Laser Flame Research Articles

Plasma-Generated X-ray Pulses: Betatron Radiation Opportunities at EuPRAXIA@SPARC_LAB

EuPRAXIA is a leading European project aimed at the development of a dedicated, ground-breaking, ultra-compact accelerator research infrastructure based on novel plasma acceleration concepts and laser technology and on the development of their users’ communities. Within this framework, the Laboratori Nazionali di Frascati (LNF, INFN) will be equipped with a unique combination of an X-band RF LINAC generating high-brightness GeV-range electron beams, a 0.5 PW class laser system and the first fifth-generation free electron laser (FEL) source driven by a plasma-based accelerator, the EuPRAXIA@SPARC_LAB facility. Wiggler-like radiation emitted by electrons accelerated in plasma wakefields gives rise to brilliant, ultra-short X-ray pulses, called betatron radiation. Extensive studies have been performed at the FLAME laser facility at LNF, INFN, where betatron radiation was measured and characterized. The purpose of this paper is to describe the betatron spectrum emitted by particle wakefield acceleration at EuPRAXIA@SPARC_LAB and provide an overview of the foreseen applications of this specific source, thus helping to establish a future user community interested in (possibly coupled) FEL and betatron radiation experiments. In order to provide a quantitative estimate of the expected betatron spectrum and therefore to present suitable applications, we performed simple simulations to determine the spectrum of the betatron radiation emitted at EuPRAXIA@SPARC_LAB. With reference to experiments performed exploiting similar betatron sources, we highlight the opportunities offered by its brilliant femtosecond pulses for ultra-fast X-ray spectroscopy and imaging measurements, but also as an ancillary tool for designing and testing FEL instrumentation and experiments.

Accurate spectra for high energy ions by advanced time-of-flight diamond-detector schemes in experiments with high energy and intensity lasers

Time-Of-Flight (TOF) methods are very effective to detect particles accelerated in laser-plasma interactions, but they show significant limitations when used in experiments with high energy and intensity lasers, where both high-energy ions and remarkable levels of ElectroMagnetic Pulses (EMPs) in the radiofrequency-microwave range are generated. Here we describe a novel advanced diagnostic method for the characterization of protons accelerated by intense matter interactions with high-energy and high-intensity ultra-short laser pulses up to the femtosecond and even future attosecond range. The method employs a stacked diamond detector structure and the TOF technique, featuring high sensitivity, high resolution, high radiation hardness and high signal-to-noise ratio in environments heavily affected by remarkable EMP fields. A detailed study on the use, the optimization and the properties of a single module of the stack is here described for an experiment where a fast diamond detector is employed in an highly EMP-polluted environment. Accurate calibrated spectra of accelerated protons are presented from an experiment with the femtosecond Flame laser (beyond 100 TW power and ~ 1019 W/cm2 intensity) interacting with thin foil targets. The results can be readily applied to the case of complex stack configurations and to more general experimental conditions.

Comparison of single crystal diamond TOF detectors in planar and transverse configuration

Single crystal diamond detectors are widely employed in laser-induced plasma experiments to retrieve information about particles generated from the interaction. In particular, diamonds are used as Time of Flight (TOF) detectors featured by good sensitivity, high radiation hardness and fast response time. In this work, we provide a detailed characterization of two different types of electrodes configuration retrieving their charge collection efficiency, temporal response, and effective active area. The so obtained information are then used to compute calibrated proton spectra from the signals collected by the two investigated detectors employed in TOF schemes during an experimental campaign performed with the femtosecond FLAME laser (reaching >100 TW power and ∼1019 W/cm2 intensity) interacting with thin foil targets. Despite the different detection characteristics of the two diamond detectors, consistent information about the detected protons were obtained.

Anticipating heat accumulation in laser oxygen cutting of thick metal plates

Excessive heating of the metal sheet during laser oxygen cutting can cause quality deterioration and even lead to cut loss and possible machine idle time, especially for cutting of thick plates, where the cutting speed is slower. There are at least three different strategies to handle quality deterioration by heat accumulation in flame laser cutting of thick plates: to optimize the process parameters for preheated zones, to generate tool paths that avoid such regions, or to use active cooling to remove the excessive heat. For any of these strategies to work, it is crucial to correctly identify when and where heat accumulations occur. This can be done by real-time temperature measurements, by simulating heat propagation on the metal plate, or by defining empirical criteria based on experimental data. This paper takes a close look at these methods of heat accumulation detection, their advantages and disadvantages, and how they can be integrated into different approaches to tackle unwanted heat accumulations in laser cutting. Furthermore, three case studies are provided, one for each above-mentioned method, where the detection of quality degradation due to heat accumulation is demonstrated with a series of experiments. For all case studies, at least one action is proposed to improve the cut quality. All experiments were conducted for 15 mm mild steel plates using a 4 kW industrial fiber laser cutting machine.

