High Power Laser Energy Research Articles

Water jet guided high-power laser energy transmission loss analysis

Water jet guided high-power laser energy transmission loss analysis

In-situ measurement and self-calibration system for high-power laser energy in ICF facilities

Precise real-time measurement of high-power laser energy is the foundation for ICF facilities to keep power and energy balance, which requires energy measurement equipment to maintain considerable linearity during a long operation period. The measurement accuracy, efficiency and calibration procedure stability were the key factors for ICF facilities' operation. This work proposed a new thermopile-type energy meter and calibration system to achieve high-precise in-situ measurement and calibrating of high-power laser energy. The study suggested that the thermal energy conversion, electric energy loading and metering, heat transfer, sensor temperature rise, sampling circuit and post-processing significantly affected the high-power laser energy measurement and calibration results. Besides, the whole numerical modeling process was established and verified by experiments on the energy transfer and physical quantity conversion process in energy measurement. The laser energy measurement and calibration system has self-calibration functions and stable operation through numerical simulation and optimization of the key factors. This study is of great significance for the high-power laser energy monitoring and output energy improvement of ICF facilities, broadening the method for the high-precision in-situ measurement system.

Effect of solid lubricant addition in coating produced by laser cladding process: A review

This present review article discusses about the effect of solid lubricant additive in surface composite coating deposited by laser cladding and alloying process. Wear and friction is challenging problem in moving machinery parts subjected to rubbing action or sliding motion. Therefore to reduce the wear and friction of sliding machinery parts, coated layer is deposited on the surface of machine component to prevent from surface damage due to wear. Laser cladding and alloying is advanced manufacturing technology by which hard and wear resistant coating material is deposited on the surface of soft conventional materials by use of high power laser energy as heat source to provide good metallurgical adherence between coating and substrate materials. The coating materials generally used for enhancing the friction and wear resistance properties of conventional materials are advanced ceramics, advanced composites, nanomaterials and advanced alloys like high entropy alloys. When solid lubricants are added to these coating materials in limited amount then the friction and wear properties of developed surface improves. The solid lubricant additive in coating materials can reduce the friction coefficient and wear rate of materials. The solid lubricant materials acts as anti-friction and anti-wear agent in the coating materials. The most commonly used solid lubricants are h-BN, CaF2, MoS2, WS2, BaF2 and graphite. In this article the effect of these solid lubricant material on wear resistance and friction coefficient of coated surfaces produced by laser alloying and cladding techniques are described. The various engineering materials used for manufacturing of moving or sliding parts are ferrous materials, titanium alloys, aluminium alloys, magnesium alloys and copper alloys. In this article the coating deposited on these materials with solid lubricant additives by laser cladding and alloying process are reviewed. The problem arises during developing solid lubricant additive coating and its remedies are described.

Antireflective laser coating with improved mechanical property and organic-contaminant resistance for high-power laser application

Mono-layer silica-based antireflective laser coating with modulated structure has been designed and fabricated, in which cross-linking network structure of polysiloxane was prepared as backbone and porous silica spheres (PSSs) were inserted to create interior porosity. Cured polysiloxane provided dense structure that could both prevent the invasion of volatile organic compounds (VOCs) and improve the mechanical property of this coating, while PSSs endowed this coating with proper porosity to adjust its refractive index and relax the high-power laser energy. With certain structure modulation, excellent transmission and laser-damage resistance of this coating at 355 nm (for the application in high-power laser system) and 1064 nm (for the application in laser-guided component) was both achieved. Meanwhile, the hardness of this coating increased significantly compared with that of the conventional porous silica coating. In addition, qualified VOCs endurance of this coating was also proved, which effectively extended the lifetime of such coating.

