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Physical review accelerators and beams 24(9), 091301 (2021). doi:10.1103/PhysRevAccelBeams.24.091301, We describe the development and operation of a regenerative, cryogenically-formed discharge waveguide formed by freezing nitrous oxide gas onto the inner wall of a sapphire capillary. We demonstrate a technique for varying the channel diameter in situ and present guiding of low-power laser pulses through 6-cm long waveguides with channel diameters of 0.7, 0.8, and 1 mm. Measurements and simulations of the output laser fluence showed that the matched spot size could be adjusted with the thickness of the solid nitrous oxide layer., Published by American Physical Society, College Park, MD

We measured the parameter reproducibility and radial electron density profile of capillary discharge waveguides with diameters of 650 $\mathrm{\mu} \mathrm{m}$ to 2 mm and lengths of 9 to 40 cm. To the best of the authors’ knowledge, 40 cm is the longest discharge capillary plasma waveguide to date. This length is important for $\ge$ 10 GeV electron energy gain in a single laser-driven plasma wakefield acceleration stage. Evaluation of waveguide parameter variations showed that their focusing strength was stable and reproducible to $ % and their average on-axis plasma electron density to $ %. These variations explain only a small fraction of laser-driven plasma wakefield acceleration electron bunch variations observed in experiments to date. Measurements of laser pulse centroid oscillations revealed that the radial channel profile rises faster than parabolic and is in excellent agreement with magnetohydrodynamic simulation results. We show that the effects of non-parabolic contributions on Gaussian pulse propagation were negligible when the pulse was approximately matched to the channel. However, they affected pulse propagation for a non-matched configuration in which the waveguide was used as a plasma telescope to change the focused laser pulse spot size.

European physical journal special topics 229(24), 3675 - 4284 (2020). doi:10.1140/epjst/e2020-000127-8, This report presents the conceptual design of a new European research infrastructure EuPRAXIA. The concept has been established over the last four years in a unique collaboration of 41 laboratories within a Horizon 2020 design study funded by the European Union. EuPRAXIA is the first European project that develops a dedicated particle accelerator research infrastructure based on novel plasma acceleration concepts and laser technology. It focuses on the development of electron accelerators and underlying technologies, their user communities, and the exploitation of existing accelerator infrastructures in Europe. EuPRAXIA has involved, amongst others, the international laser community and industry to build links and bridges with accelerator science — through realising synergies, identifying disruptive ideas, innovating, and fostering knowledge exchange. The Eu-PRAXIA project aims at the construction of an innovative electron accelerator using laser- and electron-beam-driven plasma wakefield acceleration that offers a significant reduction in size and possible savings in cost over current state-of-the-art radiofrequency-based accelerators. The foreseen electron energy range of one to five gigaelectronvolts (GeV) and its performance goals will enable versatile applications in various domains, e.g. as a compact free-electron laser (FEL), compact sources for medical imaging and positron generation, table-top test beams for particle detectors, as well as deeply penetrating X-ray and gamma-ray sources for material testing. EuPRAXIA is designed to be the required stepping stone to possible future plasma-based facilities, such as linear colliders at the high-energy physics (HEP) energy frontier. Consistent with a high-confidence approach, the project includes measures to retire risk by establishing scaled technology demonstrators. This report includes preliminary models for project implementation, cost and schedule that would allow operation of the full Eu-PRAXIA facility within 8—10 years., Published by Springer, Heidelberg

Significant challenges in the detection of laser-accelerated ions result from the high flux (1010-1012 ions/pulse) and the short bunch duration which are intrinsic to laser-driven sources. The development of diagnostic techniques able to operate in real-time and on a high-rep basis is a key step towards multidisciplinary applications of such non-conventional beams. Real time diagnosis of the main beam parameters for high-energy protons accelerated by the Vulcan Petawatt (VULCAN-PW) laser system has been performed using an on line diagnostics based on the Time of Flight (TOF) technique and the use of diamond detectors. Proton energy spectra have been measured for energies exceeding 30 MeV. The results show that the TOF method employing state-of-the-art detectors is a robust real-time diagnostics, able to operate efficiently under the harsh conditions occurring with kJ-class, PW laser systems, and offering the possibility to monitor on a shot-by-shot basis the main beam parameters of high intensity proton bunches for energies up to the 100 MeV level.

The plasma channel formation in the focus of a knife-like nanosecond laser pulse irradiating a gas target is studied theoretically, and in gas-dynamics computer simulations. The distribution of the electromagnetic field in the focus region, obtained analytically, is used to calculate the energy deposition in the plasma, which then is implemented in the magnetohydrodynamic computer code. The modelling of the channel evolution shows that the plasma profile, which can guide the laser pulse, is formed by the tightly focused short knife-like lasers. The results of the simulations show that a proper choice of the convergence angle of a knife-like laser beam (determined by the focal length of the last cylindrical lens), and laser pulse duration may provide a sufficient degree of azimuthal symmetry of the formed plasma channel.

