Deep Learning Models to Reduce Stray Light in TJ-II Thomson Scattering Diagnostic.

Nuclear fusion is a potential source of energy that could supply the growing needs of the world population for millions of years. Several experimental thermonuclear fusion devices try to understand and control the nuclear fusion process. A very interesting diagnostic called Thomson scattering (TS) is performed in the Spanish fusion device TJ-II. This diagnostic takes images to measure the temperature and density profiles of the plasma, which is heated to very high temperatures to produce fusion plasma. Each image captures spectra of laser light scattered by the plasma under different conditions. Unfortunately, some images are corrupted by noise called stray light that affects the measurement of the profiles. In this work, we propose the use of deep learning models to reduce the stray light that appears in the diagnostic. The proposed approach utilizes a Pix2Pix neural network, which is an image-to-image translation based on a generative adversarial network (GAN). This network learns to translateimages affected by stray light to images without stray light. This allows for the effective removal of the noise that affects the measurements of the TS diagnostic, avoiding the need for manual image processing adjustments. The proposed method shows a better performance, reducing the noise up to 98% inimages, which surpassesprevious works that obtained 85% for the validation dataset.

Frontiers in the Application of RF Vacuum Electronics.

The application of radio frequency (RF) vacuum electronics for the betterment of the human condition began soon after the invention of the first vacuum tubes in the 1920s and has not stopped since. Today, microwave vacuum devices are powering important applications in health treatment, material and biological science, wireless communication-terrestrial and space, Earth environment remote sensing, and the promise of safe, reliable, and inexhaustible energy. This article highlights some of the exciting application frontiers of vacuum electronics.

Factors influencing the commercialization of inertial fusion energy.

Managing the IFE pathway to fusion electricity will involve management of commericalization scope, schedule, cost and risk. The technology pathway to economical fusion power comprises the commercialization scope. Industry assumes commercialization risk in fielding its own pre-pilot plant research programme for this compact-fusion pathway without the benefit of a federally coordinated IFE research and development programme. The cost of commercializing the mass-production of inexpensive targets and insisting on high reliability, availability, maintainability and inspectability has a major impact on the economics of commercializing fusion power plants. Schedule vulnerability for inertial fusion energy arises from the sensitivity of time-based roadmap stages to uncertainties in the pace of scientific understanding and technology development, as well as to unexpected and inexplicable changes of the budgeting process. Rather than rely on a time-based roadmap, a milestone-based roadmap is maximally appropriate, especially for industry and investors who are particularly well-suited to taking the risks associated with reaching the target milestones provided by the government. Milestones must be identified and optimally sequenced and the necessary resources must be delineated. Progress on the above factors, since the outcomes of recent U.S., U.K. and EUROfusion roadmapping exercises were released, are reported. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.

Prospects for high gain inertial fusion energy: an introduction to the second edition.

Part II of this special edition contains the remaining 11 papers arising from a Hooke discussion meeting held in March 2020 devoted to exploring the current status of inertial confinement fusion research worldwide and its application to electrical power generation in the future, via the development of an international inertial fusion energy programme. It builds upon increased coordination within Europe over the past decade by researchers supported by the EUROFusion Enabling Research grants, as well as collaborations that have arisen naturally with some of America's and Asia's leading researchers, both in the universities and national laboratories. The articles are devoted to informing an update to the European roadmap for an inertial fusion energy demonstration reactor, building upon the commonalities between the magnetic and inertial fusion communities' approaches to fusion energy. A number of studies devoted to understanding the physics barriers to ignition on current facilities are then presented. The special issue concludes with four state-of-the-art articles describing recent significant advances in fast ignition inertial fusion research. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.

Preparations for a European R&D roadmap for an inertial fusion demo reactor.

A European consortium of 15 laboratories across nine nations have worked together under the EUROFusion Enabling Research grants for the past decade with three principle objectives. These are: (a) investigating obstacles to ignition on megaJoule-class laser facilities; (b) investigating novel alternative approaches to ignition, including basic studies for fast ignition (both electron and ion-driven), auxiliary heating, shock ignition, etc.; and (c) developing technologies that will be required in the future for a fusion reactor. A brief overview of these activities, presented here, along with new calculations relates the concept of auxiliary heating of inertial fusion targets, and provides possible future directions of research and development for the updated European Roadmap that is due at the end of 2020. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.

Political and commercial prospects for inertial fusion energy.

Fusion energy holds the prospect of an energy source that is clean, safe, affordable and limitless. It will transform the global energy system. Today, around $1.5 billion in private capital has been invested in companies that are working on transformative approaches to fusion. Annually, even more than that is spent on fusion research by governments around the world. However, just achieving a scientific demonstration of fusion power will not be enough on its own to transition the global energy system. It will require innovations in the legal, regulatory, commercial and political spheres to support the massive deployment of fusion power that we know will be necessary to meet the global challenges of climate change and energy scarcity. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 1)'.

Direct drive with the argon fluoride laser as a path to high fusion gain with sub-megajoule laser energy.

