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The interaction of ultraintense laser pulses with solids is largely affected by the plasma gradient at the vacuum–solid interface, which modifies the absorption and ultimately, controls the energy distribution function of heated electrons. A micrometer scale-length plasma has been predicted to yield a significant enhancement of the energy and weight of the fast electron population and to play a major role in laser-driven proton acceleration with thin foils. We report on recent experimental results on proton acceleration from laser interaction with foil targets at ultra-relativistic intensities. We show a threefold increase of the proton cut-off energy when a micrometer scale-length pre-plasma is introduced by irradiation with a low energy femtosecond pre-pulse. Our realistic numerical simulations agree with the observed gain of the proton cut-off energy and confirm the role of stochastic heating of fast electrons in the enhancement of the accelerating sheath field.

We present the design study of an innovative scheme to generate high repetition rate (multi-MHz-class) THz radiation pulses by using an Energy Recovered Super Conducting Linac operating in Continuous Wave mode driving a Free-Electron Laser Oscillator. The FEL performance is illustrated for one and two color operation. Start-to-end simulations are presented to assess the capability of this scheme for typical values of wavelengths of interest in the 10–50μm (6–30 THz) range.

In this paper we report the measurement of laser-driven proton acceleration obtained by irradiating nanotube array targets with ultrashort laser pulses at an intensity in excess of 1020 W cm−2. The energetic spectra of forward accelerated protons show a larger flux and a higher proton cutoff energy if compared to flat foils of comparable thickness. Particle-In-Cell 2D simulations reveal that packed nanotube targets favour a better laser-plasma coupling and produce an efficient generation of fast electrons moving through the target. Due to their sub-wavelength size, the propagation of e.m. field into the tubes is made possible by the excitation of Surface Plasmon Polaritons, travelling down to the end of the target and assuring a continuous electron acceleration. The higher amount and energy of these electrons result in turn in a stronger electric sheath field on the rear surface of the target and in a more efficient acceleration of the protons via the target normal sheath acceleration mechanism.

Within 2017, the ELIMED (ELI-Beamlines MEDical applications) transport beam-line and dosimetric systems for laser-generated beams will be installed at the ELI-Beamlines facility in Prague (CZ), inside the ELIMAIA (ELI Multidisciplinary Applications of laser–Ion Acceleration) interaction room. The beam-line will be composed of two sections: one in vacuum, devoted to the collecting, focusing and energy selection of the primary beam and the second in air, where the ELIMED beam-line dosimetric devices will be located. This paper briefly describes the transport solutions that will be adopted together with the main dosimetric approaches. In particular, the description of an innovative Faraday Cup detector with its preliminary experimental tests will be reported.

An experimental campaign aiming to investigate the ion acceleration mechanisms through laser-matter interaction in the femtosecond domain has been carried out at the ILIL facility at a laser intensity of up to 2 x 1019 W/cm2. A Thomson Parabola Spectrometer was used to identify different ion species and measure the energy spectra and the corresponding temperature parameters. We discuss the dependence of the protons spectra upon the structural characteristics of the targets (thickness and atomic mass) and the role of surface versus target bulk during acceleration process. (C) 2016 Elsevier B.V. All rights reserved.

This paper describes the acceleration tests performed at the Catania LNS Laboratory on a 3 GHz linac module of the side coupled type, which boosts the proton energy of a beam extracted from a cyclotron from 62 to 72 MeV. The output proton energy was measured with two devices: a NaI(Tl) crystal and a bending magnet. The experimental spectra are in good agreement with the calculated ones. From their shape it is obtained that (18±3.0)% of the transmitted protons fall in a ±2 MeV interval centered around 72 MeV. This result is in good agreement with the 20% value derived from the simulation of the acceleration process. The measured energy of the accelerated protons was used to check that the shunt impedance of the structure is equal to the computed one within 3%. This was the first time that a 3 GHz structure has been used to accelerate protons, and the results of the tests have demonstrated that a high frequency linac can be used as a cyclotron booster.

