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Advanced numerical simulations, that include modal and frequency response function finite element analysis, frequency domain and time domain finite element method – boundary element method analysis, are performed to study the vibro-acoustic behaviour of crash and splash musical cymbals. The results of the modal analysis agree well with experimental measurements found in literature. The frequency domain and time domain coupled finite – boundary element method simulations, despite their high computational resources and time demands, are used for the crucial comparison of the velocity spectrograms on the cymbal to the radiated sound pressure spectrograms in the air. The computational analysis results show that the splash cymbal is characterized by a faster decay and a higher frequency content compared to the crash cymbal. The advanced multiphysics vibro-acoustic simulations that correlate the displacements and velocities of the vibrated structure with the radiated sound pressure results demonstrate the future capability to synthesize the sounds of cymbal music instruments.

The temporal rearrangement of the spectral components of an ultrafast and intense laser pulse, i.e., the chirp of the pulse, offers significant possibilities for controlling its interaction with matter and plasma. In the propagation of ultra-strong laser pulses within the self-induced plasma, laser pulse chirp can play a major role in the dynamics of wakefield and plasma bubble formation, as well as in the electron injection and related electron acceleration. Here, we experimentally demonstrate the control of the generation efficiency of a relativistic electron beam, with respect to maximum electron energy, current, and reproducibility, by accurately varying the chirp value of a multi-10-TW laser pulse. We explicitly show that positively chirped laser pulses, i.e., pulses with instantaneous frequency increasing with time, accelerate electrons in the order of 100 MeV much more efficiently in comparison to unchirped or negatively chirped pulses. Corresponding Particle-In-Cell simulations strongly support the experimental results, depicting a smoother plasma bubble density distribution and electron injection conditions that favors the maximum acceleration of the electron beam, when positively chirped laser pulses are used. Our results, aside from extending the validity of similar studies reported for PW laser pulses, provide the ground for understanding the subtle dynamics of an efficient plasma electron accelerator driven by chirped laser pulses.

A finite element method (FEM) - boundary element method (BEM) model is developed to compute the sound generated by of a force acting on a circular membrane (drumhead). A vibro-acoustic analysis that combines modal FEM analysis, a FEM steady state dynamic analysis (SSD), considering harmonic loading and boundary element acoustics, is performed. The drumhead vibrates due to the force impact and the sound is emitted in the air. The vibration of structural response is initially computed, and the obtained results are set to be the boundary conditions of the acoustic analysis in the vibro-acoustic simulation. The radiated sound can be computed at any point of the solution domain. Various materials used by drumhead manufacturers are tested and a parametric analysis focusing on the mesh density of the models is presented. The impact sound and the acoustical characteristics of the simulated test cases are evaluated. The Rayleigh method is also applied to the acoustic simulations and is further compared to the BEM simulation results. The outcomes of this study may be further used as reverse engineering inputs, to machine learning models for the estimation of the physical and mechanical parameters of drumheads from audio signals.

In this paper we analyze the vibrational behavior of the violin top plate, for varying plate thickness and material properties via finite element method (FEM) numerical simulations. It is well known that the vibrational properties of the top plates of string instruments influence their sound emission characteristics. Due to the impact of global warming on wood formation and due to their configurability, many manufacturers investigate the use of composite materials to produce musical instruments. Therefore, composite, carbon fiber reinforced epoxy (CFRE) prepreg along with traditional wooden material, such as spruce, are adopted in this study. FEM modal analysis along with a frequency response function (FRF) FEM analysis are performed. The vibrational variations of the plate's response are computed under free conditions. The main vibrational modes and the natural frequencies obtained by the simulations show the influence of the different mechanical and geometric properties on the top plate's vibrational response. The resulting eigenmode frequencies and shapes of the plate in relation to the varying thickness and the material properties used, are discussed. The results of this study offer valuable information on the evaluation of the acoustical characteristics of violins and may be further used on their vibrational behavior optimization and control.

A high quality, compact 1GHz preamplifier suitable for operation in conjunction with micro channelplates (MCP) and silicon Photomultipliers (SiPM), that is comprised of two integrated circuits is described inthis paper. The amplifier requires no adjustment and has a flat response from low frequencies and adequatebandwidth for high speed measurement systems.