Limitations for tungsten as plasma facing material in the diverse scenarios of the European inertial confinement fusion facility HiPER: Current status and new approaches

The high-power laser energy research (HiPER) project was a European project for demonstrating the feasibility of inertial fusion energy based on using direct-drive targets in a shock ignition scheme using a drywall evacuated chamber. HiPER was intended to drive the transition from a scientific proof of principle to a demonstration power plant in Europe. The project was divided into three realistic scenarios (Experimental, Prototype, and Demo) to help identify open problems and select appropriate technologies to solve them. One of the problems identified was the lack of appropriate plasma-facing materials (PFMs) for the reaction chamber. Therefore, a major challenge was to develop radiation-resistant materials able to withstand the large thermal loads and radiation in these reactors. In this paper, we describe the main threats that coarse-grained W would face in the diverse HiPER scenarios. Based on purely thermomechanical considerations, the W lifetimes for the HiPER Prototype and Demo scenarios are limited by fatigue to 14 000 h and 28 h, respectively. The combined effects of thermal load and atomistic damage significantly reduce these lifetimes to just ∼1000 shots for the Experimental scenario and a few minutes and seconds for the Prototype and Demo scenarios, respectively. Thus, coarse-grained W is not an appropriate PFM for the Prototype or Demo scenarios. Therefore, alternatives to this material need to be identified. Here, we review some of the different approaches that are being investigated, highlight the work done to characterize these new materials, and suggest further experiments.

Analysis and design of a high power laser interrupter for MEMS based safety and arming systems

A high power laser energy interrupter is investigated and developed. The micromachined laser interrupter is a critical component of the MEMS based safety and arming (S&A) system, which acts as a switch to selectively couple optical power between input and output fibers using direct coupling technique. The switching of high power laser energy is demonstrated by taking advantage of direct thermal actuation of cantilevered large-core multimode fibers. Models describing the combined electrothermal and thermomechanical characteristics of the thermal actuators are developed with temperature-dependent parameters. The temperature distribution of the actuator is investigated, and the influence of the actuator’s geometrical parameters on its force and displacement is analyzed. Actuator displacement versus drive current is found to be in good agreement with model predictions. Switching time is 19 ms from the safety to the arming state with a maximum operational frequency of 34 Hz. Optical efficiency is predicted and a series of tests are conducted to measure transmission efficiency of the laser interrupter. The optical efficiency is found to be about 92.7% with a maximum power transfer of 2780 mW from a 3000 mW input, and the channel isolation is 57 dB.

Optimal conditions for shock ignition of scaled cryogenic deuterium–tritium targets

Within the framework of the shock-ignition (SI) scheme, ignition conditions are reached following the separation of the compression and heating phases. First, the shell is compressed at a sub-ignition implosion velocity; then an intense laser spike is launched at the end of the main drive, leading to the propagation of a strong shock through the precompressed fuel. The minimal laser energy required for ignition of scaled deuterium–tritium (DT) targets is assessed by calculations. A semi-empiric model describing the ignitor shock generation and propagation in the fuel assembly is defined. The minimal power needed in the laser spike pulse to achieve ignition is derived from the hydrodynamic model. Optimal conditions for ignition of scaled targets are explored in terms of laser intensity, shell-implosion velocity, and target scale range for the SI process. Curves of minimal laser requirements for ignition are plotted in the energy–power diagram. The most economic and reliable conditions for ignition of a millimeter DT target are observed in the 240- to 320-km/s implosion velocity range and for the peak laser intensity ranging from ∼2 × 1015 W/cm2 up to 5 × 1015 W/cm2. These optimal conditions correspond to shock-ignited targets for a laser energy of ∼250 kJ and a laser power of 100 to 200 TW. Large, self-ignited targets are particularly attractive by offering ignition at a lower implosion velocity and a reduced laser intensity than for conventional ignition. The SI scheme allows for the compression and heating phases of the high power laser energy research facility target to be performed at a peak laser intensity below 1016 W/cm2. A better control of parametric and hydrodynamic instabilities within the SI scheme sets it as an optimal and reliable approach to attain ignition of large targets.