LIBO is a proton accelerator that operates at 3 GHz , the same frequency as the one adopted in the about 7500 electron linacs used for radiotherapy all over the world. Such a high frequency was chosen to obtain a large gradient (on average more than 10 MV/m ), and thus a short linac (about 15 m ) to boost the energy of the protons, extracted at about 60 MeV from a cyclotron, up to the 200 MeV needed for the treatment of deep-seated tumours. This paper describes the design study of the full 3 GHz Side Coupled Linac (modular structure, nine modules) and the construction and tests of the LIBO prototype (first module), which was built to accelerate protons from 62 to 74 MeV with an RF peak power of 4.4 MW . The items discussed are the beam dynamics parameters of the module (longitudinal and transverse acceptances), the constructional elements and procedures, the accuracies of the various mechanical elements, the cooling system, the RF tuning, the RF measurement and the RF power tests. These tests showed that, after a short conditioning time, the gradient in each of the four tanks of the module could reach 28.5 MV/m , much larger than the nominal project value (15.8 MV/m ) . The last section of the paper describes the successful acceleration tests performed at the Laboratori Nazionali del Sud of INFN in Catania with a solid-state 3 GHz modulator lent by IBA.

FELs based on SASE are believed to be powerful tools to explore the frontiers of basic sciences, from physics to chemistry to biology. Intense R&D programs have started in the USA and Europe in order to understand the SASE physics and to prove the feasibility of these sources. The allocation of considerable resources in the Italian National Research Plan (PNR) brought about the formation of a CNR–ENEA–INFN–University of Roma “Tor Vergata” study group. A conceptual design study has been developed and possible schemes for linac sources have been investigated, leading to the SPARX proposal. We report in this paper the results of a preliminary start to end simulation concerning one option we are considering based on an S-band normal conducting linac with high-brightness photoinjector integrated in an RF compressor.

Suitable instrumentation for laser-accelerated proton (ion) beams is critical for development of integrated, laser-driven ion accelerator systems. Instrumentation aimed at beam diagnostics and control must be applied to the driving laser pulse, the laser-plasma that forms at the target and the emergent proton (ion) bunch in a correlated way to develop these novel accelerators. This report is a brief overview of established diagnostic techniques and new developments based on material presented at the first workshop on 'Instrumentation for Diagnostics and Control of Laser-accelerated Proton (Ion) Beams' in Abingdon, UK. It includes radiochromic film (RCF), image plates (IP), micro-channel plates (MCP), Thomson spectrometers, prompt inline scintillators, time and space-resolved interferometry (TASRI) and nuclear activation schemes. Repetition-rated instrumentation requirements for target metrology are also addressed. (C) 2013 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

ELI-Beamlines is one of the pillars of the pan-European project ELI (Extreme Light Infrastructure). It will be an ultra high-intensity, high repetition-rate, femtosecond laser facility whose main goal is generation and applications of high-brightness X-ray sources and accelerated charged particles in different fields. Particular care will be devoted to the potential applicability of laser-driven ion beams for medical treatments of tumors. Indeed, such kind of beams show very interesting peculiarities and, moreover, laser-driven based accelerators can really represent a competitive alternative to conventional machines since they are expected to be more compact in size and less expensive. The ELIMED project was launched thanks to a collaboration established between FZU-ASCR (ELI-Beamlines) and INFN-LNS researchers. Several European institutes have already shown a great interest in the project aiming to explore the possibility to use laser-driven ion (mostly proton) beams for several applications with a particular regard for medical ones. To reach the project goal several tasks need to be fulfilled, starting from the optimization of laser-target interaction to dosimetric studies at the irradiation point at the end of a proper designed transport beam-line. Researchers from LNS have already developed and successfully tested a high-dispersive power Thomson Parabola Spectrometer, which is the first prototype of a more performing device to be used within the ELIMED project. Also a Magnetic Selection System able to produce a small pencil beam out of a wide energy distribution of ions produced in laser-target interaction has been realized and some preliminary work for its testing and characterization is in progress. In this contribution the status of the project will be reported together with a short description of the of the features of device recently developed. Conference on Plasma Physics by Laser and Applications (PPLA), Oct 02-04, 2013, Univ Salento, Lecce, Italy