An X-pinch scheme of a low-current generator (45 kA, 50 ns rise time) is characterized as a potential efficient source of soft X-rays. The X-pinch target consists of wires of 5 μm in diameter—made from either tungsten (W) or gold (Au)-plated W—loaded at two angles of 55° and 98° between the crossed wires. Time-resolved soft X-ray emission measurements are performed to provide a secure correlation with the optical probing results. A reconstruction of the actual photodiode current profile procedure was adopted, capable of overcoming the limits of the slow rising and falling times due to the “slow” response of the diodes and the noise. The pure and Au-plated W deliver an average X-ray yield, which depends only on the angle of the crossed wires, and is measured to be ~50 mJ and ~70 mJ for the 98° and 55° crossed wire angles, respectively. An additional experimental setup was developed to characterize the X-pinch as a source of X-rays with energy higher than ~6 keV, via time-integrated measurements. The X-ray emission spectrum was found to have an upper limit at 13 keV for the Au-plated W configuration at 55°. The portable tabletop X-pinch proved to be ideal for use in X-ray radiography applications, such as the detection of interior defects in biological samples.

The quantum phases of the electron paths driven by an ultrafast laser in high harmonic generation in an atomic gas depends linearly on the instantaneous cycle-averaged laser intensity. Using high laser intensities, a complete single ionisation of the atomic gas may occur before the laser pulse peak. Therefore, high harmonic generation could be localized only in a temporal window at the leading edge of laser pulse envelope. Varying the laser frequency chirp of an intense ultrafast laser pulse, the centre, and the width of the temporal window, that the high harmonic generation phenomenon occurs, could be controlled with high accuracy. This way, both the duration and the phase of the electron trajectories, that generate efficiently high harmonics, is fully controlled. An accurate and robust method of spectral control and selection of the high harmonic extreme ultraviolet light from distinct quantum paths is experimentally demonstrated. Furthermore, a phenomenological numerical model enlightens the physical processes that take place. This novel approach of the electron quantum path selection via laser chirp is a simple and versatile way of controlling the time-spectral characteristics of the coherent extreme ultraviolet light with future applications in the fields of attosecond pulses and soft x-ray nano-imaging.

Abstract The deposition of femtosecond laser optical energy in gases leads to the emission of secondary electromagnetic and acoustic radiation. These optoacoustic components have a complex nonlinear dependency on the laser beam characteristics, such as the pulse energy, duration, wavelength and the focusing conditions, as well as on the optical and elastic characteristics of the gaseous medium. The initial interaction times are governed by the high electronic excitation and ionization. These phenomena result in a self-modulation of the laser pulse, significantly affecting the optical energy deposition on the medium. Such complex nonlinear phenomena are very difficult to be studied via analytical equations. To address this, a multiphysics Particle-In-Cell model is applied for the evaluation of the optical energy deposition and plasma generation from tightly focused femtosecond pulses in ambient air. The computational domain of the model is built to describe optical energy deposition in its full spatiotemporal scale. The model is validated by experimental results of the absorbed energy. The agreement between the computational and experimental results provides the basis for the future development of an advanced microstructural Finite Element Method model, which, combined with the Particle-In-Cell model, will have the ability of delivering detailed insights for all the sub-domains and timescales varying from nano- to femto-seconds of the laser-induced breakdown phenomenon. Graphic Abstract

The machinability of a steel workpiece through conventional and Laser-Assisted Machining (LAM) is studied by the help of the Finite Element Method (FEM). In LAM, the laser beam is applied as a heat source to ensure sufficient local heating of the workpiece at a certain distance from the cutting tool and the machinability of materials is increased since the values of the cutting forces are decreased. A thermostructural FEM model is developed to simulate the conventional and the LAM orthogonal cutting of AISI H-13 steel. The Johnson-Cook material model that takes into account the effect of plastic strain, strain rate and temperature, along with a fracture model, is used in the simulations. For varying feed rate, parametric simulations are carried out, for different test cases of the laser beam diameter and the laser heat flux. Key engineering parameters, like cutting forces, temperature distributions, Von Mises stresses and plastic strains, are compared for both cutting processes. This comparison leads to important notifications on the influence of the cutting and laser parameters to LAM. The obtained results indicate that LAM may improve the machinability of AISI H-13 steel by reducing the cutting forces to a maximum percentage of ~15%.

