This study explores the production of radionuclides in a PMMA (Polymethylmethacrylate) phantom irradiated with Very High Energy Electrons (VHEE) beams as a novel method for dose verification. In this work, Monte Carlo simulation studies using the Geant4 toolkit and experimental measurements with a VHEE beam produced by a laser-plasma accelerator were conducted. Specifically, the photonuclear production of 11C, 15O and 13N is examined, with a detailed analysis of their spatial distribution, production yields and decay time

Experimental results aimed at demonstrating the feasibility of a two-section delay mask for the generation of ultrashort pulse trains are reported. Based on the initial simulation results, a 500 um thick circular fused silica plate featuring a central aperture was designed to enable two distinct transverse portions of the incident laser pulse to be focused, ideally, with equal intensity. This fulfills one of the requirements of the resonant multipulse ionization injection (ReMPI) scheme for laser wakefield acceleration. The experiment was carried out at the CNR-INO Intense Laser Irradiation Laboratory using a 240 TW laser system operated at 120 TW, as part of the ongoing preparation for the first experimental demonstration of ReMPI.

Radiotherapy with Very High Energy Electron (VHEE) beams is being extensively investigated for the treatment of deep-seated tumours, even in view of novel protocols based on the so-called FLASH effect. Laser WakeField Acceleration (LWFA) provides a compact and affordable accelerator technology for VHEE electron beams, featuring ultra-high instantaneous dose rates and holding the promise to provide Ultra-High (average) Dose Rates (UHDRs) needed to activate the FLASH effect, with major efforts ongoing worldwide to fulfill this promise. Therapeutic doses are already at reach, using pencil beams produced via LWFA. These beams typically exhibit significant energy spread, and small transverse size. These features are rather different from those of other beams considered so far in radiotherapy studies. In view of a rapid clinical translation of LWFA-VHEE beams it is therefore of paramount importance to assess the role of these properties in the dose delivery to the patient. Here we present a study carried out via start-to-end (PIC and Monte Carlo) simulations, of the main dosimetric features of a realistic laser-driven VHEE pencil beam targeted on a brain tumor. The entire tumor coverage is achieved by a scanning procedure; the dose pattern resulting from tessellation, i.e. the overlapping of adjacent beamlets, and the role of energy spread are thoroughly discussed. Dose Volume Histograms are presented, and their quality is discussed. The impact of the FLASH effect is also considered, introducing a degree of healthy tissue sparing in the modelling. Finally, the foreseen technological path toward the achievement of FLASH dose rates with LWFA-VHEE beams is briefly outlined.

We present a numerical study on a structured plasma target to simultaneously improve the energy spread and divergence of a laser-driven very high energy electron (VHEE) beam designed for VHEE-radiotherapy (RT) application. The main concept to obtain such an enhanced quality beam is to localize the injection, acceleration, and extraction of the electrons by tailoring the plasma target density profile. The injection space is truncated by spatially confining the ionization-injection dopant, while the rest of the target is filled with He atoms. In order to reduce the emittance growth during the bunch extraction, an optimized density downramp profile is adopted. By using a 100 TW class Ti:Sa laser system and an ionization-injection scheme in the blow-out regime, a relatively high charge (>= 120 pC) beam with mean energy >= 200 MeV, rms energy spread <= 6%, and normalized emittance epsilon(nx) < 4 mm mrad can be obtained. This combination of bunch specification enables an efficient transport and focusing of the particles, thus making the beam of particular interest for VHEE-RT.

Ultra-low emittance and length-tuneable electron beams can be obtained with the Laser Wake Field Acceleration (LWFA) by employing advanced ionization injection techniques, such as the Two-Color and the Resonant Multi-Pulse Ionization injection (ReMPI) schemes. There, a tightly focused, short wavelength (ionization) pulse extracts electrons from a selected inner shell of a dopant, allowing them to be longitudinally compressed and trapped in the wakefield excited by a different (driver) pulse. In this work we demonstrate, by means of analytical results and Particle In Cell simulations, that 340 as long electron beams with 2.3 GeV energy, 6.1 pC charge, 0.15 % projected energy spread, 60 nm normalised emittance, and projected 6D-Brightness in excess of [Formula: see text] can be generated with a  200 TW Ti:Sa laser system. The beam slice analysis reveals its potentialities for driving a few-spikes attosecond X-ray Free Electron Laser. Furthermore, the ultra-high projected quality, and the extreme shortness of the beams make them ideal candidates for the generation of attosecond and quasi-monochromatic γ photons beams through Thomson/Compton backscattering, or for the injection in subsequent plasma wakefield structures so as to reach TeV energies from staged LWFA.

We report the characterization of the pump absorption and emission dynamic properties of a $\mathrm{Tm}:{\mathrm{Lu}}_2{\mathrm{O}}_3$ ceramic lasing medium using a three-mirror folded laser cavity. We measured a slope efficiency of 73%, which allowed us to retrieve the cross-relaxation coefficient. The behavior of our system was modeled via a set of macroscopic rate equations in both the quasi continuous wave and the pulsed pumping regime. Numerical solutions were obtained, showing a good agreement with the experimental findings. The numerical solution also yielded a cross-relaxation coefficient in very good agreement with the measured one, showing that the cross-relaxation phenomenon approaches the maximum theoretical efficiency.