Optical Transition Radiation (OTR) provides an attractive method for diagnostics on electron/positron beams of small dimensions at high energies (GeV). However, some limits on the geometrical resolution at very high energies have been often discussed in the literature and a minimum value given by ‘cj’ has been invoked. In order to bring an experimental contribution to the problem, systematic measurements of electron beam profiles, in the energy range of 1—2 GeV and at optical wavelength between 400 and 700 nm, have been carried out at the Orsay 2 GeV Linear Accelerator. OTR emitted from an aluminium foil at a 30i incidence angle was collected by a two-lens telescope and recorded by an intensified CCD camera. The OTR beam profiles were compared to the profiles obtained by a SEM Grid having a resolution better than 0.5 mm. After a theoretical introduction presenting the di⁄erent resolution limits, which can be invoked with di⁄raction phenomenon, and a presentation of our calibration procedure, the experimental results are presented and compared to these limits. They show that the resolution in OTR measurements is definitely better than the already invoked cj-limit. For a small size electron beam an r.m.s. beam width about 170 lm has been determined. This value can be compared to cj"2.5 mm (E"2 GeV and j"650 nm). Our theoretical analysis also provides a more precise evaluation of the resolution power of OTR, which depends on the sensitivity of the detector; this could be of interest for much higher energies. ( 1998 Elsevier Science B.V. All rights reserved.

CHICAGO

VIENNA (AUSTRIA)

The PLasma Acceleration and MONochromatic X-ray generation (PLASMONX) project foresees the installation at LNF of a 0.3 PW (6 J, 20 fs pulse) Ti:Sa laser system, named Frascati Laser for Acceleration and Multidisciplinary Experiments (FLAME), to operate in close connection with the existent SPARC electron photo-injector, allowing for advanced laser/e-beam interaction experiments. Among the foreseen scientific activities, a Thomson scattering experiment between the SPARC electron bunch and the high power laser will be performed. At the present time the linac has been tested and the electron beam characterized up to the maximum operating energy (150 MeV). The beam lines transporting the beam to the interaction chamber with the laser have been designed. The electron final focusing system, featuring a quadrupole triplet and large radius solenoid magnet (ensuring an e-beam waist of 5-10 mu m) as well as the whole interaction chamber layout has been defined. The optical transfer line issues: transport up to the interaction; tight focusing; diagnostics and fine positioning; have been solved within the final design. The construction of the building hosting the laser has been completed: delivering and installation of the laser, as much of the beam lines elements will take place in the next months. (C) 2009 Elsevier B.V. All rights reserved.

Publisher Summary This chapter discusses a system that has been designed to monitor changes in the alignment of the cavities and solenoids during pump out and cool down. TRIUMF is developing ISAC-II, a superconducting (SC) linac. It will comprise 9 cryomodules with a total of 48 niobium cavities and 12 SC solenoids. They must remain aligned at liquid He temperatures: cavities to ±400 μm and solenoids to ±200 μm after a vertical contraction of ∼4 mm. A wire position monitor (WPM) system based on a TESLA design measures the signals induced in stripline pickups by a 215 MHz signal carded by a position reference wire. The sensors, one per cavity and two per solenoid, monitor their motion during pre-alignment, pumping, and cool down. System accuracy is ∼7 μm. The device is giving a wealth of information over and above the data collected with the installed optical targets. The use of optical targets involves personnel and the readings can be taken only periodically. Conversely the WPM data is monitored continuously providing detailed data that is extremely valuable to help characterize a new structure.