The current research focuses on the characterization of the produced heat affected zone when laser heats AISI H13 steel, AISI 1045 steel and Ti6Al4V alloy workpieces via finite element simulations and experimental investigation. The surface roughness designedly varies on the surface of the samples and its influence on the absorption of laser light is investigated. Experiments are conducted at 1-4 W laser power and for two scanning speeds of 2 and 100 mm/min. A 3D transient thermo-structural finite element model for a moving Gaussian laser heat source is developed to simulate the micromachining process and predict the depth and width of the heat affected zone. The Johnson-Cook material model that takes into account the effect of plastic strain, strain rate and temperature, along with a fracture model, is adapted to the simulations. A good agreement between the experimental data and the simulation results is found. The depth and width of the heat affected zone strongly depend on the laser parameters and material properties of the irradiated samples. This study constitutes the basis to the optimization and improvement of the laser assisted micromachining process parameters and provides key insights on the roughness-absorptivity relation for the three metallic materials.

Fusion energy research is delivering impressive new results emerging from different infrastructures and industrial devices evolving rapidly from ideas to proof-of-principle demonstration and aiming at the conceptual design of reactors for the production of electricity. A major milestone has recently been announced in laser fusion by the Lawrence Livermore National Laboratory and is giving new thrust to laser-fusion energy research worldwide. Here we discuss how these circumstances strongly suggest the need for a European intermediate-energy facility dedicated to the physics and technology of laser-fusion ignition, the physics of fusion materials and advanced technologies for high-repetition-rate, high-average-power broadband lasers. We believe that the participation of the broader scientific community and the increased engagement of industry, in partnership with research and academic institutions, make most timely the construction of this infrastructure of extreme scientific attractiveness.

Background: During in-office bleaching, appropriate light sources are applied in order to enhance the activity of the bleaching gels applied onto teeth. For this method to be effective, a high absorption of light within the gel is necessary. Variation in the light attenuation capability of the gel, the duration of application and light activation can contribute towards safety hazards associated with this procedure. Methods: In this study, seven different gels and hydrogen peroxide have been evaluated for their optical properties by means of spectrophotometry (440&ndash, 1000 nm). The transmitted light spectrum was used to estimate the intensity loss for each gel. The mean intensity decreases observed were statistically analysed using an analysis of variance (ANOVA). Results: The five more-pigmented gels tested indicated a very similar intensity loss of around 80%, whereas the remaining two gels showed significantly less attenuation (predominantly, p &lt, 10&minus, 6). Conclusions: Throughout the spectrum of wavelengths examined, and according to the underlying studies evaluated, five of the gels assessed demonstrated an attenuation high enough to possibly avoid overheating of the underlying enamel dentine and pulp. An evaluation of appropriate irradiation parameters is proposed.

The second and final year of the Erasmus Plus programme "Innovative Education and Training in high power laser plasmas", otherwise known as PowerLaPs, is described. The PowerLaPs programme employs an innovative paradigm in that it is a multi-centre programme where teaching takes place in five separate institutes with a range of different aims and styles of delivery. The "in class" time is limited to four weeks a year, and the programme spans two years. PowerLaPs aims to train students from across Europe in theoretical, applied, and laboratory skills relevant to the pursuit of research in laser plasma interaction physics and inertial confinement fusion (ICF). Lectures are intermingled with laboratory sessions, and continuous assessment activities. The programme, which is led by workers from the Hellenic Mediterranean University, and supported by co-workers from Queens University Belfast, the University of Bordeaux, the Czech Technical University in Prague, Ecole Polytechnique, the University of Ioannina, the University of Salamanca, and the University of York, has just finished its second and final year. Six Learning Teaching Training (LTT) activities have been held, at the Queens University Belfast, the University of Bordeaux, the Czech Technical University, the University of Salamanca, and the Institute of Plasma Physics and Lasers (CPPL) of the Hellenic Mediterranean University. The last of these institute hosted two two-week long Intensive Programmes (IPs), whilst the activities at the other four universities were each five days in length. In addition to this a "Multiplier Event" was held at the University of Ioannina, which will be briefly described. In this second year the work has concentrated upon training in both experimental diagnostics and simulation techniques appropriate to the study of Plasma Physics, High Power Laser-Matter Interactions and High Energy Density Physics. The nature of the programme will be described in detail and some metrics relating to the activities carried out will be presented. In particular this paper will focus upon the overall assessment of the programme.