The main purpose of this paper is to quantitatively study the possibility of delivering dose distributions of clinical relevance with laser-driven proton beams. A Monte Carlo application has been developed with the Geant4 toolkit, simulating the ELIMED (MEDical and multidisciplinary application at ELI-Beamlines) transport and dosimetry beam line which is being currently installed at the ELI-Beamlines in Prague (CZ). The beam line will be used to perform irradiations for multidisciplinary studies, with the purpose of demonstrating the possible use of optically accelerated ion beams for therapeutic purposes. The ELIMED Geant4-based application, already validated against reference transport codes, accurately simulates each single element of the beam line, necessary to collect the accelerated beams and to select them in energy. Transversal dose distributions at the irradiation point have been studied and optimized to try to quantitatively answer the question if such kind of beam lines, and specifically the systems developed for ELIMED in Prague, will be actually able to transport ion beams not only for multidisciplinary applications, such as pitcher-catcher nuclear reactions (e.g. neutrons), PIXE analysis for cultural heritage and space radiation, but also for delivering dose patterns of clinical relevance in a future perspective of possible medical applications.

We present an approach for direct measurement of ultrahigh laser intensities in the range \(10^{20}\)–\(10^{24}\) W/cm\(^2\). The method is based on the use of multiple sequential tunneling ionization of heavy atoms with adequately high ionization potentials. We show that, due to the highly nonlinear dependence of tunneling ionization rates on the electromagnetic field strength, an off-set in the charge distribution of ions appears to be clearly sensitive to the peak value of intensity in the laser focus. Based on the tunnel-ionization mechanism, a simple analytic theory helps in estimating the maximal charge state produced at a given laser intensity. Our theory also allows for calculating qualitatively a distribution in charge states generated in different zones of the laser focus. These qualitative predictions are in excellent agreement with numerical simulations of the tunneling cascades, developed in the interaction of a short tightly focused laser pulse with low-density noble gas targets. The method could be particularly useful and of instrumental demand in view of the expected commissioning of several new laser facilities, capable of delivering ultra-powerful light pulses in the above mentioned domain of intensities.

Using QED PIC and hydrodynamic simulations, we optimize the -flare generation scheme from the high power laser interaction with tailored target showing the efficient conversion of the laser pulse energy to -photons.

Physics of plasmas 27(9), 093101 (2020). doi:10.1063/5.0014961, Laser-heated capillary discharge waveguides are novel, low plasma density guiding structures able to guide intense laser pulses over many diffraction lengths and have recently enabled the acceleration of electrons to 7.8 GeV by using a laser-plasma accelerator (LPA). These devices represent an improvement over conventional capillary discharge waveguides, as the channel matched spot size and plasma density can be tuned independently of the capillary radius. This has allowed the guiding of petawatt-scale pulses focused to small spot sizes within large diameter capillaries, preventing laser damage of the capillary structure. High performance channel-guided LPAs require control of matched spot size and density, which experiments and simulations reported here show can be tuned over a wide range via initial discharge and laser parameters. In this paper, measurements of the matched spot size and plasma density in laser-heated capillary discharges are presented, which are found to be in excellent agreement with simulations performed using the MHD code MARPLE. Strategies for optimizing accelerator performance are identified based on these results., Published by American Institute of Physics, [S.l.]

Physics of plasmas 27(5), 053102 (2020). doi:10.1063/5.0002769, A plasma channel created by the combination of a capillary discharge and inverse Bremsstrahlung laser heating enabled the generation of electron bunches with energy up to 7.8 GeV in a laser-driven plasma accelerator. The capillary discharge created an initial plasma channel and was used to tune the plasma temperature, which optimized laser heating. Although optimized colder initial plasma temperatures reduced the ionization degree, subsequent ionization from the heater pulse created a fully ionized plasma on-axis. The heater pulse duration was chosen to be longer than the hydrodynamic timescale of ���1 ns, such that later temporal slices were more efficiently guided by the channel created by the front of the pulse. Simulations are presented which show that this thermal self-guiding of the heater pulse enabled channel formation over 20 cm. The post-heated channel had lower on-axis density and increased focusing strength compared to relying on the discharge alone, which allowed for guiding of relativistically intense laser pulses with a peak power of 0.85 PW and wakefield acceleration over 15 diffraction lengths. Electrons were injected into the wake in multiple buckets and times, leading to several electron bunches with different peak energies. To create single electron bunches with low energy spread, experiments using localized ionization injection inside a capillary discharge waveguide were performed. A single injected bunch with energy 1.6 GeV, charge 38 pC, divergence 1 mrad, and relative energy spread below 2% full-width half-maximum was produced in a 3.3 cm-long capillary discharge waveguide. This development shows promise for mitigation of energy spread and future high efficiency staged acceleration experiments., Published by American Institute of Physics, [S.l.]

