Controlled Fusion: Comparative Insights into Magnetic Confinement and Laser-Driven Technics

This book is a collection of papers, written by specialists in the field, on advanced topics of nuclear fusion diagnostics. The 78 contributions were originally presented at the International Conference on Advanced Diagnostics for Magnetic and Inertial Fusion held at Villa Monastero, Italy in September 2001. Both magnetically confined and inertial fusion programmes are quite extensively covered, with more emphasis given to the former scheme. In the case of magnetic confinement, since the present international programme is strongly focused on next-step devices, particular attention is devoted to techniques and technologies viable in an environment with strong neutron fluxes. Indeed, in the first section, the various methods are considered in the perspective of performing the measurements of the relevant parameters in conditions approaching a burning plasma, mainly in the Tokamak configuration. The most demanding requirements, like the implications of the use of tritium and radiation resistance, are reviewed and the most challenging open issues, which require further research and development, are also clearly mentioned.The following three sections are devoted to some of the most recent developments in plasma diagnostics, which are grouped according to the following classification: `Neutron and particle diagnostics', `Optical and x-ray diagnostics' and `Interferometry, Polarimetry and Thomson Scattering'. In these chapters, several of the most recent results are given, covering measurements taken on the most advanced experiments around the world. Here the developments described deal more with the requirements imposed by the physical issues to be studied. They are therefore more focused on the approaches adopted to increase the spatial and time resolution of the diagnostics, on some methods to improve the characterisation of the turbulence and on fast particles. Good coverage is given to neutron diagnostics, which are assuming increasing relevance as the plasma parameters approach ignition. Spectroscopic systems and their recent developments are well represented, whereas edge diagnostics are somewhat thin on the ground. A dedicated section is devoted to the latest tests on radiation effects and technological issues. The problems of damage to optical components and the difficulties presented by the determination of the tritium inventory are described.In the last part, the new diagnostic systems of the most recent experiments (under construction or recently operated) are reported. Various aspects of some diagnostics not included in the three previous sections are also covered, with particular emphasis on microwaves and infrared diagnostics.The book is well suited for specialists and, more generally, for people involved in nuclear fusion, who need information about the most recent developments in the field of plasma diagnostics. The papers cover many aspects of the challenges and possible solutions for performing measurements in fusion machines approaching reactor conditions. On the other hand, the contributions are in general quite advanced and would be challenging for people without a significant background in plasma diagnostics and nuclear fusion. The quality of the paper is more than satisfactory both from the point of view of clarity and of graphics. Moreover, at the beginning of the book, several papers make a considerable effort to put diagnostic issues in the wider context of present day nuclear fusion research. For those topics, which are too involved to be completely described in a conference contribution, in general adequate references are provided for deeper investigation.A MurariApproximately one third of the papers included in this volume deal with diagnostics related to inertial confinement fusion plasmas (i.e., laser-produced plasmas and pulsed-power). These papers discuss recent developments in charged particle diagnostics, neutron diagnostics, optical and x-ray measurements along with laser and particle probing diagnostics. The resulting collection of papers is comprehensive and wide-ranging and all of the major laboratories in Europe, the US, and Japan are represented. There is important discussion on the development of diagnostics for the National Ignition Facility, LMJ, and future ultra-high intensity laser experiments as well as papers on wire array z-pinch experiments. It is especially useful to have the contributions from inertial confinement fusion experiments intermingled with those from magnetic confinement fusion. The separation between these two approaches to fusion is often unfortunately large, so one of the pleasing things about this book is that it is very easy for readers familiar with experimental research in one area to compare `state of the art' plasma diagnostics in the other area. Hopefully this will facilitate the development of new ideas in both areas. This book is a conference proceedings and as such, almost all of the papers included are quite brief and are highly technical. Consequently, the book is not particularly pedagogical and would be most useful to researchers already working in this area of physics. For these readers, however, Advanced Diagnostics for Magnetic and Inertial Confinement Fusion is an excellent overview of the present status of fusion plasma diagnostics.K Krushelnick

The Workshop: Facts and Outcome

Inertial Confinement Fusion and Magnetic Confinement Fusion (ICF and MCF) follow different paths toward goals that are largely common. In this paper, the claim is made that progress can be accelerated by learning from each other across the two fields. Examples of successful cross-community knowledge transfer are presented that highlight the gains from working together, specifically in the areas of high-resolution x-ray imaging spectroscopy and neutron spectrometry. Opportunities for near- and mid-term collaboration are identified, including in chemical vapor deposition diamond detector technology, using gamma rays to monitor fusion gain, handling neutron-induced backgrounds, developing radiation hard technology, and collecting fundamental supporting data needed for diagnostic analysis. Fusion research is rapidly moving into the igniting and burning regimes, posing new opportunities and challenges for ICF and MCF diagnostics. This includes new physics to probe, such as alpha heating; increasingly harsher environmental conditions; and (in the slightly longer term) the need for new plant monitoring diagnostics. Substantial overlap is expected in all of these emerging areas, where joint development across the two subfields as well as between public and private researchers can be expected to speed up advancement for all.

