Fast Ignition Concept Research Articles

Geant4 simulation of secondary photons generated by laser–solid interaction in the presence of external magnetic field

A parametric study of the average energy and scattering angle distribution of Bremsstrahlung x-ray photons generated in over-dense fuel were investigated using the Geant4 simulation toolkit in fast ignition concept. In our simulation, over-dense fuel with the mass ρc∼(300−1000)g.cm−3, and fast ignitor with the intensity I=(1021,1023)W.cm−2 and wavelength λ=(0.35,0.53)μm were considered in the presence of an external magnetic field with the strength Bext=(0−10)kT. Further, for the produced MeV electrons in pre-plasma, two types of energy distribution functions, i.e., exponential and quasi two-temperature, were considered. The simulation results show that by applying an external magnetic field strength Bext∼(1−2)kT, a smooth increase was observed in the x-ray photon average energy and a considerable increase in scattering angle and photon counts in over-dense plasma obtained, so that the peak values mostly obtained for Bext∼1kT. Meanwhile, between the two energy distribution functions for electrons, the optimal average energy and scattering angle values were obtained by considering the quasi-two-temperature energy distribution function and for the fast igniter intensity and wavelength, I=1021W.cm−2,λ=0.35μm respectively, and the fuel density ρc∼300g.cm−3. Finally, regarding to the obtained optimal average photon energy (i.e., Ebph<0.4MeV), which could be considered as minimum photon energy loss and maximum electron penetration toward the fuel, the minimum thickness of lead and concrete shields required to reduce the flux of photons to its one-tenth value were found to be 1.5 cm and 30.7 cm, respectively.

Simulation study of cone-in-shell target for indirect-drive ion fast ignition concept under the theory of an effective interaction potential

The stopping power of charged particles released by the deuterium–tritium nuclear reactions has been extensively studied in the weakly to moderately coupled plasma regimes. We have modified the conventional effective potential theory (EPT) stopping framework to have a practical connection to investigate the ions energy loss characteristics in fusion plasma. Our modified EPT model differs from the original EPT framework by a coefficient of order 1 + {2 mathord{left/ {vphantom {2 {(5}}} right. kern-0pt} {(5}}ln overline{Xi }),(ln overline{Xi } is a velocity-dependent generalization of the Coulomb logarithm). Molecular dynamics simulations agree well with our modified stopping framework. To study the role of related stopping formalisms in ion fast ignition, we simulate the cone-in-shell configuration under laser-accelerated aluminum beam incidence. In ignition/burn phase, the performance of our modified model is in agreement with its original form and the conventional Li-Petrasso (LP) and Brown-Preston-Singleton (BPS) theories. The LP theory indicates the fastest rate in providing ignition/burn condition. Our modified EPT model with a discrepancy of sim 9%, has the most agreement with LP theory, while that of the original EPT (with a discrepancy of sim 47% to LP) and BPS (with a discrepancy of sim 48% to LP) methods maintain the third and fourth contributions in accelerating the ignition time, respectively.

Enhanced hole boring with two-color relativistic laser pulses in the fast ignition scheme

A scheme of using two-color laser pulses for hole boring into overdense plasma as well as energy transfer into electron and ion beams has been studied using particle-in-cell simulations. Following an ultra-short ultra-intense hole-boring laser pulse with a short central wavelength in extreme ultra-violet range, the main infrared driving laser pulse can be guided in the hollow channel preformed by the former laser and propagate much deeper into an overdense plasma, as compared to the case using the infrared laser only. In addition to efficiently transferring the main driving laser energy into energetic electrons and ions generation deep inside the overdense plasma, the ion beam divergence can be greatly reduced. The results might be beneficial for the fast ignition concept of inertial confinement fusion.

A relativistic PIC model of nonlinear laser absorption in a finite-size plasma with arbitrary mass and density ratios

AbstractIn this paper, we have studied the nonlinear laser absorption in a finite-size plasma, using a fully kinetic relativistic 1½-dimensional particle-in-cell simulation code, and shown that the rate in which laser absorption increases depends on the mass ratio (δ = m+/m−) and the equilibrium density ratio (α = n0+/n0− = z−/z+), respectively. This can be attributed to the essential effects of these parameters on the nonlinear phenomena related to the laser absorption such as phase-mixing and laser-scattering process. We have indicated that the reduction of the defined mass and density ratios increases the absorption rate in the finite-size plasma as long as the laser scattering from the plasma is not considerable. Moreover, the study of kinetic phase-space distributions indicates in a specific range of mass and density ratios a large amount of laser energy leads to arise a population of charged particles having directed kinetic energy along the laser direction. These simulation results are expected to be relevant to the experiments on the intense laser–plasma interactions with applications to the particle acceleration and fast ignition concept as well as to the astrophysical environments.