The FLAME laser at SPARC_LAB

FLAME is a high power laser system installed at the SPARC_LAB Test Facility in Frascati (Italy). The ultra-intense laser pulses are employed to study the interaction with matter for many purposes: electron acceleration through LWFA, ion and proton generation exploiting the TNSA mechanism, study of new radiation sources and development of new electron diagnostics. In this work, an overview of the FLAME laser system will be given, together with recent experimental results.

First measurements of betatron radiation at FLAME laser facility

The first results on betatron radiation obtained in laser-plasma acceleration experiments at the FLAME laser facility are presented. The diagnostic apparatus for the X-ray detection available at the facility is described together with the experimental setup for the generation of betatron radiation.

The SPARC_LAB Thomson source

The SPARC_LAB Thomson source is a compact X-ray source based on the Thomson backscattering process presently under its second phase of commissioning at the LNF. The electron beam energy ranges between 30 and 150MeV, the electrons collide head-on with the Ti:Sapphire FLAME laser pulse the energy of which ranges between 1 and 5J with pulse lengths in the 25 fs–10ps range, this provides an X-ray energy tunability in the range of 20–500keV, with the further capability to generate strongly non-linear phenomena and to drive diffusion processes due to multiple and plural scattering effects. The experimental results of the obtained X-ray radiation are presented.

Laser–capillary interaction for the EXIN project

The EXIN project is under development within the SPARC_LAB facility of the National Laboratory of Frascati (LNF-INFN). This project aims to accelerate pre-existing electron bunches with high brightness by exploiting the wakefield plasma acceleration technique, while preserving the initial brightness. The wakefield is excited inside a dielectric capillary by high intensity laser pulses produced by the FLAME laser interacting with a gas. In this work, we present numerical simulations in order to optimize energy coupling between our laser with super-Gaussian transverse profile and a dielectric capillary. Moreover, an overview of the experimental layout will be given.

Resonant interaction between laser and electrons undergoing betatron oscillations in the bubble regime

The betatron radiation in the bubble regime is studied in the presence of resonant interaction between the accelerated electrons and the driver laser pulse tail. The calculations refer to experimental parameters available at the FLAME laser facility at the National Laboratories of Frascati (LNF), and represent the radiation spectra and spatial distributions to be expected in forthcoming experiments.

External-injection Experiment at SPARC_LAB

At the SPARC_LAB facility of INFN-LNF we are installing two transport lines for ultra-short electron bunches and an ultra- intense laser pulses, generated by the SPARC photo-injector and by the FLAME laser in a synchronized fashion at the tens of f s level, to co-propagate inside a hydrogen filled glass capillary, in order to perform acceleration of the electron bunch by a plasma wave driven by the laser pulse. The main aim of this experiment is to demonstrate that a high brightness electron beam can be accelerated by a plasma wave without any significant degradation of its quality. Motivations of the technical choices made and expected performances are reported.

The External-Injection experiment at the SPARC_LAB facility

At the SPARC_LAB facility of INFN-LNF we are installing a transport lines for ultra-short electron bunches and another for ultra-intense laser pulses, generated by the SPARC photo-injector and by the FLAME laser in a synchronized fashion at the tens of fs level, to co-propagate inside a hydrogen filled glass capillary, in order to perform acceleration of the electron bunch by a plasma wave driven by the laser pulse. The main aim of this experiment is to demonstrate that a high brightness electron beam can be accelerated by a plasma wave without any significant degradation of its quality. Motivations of the technical choices are made and expected performances are reported.

Laser-Plasma Acceleration with FLAME and ILIL Ultraintense Lasers

We report on the development of radiation and electron sources based on laser-plasma acceleration for biomedical and nuclear applications, using both the table top TW laser at ILIL and the 220 TW FLAME laser system at LNF. We use the ILIL laser to produce wakefield electrons in a self-focusing dominated regime in a mm scale gas-jet to generate large, uniform beams of MeV electrons for electron radiography and radiobiology applications. This acceleration regime is described in detail and key parameters are given to establish reproducible and reliable operation of this source. We use the FLAME laser to drive laser-plasma acceleration in a cm-scale gas target to obtain stable production of >100 MeV range electrons to drive a Thomson scattering ɣ-ray source for nuclear applications.

Acceleration with self-injection for an all-optical radiation source at LNF

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.

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.

Multi-GeV electron spectrometer

The advance in laser–plasma acceleration techniques pushes the regime of the resulting accelerated particles to higher energies and intensities. In particular the upcoming experiments with the FLAME laser at LNF will enter the GeV regime with almost 1nC of electrons. From the current status of understanding of the acceleration mechanism, relatively large angular and energy spreads are expected. There is therefore the need to develop a device capable to measure the energy of electrons over three orders of magnitude (few MeV to few GeV) under still unknown angular divergences. Within the PlasmonX experiment at LNF a spectrometer is being constructed to perform these measurements. It is made of an electro-magnet and a screen made of scintillating fibers for the measurement of the trajectories of the particles. The large range of operation, the huge number of particles and the need to focus the divergence present unprecedented challenges in the design and construction of such a device. We will present the design considerations for this spectrometer and the first results from a prototype.