Argon fluoride (ArF) is currently the shortest wavelength laser that can credibly scale to the energy and power required for high gain inertial fusion. ArF's deep ultraviolet light and capability to provide much wider bandwidth than other contemporary inertial confinement fusion (ICF) laser drivers would drastically improve the laser target coupling efficiency and enable substantially higher pressures to drive an implosion. Our radiation hydrodynamics simulations indicate gains greater than 100 are feasible with a sub-megajoule ArF driver. Our laser kinetics simulations indicate that the electron beam-pumped ArF laser can have intrinsic efficiencies of more than 16%, versus about 12% for the next most efficient krypton fluoride excimer laser. We expect at least 10% 'wall plug' efficiency for delivering ArF light to target should be achievable using solid-state pulsed power and efficient electron beam transport to the laser gas that was demonstrated with the U.S. Naval Research Laboratory's Electra facility. These advantages could enable the development of modest size and lower cost fusion power plant modules. This would drastically change the present view on inertial fusion energy as being too expensive and the power plant size too large. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 1)'.

How might controlled fusion fit into the emerging low-carbon energy system of the mid-twenty-first century?

We examine the characteristics that fusion-based generation technologies will need to have if they are to compete in the emerging low-carbon energy system of the mid-twenty-first century. It is likely that the majority of future electric energy demand will be provided by the lowest marginal cost energy technology-which in many regions will be stochastically varying renewable solar and wind electric generation coupled to systems that provide up to a few days of energy storage. Firm low-carbon or zero-carbon resources based on gas-fired turbines with carbon capture, advanced fission reactors, hydroelectric and perhaps engineered geothermal systems will then be used to provide the balance of load in a highly dynamic system operating in competitive markets governed by merit-order pricing mechanisms that select the lowest-cost supplies to meet demand. These firm sources will have overnight capital costs in the range of a few $/Watt, be capable of cycling down to a fraction of their maximum power output, operate profitably at low utilization fraction, and have a suitable unit size of order 100 MWe. If controlled fusion using either magnetic confinement or inertial confinement approaches is to have any chance of providing a material contribution to future electrical energy needs, it must demonstrate these key qualities and at the same time prove robust safety characteristics that avoid the perceived dread risk that plagues nuclear fission power, avoid the generation of long-lived radioactive waste and demonstrate highly reliable operations. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 1)'.

Prospects for high gain inertial fusion energy: an introduction to the first special edition.

A European consortium of 15 laboratories across nine nations have worked together under the EUROFusion Enabling Research grants for the past decade with three principle objectives. These are: (a) investigating obstacles to ignition on megaJoule-class laser facilities; (b) investigating novel alternative approaches to ignition, including basic studies for fast ignition (both electron and ion-driven), auxiliary heating, shock ignition etc.; and (c) developing technologies that will be required in the future for a fusion reactor. The Hooke discussion meeting in March 2020 provided an opportunity to reflect on the progress made in inertial confinement fusion research world-wide to date. This first edition of two special issues seeks to identify paths forward to achieve high fusion energy gain. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 1)'.

Can the development of fusion energy be accelerated? An introduction to the proceedings.

This introduction reviews the unique opportunity of fusion power to deliver safe, carbon-free, abundant, base-load power. The differences from fission power are considered: especially why a Chernobyl, Three Mile Island or Fukushima accident could not happen with a fusion reactor. The Lawson triple product is introduced, along with tokamaks, or magnetic bottles, whose ability to approach close to the fusion burn conditions has so far put them above their competitors. Our last fusion power Discussion Meeting was organized by Derek Robinson FRS in 1998, and the progress since then is reviewed. Tokamaks are introduced, and the advantages of spherical tokamaks are listed along with the special engineering challenges that they introduce. Their key advantage is high plasma pressure, and the important ß parameter indicating the efficiency of the magnetic field use is introduced. High-temperature superconductors are described along with the opportunities they allow for higher magnetic fields at higher current densities and more modest cryogenic temperatures. The question posed is whether the two developments of spherical tokamaks and high-temperature superconductors could lead to more economical fusion power plants and faster development than the current route through ITER and DEMO. This article is part of a discussion meeting issue 'Fusion energy using tokamaks: can development be accelerated?'.

Small, modular and economically attractive fusion enabled by high temperature superconductors.

The advantages of high magnetic fields in tokamaks are reviewed, and why they are important in leading to more compact tokamaks. A brief explanation is given of what limits the magnetic field in a tokamak, and why high temperature superconductors (HTSs) are a game changer, not just because of their higher magnetic fields but also for reasons of higher current density and higher operating temperatures. An accelerated pathway to fusion energy is described, defined by the SPARC and ARC tokamak designs. This article is part of a discussion meeting issue 'Fusion energy using tokamaks: can development be accelerated?'.

Economic aspects of the deployment of fusion energy: the valley of death and the innovation cycle.