HiPER: The European path to laser energy

While for decades, energy production relying on laser inertial fusion has been a strong motivation for the development in Europe of a few high-energy laser facilities and dedicated scientific programs, the HiPER initiative launched in 2004 fostered an ambitious large-scale coordinated European program toward inertial fusion energy. Anticipating the successful demonstration of fusion ignition and gain at the National Ignition Facility (NIF) in the USA, scientists and engineers from across Europe are developing the case for a next generation laser fusion facility, HiPER, to be constructed in Europe. The single-facility build strategy of HiPER (High Power Laser Energy Research Facility) aims at first demonstrating some key elements of a fusion reactor in a high rep-rate few-second cycle mode, before addressing energy production on a high rep-rate continuous mode in a second area.

Silica final lens performance in laser fusion facilities: HiPER and LIFE

Nowadays, the projects LIFE (Laser Inertial Fusion Energy) in USA and HiPER (High Power Laser Energy Research) in Europe are the most advanced ones to demonstrate laser fusion energy viability. One of the main points of concern to properly achieve ignition is the performance of the final optics (lenses) under the severe irradiation conditions that take place in fusion facilities. In this paper, we calculate the radiation fluxes and doses as well as the radiation-induced temperature enhancement and colour centre formation in final lenses assuming realistic geometrical configurations for HiPER and LIFE. On these bases, the mechanical stresses generated by the established temperature gradients are evaluated showing that from a mechanical point of view lenses only fulfil specifications if ions resulting from the imploding target are mitigated. The absorption coefficient of the lenses is calculated during reactor startup and steady-state operation. The obtained results reveal the necessity of new solutions to tackle ignition problems during the startup process for HiPER. Finally, we evaluate the effect of temperature gradients on focal length changes and lens surface deformations. In summary, we discuss the capabilities and weak points of silica lenses and propose alternatives to overcome predictable problems.

Three-Dimensional Simulations of Cylindrical Target Implosion Imaging Using Laser-Driven Proton Source

Many experiments, based on the road map of the European High Power laser Energy Research facility project, were performed to study fast electron transport in compressed matter in the context of fast ignition approach to inertial confinement fusion. The generation of high intensity beams from laser-matter interaction extends the possibility to use protons as a diagnostic to image imploding targets in these experiments. The analysis of experimentally obtained proton images requires a careful analysis and accurate numerical simulations using both hydrodynamic and Monte Carlo (MC) codes. An experiment has been performed in 2008 at Rutherford Appleton Laboratory to study fast electron propagation in cylindrical imploding targets illuminated by four laser pulses. In this paper, we present new simulation results in 3-D geometry. Three-dimensional density map is generated by running the 3-D version of the MULTI code. Proton radiography images are then simulated using the MC code MCNPX.

Laser-driven cylindrical compression of targets for fast electron transport study in warm and dense plasmas

Fast ignition requires a precise knowledge of fast electron propagation in a dense hydrogen plasma. In this context, a dedicated HiPER (High Power laser Energy Research) experiment was performed on the VULCAN laser facility where the propagation of relativistic electron beams through cylindrically compressed plastic targets was studied. In this paper, we characterize the plasma parameters such as temperature and density during the compression of cylindrical polyimide shells filled with CH foams at three different initial densities. X-ray and proton radiography were used to measure the cylinder radius at different stages of the compression. By comparing both diagnostics results with 2D hydrodynamic simulations, we could infer densities from 2 to 11 g/cm3 and temperatures from 30 to 120 eV at maximum compression at the center of targets. According to the initial foam density, kinetic, coupled (sometimes degenerated) plasmas were obtained. The temporal and spatial evolution of the resulting areal densities a...

Proton radiography of cylindrical laser-driven implosions

We report on the results of a recent experiment at the Rutherford Appleton Laboratory investigating fast electron propagation in cylindrically compressed targets; a subject of interest for fast ignition. This experiment was performed within the framework of the road map of HiPER (the European High Power laser Energy Research facility Project). Protons accelerated by a ps-laser pulse are used to radiograph a 220 µm diameter, imploded with ∼200 J of laser light (1 ns λ = 0.53 µm) in four symmetrically incident beams. Results are also compared with those from hard x-ray radiography. Detailed comparison with 2D radiation hydrodyamics simulations is performed with the aid of a Monte Carlo code adapted to describe plasma effects. Finally, a simple analytical model is developed to estimate the performance of proton radiography for given implosion conditions.