Differences between neutron damage in inertial and magnetic confinement fusion materials test facilities

As far as is known, nuclear fusion is the primary source of energy in the universe. It occurs when the nuclei of lighter elements, such as hydrogen, are fused together at extremely high temperatures and pressure to form heavier elements, such as helium. Whereas practical methods for harnessing fusion reactions and realizing the potential of this energy source have been sought since the 1950s, achieving the benefits of power from fusion has proved to be a difficult, long‐term challenge. Fusion is widely held to be the ultimate resource for the world's long‐term energy needs. The fuel reserves for fusion are virtually limitless and available to all countries. Fusion fuels can be extracted from water. Fusion promises to be an energy source which is potentially safe and environmentally benign. Radiological and proliferation hazards are much smaller than for fission power plants. The atmospheric impact is negligible compared to fossil fuels, and adverse impacts on the Earth's ecological and geophysical processes are smaller than for large‐scale renewable energy sources. The economics and costs of fusion power plants are still being studied, but appear comparable to those for other medium‐ and long‐term energy sources. The promise of affordable essentially unlimited supplies of clean, safe energy, free of political boundaries, has motivated a world‐wide research effort to develop this energy resource. The reactions of deuterium, tritium, and helium‐3, 3 He, having nuclear charges of 1, 1, and 2, respectively, are the easiest to initiate. These have the highest fusion reaction probabilities and the lowest reactant energies. Two diverse technical approaches to fusion power, magnetic confinement fusion, also known as magnetic fusion energy (MFE) and inertial confinement fusion, also known as inertial fusion energy (IFE) are being pursued worldwide. These form the basis of a large number of fusion research programs. Fusion energy research is also the primary avenue for the development of plasma physics as a scientific discipline.

Geometrical and spectral differences between inertial confinement fusion (ICF) and magnetic confinement fusion (MCF) facilities lead to significant variation of up to ∼ 60% in peak values and profiles of the time averaged blanket nuclear parameters for the same first wall exposure. Simple scaling of radiation effects with neutron wall loading is inappropriate. These effects together with the temporal effects, that result in ∼ 5 to 8 orders of magnitude higher instantaneous reaction rates in the pulsed ICF reactors, lead to significantly different blanket performances in the ICF and MCF reactor environments.

The paper reviews the present status of the available key technologies for implosion experiments as regards the energy driver, pellet fabrication, diagnostics of dense and hot plasmas, and numerical simulations. It is shown that the development of the necessary conditions is well advanced so that it is now possible to proceed to the next step in the achievement of ignition and break-even. Various design studies for inertial confinement fusion reactors are also reviewed; from these studies it has become clear that inertial confinement fusion and magnetic confinement fusion are technologically complementary systems for future fusion reactors.

Currently, laboratory created energy density of laser-driven inertial confinement fusion (ICF) is extremely close to that for ignition, while the divergence between experiment and simulation is increasing. One of the key issues is the lack of advanced knowledge of laser-hohlraum coupling process, which has shown the complexity of hohlraum environment. Optical Thomson scattering (OTS) becomes the standard technique for diagnosing the ICF hohlraum plasma parameters, due to its capability of providing unperturbed, local and precise measurement. The development of OTS in China is closely related with the Shenguang series laser facilities, on which most of the ICF experiments are carried out. In recent years, 4ω(263 nm) Thomson scattering technique has been set up on Shenguang-III prototype and 100 kJ-level laser facility, the corresponding results help the understanding of ICF physics. In the near future, several novel methods will be developed, for high-precision diagnostics of ICF ignition hohlraum plasmas and the research of new physical phenomena.