In this work we focus on the reconstruction of the density profiles from tomographic measurements. We compare different analytical and iterative methods, and we propose a new one tailored for the reconstruction of gas targets.

As an alternative to Compton backscattering and bremsstrahlung, the process of colliding high-energy electron beams with strong laser fields can more efficiently provide both cleaner and brighter source of photons in the multi-GeV range for fundamental studies in nuclear and quark-gluon physics. In order to favor the emission of high-energy quanta and minimize their decay into electron-positron pairs the fields must not only be sufficiently strong, but also well localized. We here examine these aspects and develop the concept of a laser-particle collider tailored for high-energy photon generation. We show that the use of multiple colliding laser pulses with 0.4 PW of total power is capable of converting more than 18% of the initial multi-GeV electron beam energy into photons, each of which carries more than half of the electron energy., Comment: 6 pages, 4 figures

In vacuum with an induced by strong electromagnetic wave refraction index larger than unity, an ultra-relativistic electron emits Cherenkov radiation. During the interaction with this wave the electron also radiates photons via the Compton scattering. Synergic Cherenkov-Compton process can be observed by colliding laser accelerated electrons with a high intensity electromagnetic pulse. Extremely high energy photons cannot be emitted via the Cherenkov radiation because the vacuum refraction index tends to unity at these energies. Experiments on studying these phenomena will reveal the properties of vacuum predicted by nonlinear quantum electrodynamics., Comment: 5 pages, 1 figure

Nanostructured and microstructured thin foils have been fabricated and used experimentally as targets to manipulate the spatial profile of proton bunches accelerated through the interaction with high intensity laser pulses (6×10^{19} W/cm^{2}). Monolayers of polystyrene nanospheres were placed on the rear surfaces of thin plastic targets to improve the spatial homogeneity of the accelerated proton beams. Moreover, thin targets with grating structures of various configurations on their rear sides were used to modify the proton beam divergence. Experimental results are presented, discussed, and supported by 3D particle-in-cell numerical simulations.

With the advent of 10 PW laser facilities, new regimes of laser-matter interaction are opening since effects of quantum electrodynamics, such as electron-positron pair production and cascade development, start to be important. The dynamics of light charged particles, such as electrons and positrons, is affected by the radiation reaction force. This effect can strongly influence the interaction of intense laser pulses with matter since it lowers the energy of emitting particles and transforms their energy to the gamma radiation. Consequently, electron-positron pairs can be generated via Breit-Wheeler process. To study this new regime of interaction, numerical simulations are required. With their help it is possible to predict and study quantum effects which may occur in future experiments at modern laser facilities. In this work we present results of electron interaction with an intense standing wave formed by two colliding laser pulses. Due to the necessity to achieve ultra intense laser field, the laser beam has to be focused to a ~μm-diameter spot. Since the paraxial approximation is not valid for tight focusing, the appropriate model describing the tightly focused laser beam has to be employed. In tightly focused laser beam the longitudinal component of the electromagnetic field becomes significant and together with the ponderomotive force they affect the dynamics of interacting electrons and also newly generated Breit-Wheeler electron-positron pairs. Using the Particle-In-Cell code we study electron dynamics, gamma radiation and pair production in such a configuration for linear polarization and different types of targets.

Synopsis We suggest and discuss a method for precise measurement of ultrahigh laser intensities in the 1020 – 1024W/cm2 range of intensities. The method is based on the observation of multiple sequential tunneling ionization of heavy atoms in the focus of an intense laser beam. It can be of use for probing electromagnetic fields of record power expected to achieve at new multi-petawatt laser facilities.

Under typical experimental conditions related to the interaction of a short pulse laser with a nanometer foil target, the assumption of a target step-function number density profile ceases to be valid due to the existence of a nanosecond long amplified spontaneous emission pedestal prior to the arrival of the main pulse. As a consequence, the formation of a low density extended preplasma should be considered, making the achievement of high ion energy extremely challenging. In this work, a multiparametric study of various preplasma distributions is presented, obtained by combinations of the pedestal intensity, initial foil thickness, and main pulse intensity. Hydrodynamic simulations have been employed to find the target number density distribution prior to the arrival of the main laser pulse. The output of the hydrodynamic simulations is then combined with particle-in-cell simulations, providing a detailed understanding of the complete nanosecond-long laser-foil interaction. Once the laser pulse interacts with the preplasma, it deposits a fraction of its energy on the target, before it is either reflected from the critical density surface or transmitted through an underdense plasma channel. A fraction of hot electrons is ejected from the target, leaving the foil in a net positive potential, which in turn results in proton and heavy ion acceleration. The results of our multiparametric studies are important for forthcoming experiments on the ion acceleration with multipetawatt laser facilities.