Channeling of multikilojoule high-intensity laser beams in an inhomogeneous plasma

Channeling experiments were performed that demonstrate the transport of high-intensity (>10(18)W/cm(2)), multikilojoule laser light through a millimeter-sized, inhomogeneous (∼300-μm density scale length) laser-produced plasma up to overcritical density, which is an important step forward for the fast-ignition concept. The background plasma density and the density depression inside the channel were characterized with a novel optical probe system. The channel progression velocity was measured, which agrees well with theoretical predictions based on large scale particle-in-cell simulations, confirming scaling laws for the required channeling laser energy and laser pulse duration, which are important parameters for future integrated fast-ignition channeling experiments.

Generation of collimated quasi-monoenergetic target surface electron beams in laser solid interaction

Collimated quasi-monoenergetic target surface electron beams with divergence angle as small as 2° and energy peaked at 3-4 MeV were first generated in 200 TW sub-picoseconds laser interacted with solid target. We found that the laser contrast plays an important role in generating such kind of target surface electron beams. Resonant absorption might be the main heating regime through Back Scattering spectra analyses. Fine structures of shadow imaging of probe beam and plasma self-emission illustrate that over dense pre-plasma were generated. Such pre-plasma acts as a plasma reflective mirror which confines the main pulse propagating in the channel between pre-plasma and target surface and eventually guiding the electron beams along target surface. Such kind of electron beams might be used as an igniter in inertial confinement fusion, especially in the fast ignition concept.

Implementation of the Kinetic Plasma Code with Locally Recursive non-Locally Asynchronous Algorithms

Numerical simulation is presently considered impractical for several relevant plasma kinetics problems due to limitations of computer hardware even with the use of supercomputers. To overcome the existing limitations it is suggested to develop algorithms which would effectively utilize the computer memory subsystem hierarchy to optimize the dependency graph traversal rules. The ideas for general cases of numerical simulation and implementation of such algorithms to particle-in-cell code is discussed in the paper. This approach enables the simulation of previously unaccessible for modeling problems and the execution of series of numerical experiments in reasonable time. The latter is demonstrated on a multiscale problem of the development of filamentation instability in laser interaction with overdense plasma. One variant of the simulation with parameters typical for simulations on supercomputers is performed with the use of one cluster node. The series of such experiments revealed the dependency of energy loss on incoming laser pulse amplitude to be nonmonotonic and reach over 4%, an interesting result for research of fast ignition concept.

Investigation of Fuel Energy Gain for Tritium-Poor Fuels in Fast Ignition Fusion Approach

One of the most fascinating ignition schemes for the inertial fusion energy that might be feasible is fast ignition. Its targets are ignited on the outside surface so there is no need to low density and high temperature center is required by central hot spot ignition. Fast ignition concept is noteworthy for a simple but fundamental reason: In principle it requires less total energy input to achieve ignition. In this paper, fuel energy and fuel energy gain of nearly pure deuterium capsule are calculated. This capsule is ignited by a deuterium-tritium seed, which would reduce the tritium inventory to a few percentages. The variations of fuel energy gain versus fuel density have been studied and submitted. On the basis of different physical parameters the following results of the investigation are presented and discussed. The energy gain curves for different tritium concentrations are found and limiting gain curves are derived. Finally, tritium-poor fast ignitor is compared to equimolar deuterium-tritium fast ignitor.