Vladislav Nikolaevich Mokhov, an outstanding scientist, Doctor of Science in Physics and Mathematics, professor, died on December 27, 2011 after long time of severe disease. Before this illness he was Deputy Scientific Leader of the All-Russian Research Institute of Experimental Physics (VNIIEF). V.N. Mokhov was born on April 12, 1931 in the town of Atkarsk, Saratov region, Russia. In 1955, after graduation from the Moscow Engineering Physics Institute, he in a group of the most brilliant and talented young theoreticians was selected by Academicians Ya.B. Zel'dovich and A.D. Sakharov for work on the nuclear weapons program at VNIIEF. In 1963, he was awarded the Lenin Prize for the development of new principles and new approaches to nuclear and thermonuclear weapons design and controlled fusion; in 1964, he received the degree of Candidate of Science, and four years later, the degree of Doctor of Science. V.N. Mokhov was always inspired by challenging projects that required teamwork of theoreticians, designers, and experimentalists. His major scientific and practical results include: Development of the theory of turbulent mixing in layered structures at intense compression. The results obtained are relevant for studying the processes occurring in inertial confinement fusion (ICF) targets.; Ignition of thermonuclear fuel by its heating with fast compression, which was and continues to be very important for the development of a number of special-purpose nuclear charges and fusion targets.; Development of “clean” nuclear charges for peaceful applications (jointly with the team of colleagues).; The new approach to the controlled thermonuclear fusion - the MAGO (MAGnitnoye Obzhatiye, or magnetic compression) - was proposed and developed jointly with his team. V.N. Mokhov considered MAGO to be a system that now made it possible to achieve the scientific breakeven point for fusion without the large initial capital investment that is required by the two more conventional approaches, magnetic confinement fusion and ICF.; Investigation of physical properties of materials at high energy densities provided by explosive magnetic flux compression generators (EMG). Jointly with his team, V.N. Mokhov proposed and developed methods of this investigation, obtained novel results on dynamic strength of a number of materials (aluminum, copper, polyethylene). In 1998, he and some of his colleagues were awarded the RF Government Prize for the development of EMGs and their application for scientific investigations. V.N. Mokhov was one of the pioneers of scientific cooperation between US and Russian nuclear laboratories. This mutually beneficial cooperation between the two countries produced extremely interesting scientific results obtained during joint research activities, including more than 20 series of experiments, and published in more than 400 papers and presentations. Equally important is that he was a true friend of many US scientists, and this friendship between people from different countries and trust in each other made the world better. V.N. Mokhov was a very interesting person having his original opinion on nearly any issue - whether related to science, history or politics. Many of his ideas on these issues were reflected in his papers available to a broad public and in his book “Nuclear Weapons and Safe Stable World. These ideas were extremely up-to-date in due time, and they continue to be relevant these days.

On October 24, 2021, the Chinese government unveiled a guiding document about state-level work to achieve carbon peaking and carbon neutrality goals under a new development philosophy, laying out key targets and measures for upcoming decades. The documment, titled “Working Guidance For Carbon Dioxide Peaking and Carbon Neutrality In Fully And Faithful Implementation Of The New Development Philosophy.” stated that China's carbon dioxide emissions per unit GDP would have dropped by 18% from the level in 2020 by 2025 and by more than 68% from the level in 2005 by 2030. Fusion energy, as an environment-friendly and intrinsically safe energy source with an abundant fuel supply, is considered an effective low-carbon ultimate solution. Fusion research has been conducted for 60 years, and has been demonstrated that magnetic confinement controlled fusion is very effective magnetic confinement fusion research has progressed significantly over the years. Generally, it is believed in the magnetic confinement fusion plasma community that the next pivotal step in magnetic confinement fusion plasma research is to create burning plasma, where the dominant method of heating plasmas is alpha particle self-sustaining heating. The research aims to understand the underlying physics of the confinement, heating, and instability of burning plasma and to explore the technologies associated with the power-producing fusion reactor. In future burning plasmas, multiple mode-number instabilities are very important but complicated physics issues because of the employment of strong power auxiliary heating schemes. Compared with the time-consuming large-scale computer simulation, the machine learning can bring an advantage for the investigations concerning multiple mode-number instabilities, especially in predictions compared to the time-consuming large-scale computer simulation.

The issue of laser plasma instabilities (LPIs) including stimulated Raman scattering, stimulated Brillouin scattering and so on is one of the most fascinating subjects in laser plasma physics. In particular, LPIs may cause significant laser energy loss and produce hot electrons to preheat fusion targets, which affect target compression and fusion energy gain in laser-driven inertial confinement fusion. Recent experiments carried out on the National Ignition Facility, the largest laser facility in the world for laser fusion, indicate that the understanding and the control of LPIs are essential to the realization of laser fusion. In this paper, we present a review on recent studies of LPIs. Firstly, we retrospect the classical theoretical model of LPIs, which offers a good estimation of growth rate in the linear development stage. Then, we discuss some progresses on the understanding of LPIs in more complex and real scenarios, such as LPI development in the nonlinear regions, cascaded LPIs, multi-beam LPIs, and nonlinear couplings between LPIs. Following the exploration of LPI physics, we emphasize on the strategies for the control of LPIs, including beam smoothing techniques, temporal profile shaping, broadband laser, laser polarization rotation, external magnetic field and so on.