Effects of Residual Stress on Interfacial Bonding Strength of WC Coating

The residual stresses of WC coating prepared by flame spraying and laser re-melting were measured quantitatively with X-ray diffraction (XRD) stress tester, and its micro-structures were observed with SEM, and the effects of residual stress on bonding strength of coating interface were analyzed. The experimental results are shown that residual stresses of WC coating are all tensile, and the effects of coating thickness on its residual stress is obvious, and residual stress is verse ratio with its thickness; Coating stress influences its cracking, tensile stress speeds its cracking, which causes its bonding strength decrease; The stress state is improved by decreasing its thickness, and its bonding strength can be increased.

AN EXPERIMENTAL STUDY OF FREELY PROPAGATING TURBULENT PROPANE/AIR FLAMES IN STRATIFIED INHOMOGENEOUS MIXTURES

Experiments of freely propagating turbulent flames in nonhomogeneous propane/air mixtures are performed for various initial distributions of heterogeneities and compared with homogeneous cases. For various flame propagation times, laser tomography and planar laser-induced fluorescence on acetone are performed simultaneously to characterize the flame-front structure as well as the local mixture fraction in front of the flame. The two-dimensional scalar fields are characterized by a mean stratified mixture fraction field, symmetrical around ignition, and by a fluctuation field. The scalar scales are determined from the spatial autocorrelation coefficients and are compared with the turbulence scales, because the turbulence grid is responsible for the mixing. From the flame contours, global parameters (flame radii and wrinkling ratio) and local curvature distributions are also studied to evaluate the contribution of heterogeneities on the topology of the turbulent flame front. At the early stages of flame propagation, the flame structure is weakly affected by the local heterogeneities. Then, at higher propagation times, the heterogeneities tend to smooth the wrinkling produced by the turbulent flow field. A characteristic scale of flame curvature is then compared with the integral length scale of the flow field, L T , and scalar scale L Z . For heterogeneous conditions, the flame front presents small wrinkles with positive and negative curvatures equally distributed all around the flame with a characteristic size strongly depending on L Z .

Characterization of a tunable optical parametric oscillator laser system for multielement flame laser excited atomic fluorescence spectrometry of cobalt, copper, lead, manganese, and thallium in buffalo river sediment.

A pulsed (10 Hz) optical parametric oscillator (OPO) laser system based on beta-barium borate (BBO) crystals and equipped with a frequency-doubling option (FDO) was characterized for use in laser excited atomic fluorescence spectrometry (LEAFS). This all-solid-state laser has a narrow spectral line width, a wide spectral tuning range (220-2200 nm), and a rapid, computer-controlled slew scan of wavelength (0.250 nm s-1 in the visible and infrared, and 0.125 nm s-1 in the ultraviolet). The output power characteristics (15-90 mJ/pulse in the visible, 1-40 mJ in the infrared, and 1-11 mJ in the ultraviolet), laser pulse-to-pulse variability (3-13% relative standard deviation, RSD, of the laser pulses), conversion efficiency of the FDO (2-17%), and spectral bandwidth in the visible spectrum (0.1-0.3 cm-1) were measured. The laser was used as the excitation source for a flame LEAFS instrument for which rapid, sequential, multielement analysis was demonstrated by slew scan of the laser. The instrument allowed about 640 measurements to be made in about 6 h, with triplicate measurements of all solutions and aqueous calibration curves, which yielded accurate analyses of a river sediment (National Institute of Standards and Technology, Buffalo River Sediment, 2704) for five elements with precisions < 5% RSD. Comparable or improved flame LEAFS detection limits over literature values were obtained for cobalt (2 ng mL-1), copper (2 ng mL-1), lead (0.4 ng mL-1), manganese (0.2 ng mL-1), and thallium (0.9 ng mL-1) by flame LEAFS.

Temperature and Mass Flow Effects in 10 Torr Methane/Oxygen Flames

ABSTRACT We have investigated the effect of burner surface temperature and mass flow on OH and CH radical mole fraction profiles in 10 Torr premixed methane/oxygen flames. Experimental flames were monitored using both flame emission and laser induced fluorescence. Modeling predictions using Sandia flame codes are compared to experimental results. An inverse relationship between mass flow and flame front distance from the burner is observed and modeled. Lean methane/oxygen flames stabilize closer to the burner than rich flames when mass flow is held constant. For methane/oxygen flames at 10 Torr, the effect on the location of the flame front as judged by the OH and CH profiles of a ± 10% measurement uncertainty in the experimental gas flow or a ± 10% uncertainty in the burner surface temperature, cannot be measured within experimental precision.

Experimental study of CS 2/O 2/ additive flame laser output spectra

This letter describes an experimental investigation of the spectral composition of the output of CS 2/O 2/N 2O and CS 2/O 2/CO 2 flame lasers with nondispersive optical cavity. CO-additive V-V exchange probabilities were used to explain spectral composition of the laser power output.