Fast ignition of inertial confinement fusion targets

Results of studies on fast ignition of inertial confinement fusion (ICF) targets are reviewed. The aspects of the fast ignition concept, which consists in the separation of the processes of target ignition and compression due to the synchronized action of different energy drivers, are considered. Criteria for the compression ratio and heating rate of a fast ignition target, the energy balance, and the thermonuclear gain are discussed. The results of experimental and theoretical studies of the heating of a compressed target by various types of igniting drivers, namely, beams of fast electrons and light ions produced under the action of a petawatt laser pulse on the target, a heavy-ion beam generated in the accelerator, an X-ray pulse, and a hydrodynamic flow of laser-accelerated matter, are analyzed. Requirements to the igniting-driver parameters that depend on the fast ignition criteria under the conditions of specific target heating mechanisms, as well as possibilities of practical implementation of these requirements, are discussed. The experimental programs of various laboratories and the prospects of practical implementation of fast ignition of ICF targets are reviewed. To date, fast ignition is the most promising method for decreasing the ignition energy and increasing the thermonuclear gain of an ICF plasma. A large number of publications have been devoted to investigations of this method and adjacent problems of the physics of igniting drivers and their interaction with plasma. This review presents results of only some of these studies that, in the author’s opinion, allow one to discuss in detail the main physical aspects of the fast ignition concept and understand the current state and prospects of studies in this direction.

Guiding of a laser beam in a collisionless magnetoplasma channel

We present an investigation of laser guiding through an axially nonuniform collisionless magnetoplasma channel formed by the ionizing laser prepulse. With the propagation of a guided laser beam through such a preformed plasma channel, a ponderomotive force on account of the nonuniform intensity distribution of the laser beam comes into play, which further enhances the plasma channel. Unbalanced diffraction and refraction phenomena through such an axially nonuniform collisionless magnetoplasma channel results in alternate convergence and divergence of the laser beam. Wave equations governing the propagation characteristics of the ionizing prepulse and delayed pulse through an axialy nonuniform collisionless magnetoplasma channel have been solved by the moment theory approach. The effect of the magnetic field and intensity of a guided beam has been seen on the propagation of the second guided beam in the plasma channel. It is observed that there is an increase in the propagation of a guided beam with the increase in the magnetic field and intensity of the guided beam. This observation is very useful for the fast-ignitor concept, where the guided laser pulse is propagated through the plasma region without any absorption up to several Rayleigh lengths.

The comeback of shock waves in inertial fusion energy

AbstractThe shock waves in laser plasma interaction have played an important role in the study of inertial fusion energy (IFE) since the 1970's and perhaps earlier. The interaction of laser, or any other high power beam, induced shock waves with matter was one of the foundations of the target design in IFE. Even the importance of shock wave collision was studied and its importance forgotten. In due course, the shock waves were taken as granted and became “second fiddle” in IFE scenario. The analysis of the shock wave in the context of IFE is revived in this paper. At the forefront of the past decade the concept of fast ignition was introduced. The different ideas of fast ignition are summarized with special emphasis on shock wave fast ignition. The ignition is achieved by launching a shock wave during the final stages of the implosion. In this paper, a possible instability in the propagation of the igniting shock wave is analyzed. The idea of combining the fast ignition fusion with an impact shock wave is suggested and analyzed. This is achieved by launching a shock wave by an accelerated foil during the final stage of the implosion in order to ignite the compressed fuel. In this scheme, like other fast ignition schemes, a significant reduction of the driver energy in comparison with standard IFE scenarios is required for the same high gain fusion.

Enhanced Propagation for Relativistic Laser Pulses in Inhomogeneous Plasmas Using Hollow Channels

The influence of long (several millimeters) and hollow channels, bored in inhomogeneous ionized plasma by using a long pulse laser beam, on the propagation of short, ultraintense laser pulses has been studied. Compared to the case without a channel, propagation in channels significantly improves beam transmission and maintains a beam quality close to propagation in vacuum. In addition, the growth of the forward-Raman instability is strongly reduced. These results are beneficial for the direct scheme of the fast ignitor concept of inertial confinement fusion as we demonstrate, in fast-ignition-relevant conditions, that with such channels laser energy can be carried through increasingly dense plasmas close to the fuel core with minimal losses.