The goal of the revised ELFA project (Electron Laser Facility for Acceleration) is to operate with short bunches a high-gain free electron laser. The paper describes the main components of the experiment and discusses the choice of the parameters for the linac, the electromagnetic wiggler, the microwave generator, the waveguide and the beam and radiation diagnostics. >

A system able to measure, on-line, movements and vibrations of the cold mass (CM) during cool down and steady state operation has been developed and installed inside the first TTF Cryomodule. The system includes two independent lines, with 18 WPMs each, and an improved version of BPM type. Laboratory tests on a shorter prototype have shown that the system is able to monitor the CM displacements with a few micron sensitivity, the absolute error being less than 50 microns in the range of /spl plusmn/2.5 mm. Fast read out and an FFT technique allow also to detect and analyze possible CM vibrations.

The cryostat designed for the superconducting cavities of the Tesla Test Facility (TTF) is quite a complex structure with strict requirements on the alignment of the different components at the LHe temperature. A system able to measure on-line misalignments on the full length of the cryostat module (12 meters long) during cool down and operation procedures seems a very useful tool in order to verify structural analysis computation. A microstrip based system using a stretched wire has been designed for this purpose in our laboratory. DESY will provide the stretching system for the wire and the support system for the position transducers. In this paper we will present and discuss the design based on warm and cold tests on a prototype.

Optical Transition Radiation (OTR) provides an attractive mothod for diagnostics on electron/positron beams of small dimensions at high energies (GeV). However, some limits on the geometrical resolution at very high energies have been often discussed in the literature and a minimum value given by 'γλ' has been invoked. In order to bring an experimental contribution to the problem, systematic measurements of electron beam profiles, in the energy range of 1-2 GeV and at optical wavelength between 400 and 700 nm, have been carried out at the Orsay 2 GeV Linear Accelerator. OTR emitted from an alluminium foil at a 30° incidence angle was collected by a two-lens telescope and recorded by an intensified CCD camera. The OTR beam profiles were compared to the profiles obtained by a SEM Grid having a resolution better than 0. mm.After a theoretical introduction presenting the different resolution limits, which can be invoked with diffraction phenomenon, and a presentation of our calibration procedure, the experimental results are presented and compared to these limits. They show that the resolution OTR measurements is definitely better than the already invoked gl -limit. For a small size electron beam an rms beam width as small as 170 mm, comapred to gl = 2.5mm (E=2 GeV and l = 650 nm), has been measured. Our theoretical analysis also provides a more precise evaluation of the resolution power of OTR, which depends on the sensitivity of the detector; this could be of interest for much higher energies.

The Project SPARC (Sorgente Pulsata e Amplificata di Radiazione Coerente), proposed by a collaboration among ENEA-INFN-CNR-Universitadi Roma Tor Vergata- INFM-ST, was recently funded by the Italian Government. The aim of the project is to promote an R&D activity oriented to the development of a coherent ultra-brilliant X-ray source in Italy (SPARX proposal (1)). The SPARC collaboration identified a program based on two main issues: the generation of ultra-high peak brightness electron beams and experimental study of SASE-FEL process with generation of resonant higher harmonics. The SPARC project is being designed in order to encompass the construction of an advanced photo- injector producing a 150-200 MeV beam to drive a SASE-FEL in the optical range. The machine will be built at LNF, inside an underground bunker: it is comprised of an rf gun driven by a Ti:Sa laser, injecting into three SLAC accelerating sections. We foresee conducting investigations on the emittance correction(2) and on the rf compression techniques(3), which are expected to increase the peak current achievable at the injector exit up to kA level, with proper preservation of the transverse emittance. Although the system is expected to drive a FEL experiment, it can be used also to investigate beam physics issues like surface-roughness-induced wake fields, bunch-length measurements in the sub-ps range, emittance degradation in magnetic compressors due to CSR, and Compton backscattering production of sub-ps X-ray pulses.

