Ionisation dynamics on the nanoscale seed the processes that govern pathways to macroscopic equilibrium in irradiated matter. Therefore, understanding the conditions that underpin this transition is critical in a wide range of applications from healthcare to radiation science. Here we investigate these interactions in real time using a novel optical streaking technique that exploits the ultrafast nature and highly synchronous pump-probe capabilities of laser driven accelerators. This work reveals behaviour in the recovery of matter irradiated by protons and X-rays that can only be reconciled by considering the nanoscopic structure of the irradiated matter.

An electron beam generated by a laser-plasma accelerator is converted into an X-ray source by means of bremsstrahlung radiation in a dense material. This radiation source can be used to perform non-destructive testing (NDT) of dense objects. To perform this type of X-ray imaging, it is necessary to work with a point-like source of high energy X-rays. For this purpose, a numerical optimization of the whole experiment is essential, we have to deal with two main parts, the laser-matter interaction for which we use a Particle-In-Cell code, and the X-ray emission part for which we use a Monte Carlo code. In this talk we will discuss our recent approaches for tackling the limitations of NDT for dense objects : increasing the energy of the source and reducing its size.

Compact laser-based neutron sources have attracted great interest in the last years due to a growing field of applications. Neutrons interact via the nuclear force which results in relatively large penetration depths and isotope specific interaction cross-sections. This can be used to identify the isotopic composition of samples. This allows applications like the inspection of cargo containers for fissile material or explosives as well as the tracing of artifacts to their geological origin. While conventional neutron sources such as reactors and spallation sources are large in size, expensive and produce strong background radiation with large pulse widths, it is more desirable to have compact neutron sources with short pulse lengths which require less shielding. Laser-based neutron sources can fill this gap in the near future when modern high repetition rate laser systems can be used. In addition, the short neutron pulse length in the order of one nanosecond facilitates new applications such as neutron resonance spectroscopy and neutron resonance imaging. Here, we present recent results from experimental campaigns at the PHELIX laser system at the GSI Darmstadt. In the experiment, protons and deuterons have been accelerated from thin foils up to 50 MeV. These ions were converted by nuclear reactions inside a catcher material into 10^10 neutrons per shot which were subsequently moderated down into the eV regime. With this epithermal neutron beam, it was possible to identify several isotopes inside a 2.7 mm thick sample using neutron resonance spectroscopy. In addition, laser-driven thermal neutron radiography was applied for measuring the thickness of indium cadmium plates behind a lead shielding. Also, the first demonstration of neutron resonance radiography will be presented. I will further give an outlook for future applications that will be enabled by high repetition rate laser systems and liquid leaf targets. Laser-based neutron sources will be developed and applied at the international center for nuclear photonics at the TU Darmstadt in close cooperation with their industrial partner Focused Energy GmbH.

The abovementioned authors are named on behalf of their respective groups. The recent rediscovery of the “Flash Effect” revived the interest in high and ultra-high dose-rate radiation effects throughout the radiobiology community, promising protection of normal tissue, while simultaneously not altering tumour control. Systematic preclinical studies at (modified) clinical accelerators resulted in a recipe of necessary beam parameters for the induction of electron Flash effect (doi:10.3389/fonc.2019.01563), whereas for protons the optimal parameter setting is still under investigation. Expanding the clinical parameter range the “Dresden platform for high-dose rate radiobiology” enables electron and proton experiments with dose rates of up to 109 Gy/s and more flexible beam pulse structures. The general applicability of these beams for radiobiological studies was proven with zebrafish embryos a simple but robust normal tissue in vivo model. Overall, the analysis of the induced radiation effects reveal a clear normal tissue protecting Flash effect for ultra-high dose rate electron and proton beams relative to their conventional beam delivery.

This conference presentation was prepared for SPIE Optics + Optoelectronics, 2023.

Laser Plasma Accelerator (LPA) produces very highly energetic electron (VHEE) beam that can be used for medical applications such as radiotherapy. This has the potential to improve cancer treatments at a cost-comparable to X-ray radiotherapy. In this context, we have performed a dedicated study considering realistic VHEE beam, produced by compact tens of TW LPA to validate the approach, considering various scenario. A full study of the dose deposition properties of a focused VHEE beam with a wide energy spectrum and maximum energy of 250 MeV based on Monte Carlo Geant4 simulations is reported. We consider a realistic manipulation of the electron beam parameters using a quadrupole triplet lattice, allowing to focus the beam into the phantom of 30 cm^3 which is placed further downstream of the beamline. To reduce the effects of unwanted ionizing radiation, a tungsten collimator is also placed in front of the last quadrupole to filter out lower energetic particles, reducing the entrance dose. The on-axis and transverse dose profiles that have been investigated when varying longitudinal positioning of the phantom, confirms the potential of VHEE for radiotherapy.