Fast plasma particle streams have been produced from the interaction of thin solid targets with the recently commissioned 25 TW, Ti:Sapphire, femtosecond laser operating at PALS Centre in Prague. A real-time diagnostic system was employed to characterize the produced particles. Low-current proton beams with energies exceeding 2 MeV were detected by a silicon-carbide detector and their typical energy spectrum is reported. High-current slow plasma ions were recorded by ion collectors placed at different distances and angles. Particle streams were characterized with the future aim to use them as probe beams in combination with the kJ-class, iodine, sub-nanosecond laser beamline available at PALS.

The utilization of a conical target irradiated by a high power laser is proposed to study fast magnetic reconnection in relativistic plasma interactions. Such target, placed in front of the near critical density gas jet, splits the laser pulse, forming two parallel laser pulses in the 2D case and a donut shaped pulse in the 3D case. The magnetic annihilation and reconnection occur in the density downramp region of the subsequent gas jet. The magnetic field energy is converted into the particle kinetic energy. As a result, a backward accelerated electron beam is obtained as a signature of reconnection. The above mechanisms are demonstrated using particle-in-cell simulations in both 2D and 3D cases. Facilitating the synchronization of two laser beams, the proposed approach can be used in designing the corresponding experiments on studying fundamental problems of relativistic plasma physics.

A coil-capacitor target is modeled using FEM simulations and analytical calculations, which allow to explain the time evolution of such complex target during magnetic field production driven by the flow of an extremely high current generated through the interaction with a high power laser. The numerical model includes a detailed study of the magnetic field produced by the coil-capacitor target, both in the static and transient cases, as well as magnetic force and Joule heating. The model is validated by experimental data reported in literature and can be of interest for several applications. As an example, the combination of two synchronized nanosecond lasers with the purpose of producing a plasma responsible of the proton-boron (p+ + 11B → 8.5 MeV + 3α) fusion reaction, and energizing two multi-turn coils with the main purpose of confining such a plasma could enhance the reaction rate. The preliminary conceptual design of a magnetic mirror configuration to be used for confining protons and boron ions up to a few MeV/u in a region of less than 1 mm2 is briefly reported.

Laser acceleration of helium ions from near-critical density targets is studied as an ion source for hadron therapy of oncological diseases. Helium ions are considered a promising candidate for therapy due to higher precision in dose deposition and possibly higher Relative Biological Effectiveness. The feasibility of using PW-class lasers to produce 250 MeV per nucleon helium ion beams that meet the hadron therapy requirements is discussed. The relative effectiveness of laser acceleration of He3 and He4 ions is studied.

A target irradiated with a high power laser pulse, blows off a large amount of charge and as a consequence the target itself becomes a generator of electromagnetic pulses (EMP) owing to high return current flowing to the ground through the target holder. The first measurement of the magnetic field induced by the neutralizing current reaching a value of a few kA was performed with the use of an inductive target probe at the PALS Laser Facility (Cikhardt et al. Rev. Sci. Instrum. 85 (2014) 103507). A full description of EMP generation should contain information on the spatial distribution and temporal variation of the electromagnetic field inside and outside of the interaction chamber. For this reason, we consider the interaction chamber as a resonant cavity in which different modes of EMP oscillate for hundreds of nanoseconds, until the EMP is transmitted outside through the glass windows and EM waves are attenuated. Since the experimental determination of the electromagnetic field distribution is limited by the number of employed antennas, a mapping of the electromagnetic field has to be integrated with numerical simulations. Thus, this work reports on a detailed numerical mapping of the electromagnetic field inside the interaction chamber at the PALS Laser Facility (covering a frequency spectrum from 100 MHz to 3 GHz) using the commercial code COMSOL Multiphysics 5.2. Moreover we carried out a comparison of the EMP generated in the parallelepiped-like interaction chamber used in the Vulcan Petawatt Laser Facility at the Rutherford Appleton Laboratory, against that produced in the spherical interaction chamber of PALS.

A growing interest of the scientific community towards multidisciplinary applications of laser-driven beams has led to the development of several projects aiming to demonstrate the possible use of these beams for therapeutic purposes. Nevertheless, laser-accelerated particles differ from the conventional beams typically used for multiscipilinary and medical applications, due to the wide energy spread, the angular divergence and the extremely intense pulses. The peculiarities of optically accelerated beams led to develop new strategies and advanced techniques for transport, diagnostics and dosimetry of the accelerated particles. In this framework, the realization of the ELIMED (ELI-Beamlines MEDical and multidisciplinary applications) beamline, developed by INFN-LNS (Catania, Italy) and that will be installed in 2017 as a part of the ELIMAIA beamline at the ELI-Beamlines (Extreme Light Infrastructure Beamlines) facility in Prague, has the aim to investigate the feasibility of using laser-driven ion beams for multidisciplinary applications. In this contribution, an overview of the beamline along with a detailed description of the main transport elements as well as the detectors composing the final section of the beamline will be presented.

