Fusion power

Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion reactions. In a fusion process, two lighter atomic nuclei combine to form a heavier nucleus, while releasing energy. Devices designed to harness this energy are known as fusion reactors. Research into fusion reactors began in the 1940s, but as of 2023, no device has reached net power. Fusion processes require fuel and a confined environment with sufficient temperature, pressure, and confinement time to create a plasma in which fusion can occur. The combination of these figures that results in a power-producing system is known as the Lawson criterion. In stars, the most common fuel is hydrogen, and gravity provides extremely long confinement times that reach the conditions needed for fusion energy production. Proposed fusion reactors generally use heavy hydrogen isotopes such as deuterium and tritium (and especially a mixture of the two), which react more easily than protium (the most common hydrogen isotope), to allow them to reach the Lawson criterion requirements with less extreme conditions. Most designs aim to heat their fuel to around 100 million degrees, which presents a major challenge in producing a successful design. As a source of power, nuclear fusion has a number of potential advantages compared to fission. These include reduced radioactivity in operation, little high-level nuclear waste, ample fuel supplies, and increased safety. However, the necessary combination of temperature, pressure, and duration has proven to be difficult to produce in a practical and economical manner. A second issue that affects common reactions is managing neutrons that are released during the reaction, which over time degrade many common materials used within the reaction chamber. Fusion researchers have investigated various confinement concepts. The early emphasis was on three main systems: z-pinch, stellarator, and magnetic mirror. The current leading designs are the tokamak and inertial confinement (ICF) by laser.

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Summary

Study of impurity ion transport using charge exchange spectroscopy on TCV

Filippo Bagnato

The study of impurity transport in fusion plasmas has gained interest over the years due to its implication with tokamak performances. In TCV (Tokamak à Configuration Variable), as in many other facilities, impurity ions can be studied through the CXRS (Charge Exchange Recombination Spectroscopy) diagnostic.The following research plan first presents the principles of CXRS. The main components of the diagnostic are described, as well as the data analysis methods used to infer ion temperature, density and velocity radial profiles. One of the main goals of the thesis is to measure accurate density profiles. Many transport models, in fact, are still developed without a consistent prediction of the density profile, which in many cases is assumed flat. In recent years, however, experiments have been performed to study ion transport in various plasma scenarios with the aim of providing a conncetion between theoretical predictions and actual measurements.This works present a study of impurity transport in negative triangularity. A large part of the thesis is dedicated to the investigation of the LOC/SOC transition and the rotation reversal, two phenomena often observed during density ramps that, in specific cases, appear to occur at the same critical density. This work shows a clear separation of the two phenomena, with an extensive study performed in discharges of different majority species (D, H, He), plasma configurations and shapes (limited, diverted, positive and negative triangularity).

EPFL2022

Heavy impurity transport in the presence of 3D MHD ideal perturbations

Eduardo José Lascas Neto

Heavy impurity accumulation poses a problem for the operation of tokamaks featuring tungsten plasma facing components. Early termination of the plasma due to tungsten accumulation is often observed following long living 3D MHD perturbations. Such scenarios areoften observed in present tokamaks like JET and ASDEX-U, and may be of concern for futuremachines like ITER and the European DEMO. Finding a way of designing high performancescenarios while preventing tungsten accumulation is therefore crucial. This thesis aims atunderstanding and modelling heavy impurity transport in tokamak plasmas in the presenceof long living 3D MHD ideal perturbations. In the first part of the thesis, we develop thetheoretical framework to treat the problem, building on stellarator theory for the main ions,while including the effect of strong toroidal rotation that is only present in tokamaks. Theorderings of the background ion species and the heavy impurity species are developed indetail. The background ions are subsonic which allows for the calculation of their flows usingthe stellarator 1/Îœ collisional regime, while the heavy impurities flow supersonically whichrequires the inclusion of centrifugal effects for the impurity description. An expression forthe neoclassical heavy impurity flux is obtained which helps identify the contrasting physicsinvolved. In the second part of the thesis, we present the development of the numerical toolsused to model the problem according to the theoretical framework presented. The usage ofthe VMEC code to obtain suitable 3D MHD equilibria is explained. Also, the development ofnew codes for calculating the background ion and heat flux flow of the ions, and the impurityflow from such magnetic equilbria is described. The heavy impurities are followed in thisbackground plasma using the VENUS-LEVIS code. This code describes the guiding-centermovement of the heavy impurities, accounting for the centrifugal and Coriolis drifts, as wellas for the correct effect of friction and thermal forces exerted by the background ions onthe impurities through a newly implemented collision operator. Finally, the numerical toolsdeveloped in this thesis are used to model the impact of long living 1/1 internal kink modeson heavy impurity transport. Heavy impurity accumulation is observed to occur rapidly inthe presence of a 1/1 internal kink mode, contrary to what is observed in axisymmetry, inwhich off-axis accumulation occurs due to the strong rotation. These cases agree well witha JET pulse where tungsten accumulates following rapid growth of a continuous 1/1 mode.In the weakly 3D phase of the pulse, off-axis accumulation of tungsten is observed, whilstin the strong 3D phase of the pulse, strong tungsten on-axis accumulation is observed. Thetheoretical developments allow us to break down all the relevant physics effects. It is seen thatsuch on-axis accumulation is due to the synergetic effect of the 1/1 mode, the strong toroidalrotation and the NTV ambipolar electric field.