The speed at which fusion energy can be deployed is considered. Several economical factors are identified that impede this speed. Most importantly, the combination of an unprecedentedly high investment level needed for the proof of principle and the relatively long construction time of fusion plants precludes an effective innovation cycle. The valley of death is discussed, i.e. the period when a large investment is needed for the construction of early generations of fusion reactors, when there is no return yet. It is concluded that, within the mainstream scenario-a few DEMO reactors towards 2060 followed by generations of relatively large reactors-there is no realistic path to an appreciable contribution to the energy mix in the twenty-first century if economic constraints are applied. In other words, fusion will not contribute to the energy transition in the time frame of the Paris climate agreement. Within the frame of this analysis, the development of smaller, cheaper and most importantly, fast-to-build fusion plants could possibly represent an option to accelerate the introduction of fusion power. Whether this is possible is a technical question that is outside the scope of this paper, but this question is addressed in other contributions to the Royal Society workshop. This article is part of a discussion meeting issue 'Fusion energy using tokamaks: can development be accelerated?'.

An exploratory study on the possibilities of microalgal biotechnology to obtain the essential 6Li isotope as fusion fuel.

Future energy supply needs to overcome two challenges: environmental impact and dependence on geopolitically unstable countries. A very promising alternative is based on lithium, an element for batteries, and whose isotope 6Li will be essential in nuclear fusion. The objective of this research has been to determine if it is possible to achieve isotopic fractionation of lithium through a process mediated by microalgae. For this purpose, Chlamydomonas reinhardtii was selected and grown in presence of 5 mg/L of lithium. Results revealed that this specie survives at the selected lithium concentration, discriminates isotopes and preferentially capture 6Li (6δ = 10.029 ± 3.307) through a process independent of the cellular growth. Concomitate recovered up 0.206 mg/L of lithium along a process of 21 days. The result of this study lets to affirm that Chlamydomonas reinhardtii might be used to obtain lithium enriched in the lighter isotope.

Post-tetanic potentiation lowers the energy barrier for synaptic vesicle fusion independently of Synaptotagmin-1.

Previously, we showed that modulation of the energy barrier for synaptic vesicle fusion boosts release rates supralinearly (Schotten, 2015). Here we show that mouse hippocampal synapses employ this principle to trigger Ca2+-dependent vesicle release and post-tetanic potentiation (PTP). We assess energy barrier changes by fitting release kinetics in response to hypertonic sucrose. Mimicking activation of the C2A domain of the Ca2+-sensor Synaptotagmin-1 (Syt1), by adding a positive charge (Syt1D232N) or increasing its hydrophobicity (Syt14W), lowers the energy barrier. Removing Syt1 or impairing its release inhibitory function (Syt19Pro) increases spontaneous release without affecting the fusion barrier. Both phorbol esters and tetanic stimulation potentiate synaptic strength, and lower the energy barrier equally well in the presence and absence of Syt1. We propose a model where tetanic stimulation activates Syt1-independent mechanisms that lower the energy barrier and act additively with Syt1-dependent mechanisms to produce PTP by exerting multiplicative effects on release rates.

An integrated digital framework for the design, build and operation of fusion power plants.

The development of a commercial fusion power plant presents a unique set of challenges associated with the complexity of the systems, the integration of novel technologies, the likely diversity and distribution of the organizations involved, and the scale of resources required. These challenges are reviewed and compared to those for other complex engineering systems. A framework for creating a digital environment that integrates research, test, design and operational data is discussed and is based on combining the integrated nuclear digital environment (INDE), proposed recently for nuclear fission power plants, with the hierarchical pyramid of test and simulation used in the aerospace industry. The framework offers the opportunity to plan modelling strategies that allow large design domains to be explored prior to optimizing a detailed design for construction; and in this context, the relationship between measurements and predictions are explored. The use of the framework to guide the socio-technical activity associated with a distributed and collaborative design process is discussed together with its potential benefits and the technology gaps that need to be addressed in order to realize them. These benefits include shorter development times, reduced costs and improvements in credibility, operability, reliability and safety.

Additive effects on the energy barrier for synaptic vesicle fusion cause supralinear effects on the vesicle fusion rate.

The energy required to fuse synaptic vesicles with the plasma membrane ('activation energy') is considered a major determinant in synaptic efficacy. From reaction rate theory, we predict that a class of modulations exists, which utilize linear modulation of the energy barrier for fusion to achieve supralinear effects on the fusion rate. To test this prediction experimentally, we developed a method to assess the number of releasable vesicles, rate constants for vesicle priming, unpriming, and fusion, and the activation energy for fusion by fitting a vesicle state model to synaptic responses induced by hypertonic solutions. We show that complexinI/II deficiency or phorbol ester stimulation indeed affects responses to hypertonic solution in a supralinear manner. An additive vs multiplicative relationship between activation energy and fusion rate provides a novel explanation for previously observed non-linear effects of genetic/pharmacological perturbations on synaptic transmission and a novel interpretation of the cooperative nature of Ca(2+)-dependent release.