The dynamics of plasmas produced by low current X-pinch devices are explored. This comprehensive computational study is the first step in the preparation of an experimental campaign aiming to understand the formation of plasma jets in table-top pulsed power X-pinch devices. Two state-of-the-art magneto-hydro-dynamic codes, GORGON and PLUTO, are used to simulate the evolution of the plasma and describe its key dynamic features. GORGON and PLUTO are built on different approximation schemes and the simulation results obtained are discussed and analyzed in relation to the physics adopted by each code. Both codes manage to accurately handle the numerical demands of the X-pinch plasma evolution and provide precise details on the mechanisms of the plasma expansion, the jet-formation, and the pinch generation. Furthermore, the influence of electrical resistivity, radiation transport and optically thin losses on the dynamic behaviour of the simulated X-pinch produced plasma is studied in PLUTO. Our findings highlight the capabilities of the GORGON and PLUTO codes in simulating the wide range of plasma conditions found in X-pinch experiments, enabling a direct comparison to the scheduled experiments.

The original publication omitted the following authors from the list of authors on the title page: Jon Imanol Api˜naniz, Massimo de Marco, Mauricio Rico and Michael Touati and mis-spelled the surname of Ghassan Zeraouli.

We study the optimization of collisionless shock acceleration of ions based on hydrodynamic modelling and simulations of collisional shock waves in gaseous targets. The models correspond to the specifications required for experiments with the $\text{CO}_{2}$ laser at the Accelerator Test Facility at Brookhaven National Laboratory and the Vulcan Petawatt system at Rutherford Appleton Laboratory. In both cases, a laser prepulse is simulated to interact with hydrogen gas jet targets. It is demonstrated that by controlling the pulse energy, the deposition position and the backing pressure, a blast wave suitable for generating nearly monoenergetic ion beams can be formed. Depending on the energy absorbed and the deposition position, an optimal temporal window can be determined for the acceleration considering both the necessary overdense state of plasma and the required short scale lengths for monoenergetic ion beam production.

Femtosecond laser pulses are used for the excitation of surface acoustic waves (SAWs) in a gold thin film transducer deposited on a glass substrate, while a single longitudinal nanosecond laser source is employed for their full-field, high-resolution dynamic interferometric imaging in a pump–probe experimental set-up. The successful combination of the two laser sources in one integrated pump–probe set-up, poses no restrictions in the time-delays. The experimental results are supported by numerical simulations implemented by the connection of a finite difference two-temperature model (TTM) with a finite element method (FEM) model. The new integrated method allows for the investigation of the dynamic response of matter for long timescale ranges. Representative applications for SAWs characterization and surface structural defects detection on Au thin metal film deposited on BK7 glass substrate samples, demonstrate the efficiency of the proposed method and the influence of the pulse duration of the excitation pulses.

The surface roughness and the evolution of its morphology of a pulsed laser irradiated aluminum workpiece, is investigated via numerical simulations and experimental measurements. A three-dimensional transient thermo-structural finite element model is developed to simulate the machining process. The developed finite element material model considers the effects of plastic strain, strain rate and temperature, along with a fracture model. For the experiments, a single laser pulse of 6 ns duration and 0.7 mJ of energy at 532 nm is employed as the heat source, and the surface roughness is measured using white light interferometry set-up and related experimental diagnostics. A step-like linear approximation is used to model the surface roughness. A satisfactory agreement between the experimental data and the simulation results is found. This preliminary study aims to contribute to a better understanding of the initial physical processes involved in pulsed laser machining considering the influence of surface roughness and is beneficial for industrial applications such as laser polishing, engraving and cutting.

