T. Levato

Acceleration with Self-Injection for an All-Optical Radiation Source at LNF

Abstract We discuss a new compact γ -ray source aiming at high spectral density, up to two orders of magnitude higher than currently available bremsstrahlung sources, and conceptually similar to Compton sources based on conventional linear accelerators. This new source exploits electron bunches from laser-driven electron acceleration in the so-called self-injection scheme and uses a counter-propagating laser pulse to obtain X and γ -ray emission via Thomson/Compton scattering. The proposed experimental configuration inherently provides a unique test-bed for studies of fundamental open issues of electrodynamics. In view of this, a preliminary discussion of recent results on self-injection with the FLAME laser is also given.

Thomson Scattering Imaging From Ultrashort Ultraintense Laser Interaction With Gas

Laser-plasma acceleration can provide acceleration gradients which are thousands of times stronger than conventional electron accelerators. The laser propagation length is a crucial parameter that must be extended to achieve high-energy electrons. Here, we show that color images of the laser-plasma interaction region taken from the direction perpendicular to the polarization plane are a powerful tool to discriminate between Thomson scattering and plasma self-emission, leading to a precise measurement of the propagation length.

Small-scale laser based electron accelerators for biology and medicine: a comparative study of the biological effectiveness

Laser-driven electron accelerators based on the Laser Wakefield Acceleration process has entered a mature phase to be considered as alternative devices to conventional radiofrequency linear accelerators used in medical applications. Before entering the medical practice, however, deep studies of the radiobiological effects of such short bunches as the ones produced by laser-driven accelerators have to be performed. Here we report on the setup, characterization and first test of a small-scale laser accelerator for radiobiology experiments. A brief description of the experimental setup will be given at first, followed by an overview of the electron bunch characterization, in particular in terms of dose delivered to the samples. Finally, the first results from the irradiation of biological samples will be briefly discussed.

Laboratory measurements of resistivity in warm dense plasmas relevant to the microphysics of brown dwarfs.

Since the observation of the first brown dwarf in 1995, numerous studies have led to a better understanding of the structures of these objects. Here we present a method for studying material resistivity in warm dense plasmas in the laboratory, which we relate to the microphysics of brown dwarfs through viscosity and electron collisions. Here we use X-ray polarimetry to determine the resistivity of a sulphur-doped plastic target heated to Brown Dwarf conditions by an ultra-intense laser. The resistivity is determined by matching the plasma physics model to the atomic physics calculations of the measured large, positive, polarization. The inferred resistivity is larger than predicted using standard resistivity models, suggesting that these commonly used models will not adequately describe the resistivity of warm dense plasma related to the viscosity of brown dwarfs.

Space- and time-resolved observation of extreme laser frequency upshifting during ultrafast-ionization

A 65-fs, 800-nm, 2-TW laser pulse propagating through a nitrogen gas jet has been experimentally studied by 90° Thomson scattering. Time-integrated spectra of scattered light show unprecedented broadening towards the blue which exceeds 300 nm. Images of the scattering region provide for the first time a space- and time-resolved description of the process leading quite regularly to such a large upshift. The mean shifting rate was as high as δλ/δt ≈ 3 A/fs, never observed before. Interferometry shows that it occurs after partial laser defocusing. Numerical simulations prove that such an upshift is consistent with a laser-gas late interaction, when laser intensity has decreased well below relativistic values (a0 ≪ 1) and ionization process involves most of the laser pulse. This kind of interaction makes spectral tuning of ultrashort intense laser pulses possible in a large spectral range.

On the effect of rear-surface dielectric coatings on laser-driven proton acceleration

Laser-driven ion acceleration has been experimentally investigated by irradiating, with tightly focused femtosecond laser pulses at 5×1019 W/cm2, thin metal foils, which have been back-coated with a μm thick dielectric layer. The observation we report shows the production of MeV proton bunches with an unexpected highly uniform spatial cross section.

Experimental investigation of fast electron transport in solid density matter: Recent results from a new technique of X-ray energy-encoded 2D imaging

The development activity of a new experimental technique for the study of the fast electron transport in high density matter is reported. This new diagnostic tool enables the X-ray 2D imaging of ultrahigh intensity laser plasmas with simultaneous spectral resolution in a very large energy range to be obtained. Results from recent experiments are discussed, in which the electron propagation in multilayer targets was studied by using the Kα. In particular, results highlighting the role of anisotropic Bremsstrahlung are reported, for the sake of the explanation of the capabilities of the new diagnostics. A discussion of a test experiment conceived to extend the technique to a single-shot operation is finally given.

High-charge divergent electron beam generation from high-intensity laser interaction with a gas-cluster target

We report on an experimental study on the interaction of a high-contrast 40 fs duration 2.5 TW laser pulse with an argon cluster target. A high-charge, homogeneous, large divergence electron beam with moderate kinetic energy (~2 MeV) is observed in the forward direction. The results show, that an electron beam with a charge as high as 10 nC can be obtained using a table-top laser system. The accelerated electron beam is suitable for a variety of applications such as radiography of thin samples with a spatial resolution better than 100 micron.

A self-injection acceleration test experiment for the FLAME laser

A 250-TW laser system (FLAME – Frascati laser for acceleration and multidisciplinary experiments) is now in its commissioning phase in a new laboratory at LNF–INFN in the framework of the PLASMONX (Plasma acceleration and monochromatic X-ray generation) project. The laser will deliver<25 fs duration pulses with an energy up to 6 J, at a 10 Hz repetition rate. An ad hoc target area has also been designed and is currently being set up, allowing the first test experiments of electron laser wakefield acceleration to be carried out over the next few months in a safe, radiation-protected environment. An overview of the main features of the laser system and target area is given, along with a survey of the design and set-up of the self-injection test experiment, which is expected to reach the production of sub-GeV electron bunches.

Design and development of the HELL User Station for multi-disciplinary experiments

HELL is the high energy electron beamline under development at ELI-Beamlines, which is expected to produce GeV electrons at high repetition rate. The aim of HELL is dual: to improve the performances of the laser electron accelerator, and to deliver stable beams for external users. In this work, we present the recent developments towards the delivery of stable and calibrated beams for external users. The design of the HELL User Station will be presented and discussed along with simulations and experimental data collected in different facilities.