Proton radiography of laser-driven imploding target in cylindrical geometry

An experiment was done at the Rutherford Appleton Laboratory (Vulcan laser petawatt laser) to study fast electron propagation in cylindrically compressed targets, a subject of interest for fast ignition. This was performed in the framework of the experimental road map of HiPER (the European high power laser energy research facility project). In the experiment, protons accelerated by a picosecond-laser pulse were used to radiograph a 220 μm diameter cylinder (20 μm wall, filled with low density foam), imploded with ∼200 J of green laser light in four symmetrically incident beams of pulse length 1 ns. Point projection proton backlighting was used to get the compression history and the stagnation time. Results are also compared to those from hard x-ray radiography. Detailed comparison with two-dimensional numerical hydrosimulations has been done using a Monte Carlo code adapted to describe multiple scattering and plasma effects. Finally we develop a simple analytical model to estimate the performance of prot...

An Update of Target Fabrication Techniques for the Mass Production of Advanced Fast Ignition Cone Targets

The United States and France are constructing multi-billion-dollar laser facilities to demonstrate inertial fusion as a potential source of energy for the future. These facilities aim to use the inertial confinement fusion scheme to demonstrate ignition on the 2010-2012 timescale. The recently launched High Power Laser Energy Research facility (HiPER) project is a European initiative to offer a credible way to build upon this work and demonstrate the possibility of opening up inertial fusion energy as a commercial process for energy generation. These facilities pose huge engineering and scientific challenges not only in their design but also in the technical challenges of providing the targets that will contain the fuel required to run them. We review the current manufacturing techniques of the cone target component as well as the work toward mass production of this component.

Status of the Development of the HiPER Single-Shot Target

The High Power laser Energy Research facility (HiPER) is a European project dedicated to demonstrating the feasibility of producing energy by laser-driven inertial confinement fusion. A first design of the fast ignition cryogenic target has been established. It is composed of a thin-walled microshell with an inserted gold cone and filled with deuterium-tritium (DT) fuel by means of a capillary (conically guided capsule). After assembly, targets must be tight at cryogenic temperatures (16 to 19.6 K).In order to evaluate the manufacturing feasibility of a single-shot target prototype, a program has been adapted from the Laser Mégajoule (LMJ) cryogenic target fabrication know-how. Target component study for HiPER concerns a hollow gold cone (25-deg half-angle and ˜25-μm thickness), a thin polymeric microshell (2-mm diameter and 3- to 10-μm thickness), and a silica capillary (30-μm outer diameter).First gas-tight targets at 77 K have been produced (helium gas leak rate ˜1.4 × 10-11 Pa·m3/s). Major efforts have been focused on thin-walled microshells, robust gold cone fabrication, and target assembly (minimizing of the glue quantity as well as helium gas leak tests) and will be discussed in this paper.

Ignition studies in support of the European High Power Laser Energy Research Facility project

The European High Power Laser Energy Research Facility (HiPER) project is one of a number of large-scale scientific infrastructure projects supported by the European Commission’s Seventh Framework Programme (FP7). Part of this project involves the development of a target area for the exploration of inertial fusion energy. This paper describes some of the research that is being carried out by the author in support of this aspect of the program. The effects of different regions of the fusion target mixing prior to thermonuclear ignition have been investigated using the 1D Lagrangian radiation hydrodynamics simulation code HYADES. Results suggest that even low (few parts per million) levels of contamination of fuel by high-Z ion species may inhibit ignition due to radiative cooling of the ignition spot.