The Z-pinch plasma device is a type of plasma confinement system that uses electrical current to generate a magnetic field which compresses a current-carrying wire. In a previous proof-of-principle study, we demonstrated that in the interaction of a single wire with a pulsed current, the generated Electro-Thermo-Mechanical (ETM) instability in the solid phase acts as a seeding mechanism for the later developed instabilities observed in the plasma phase. In this study, the influence of the geometrical characteristics, such as length and thickness of the load-wire, on the generation of the ETM instability are investigated. Finite element multiphysics-multiphase simulations starting from the solid state are coupled with Magneto-Hydro-Dynamics (MHD) simulations to study the solid to plasma phase transition and the matter’s dynamics. The numerical results of the wire expansion dynamics prior to plasma formation are validated by experimental results from a modified Fraunhofer diffraction diagnostic, while in the plasma phase the simulated plasma dynamics is validated by shadowgraphic and interferometric experimental results. The numerical and experimental results demonstrate a satisfactory agreement for the wire expansion dynamics and the growth rate of the developed instabilities, for varying wire thickness and length.

The computational study of x-pinch plasmas driven by pulsed power generators demands the development of advanced numerical models and simulation schemes, able to enlighten the experiments. The capabilities of PLUTO code are here extended to enable the investigation of low current produced x-pinch plasmas. The numerical modules of the code used and modified are presented and discussed. The simulations results are compared to experiments, carried out on a table-top pulsed power plasma generator implemented in a mode of producing a peak current of ∼45 kA with a rise time (10%–90%) of 50 ns, loaded with Tungsten wires. The structural evolution of plasma density is studied and its influence on the magnetic field is analyzed with the help of the new simulation data. The simulated areal mass density is compared with the experimentally measured dense opaque region to enlighten the dense plasma evolution. In addition, the measured areal electron density is compared to the simulation results. Moreover, the new simulation data offer valuable insights to the main jet formation mechanisms, which are further analyzed and discussed in relation to the influence of the J × B force and the momentum.

This work presents studies which demonstrate the importance of the very early heating dynamics of the ablator long before the ablation plasma phase begins in laser driven inertial confinement fusion (ICF) studies. For the direct-drive fusion concept using lasers, the development of perturbations during the thermo-elasto-plastic (TEP) and melting phases of the interaction of the laser pulse with the ablator's surface may act as seeding to the subsequent growth of hydro-dynamic instabilities apparent during the acceleration phase of the interaction such as for instance the Rayleigh–Taylor and the Richtmyer–Meshkov, which strongly affect the implosion dynamics of the compression phase. The multiphysics-multiphase finite-element method (FEM) simulation results are experimentally validated by advanced three-dimensional whole-field dynamic imaging of the surface of the ablator allowing for a transverse to the surface spatial resolution of only approximately 1 nm. The study shows that the TEP and melting phases of the interaction are of crucial importance since transverse perturbations of the ablator's surface can reach tens of nanometres in amplitude within the TEP and melting phases. Such perturbations are of Rayleigh type and are transferred from the ablator to the substrate from the very first moments of the interaction.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 1)’.

The Heat Affected Zone - HAZ of a laser irradiated AISI H-13 steel workpiece, is investigated via numerical simulations and experimental measurements. A three-dimensional transient thermo-structural finite element model is developed to simulate the machining process. A Gaussian laser beam is employed as the heat source. The developed finite element material model considers the effects of plastic strain, strain rate and temperature, along with a fracture model. The experiments are carried out with a laser of 1-4 W power and with a scanning speed of 100 mm/min. Thermocouple sensors are used for the temperature measurements, while the surface roughness is measured using white light interferometry and related experimental diagnostics. A parametric numerical analysis regarding the average absorptivity of the workpiece is performed and is compared to the experimental findings. The depth and width of HAZ and the induced strains are studied for the plastic and melting regimes. The influence of the surface roughness of the metal workpiece on the dynamics of HAZ is also experimentally demonstrated. The findings of this study highlight the role of the absorption coefficient and the surface roughness on the HAZ below the ablation threshold and can be applied to related laser machining processes.