We consider a hybrid acceleration scheme for protons where the laser generated beam is selected in energy and angle and injected into a compact linac, which raises the energy from 30 to 60 MeV. The laser acceleration regime is TNSA and the energy spectrum is determined by the cutoff energy and proton temperature. The dependence of the spectrum on the target properties and the incidence angle is investigated with 2D PIC simulations. We base our work on widely available technologies and on laser with a short pulse, having in mind a facility whose cost is approximately 15 ME. Using a recent experiment as the reference, we choose the laser pulse and target so that the energy spectrum obtained from the 3D PIC simulation is close to the one observed, whose cutoff energy was estimated to be over 50 MeV. Laser accelerated protons in the TNSA regime have wide energy spectrum and broad divergence. In this paper we compare three transport lines, designed to perform energy selection and beam collimation. They are based on a solenoid, a quadruplet of permanent magnetic quadrupoles and a chicane. To increase the maximum available energy, which is actually seen as an upper limit due to laser properties and available targets, we propose to inject protons into a small linac for post acceleration The number of selected and injected protons is the highest with the solenoid and lower by one and two orders of magnitude with the quadrupoles and the chicane respectively. Even though only the solenoid enables achieving to reach a final intensity at the threshold required for therapy with the highest beam quality, the other systems will be very likely used in the first experiments. Realistic start-to-end simulations, as the ones reported here, are relevant for the design of such experiments. (C) 2013 Elsevier B.V. All rights reserved.

SPARC-X is a two branch project consisting in the SPARC test facility dedicated to the development and test of critical subsystems such as high brightness photoinjector and a modular expandable undulator for SASE-FEL experiments at 500 nm with seeding, and the SPARK facility aiming at generation of high brilliance coherent radiation in the 1.5-13 nm range, based on the achieved expertise. The projects are supported by MIUR (Research Department of Italian Government) and Regione Lazio. SPARC has completed the commissioning phase of the photoinjector in November 2006. The achieved experimental results are here summarized together with the status of the second phase commissioning plans. The SPARK project is based on the generation of ultra high peak brightness electron beams at the energy of 1 and 2 GeV generating radiation in the 1.5-13 nm range. The construction is at the moment planned in two steps starting with a 1 GeV Linac. The project layout including both RF-compression and magnetic chicane techniques has been studied.

The LILIA experiment is planned at the SPARCLAB facility of the Frascati INFN laboratories. We have simulated the laser acceleration of protons, the transport and energy selection with collimators and a pulsed solenoid and the post-acceleration with a compact high field linac. For the highest achievable intensity corresponding to a = 30 over 108 protons at 30 MeV with a 3% spread are selected, and at least107 protons are post-accelerated up to 60 MeV. If a 10 Hz repetition rated can be achieved the delivered dose would be suitable for the treatment of small superficial tumors.

For an assembled structure (module, tank) of a linac, the single cells, when coupled, loose their individuality and in cooperation contribute to the generation of the structure modes (resonant frequencies) Fm. On the other end these modes are the only measurable quantities. The system of the coupled cells can be modelled, in a narrow frequency band, as a lumped constant circuit. The modes are solution of an equation obtained equating to zero the determinant relevant to the lumped circuit representation. This is an algebraic equation of the same order as the number N of cells. A plausible question can be posed: is it possible from a manipulation of the measurable quantities (Fm) to draw the lumped circuit parameters, namely coupling constants and single cell resonant frequencies? The answer is positive if a certain degree of symmetry is satisfied. The coefficients of above mentioned equation can be easily related to the measured modes Fm. By varying, by means of tuners, the tune of a single cell of a small unknown amount, any couple of equation coefficient moves on a straight line. Therefore, we have N(N-1)/2 known straight line coefficients which may give the unknowns with extremely high accuracy.