X-ray free electron laser (XFEL) sources coupled to high-power laser systems offer an avenue to study the structural dynamics of materials at extreme pressures and temperatures. The recent commissioning of the DiPOLE 100-X laser on the high energy density (HED) instrument at the European XFEL represents the state-of-the-art in combining x-ray diffraction with laser compression, allowing for compressed materials to be probed in unprecedented detail. Here, we report quantitative structural measurements of molten Sn compressed to 85(5) GPa and ∼3500 K. The capabilities of the HED instrument enable liquid density measurements with an uncertainty of ∼1% at conditions which are extremely challenging to reach via static compression methods. We discuss best practices for conducting liquid diffraction dynamic compression experiments and the necessary intensity corrections which allow for accurate quantitative analysis. We also provide a polyimide ablation pressure vs input laser energy for the DiPOLE 100-X drive laser which will serve future users of the HED instrument.

The thermal properties of ultra-high temperature ceramics (UHTCs) in the MB2-WC (M = Ti, Zr, Hf) system and tungsten were studied for potential application as plasma-facing materials in fusion power plants. The sintered UHTC and tungsten samples were subjected to deuterium plasma or protons irradiation. Thermal diffusivity was measured using the laser flash method, and superficial thermal conductivity was analyzed through atomic force microscopy. Results showed that the thermal properties did not degrade when exposed to relevant environments and remained stable over a range of temperatures, unlike the reference tungsten material. Thermal conductivity ranged from 61 to 68 W m(-1) K-1 for TiB2-2(WC-6Co), from 53 to 63 W m(-1) K-1 for ZrB2-6WC, from 67 to 75 W m(-1) K-1 for HfB2-6WC, and from 180 to 119 W m(-1) K-1 for tungsten across the temperature range from room temperature to 1200 degrees C. The increasing trend of thermal effusivity, over 19000 J s(-0.5) m(-2) K-1 at 1200 degrees C, justifies further testing and of UHTC materials for fusion applications.

Major strides have been made in the development of FLASH radiotherapy (FLASH RT) in the last ten years, but there are still many obstacles to overcome for transfer to the clinic to become a reality. Although preclinical and first-in-human clinical evidence suggests that ultra-high dose rates (UHDRs) induce a sparing effect in normal tissue without modifying the therapeutic effect on the tumor, successful clinical translation of FLASH-RT depends on a better understanding of the biological mechanisms underpinning the sparing effect. Suitable in vitro studies are required to fully understand the radiobiological mechanisms associated with UHDRs. From a technical point of view, it is also crucial to develop optimal technologies in terms of beam irradiation parameters for producing FLASH conditions. This review provides an overview of the research progress of FLASH RT and discusses the potential challenges to be faced before its clinical application. We critically summarize the preclinical evidence and in vitro studies on DNA damage following UHDR irradiation. We also highlight the ongoing developments of technologies for delivering FLASH-compliant beams, with a focus on laser-driven plasma accelerators suitable for performing basic radiobiological research on the UHDR effects.

Electron plasma waves can be efficiently excited by a resonant train of ultrashort pulses, spatially separated by a plasma wavelength. Generating a pulse train from a single amplified ultrashort pulse may be challenging when dealing with large beams. Here we discuss a pulse splitting technique using a simple delay mask that can be adapted to large diameter petawatt beams. We show via detailed numerical simulations that unique signatures of electrons accelerated by a resonantly excited wakefield can be obtained from realistic focused double-pulse trains obtained from a single-region delay mask.

The next years will see the completion of several new facilities at Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali del Sud (LNS) opening up new possibilities in the fields of nuclear structure, nuclear dynamics, nuclear astrophysics and applications. These include a new line for high-intensity cyclotron beams, a new facility for in-flight production of radioactive ion beams, the PANDORA plasma trap for multidisciplinary studies and a high-power laser for basic science and applied physics. The nuclear physics community has organized a workshop to discuss the new physics opportunities that will be possible in the middle term (5–7 years) by employing state-of-the-art detection systems. A detailed discussion of the outcome from the workshop is presented in this report.

PURPOSE:Flash radiotherapy (FLASH-RT) is currently being regarded as the next breakthrough in radiation treatment of cancer, delivering ultrahigh radiation doses in a very short time, and sparing normal tissues from detrimental injury. Here we review the current evidence on the preclinical findings as well as the radiobiological mechanisms underlying the FLASH effect. We also briefly examine the scenario of available technologies for delivering FLASH dose-rates for research and their implications for future clinical use.CONCLUSIONS:Preclinical studies report that the FLASH-RT reduces radiation-induced toxicity whilst maintaining an equivalent tumor response across different animal models. However, the molecular radiobiology underlying FLASH effect is not fully understood and further experiments are necessary to understand the biological response. Future studies also includes the design of a FLASH delivery system able to produce beams appropriate for treatment of tumors with ultra-high dose rates. All these research activities will greatly benefit from a multidisciplinary collaboration across biology, physics and clinical oncology, increasing the potential of a rapid clinical translation of FLASH-RT.