The National Ignition Facility and the National Ignition Campaign

The National Ignition Facility (NIF), the world's largest and most powerful laser system for inertial confinement fusion (ICF) and experiments studying high-energy-density (HED) science, is now operational at Lawrence Livermore National Laboratory (LLNL). NIF construction was certified by the Department of Energy as complete on March 27, 2009. NIF, a 192-beam Nd:glass laser facility, will ultimately produce 1.8 MJ 500 TW of 351-nm third-harmonic ultraviolet light. On March 10, 2009, a total of 192-beam energy of 1.1 MJ was demonstrated; this is approximately 30 times more energy than ever produced in an ICF laser system. The principal goal of NIF is to achieve ignition of a deuterium-tritium (DT) fuel capsule and provide access to HED physics regimes needed for experiments related to national security, fusion energy, and broader frontier scientific exploration. NIF experiments in support of indirect-drive ignition began in August 2009. These first experiments represent the next phase of the National Ignition Campaign (NIC). The NIC is a national effort to achieve fusion ignition and is coordinated through a detailed execution plan that includes science, technology, and equipment. The equipment required for ignition experiments includes diagnostics, a cryogenic target manipulator, and user optics. Participants in this effort include LLNL, General Atomics, Los Alamos National Laboratory, Sandia National Laboratory, and the University of Rochester Laboratory for Energetics. The primary goal for NIC is to have all of the equipment operational, integrated into the facility, and ready to begin a credible ignition campaign in 2010. With NIF now operational, the long-sought goal of achieving self-sustained nuclear fusion and energy gain in the laboratory is much closer to realization. Successful demonstration of ignition and net energy gain on NIF will be a major step toward demonstrating the feasibility of inertial fusion energy (IFE) and will likely focus the world's attention on the possibility of an ICF energy option. NIF experiments to demonstrate ignition and gain will use central-hot-spot (CHS) ignition, where a spherical fuel capsule is simultaneously compressed and ignited. The scientific basis for CHS has been intensively developed. Achieving ignition with CHS will open the door for other advanced concepts, such as the use of high-yield pulses of visible wavelength rather than ultraviolet and fast-ignition concepts. Moreover, NIF will have important scientific applications in such diverse fields as astrophysics, nuclear physics, and materials science. The NIC will develop the full set of capabilities required to operate NIF as a major national and international user facility. A solicitation for NIF frontier science experiments is planned for summer 2009. This paper summarizes the design, performance, and status of NIF and plans for the NIF ignition experimental program. A brief summary of the overall NIF experimental program is also presented.

Ignition on the National Ignition Facility: a path towards inertial fusion energy

The National Ignition Facility (NIF), the world's largest and most powerful laser system for inertial confinement fusion (ICF) and experiments studying high-energy-density (HED) science, is nearing completion at Lawrence Livermore National Laboratory (LLNL). NIF, a 192-beam Nd-glass laser facility, will produce 1.8 MJ, 500 TW of light at the third-harmonic, ultraviolet light of 351 nm. The NIF project is scheduled for completion in March 2009. Currently, all 192 beams have been operationally qualified and have produced over 4.0 MJ of light at the fundamental wavelength of 1053 nm, making NIF the world's first megajoule laser. The principal goal of NIF is to achieve ignition of a deuterium–tritium (DT) fuel capsule and provide access to HED physics regimes needed for experiments related to national security, fusion energy and for broader scientific applications.The plan is to begin 96-beam symmetric indirect-drive ICF experiments early in FY2009. These first experiments represent the next phase of the National Ignition Campaign (NIC). This national effort to achieve fusion ignition is coordinated through a detailed plan that includes the science, technology and equipment such as diagnostics, cryogenic target manipulator and user optics required for ignition experiments. Participants in this effort include LLNL, General Atomics, Los Alamos National Laboratory, Sandia National Laboratory and the University of Rochester Laboratory for Energetics (LLE). The primary goal for NIC is to have all of the equipment operational and integrated into the facility soon after project completion and to conduct a credible ignition campaign in 2010. When the NIF is complete, the long-sought goal of achieving self-sustaining nuclear fusion and energy gain in the laboratory will be much closer to realization.Successful demonstration of ignition and net energy gain on NIF will be a major step towards demonstrating the feasibility of inertial fusion energy (IFE) and will likely focus the world's attention on the possibility of an ICF energy option. NIF experiments to demonstrate ignition and gain will use central-hot-spot (CHS) ignition, where a spherical fuel capsule is simultaneously compressed and ignited. The scientific basis for CHS has been intensively developed (Lindl 1998 Inertial Confinement Fusion: the Quest for Ignition and Energy Gain Using Indirect Drive (New York: American Institute of Physics)) and has a high probability of success. Achieving ignition with CHS will open the door for other advanced concepts, such as the use of high-yield pulses of visible wavelength rather than ultraviolet and fast ignition concepts (Tabak et al 1994 Phys. Plasmas 1 1626–34, Tabak et al 2005 Phys. Plasmas 12 057305). Moreover, NIF will have important scientific applications in such diverse fields as astrophysics, nuclear physics and materials science.This paper summarizes the design, performance and status of NIF, experimental plans for NIC, and will present laser inertial confinement fusion–fission energy (LIFE) as a path to achieve carbon-free sustainable energy.