EPFL2022

Magnetic control of tokamak plasmas through deep reinforcement learning

Olivier Sauter, Ambrogio Fasoli, Basil Duval, Stefano Coda, Jean-Marc Moret, Federico Alberto Alfredo Felici, Cristian Sommariva, Antoine Pierre Emmanuel Alexis Merle, Cristian Galperti, Francesco Carpanese, Jonas Buchli, Federico Pesamosca, Brendan Tracey, Jonas Degrave

Nuclear fusion using magnetic confinement, in particular in the tokamak configuration, is a promising path towards sustainable energy. A core challenge is to shape and maintain a high-temperature plasma within the tokamak vessel. This requires high-dimensional, high-frequency, closed-loop control using magnetic actuator coils, further complicated by the diverse requirements across a wide range of plasma configurations. In this work, we introduce a previously undescribed architecture for tokamak magnetic controller design that autonomously learns to command the full set of control coils. This architecture meets control objectives specified at a high level, at the same time satisfying physical and operational constraints. This approach has unprecedented flexibility and generality in problem specification and yields a notable reduction in design effort to produce new plasma configurations. We successfully produce and control a diverse set of plasma configurations on the Tokamak à Configuration Variable1,2, including elongated, conventional shapes, as well as advanced configurations, such as negative triangularity and ‘snowflake’ configurations. Our approach achieves accurate tracking of the location, current and shape for these configurations. We also demonstrate sustained ‘droplets’ on TCV, in which two separate plasmas are maintained simultaneously within the vessel. This represents a notable advance for tokamak feedback control, showing the potential of reinforcement learning to accelerate research in the fusion domain, and is one of the most challenging real-world systems to which reinforcement learning has been applied.

2022

Helyssen

Active in plasma technology, inductive plasma source and RF plasma sources. Helyssen specializes in advanced inductive plasma sources, offering exceptional performance and breakthrough technology for various industries.

PHYS-424: Plasma II

This course completes the knowledge in plasma physics that students have acquired in the previous two courses, with a discussion of different applications, in the fields of magnetic confinement and co

PHYS-325: Introduction to plasma physics

Introduction à la physique des plasmas destinée à donner une vue globale des propriétés essentielles et uniques d'un plasma et à présenter les approches couramment utilisées pour modéliser son comport

PHYS-445: Nuclear fusion and plasma physics

The goal of the course is to provide the physics and technology basis for controlled fusion research, from the main elements of plasma physics to the reactor concepts.

Magnetohydrodynamic Equilibrium Configurations PHYS-424: Plasma II

Covers MHD equilibrium configurations, including tokamak and stellarator concepts, force balance equations, and safety factors.

From Fusion to DEMO MOOC: Plasma Physics: Introduction

Explores the progress in magnetic confinement fusion, roadmaps to fusion power, ITER components, and the path towards DEMO.

MHD Equilibrium & Stability PHYS-325: Introduction to plasma physics

Explores Magnetohydrodynamic equilibrium and stability, ideal MHD solutions, 'hairy ball' theorem, and boundary conditions.

Topics in nuclear physics

Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter. Nuclear physics should not be confused with atomic physics, which studies the atom as a whole, including its electrons. Discoveries in nuclear physics have led to applications in many fields. This includes nuclear power, nuclear weapons, nuclear medicine and magnetic resonance imaging, industrial and agricultural isotopes, ion implantation in materials engineering, and radiocarbon dating in geology and archaeology.

Topics in nuclear power

Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced by nuclear fission of uranium and plutonium in nuclear power plants. Nuclear decay processes are used in niche applications such as radioisotope thermoelectric generators in some space probes such as Voyager 2. Generating electricity from fusion power remains the focus of international research.

Nuclear weapons

A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions (thermonuclear bomb), producing a nuclear explosion. Both bomb types release large quantities of energy from relatively small amounts of matter. The first test of a fission ("atomic") bomb released an amount of energy approximately equal to . The first thermonuclear ("hydrogen") bomb test released energy approximately equal to .