Summarization: The thermomechanical transient response of matter illuminated by nanosecond laser pulses is modeled and simulated using the Finite Element Analysis (FEA). Matter’s behavior is numerically described by a three-dimensional (3D) multiphysics, coupled thermal structural, transient FEA, experimentally validated, model. FEA offers substantial insights into the materials’ micro-mechanical behaviour providing detailed information for the spatiotemporal evolution of acoustic waves. In this computational approach the impact of the geometric characteristics of the modeled metallic films to the generation and propagation of the ultrasonic waves, in relation to temperature, is investigated. The study is expanded to the dynamic reactions of matter in the presence of surface and solid volume defects and enclosures e.g.: gaps, holes or bubbles. The transient behavior of matter in the time and the space solution domains is obtained by the FEA model and presented. Presented on: Key Engineering Materials

The elastoplastic dynamic mechanical behavior of thin metallic films excited by a nanosecond laser pulse is studied. The dynamic response of the metal films is numerically described by a coupled thermal–structural, transient three-dimensional model based on the finite element method. The developed finite element model takes into account the temperature-dependent true stress–strain curves, the temperature-dependent thermal properties and matters phase changes. Since the numerical simulations include the dynamic changes of the metallic materials mechanical properties, the obtained spatiotemporal numerical solutions provide detailed descriptions of their elastoplastic response. Thus, the experimentally validated model is able to diagnose and predict spatiotemporally matters elastic and plastic deformations that occur during the interaction with a nanosecond laser pulse. Gold, copper, and aluminum thin metallic films are used as test cases to demonstrate the effectiveness of the proposed finite element modeling and simulation.

Nanoacoustic strains are generated in Silicon by chirped femtosecond laser pulses using thin Titanium films as transducers. We investigate the effect that the generating laser pulse chirp has on the amplitude of the induced strains, manifested as Brillouin oscillations observed in degenerate femtosecond pump-probe transient reflectivity measurements. The strain amplitude is larger when negatively chirped pulses are used, which is attributed to the more efficient conversion of laser pulse light into acoustic strain in the Titanium transducer. Our present studies clearly show that the dependence of the Brillouin amplitude and the lattice strain is a non-monotonous function of the laser chirp parameter. An optimum negative laser pulse chirp is found for which the strain amplitude is maximized. A detailed thermomechanical model satisfactorily supports the experimental findings. In such a way, it is possible to suppress or enhance the induced nanoacoustic strain amplitude, thus all-optically controlling it by at least a factor of two.

This article presents experimental results supported by advanced three-dimensional modeling for the dynamics emerging from the interaction of nanosecond laser pulses with thin metal films on dielectric substrates, especially at the melting and ablation regimes. Matter dynamics, such as the generation and propagation of surface acoustic waves and permanent deformations, are imaged with the use of a very high spatial and temporal resolution interferometric method accompanied by white-light interferometry. A three-dimensional finite element model is developed aiming to fully describe the spatiotemporal dynamics and predict with high accuracy the thermo-mechanical phenomena around melting and ablation regimes where phase changes take place. The ability of very high spatial and temporal resolution, the whole-field three-dimensional imaging as well as the simultaneous study of the laser pulse–thin film interaction regimes, makes this study valuable for applications where detailed knowledge of the thermo-mechanical behavior of matter under pulsed laser excitation is critical.

A novel integrated method for the study of nano-structured materials.The method is based on short laser-generated Surface Acoustic Waves.Combination of a 3D whole-field imaging laser diagnostic and finite element modeling.The applicability and the potentiality of the method are validated. A novel integrated method enabling the study of nano-structured materials is presented, which is based on the imaging and monitoring of the spatiotemporal evolution of short-pulse-laser-generated Surface Acoustic Waves (SAWs). The method combines a 3D whole-field imaging laser interferometric experimental diagnostic technique and Finite Element Analysis (FEA) theoretical simulations.The experimental technique utilizes a single-longitudinal mode nanosecond laser source for both the generation and recording of the SAWs. It provides nanometer transverse spatial resolution vertical to the material surface, via direct whole-field imaging with nanosecond temporal resolution, thus avoiding extensive surface scanning. The theoretical model simulates the laser-material interaction as well as the generation and propagation of SAWs. FEA offers substantial insights into the materials' micro-elastomechanic behavior providing detailed information for the spatiotemporal evolution of SAWs.This integrated method is here applied on simple material samples consisted of thin metal films coated on dielectric substrates. The results validate the applicability and the potential of the proposed method in the area of nanostructured materials micromechanical characterization.

