Experiments were performed to study electron acceleration by intense sub-picosecond laser pulses propagating in sub-mm long plasmas of near critical electron density (NCD). Low density foam layers of 300-500 μm thickness were used as targets. In foams, the NCD-plasma was produced by a mechanism of super-sonic ionization when a well-defined separate ns-pulse was sent onto the foamtarget forerunning the relativistic main pulse. The application of sub-mm thick low density foam layers provided a substantial increase of the electron acceleration path in a NCD-plasma compared to the case of freely expanding plasmas created in the interaction of the ns-laser pulse with solid foils. The performed experiments on the electron heating by a 100 J, 750 fs short laser pulse of 2-5×10 19 W cm −2 intensity demonstrated that the effective temperature of supra-thermal electrons increased from 1.5-2 MeV in the case of the relativistic laser interaction with a metallic foil at high laser contrast up to 13 MeV for the laser shots onto the pre-ionized foam. The observed tendency towards a strong increase of the mean electron energy and the number of ultra-relativistic laseraccelerated electrons is reinforced by the results of gamma-yield measurements that showed a 1000fold increase of the measured doses. The experiment was supported by 3D-PIC and FLUKA simulations, which considered the laser parameters and the geometry of the experimental set-up. Both, measurements and simulations showed a high directionality of the acceleration process, since the strongest increase in the electron energy, charge and corresponding gamma-yield was observed close to the direction of the laser pulse propagation. The charge of super-ponderomotive electrons with energy above 30 MeV reached a very high value of 78 nC.

Helium ion beam therapy for the treatment of cancer was one of several developed and studied particle modalities in the 1950’s, leading to clinical trials beginning in 1975 at the Lawrence Berkeley National Laboratory. The trial shutdown was followed by decades of research and clinical silence on the topic while proton and carbon ion therapy made debuts at research facilities and academic hospitals worldwide. The lack of progression in understanding of principle facets of helium ion beam therapy in terms of physics, biological and clinical findings persist today, mainly attributable to its highly limited availability. Despite this major setback, there has been an increasing focus on evaluating and establishing clinical and research programs using helium ion beams, with both therapy and imaging initiatives to supplement the clinical palette of radiotherapy in the treatment of aggressive disease and sensitive clinical cases. Moreover, due its intermediate physical and radio-biological properties between proton and carbon ion beams, helium ions may provide a streamlined economic steppingstone towards an era of widespread use of multi-particle approaches to light and heavy ion therapy. This roadmap presents an overview of the current state-of-the-art and future directions of helium ion therapy: understanding physics and improving modeling, understanding biology and improving modeling, imaging techniques using helium ions and refining and establishing clinical approaches and aims from learned experience with protons. These topics are organized and presented into three main sections, outlining current and future tasks in establishing clinical and research programs using helium ion beams — A. Physics B. Biological and C. Clinical Perspectives.

Measured charge-and mass-changing cross sections for the systems 4 He + 12 C, 4 He + 16 O, 4 He + 28 Si, and 4 He + 1 H in the energy range 70-220 MeV/u are presented. The cross sections were obtained via the attenuation method where a E-E scintillator telescope was used for particle identification. These new data

Measured cross sections for the production of the PET isotopes , and from carbon and oxygen targets induced by protons (40–220 ) and carbon ions (65–430 ) are presented. These data were obtained via activation measurements of irradiated graphite and beryllium oxide targets using a set of three scintillators coupled by a coincidence logic. The measured cross sections are relevant for the PET particle range verification method where accurate predictions of the emitter distribution produced by therapeutic beams in the patient tissue are required. The presented dataset is useful for validation and optimization of the nuclear reaction models within Monte Carlo transport codes. For protons the agreement of a radiation transport calculation using the measured cross sections with a thick target PET measurement is demonstrated.