Cancer is the second most common cause of death globally. In 2018, 18.1 million new cancer cases were diagnosed, 9.6 million people died of cancer-related disease, and 43.8 million people were living with cancer. Radiotherapy (RT) is used in 50% of cancer patients and is involved in 40% of cancer cures. It is estimated that 26.9 million life-years could be saved in low- and middle-income countries if capacity could be scaled up. The beam characteristics that can be exploited in proton- and ion-beam therapy (IBT) facilities today are restricted to low dose rates, a small number of temporal schemes, and a small number of spatial distributions. The use of novel beams with strikingly different characteristics has led to exciting evidence of enhanced therapeutic benefit. This evidence, together with developments in our understanding of personalised medicine based on the biology of individual tumours, now provides the impetus for a radical transformation of IBT. The ‘Laser-hybrid Accelerator for Radiobiological Applications’, LhARA, is conceived as a novel, uniquely flexible facility dedicated to the study of radiobiology. The technologies that will be demonstrated in LhARA have the potential to allow particle-beam therapy to be delivered in a completely new regime, combining a variety of ion species in a single treatment fraction and exploiting ultra-high dose rates. The laser-hybrid approach will allow the exploration of the vast “terra incognita” of the mechanisms by which the biological response is modulated by the physical characteristics of the beam. I will describe the motivation for LhARA, present the status of its development and summarise the programme upon which the LhARA consortium has embarked to drive a step-change in clinical capability.

Recent oncological studies identified beneficial properties of radiation applied at ultra-high dose rates several orders of magnitude higher than the clinical standard of ~1 Gy/min. At the high-power laser source Draco, operated at Helmholtz-Zentrum Dresden-Rossendorf, a complete laser-driven proton research platform for diverse user-specific small animal models was demonstrated. Tunable single-shot doses up to around 20 Gy to millimeter-scale volumes on nanosecond time scales, equivalent to instantaneous dose rates of around 10^9 Gy/s. Spatially homogenized dose distributions tailored to the sample can be delivered with polychromatic proton beams of energies greater than 60 MeV, which have been provided with unprecedented stability and long-term reliability. These achievements allowed to successfully conduct the first radiobiological in vivo study using a laser-driven proton source. The pilot irradiation study was performed on human tumors in a mouse model, showing the concerted preparation of mice and laser accelerator, the dose-controlled, tumor-conform irradiation using a laser-driven as well as a clinical reference proton source, and the radiobiological evaluation of irradiated and unirradiated mice for radiation-induced tumor growth delay. The prescribed homogeneous dose of 4 Gy was precisely delivered at the laser-driven source. The laser-based proton irradiation platform at the Draco PW facility enables systematic radiobiological studies within an unprecedented range of beam parameters and demonstrate a solution for minimally invasive volumetric dosimetry at ultra-high dose rates.

In this contribution, we present the results of laser-target interaction studies with intensities ranging from the relativistic regime down to the intensities of dielectric breakdown of hydrogen. They were conducted using the cryogenic hydrogen jet platforms together with the high-resolution optical probing capabilities at the Draco laser facility at Helmholtz-Zentrum Dresden-Rossendorf and the HiBEF facility at European XFEL. Changing the laser parameters enables to utilize specific plasma processes for controlled plasma density tailoring. These results, together with technical advancements of the target, pave the way towards a stable platform for near-critical density targets that will enable stable, repetition-rated proton sources for a multitude of applications at superb energies.

The proposed ‘fission-fusion’ reaction mechanism aims at investigating the rapid neutron-capture process, contributing to the formation of heavy elements, by using laser-accelerated thorium ions in a sandwich target configuration [1]. In a first step, the efficient acceleration of gold ions is investigated, as recently achieved in our measurement at the PHELIX laser with 500 fs long pulses [2]. In this experiment, for the first time, the laser-based acceleration of gold ions above 7 MeV/u was demonstrated. Additionally, individual gold charge states were resolved with unprecedent resolution. This allowed to investigate the role of collisional ionization using a developmental branch of the particle-in-cell simulation code EPOCH [3], showing a much better agreement of the simulated charge state distributions with the experimentally measured ones than when only considering field ionization. This work is continued at the Centre for Advanced Laser Applications (CALA), using the ATLAS 3000 laser (800 nm central wavelength, 25 fs pulse length). [1] D. Habs et al., Appl. Phys. B 103, 471-484 (2011) [2] F.H. Lindner et al., Sci. Rep. 12, 4784 (2022) [3] M. Afshari et al., Sci. Rep. 12, 18260 (2022)