Fusion energy from reacting hydrogen (protons) with the boron isotope 11 (HB11) resulting in three stable helium nuclei, is without problem of nuclear radiation in contrast to DT fusion. But the HB11 reaction driven by nanosecond laser pulses with thermal compression and ignition by lasers is extremely difficult. This changed radically when irradiation with picosecond laser pulses produces a non-thermal plasma block ignition with ultrahigh acceleration. This uses the nonlinear (ponderomotive) force to surprisingly resulting in same thresholds as DT fusion even under pessimistic assumption of binary reactions. After evaluation of reactions trapped cylindrically by kilotesla magnetic fields and using the measured highly increased HB11 fusion gains for the proof of an avalanche of the three alphas in secondary reactions, possibilities for an absolutely clean energy source at competitive costs were concluded., 4 pages, 3 figures, presented at IFSA 2015 conference, Seattle WA 22 SEP 2015

A high-energy, high-yield proton beam with a good homogeneous profile has been generated from a nanosphere target irradiated by a short (30-fs), intense ($7\ifmmode\times\else\texttimes\fi{}{10}^{20}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$) laser pulse. A maximum proton energy of 30 MeV has been observed with a high proton number of $7\ifmmode\times\else\texttimes\fi{}{10}^{10}$ in the energy range 5--30 MeV. A homogeneous spatial profile with a uniformity (standard deviation from an average value within 85% beam area) of 15% is observed with the nanosphere dielectric target. Particle-in-cell simulations show the enhancement of proton cutoff energy and proton number with the nanosphere target and reveal that the homogeneous beam profile is related with a broadened angular distribution of hot electrons, which is initiated by the nanosphere structure. The homogeneous spatial properties obtained with the nanosphere target will be advantageous in developing laser-driven proton sources for practical applications in which high-quality beams are required.

The quadrupole lens free multiple profile emittance measurement method is an adaptation of the standard multiple profile monitor method for electron beam emittance measurement which was tested at PW laser system. This single shot technique allows to obtain the emittance from beam profile radii fit by means of Twiss (Courant-Snyder) parameters. Lanex scintillating screens were used as profile monitors due to their high yield of visible photons. However, on the other hand, the screen is a source of multiple Coulomb scattering which can influence the beam profile on the following screens at relatively low electron energies. Nevertheless, the contribution of the multiple scattering can be effectively subtracted from the signal by e.g. Bayes unfolding. For high energy beams (E > 0.5 GeV), the multiple scattering contribution is negligible. The presented diagnostics is easy to be implemented into standard experimental setups without any special requests for alignment procedure. Moreover, it can be useful in the optimization phase of the laser plasma accelerator where beam fundamental parameters (energy, energy spread, divergence, pointing) typically fluctuate shot-to- shot.

Relativistically induced transparency regime has been already achieved experimentally by the expansion of ionized solid target during laser-target interaction for relatively longer laser pulses (about 500 fs), but not for ultrashort pulses (about 30 fs), where the expansion is not significant, and, thus, too high laser intensity (close to 10 23 W/cm 2 ) is required. However, when ultrashort intense laser pulse at higher harmonic frequency irradiates a thin solid foil, the target may become relativistically transparent for significantly lower laser pulse intensity compared with the irradiation at fundamental laser frequency. The relativistically induced transparency results in an enhanced heating of hot electrons as well as increased maximum energy of accelerated ions and their numbers. When fundamental laser frequency is converted to the third harmonics, we observed the increase of maximum energy of accelerated protons and numbers of high energy protons by factor of 2 in our two-dimensional particle-in-cell simulations. Lengthening of the laser pulse due to frequency conversion should not decrease the energy and numbers of accelerated protons. The proposed scheme enables to accelerate protons to energies over 250 MeV by ultrashort laser pulse of maximum intensity below 10 22 W/cm 2 irradiating 200 nm thick solid foil.

The use of a low contrast nanosecond laser pulse with a relatively low intensity (3?????1016?W?cm?2) allowed the enhancing of the yield of induced nuclear reactions in advanced solid targets. In particular the ?ultraclean? proton?boron fusion reaction, producing energetic alpha particles without neutron generation, was chosen. A spatially well-defined layer of boron dopants in a hydrogen-enriched silicon substrate was used as a target. A combination of the specific target composition and the laser pulse temporal shape allowed the enhancing of the yield of alpha particles up to 109 per steradian. This result can be ascribed to the interaction of the long-laser pre-pulse with the target and to the optimal target geometry and composition.

