8 from the Nature Publishing Group, 7 from Advanced (Functional) Materials, 4 from ACS Nano, and 2 from Angewandte Chemie. Our excellence was further recognized by the HZDR Research Award, which again went to our Institute, this time awarded to Dr. Oleksii Volkov and Dr. Oleksandr Pylypovskyi from the Department of Intelligent Materials and Devices for their theoretical and experimental investigations into chiral symmetry breaking in magnetic 3D textures. Furthermore, Dr. Lukas Körber, who completed his PhD in 2023 with summa cum laude, was the recipient of both the Helmholtz Doctoral Award in the research field of Matter and the HZDR Doctoral Award. Prof. Manfred Helm was honored as an APS Fellow.
In 2023, the majority of newly approved projects are financed by the Saxonian Ministry of Science, Culture and Tourism and the Helmholtz Initiative and Networking Fund which is a confirmation of the application relevance of our research.
Our infrastructure upgrades are progressing as planned. The new AMS (Accelerator Mass Spectrometry) building was handed over to us in fall 2023. This year, we anticipate the arrival of our new 1 MV accelerator, which will be a dedicated AMS system. We aim to achieve full user operation by 2025.
Finally, we extend our heartfelt thanks to all partners, friends, and organizations who supported our progress in 2023. We are particularly grateful to the Executive Board of the Helmholtz-Zentrum Dresden-Rossendorf, the Ministry of Science, Culture and Tourism of the Free State of Saxony, and the Federal Ministries of Education and Research, and of Economic Affairs and Climate Action. Many partners from universities, industry, and research institutes worldwide have been essential to our development. Lastly, the directors wish to thank all members of our institute for their exceptional efforts and contributions in these extraordinary times