While the long-term vision of the advanced accelerator community is aimed at addressing the challenges of future collider technology, it is critical that the community takes advantage of the opportunity to make large societal impact through its near-term applications. In turn, enabling robust applications strengthens the quality, control, and reliability of the underlying accelerator infrastructure. The white paper contributions that are solicited here will summarize the near-term applications ideas presented by the advanced accelerator community, assessing their potential impact, discussing scientific and technical readiness of concepts, and providing a timeline for implementation.

Abstract After the introduction of the ionization-injection scheme in laser wake field acceleration and of related high-quality electron beam generation methods, such as two-color and resonant multi-pulse ionization injection (ReMPI), the theory of thermal emittance has been used to predict the beam normalized emittance obtainable with those schemes. We recast and extend such a theory, including both higher order terms in the polynomial laser field expansion and non-polynomial corrections due to the onset of saturation effects on a single cycle. Also, a very accurate model for predicting the cycle-averaged distribution of the extracted electrons, including saturation and multi-process events, is proposed and tested. We show that our theory is very accurate for the selected processes of ${\mathrm{Kr}}^{8^{+}\to {10}^{+}}$ and ${\mathrm{Ar}}^{8^{+}\to {10}^{+}}$ , resulting in a maximum error below 1%, even in a deep-saturation regime. The accurate prediction of the beam phase-space can be implemented, for example, in laser-envelope or hybrid particle-in-cell (PIC)/fluid codes, to correctly mimic the cycle-averaged momentum distribution without the need for resolving the intra-cycle dynamics. We introduce further spatial averaging, obtaining expressions for the whole-beam emittance fitting with simulations in a saturated regime, too. Finally, a PIC simulation for a laser wakefield acceleration injector in the ReMPI configuration is discussed.

We report on the conceptual design of a 2 μm, broadband laser multipass amplifier system based on Tm-doped gain medium, including an overview of the model established to optimize the performance of a diode edge-pumped high-power solid-state thin-disk configuration.

A model for the calculation of the pump energy coupling to a disk amplifier is presented. The disk is considered to be pumped on its edge by diode bars. A composite geometry, namely a disk with a doped (pump absorbing) inner region surrounded by an undoped region is considered. The model allows the overall pump energy coupling as well as the absorption 3D map to be obtained for different geometric diode bars arrangements on an N-sided polygon. A set of fundamental conditions for the maximization of the total energy coupled to the active region is laid out first. Using the model, we then show that once these conditions are fulfilled, the precise diode bars arrangement and focusing can be tuned to get the desired energy absorption spatial distribution, while preserving the highest overall energy coupling to the doped region. The most interesting case of a cylindrically symmetric, radially uniform absorption profile is discussed, providing some general hints on achieving such a condition.

We describe the initial development of an edge-pumped ceramic Tm:Lu2O3 multipass amplifier for ultra-short pulse laser with high-repetition rate, high-peak power and high-average power, with an overview of the laser chain and the amplifiers specifications

The direct use of so-called Very High Energy Electrons for radiotherapy is currently deserving a renewed and growing attention. This is mostly due to the recent emergence of the so-called FLASH effect in radiobiology [1], consisting in a surprising reduction of adverse effects on healthy tissue by ionizing radiation when dose delivery occurs at very high average dose rates (greater than a few tens of Gy/s). In order for a real clinical translation of this new protocol in the clinical practice, the development of novel kind of ionizing radiation sources featuring such very high dose rates, which are basically hindered by the relatively low Bremsstrahlung conversion efficiency in current machines, is considered as an essential step. With this respect, laser-driven accelerators of Very High Energy Electron (VHEE) beams, with energy in the range 100-250 MeV, are regarded as one of the most promising tool [2]. Furthermore, both early studies, dating back to 1990s, and more recent works suggest that an improved dose deposition pattern can be expected from electron beams, as compared to photon beams, when the very high energy region is reached. In this talk, we report on a recent experiment aimed at assessing dose deposition for deep seated tumors using advanced irradiation schemes, typical of current radiotherapy protocols, with an existing laser-driven VHEE source [3]. In particular, our measurements showed control of localized dose deposition and modulation, suitable to target a volume at depths in the range from 5 to 10 cm with mm resolution. Based on this experimental findings and on further numerical simulations, we also discuss the features and potentialities of laser-driven VHEE sources for radiobiology experiments aimed at deepening the understanding of the mechanisms underpinning the FLASH effect. The main requirements and the perspectives for a longer term translation of an electron-based radiotherapy into the real clinical practice will be also addressed. [1] M.-C. Vozenin et al., Biological Benefits of Ultra-high Dose Rate FLASH Radiotherapy: Sleeping Beauty Awoken, Clin. Oncol. 31 (2019), 407 [2] A. Giulietti (Eds), Laser-Driven Particle Acceleration Towards Radiobiology and Medicine, Springer (2016) [3] L. Labate et al., Toward an effective use of laser‐driven very high energy electrons for radiotherapy: Feasibility assessment of multi‐field and intensity modulation irradiation schemes, Sci. Rep. 10 (2020), 17307