The Laser Inertial Confinement Fusion Fission Energy (LIFE) Program being developed at Lawrence Livermore National Laboratory (LLNL) aims to design a hybrid fission-fusion subcritical nuclear engine that uses a laser-driven Inertial Confinement Fusion (ICF) system to drive a subcritical fission blanket. This combined fusion-fission hybrid system could be used for generating electricity, material transmutation or incineration, or other applications. LIFE does not require enriched fuel since it is a sub-critical system and LIFE can sustain power operation beyond the burnup levels at which typical fission reactors need to be refueled. In light of these factors, numerous options have been suggested and are being investigated. Options being investigated include fueling LIFE engines with spent nuclear fuel to aid in disposal/incineration of commercial spent nuclear fuel or using depleted uranium or thorium fueled options to enhance proliferation resistance and utilize non-fissile materials [1]. LIFE engine blanket designs using a molten salt fuel system represent one area of investigation. Possible applications of a LIFE engine with a molten salt blanket include uses as a spent nuclear fuel burner, fissile fuel breeding platform, and providing a backup alternative to other LIFE engine blanket designs using TRISO fuel particles in case the TRISO particles are found to be unable to withstand the irradiation they will be subjected to. These molten salts consist of a mixture of LiF with UF{sub 4} or ThF{sub 4} or some combination thereof. Future systems could look at using PuF{sub 3} or PuF{sub 4} as well, though no work on such system with initial plutonium loadings has been performed for studies documented in this report. The purpose of this report is to document preliminary neutronics design studies performed to support the development of a molten salt blanket LIFE engine option, as part of the LIFE Program being performed at Lawrence Livermore National laboratory. Preliminary design studies looking at fast ignition and hot spot ignition fusion options are documented, along with limited scoping studies performed to investigate other options of interest that surfaced during the main design effort. Lastly, side studies that were not part of the main design effort but may alter future work performed on LIFE engine designs are shown. The majority of all work reported in this document was performed during the Molten Salt Fast Ignition Moderator Study (MSFIMS) which sought to optimize the amount of moderator mixed into the molten salt region in order to produce the most compelling design. The studies in this report are of a limited scope and are intended to provide a preliminary neutronics analysis of the design concepts described herein to help guide decision processes and explore various options that a LIFE engine with a molten salt blanket might enable. None of the designs shown in this report, even reference cases selected for detailed description and analysis, have been fully optimized. The analyses were performed primarily as a neutronics study, though some consultation was made regarding thermal-hydraulic and structural concerns during both scoping out an initial model and subsequent to identifying a neutronics-based reference case to ensure that the design work contained no glaring mechanical or thermal issues that would preclude its feasibility. Any analyses and recommendations made in this report are either primarily or solely from the point of view of LIFE neutronics and ignore other fundamental issues related to molten salt fuel blankets such as chemical processing feasibility and political feasibility of a molten salt system.

In laser-driven inertial confinement fusion (ICF) specifically with high laser intensities, energetic (hot) electrons (HEs) can be generated via laser-plasma instabilities. HEs can significantly impact the target performance by modifying the implosion hydrodynamics. In this paper, the effects of moderate-energy (about 20 to 40 keV) HEs on the evolution of two-dimensional single-mode ablative Rayleigh–Taylor instability (ARTI) are studied through numerical simulations with a multigroup diffusion model in which the HE population is treated as a high-energy group launched from the boundary. With HEs present, it is found that ARTI linear growth rates are reduced even though the acceleration of the implosion shell is enhanced by HEs. The reduction in the linear growth rate is owing to the increase in the ablation velocity and the density scale length, and this stabilization effect is greater in the shorter-wavelength modes and/or higher-energy HE cases. The ARTI linear growth does not get mitigated monotonically as the HE number density increases for a given fixed HE kinetic energy. The HE number density minimizing the ARTI growth rate is found, likely due to the competition of the stabilizing and destabilizing hydrodynamic-parameter variations caused by HEs.

Beam positioning stability in a laser-driven inertial confinement fusion (ICF) facility is a vital problem that needs to be fixed. Each laser beam in the facility is transmitted in lots of optics for hundreds of meters, and then targeted in a micro-sized pellet to realize controllable fusion. Any turbulence in the environment in such long-distance propagation would affect the displacement of optics and further result in beam focusing and positioning errors. This study concluded that the errors on each of the optics contributed to the target, and it presents an efficient method of enhancing the beam stability by eliminating errors on error-sensitive optics. Optimizations of the optical system and mechanical supporting structures are also presented.

Aiming at the requirement of illumination uniformity and backscattering suppression in laser-driven inertial confinement fusion (ICF) facilities, we propose a polarization smoothing (PS) scheme based on stress-engineered optical element that can modulate linearly polarized light into a full Poincare beam. The unique law of modulation of the polarization state by glass window under symmetrical loads is revealed by numerical simulations, the results indicate that the glass window exhibits a fast axis orientation that rotates with the polar angle and a phase retardance that increases with the radius under more than two symmetrical pressure loads. Further optical calculations show that when the pressure of the loads and the thickness of the glass are sufficient, the window can modulate the linearly polarized light into a full Poincarebeam.