Nano and micro structured thin (μ m-scale) foils were designed, fabricated and irradiated with the high intensity laser system operating at LLC (Lund Laser Centre, Sweden) in order to systematically study and improve the main proton beam parameters. Nano-spheres deposited on the front (laser irradiated) surface of a flat Mylar foil enabled a small enhancement of the maximum energy and number of the accelerated protons. Nano-spheres on the rear side allowed to modify the proton beam spatial profile. In particular, with nanospheres deposited on the rear of the target, the proton beam spatial homogeneity was clearly enhanced. Silicon nitride thin foils having micro grating structures (with different step dimensions) on the rear surface were also used as targets to influence the divergence of the proton beam and drastically change its shape through a sort of stretching effect. The target fabrication process used for the different target types is described, and representative experimental results are shown and discussed along with supporting 3D particle-in-cell simulations.

We show that a spatially well-defined layer of boron dopants in a hydrogen-enriched silicon target allows the production of a high yield of alpha particles of around 10^{9} per steradian using a nanosecond, low-contrast laser pulse with a nominal intensity of approximately 3×10^{16} W cm^{−2}. This result can be ascribed to the nature of the long laser-pulse interaction with the target and with the expanding plasma, as well as to the optimal target geometry and composition. The possibility of an impact on future applications such as nuclear fusion without production of neutron-induced radioactivity and compact ion accelerators is anticipated.

Laser accelerated proton beams represent nowadays an attractive alternative to the conventional ones and they have been proposed in different research fields. In particular, the interest has been focused in the possibility of replacing conventional accelerating machines with laser-based accelerators in order to develop a new concept of hadrontherapy facilities, which could result more compact and less expensive. With this background the ELIMED (ELIMED: ELI-Beamlines MEDical applications) research project has been launched by LNS-INFN researchers (Laboratori Nazionali del Sud-Istituto Nazionale di Fisica Nucleare, Catania, IT) and ASCR-FZU researchers (Academy of Sciences of the Czech Republic-Fyzikalni ustar, Prague, Cz), within the pan-European ELI-Beamlines facility framework. Its main purposes are the demonstration of future applications in hadrontherapy of optically accelerated protons and the realization of a laser-accelerated ion transport beamline for multidisciplinary applications. Several challenges, starting from laser-target interaction and beam transport development, up to dosimetric and radiobiological issues, need to be overcome in order to reach the final goals. The design and the realization of a preliminary beam handling and dosimetric system and of an advanced spectrometer for high energy (multi-MeV) laser-accelerated ion beams will be shortly presented in this work.

Nowadays, laser-driven proton beams generated by the interaction of high power lasers with solid targets represent a fascinating attraction in the field of the new acceleration techniques. These beams can be potentially accelerated up to hundreds of MeV and, therefore, they can represent a promising opportunity for medical applications. Laser-accelerated proton beams typically show high flux (up to 1011 particles per bunch), very short temporal profile (ps), broad energy spectra and poor reproducibility. In order to overcome these limitations, these beams have be controlled and transported by means of a proper beam handling system. Furthermore, suitable dosimetric diagnostic systems must be developed and tested. In the framework of the ELIMED project, we started to design a dedicated beam transport line and we have developed a first prototype of a beam line key-element: an Energy Selector System (ESS). It is based on permanent dipoles, capable to control and select in energy laser-accelerated proton beams. Monte Carlo simulations and some preliminary experimental tests have been already performed to characterize the device. A calibration of the ESS system with a conventional proton beam will be performed in September at the LNS in Catania. Moreover, an experimental campaign with laser-driven proton beam at the Centre for Plasma Physics, Queens University in Belfast is already scheduled and will be completed within 2014.

Thomson Spectrometers (TPs) are widely used for beam diagnostic as they provide simultaneous information on charge over mass ratio, energy and momentum of detected ions. A new TP design has been realized at INFN-LNS within the LILIA (Laser Induced Light Ion Acceleration) and ELIMED (MEDical application at ELI-Beamlines) projects. This paper reports on the construction details of the TP and on its experimental tests performed at PALS laboratory in Prague, with the ASTERIX IV laser system. Reported data are obtained with polyethylene and polyvinyl alcohol solid targets, they have been compared with data obtained from other detectors. Consistency among results confirms the correct functioning of the new TP. The main features, characterizing the design, are a wide acceptance of the deflection sector and a tunability of the, partially overlapping, magnetic and electric fields that allow to resolve ions with energy up to about 40 MeV for protons.

The enhancement of laser-driven proton acceleration mechanism in TNSA regime has been demonstrated through the use of advanced nanostructured thin foils. The presence of a monolayer of polystyrene nanospheres on the target frontside has drastically enhanced the absorption of the incident laser beam, leading to a consequent increase in the maximum proton beam energy and total laser conversion efficiency. The experimental measurements have been carried out at the 100 TW and 1 PW laser systems available at the APRI-GIST facility. Experimental results and comparison with particle-in-cell numerical simulations are presented and discussed.