Comparison of Potential Ceramic Gain Media

The real advantage of the laser driver as compared to other drivers is its ability to provide a high quality focal spot on target. Heat generation in solid-state media has always been recognized as a limiting feature because at high repetition rate, the quality of this focal spot depends on the beam wave-front distortions. It is not easy to design the driver baseline because there are too many different parameters to deal with. In this paper, we introduce two figures of merit that show that Yb doped ceramics (either garnets or sesquioxides) are promising laser materials opening new fields during the research phase to demonstrate ignition and fusion gain (including the fast ignitor concept). When driven at low temperature (cryogenic cooling), all of the operational features of the laser amplifier can be demonstrated at an aperture scale of only 10-15 cm.

Fast ignition by detonation in a hydrodynamic flow

A general concept of fast ignition by a hydrodynamic pulse is developed. The main statements of the concept are formulated having in mind the need to ignite the pre-compressed thermonuclear fuel of the inertial confinement fusion (ICF) target. Initially, combustion must be initiated inside the hydrodynamic flow during its action on the target. The conditions for propagating a self-sustaining thermonuclear-detonation wave from an igniter on the thermonuclear fuel of the ICF-target must be provided. For this, the deuterium–tritium (DT) igniter placed in the forward part of the hydrodynamic flow should not only be heated up to thermonuclear temperature, but also compressed to a density close to the density of the ICF-target fuel. It is shown that the detonation of the multilayer conical target (containing DT-ice and a heavy pusher) enables fast ignition of the ICF target fuel of 200–500 g/cm3 density at an implosion velocity of 300–500 km/s.

A simulation study of fast ignition with ultrahigh intensity lasers

The coupling efficiency between the ignition laser and the target core for the fast ignition concept is studied using two-dimensional particle-in-cell simulations. The details of the energy transport within the weakly collisional overdense plasma of a fast ignition target are examined by performing a series of particle-in-cell simulations, where the intensity incident on a 100 times critical plasma with 50 μm radius is varied between each simulation. The simulations show that the peak energy flux of the ignition electrons is significantly lowered as the electrons traverse the collisionless plasma from the critical density through a weakly collisional overdense plasma region. This allows higher intensity lasers to be used thereby improving the coupling efficiency. In addition, we find that a higher percentage of the ignition laser energy is delivered to the core of the simulation target at higher intensity. The coupling efficiency increases in time during the simulations which are run for 2.5 ps. For a laser intensity of 8×1020 W/cm2 the simulations indicate that more than 15% of the incident laser energy is eventually absorbed in a dense plasma core.

Anomalous energy dissipation of electron current pulses propagating through an inhomogeneous collisionless plasma medium

The evolution of fast rising electron current pulses propagating through an inhomogeneous plasma has been studied through electron magnetohydrodynamic fluid simulations. A novel process of anomalous energy dissipation and stopping of the electron pulse in the presence of plasma density inhomogeneity is demonstrated. The electron current essentially dissipates its energy through the process of electromagnetic shock formation in the presence of density inhomogeneity. A direct relevance of this rapid energy dissipation process to the fast ignition concept of laser fusion is shown.

Observation of the transient charging of a laser-irradiated solid

The proton radiography technique has been used to investigate the incidence of a 3 ×1019 W/cm2 infrared pulse with a 125 μm-diameter gold wire. The laser interaction is observed to drive the growth of a radial electric field ∼ 1010 V/m on the surface of the wire which rises and decays over a temporal window of 20 ps. Such studies of the ultrafast charging of a solid irradiated at high-intensity may be of relevance to schemes for laser-driven ion acceleration and the fast-ignitor concept for inertial confinement fusion.

Review on the current status and prospects of fast ignition in fusion targets driven by intense, laser generated proton beams

The concept of fast ignition (FI) in fusion targets is a technique to significantly reduce the constraints to the driving laser or ion beam systems and to simultaneously enhance the gain of the fusion reaction. FI by intense beams of electrons meanwhile has been investigated over the last two decades. Since the discovery of intense laser-driven proton and ion beams the idea has been introduced using those beams to ignite a pre-compressed fusion target. At the 10th Workshop of Fast Ignition on Fusion Targets the current status and the prospects of proton fast ignition have been reviewed.