The possibility of using high-intensity laser-produced plasmas as a source of energetic ions for heavy ion accelerators is addressed. Experiments have shown that neon ions greater than 6 MeV can be produced from gas jet plasmas, and well-collimated proton beams greater than 20 MeV have been produced from highintensity laser solid interactions. The proton beams from the back of thin targets appear to be more collimated and reproducible than are high-energy ions generated in the ablated plasma at the front of the target and may be more suitable for ion injection applications. Lead ions have been produced at energies up to 430 MeV. © 2000 IEEE.

A two-dimensional magneto-hydrodynamic simulation incorporating cold start conditions is used to explain the early phase of carbon fiber Z-pinch experiments. The rapid development of large scale, nonlinear m=0 perturbations in the plasma corona is reproduced. X-ray bright spot formation in the necks of the instability is followed by bright spot bifurcation and fast axial motion. Bright spot bifurcation is found to be due to axial components of the j×B force and occurs off-axis due to the presence of a residual core of unionized carbon. Artificial diagnostic images are generated from the simulations data to allow direct comparison with experimental x-ray imaging and laser probing diagnostics. The accurate reproduction of the experimental images provides confirmation that the experimentally observed features are a repercussion of the non-linear development of the m=0 instability in an ionizing medium.

Experiments where a laser-generated proton beam is used to probe the megagauss strength self-generated magnetic fields from a nanosecond laser interaction with an aluminum target are presented. At intensities of 1015 Wcm(-2) and under conditions of significant fast electron production and strong heat fluxes, the electron mean-free-path is long compared with the temperature gradient scale length and hence nonlocal transport is important for the dynamics of the magnetic field in the plasma. The hot electron flux transports self-generated magnetic fields away from the focal region through the Nernst effect [A. Nishiguchi et al., Phys. Rev. Lett. 53, 262 (1984)] at significantly higher velocities than the fluid velocity. Two-dimensional implicit Vlasov-Fokker-Planck modeling shows that the Nernst effect allows advection and self-generation transports magnetic fields at significantly faster than the ion fluid velocity, v(N)/C(s) approximate to 10.

Laser-driven magnetic reconnection is investigated using proton deflectometry. Two laser beams of nanosecond duration were focused in close proximity on a solid target to intensities of I∼1×1015 W cm−2. Through the well known ∇ne×∇Te mechanism, azimuthal magnetic fields are generated around each focal spot. During the expansion of the two plasmas, oppositely oriented field lines are brought together resulting in magnetic reconnection in the region between the two focal spots. The spatial scales and plasma parameters are consistent with the reconnection proceeding due to a Hall mechanism. An optimum focal spot separation for magnetic reconnection to occur is found to be ≈400±100 μm. Proton probing of the temporal evolution of the interaction shows the formation of the boundary layer between the two expanding plasma plumes and associated magnetic fields, as well as an instability later in the interaction. Such laboratory experiments provide an opportunity to investigate magnetic reconnection under unique conditions and have possible implications for multiple beam applications such as inertial confinement fusion experiments.Laser-driven magnetic reconnection is investigated using proton deflectometry. Two laser beams of nanosecond duration were focused in close proximity on a solid target to intensities of I∼1×1015 W cm−2. Through the well known ∇ne×∇Te mechanism, azimuthal magnetic fields are generated around each focal spot. During the expansion of the two plasmas, oppositely oriented field lines are brought together resulting in magnetic reconnection in the region between the two focal spots. The spatial scales and plasma parameters are consistent with the reconnection proceeding due to a Hall mechanism. An optimum focal spot separation for magnetic reconnection to occur is found to be ≈400±100 μm. Proton probing of the temporal evolution of the interaction shows the formation of the boundary layer between the two expanding plasma plumes and associated magnetic fields, as well as an instability later in the interaction. Such laboratory experiments provide an opportunity to investigate magnetic reconnection under unique co...

A laser generated proton beam was used to measure the megagauss strength self-generated magnetic fields from a nanosecond laser interaction with an aluminum target. At intensities of 10 15 W cm -2, the significant hot electron production and strong heat fluxes result in non-local transport becoming important to describe the magnetic field dynamics. Two-dimensional implicit Vlasov-Fokker-Planck modeling shows that fast advection of the magnetic field from the focal region occurs via the Nernst effect at significantly higher velocities than the sound speed, v N/c s ≈ 10. © 2011 IOP Publishing Ltd.