We present an overview of the projected and/or implemented laser systems for ELI-Beamlines. The ELI-Beamlines facility will be a high-energy, high repetition-rate laser pillar of the ELI (Extreme Light Infrastructure) project. The facility will make available high-brightness multi-TW ultrashort laser pulses at kHz repetition rate, PW 10 Hz repetition rate laser pulses, and kilojoule nanosecond laser pulses that will be used for generation of 10 PW, and potentially higher, peak power. These systems will allow meeting user requirements for cutting-edge laser resources for programmatic research in generation and applications of high-intensity X-ray sources, in electron and proton/ion acceleration, and in dense plasma and high-field frontier physics.

The ELI (Extreme Light Infrastructure) Beamlines facility in the Czech Republic, which is planned to complete the installation in 2015, is one of the four pillars of the ELI European project. Several laser beamlines with ultrahigh intensities and ultrashort pulses are foreseen, offering versatile radiation sources in an unprecedented energy range: laser-driven particle beams are expected to range between 1 and 50 GeV for electrons and from 100 MeV up to 3 GeV for protons. The number of particles delivered per laser shot is estimated to be 10 9 –10 10 for the electron beams and 10 10 –10 12 for the proton beams. The high energy and current values of the produced particles, together with the potentiality to operate at 10 Hz laser repetition rate, require an accurate study of the primary and secondary radiation fields to optimize appropriate shielding solutions: this is a key issue to minimize prompt and residual doses in order to protect the personnel, reduce the radiation damage of electronic devices and avoid strong limitations in the operational time. A general shielding study for the 10 PW (0.016 Hz) and 2 PW (10 Hz) laser beamlines is presented here. Starting from analytical calculations, as well as from dedicated simulations, the main electron and proton fields produced in the laser-matter interaction have been described and used to characterize the “source terms” in full simulations with the Monte Carlo code FLUKA. The secondary radiation fields have been then analyzed to assess a proper shielding. The results of this study and the proposed solutions for the beam dumps of the high energy beamlines, together with a cross-check analysis performed with the Monte Carlo code GEANT4, are presented.

New particle acceleration regimes driven by PW class lasers imply the development of new in-situ diagnostics. Before constructing new types of detectors one must test currently available diagnostics in these new regimes of high intensity laser-matter interaction. Experimental tests on two types of time of flight detectors are presented, demonstrating the possibility of their measuring capabilities in harsh conditions, namely the strong laser induced electromagnetic pulse. A recently developed silicon carbide detector was successfully tested and particle beams were characterized. Further tests were performed on a detector based on secondary emission of electrons during the transition of laser accelerated particle beams. The presented results show a clear consistency and sufficient capabilities for high intensity laser driven particle beam detection.

Laser-target acceleration represents a very promising alternative to conventional accelerators for several potential applications, from the nuclear physics to the medical ones. However, some extreme features, not suitable for multidisciplinary applications, as the wide energy and angular spreads, characterize optically accelerated ion beams. Therefore, beyond the improvements at the laser-target interaction level, a lot of efforts have been recently devoted to the development of specific beam-transport devices in order to obtain controlled and reproducible output beams. In this framework, a three years contract has been signed between the INFN-LNS (IT) and Eli-Beamlines-IoP (CZ) to provide the design and the realization of a complete transport beam-line, named ELIMED, dedicated to the transport, diagnostics and dosimetry of laser-driven ion beams. The transport devices will be composed by a set of super-strong permanent magnet quadrupoles able to collect and focus laser driven ions up to 70 MeV/u, and a magnetic chicane made of conventional electromagnetic dipoles to select particles within a narrow energy range. Here, the actual status of the design and development of these magnetic systems is described.

A mechanism of high energy and high density positron beam creation is proposed in ultra-relativistic laser-plasma interaction. Longitudinal electron self-injection into a strong laser field occurs in order to maintain the balance between the ponderomotive potential and the electrostatic potential. The injected electrons are trapped and form a regular layer structure. The radiation reaction and photon emission provide an additional force to confine the electrons in the laser pulse. The threshold density to initiate the longitudinal electron self-injection is obtained from analytical model and agrees with the kinetic simulations. The injected electrons generate γ-photons which counter-propagate into the laser pulse. Via the Breit–Wheeler process, well collimated positron bunches in the GeV range are generated of the order of the critical plasma density and the total charge is about nano-Coulomb. The above mechanisms are demonstrated by particle-in-cell simulations and single electron dynamics.

Ever increasing circulating currents in electron‐positron colliders and light sources demand lower and lower photodesportion (PSD) from the surfaces of their vacuum chambers and their photon absorbers. This is particularly important in compact electron storage rings and B meson factories where photon power of several kW cm−1 is deposited on the surfaces. Given the above factors we have measured PSD from 1 m long bars of (a) solid copper and solid beryllium, and (b), TiN, Au, and C thin films deposited on solid copper bars. Each sample was exposed to about 1023 photons/m with a critical energy of 500 eV at the vacuum ultraviolet ring of the National Synchrotron Light Source. PSD was recorded for two conditions: after a 200 °C bakeout and after an Ar glow discharge cleaning. In addition, we also measured reflected photons, photoelectrons, and desorption as functions of normal, 75, 100, and 125 mrad incident photons.