Proton Radiography and Fast Electron Propogation Through Cyliderically Compressed Targets

The paper describes the key points contained in the short term HiPER (High Power laser Energy Research) experimental road map, as well as the results of two phases of the experiment performed in "HiPER dedicated time slots. Experimental and theoretical results of relativistic electron transport in cylindrically compressed matter are presented. This experiment was achieved at the VULCAN laser facility (UK) by using four long pulse beams (similar to 4 x 50 J, 1 us, at 0.53 mu m) to compress a hollow plastic cylinder filled with plastic foam of three different densities (0.1, 0.3, and 1 g cm(-3)). In the first phase of the experiment, protons accelerated by a picosecond laser pulse were used to radiograph a cylinder filled with 0.1 g/cc foam. Point projection proton backlighting was used to measure the degree of compression as well as the stagnation time. Results were compared to those from hard X-ray radiography. Finally, Monte Carlo simulations of proton propagation in cold and compressed targets allowed a detailed, comparison with 2D numerical hydro simulations. 2D simulations predict a density of 2-5 g cm(-3) and a plasma temperature up to 100 eV at maximum compression. In the second phase of the experiment, a short pulse (10 ps, 160 J) beam generated fast electrons that propagated through the compressed matter by irradiating a nickel foil at an intensity of 5 x 10(18) Wcm(-2). X-ray spectrometer and imagers were implemented in order to estimate the compressed plasma conditions and to infer the hot electron characteristics. Results are discussed and compared with simulations.

Numerical simulations of the HiPER baseline target

The European High Power laser Energy Research (HiPER) project aims at demonstrating the feasibility of high gain inertial confinement fusion (ICF) using the fast ignitor approach. A baseline target has been recently developed by Atzeni et al. [Phys. Plasmas 14, 052702 (2007)]. The radiative transport have a minor effect on the peak areal density but decreased by 20% the peak density. We have found that with 95 kJ of absorbed laser energy one can assemble the fuel with a peak density around 500 g/cm3 and a peak areal density of 1.2 g/cm2. This implies a total target gain of about 60.

Studies on targets for inertial fusion ignition demonstration at the HiPER facility

Recently, a European collaboration has proposed the High Power Laser Energy Research (HiPER) facility, with the primary goal of demonstrating laser driven inertial fusion fast ignition. HiPER is expected to provide 250 kJ in multiple, 3ω (wavelength λ = 0.35 µm), nanosecond beams for compression and 70 kJ in 10–20 ps, 2ω beams for ignition. The baseline approach is fast ignition by laser-accelerated fast electrons; cones are considered as a means to maximize ignition laser–fuel coupling. Earlier studies led to the identification of an all-DT shell, with a total mass of about 0.6 mg as a reference target concept. The HiPER main pulse can compress the fuel to a peak density above 500 g cm−3 and an areal density ρR of about 1.5 g cm−2. Ignition of the compressed fuel requires that relativistic electrons deposit about 20 kJ in a volume of radius of about 15 µm and a depth of less than 1.2 g cm−2. The ignited target releases about 13 MJ. In this paper, additional analyses of this target are reported. An optimal irradiation pattern has been identified. The effects on fuel compression of the low-mode irradiation non-uniformities have been studied by 2D simulations and an analytical model. The scaling of the electron beam energy required for ignition (versus electron kinetic energy) has been determined by 2D fluid simulations including a 3D Monte Carlo treatment of relativistic electrons, and agrees with a simple model. Integrated simulations show that beam-induced magnetic fields can reduce beam divergence. As an alternative scheme, shock ignition is studied. 2D simulations have addressed optimization of shock timing and absorbed power, means to increase laser absorption efficiency and the interaction of the igniting shocks with a deformed fuel shell.

Numerical simulations of the HiPER baseline target

The European High Power laser Energy Research (HiPER) project aims at demonstrating the feasibility of high gain inertial confinement fusion (ICF) using the fast ignitor approach. A baseline target has been recently developed by Atzeni et al. [Phys. Plasmas 14, 052702 (2007)]. The comparison between a standard and a relaxation pulse shows that the latter one allows to reduce both the laser power contrast and the growth of perturbation under Rayleigh-Taylor instability. We have found that with 95 kJ of absorbed laser energy one can assemble the fuel with to a peak density around 500 g/cm3 and to a peak areal density of 1.2 g/cm2. This implies a total target gain of about 55.