We report on a specially designed actively-passively modelocked Nd-glass laser. Negative feedback control and frequency tuning by a Lyot filter allows the generation of subpisecond pulses if the generated wavelength is shifted to the red side of the fluorescence spectrum of the active material. Experimental results and possible explanations for the observed spectral broadening and pulse shortening are given and discussed in the approximation of a linear amplification model. The oscillator should be useful for the chirped pulse amplification experiments.

Results are presented of calculation of x-ray plasma images of glass shell targets with diagnostic additives Na, K, and Ca in the light of the intrinsic radiation of the resonance lines of H and He ions with Zn = 8, ii, 14, and 20, and also in the light of cw radiation in the wavelength range λ = 1-300 A. The calculation results are compared with laser-plasma images obtained in experiments with the “Del'fin-l” thermonuclear facility. The temperature and density of the plasma, the rate of corona expansion, the target mass ablation rate, and the hydrodynamic coefficient of laser-energy transfer into kinetic energy of the ablating shell are determined. The plasma images obtained by backlighting the shell target with an auxiliary x-ray source are analyzed with account taken of the radiation refraction. The required energy, temporal, and spectral characteristics of the auxiliary source are determined.

Fast magnetic annihilation is investigated by using 2.5-dimensional particle-in-cell simulations of two parallel ultra-short petawatt laser pulses co-propagating in underdense plasma. The magnetic field generated by the laser pulses annihilates in a current sheet formed between the pulses. Magnetic field energy is converted to an inductive longitudinal electric field, which efficiently accelerates the electrons of the current sheet. This new regime of collisionless relativistic magnetic field annihilation with a timescale of tens of femtoseconds can be extended to near-critical and overdense plasma with the ultra-high intensity femtosecond laser pulses.

We show first deep UV ablation results achieved with our new all solid state laser system. The system parameters allow high repetition rate ablation with a small spot diameter of about 0.250mm and a fluence of 350 mJ/cm 2 at a wavelength of 210 nm using sequential frequency conversion of a diode pumped laser source. The single shot and multishot ablation rates as well as the ablation profiles have been defined using MicroProf (Fries Research and Technology GmbH, Germany). By means of computer controlled scanning we produce smooth ablation profiles corresponding to a correction of myopia, hyperopia or astigmatism. Due to the small spot size and high repetition rate of the laser we are able to generate in short time intervals complicated ablation profiles described by higher order polynomial functions which are required for the needs of customized corneal ablation.

Summary form only given. We present the first results which have been achieved with a diode pumped Q-switched and frequency doubled "Corona" laser as a pump source for the Ti:sapphire based laser and regenerative amplifier operating at 10-20 kHz repetition rates. The practical, single-stage, high-average-power, high-repetition rate, all-solid-state laser system demonstrated output power of 27.2 W in a gain-switched regime and 15.2 W after short pulse regenerative amplification. These are presently the highest values obtained from a single stage system and 20 kHz is a highest repetition rate obtained for millijoule-level systems.

Summary form only given. In recent years we could demonstrate new interesting nonlinear effects of propagation of a short intense fs-pulse through a hollow waveguide (HW) filled with a Raman-active gas and probing it with a second delayed fs-pulse. The idea of using waveguides for this investigation was borrowed from the famous work on pulse compression using self phase modulation in atomic gases. The main advantage of HW for fs-nonlinear interaction experiments is the enlargement of the interaction length of the pulse with the low density gaseous medium and a spatially uniform nonlinear interaction with excellent mode properties of the transmitted beam. Our first pump-probe experiments with Raman gases showed a self-conversion of the pulse-frequency and an impulsive excitation of the Raman medium (SF/sub 6/) with intense fs-laser pulses from a 30 fs Ti:sapphire laser.

PEP-II will be a meson factory circulating asymmetric beams of 9 GeV and 3.1 GeV having maximum currents of 3.0 A. Copper beam chambers and absorbers will intercept resulting synchrotron radiation and it is critical that the dynamic gas load from photo stimulated desorption (PSD) and thermal outgassing is below 2 × 10 −6 molecules per photon. An experiment was set up to measure PSD from 1 m long bar samples and a chamber sample, fabricated from selected copper and copper alloys, then exposed to white light with a critical energy of 500 eV, on beamline U10B at the VUV ring of the National Synchrotron Light Source (NSLS). Based on U10B results a prototype chamber was built and will be exposed to white light with higher critical energies up to 5 keV, on beamline X-28A at the X-ray ring of the NSLS. This paper presents the measurements of H 2 , CO, CO 2 and CH 4 desorption yields as function of accumulated photon flux, angle of incidence, sample material, and surface condition. The results are compared with that of previous work on similar materials and with that of others for copper.