Nuclear Fusion by Inertial Confinement

A Comprehensive Treatise

Guillermo Velarde, Yigal Ronen, Jose M. Martinez-Val

• Éditeur: CRC Press
• Année: 2020
• ISBN:
  9781000141986
• Édition: 1
• Sujet: Naturwissenschaften
• Sous-sujet: Nuklearphysik

Nuclear Fusion by Inertial Confinement provides a comprehensive analysis of directly driven inertial confinement fusion. All important aspects of the process are covered, including scientific considerations that support the concept, lasers and particle beams as drivers, target fabrication, analytical and numerical calculations, and materials and engineering considerations. Authors from Australia, Germany, Italy, Japan, Russia, Spain, and the U.S. have contributed to the volume, making it an internationally significant work for all scientists working in the Inertial Confinement Fusion (ICF) field, as well as for graduate students in engineering and physics with interest in ICF.

Chapter 1

AN INTRODUCTION TO NUCLEAR FUSION BY INERTIAL CONFINEMENT

José M. Martínez-Val, Guillermo Velarde and Yigal Ronen

TABLE OF CONTENTS

I.	Fundamentals of Fusion Engineering A. Introduction B. Fusion Reactions C. Methods of Fusion Reaction Induction 1. Muon-Catalyzed Fusion 2. Thermonuclear Fusion a. Inertial Confinement Fusion: An Introduction b. Hypervelocity Fusion and the Ignition Phase of ICF Targets D. Energy Balance in a Fusion System 1. The Ignition Temperature Concept a. Bremsstrahlung Radiation Losses b. Energy Balance within the Plasma 2. The Lawson Criterion
II.	Fundamentals of Inertial Confinement Fusion A. Introduction B. An Overall View of the ICF Target Performance 1. The Interaction Phase a. Laser Beams b. Ion Beams c. The Focusing Problem 2. The Compression Phase a. The Accelerating Period of the Implosion b. Decelerating Period and Void Closure c. Compression Stability d. Rayleigh-Taylor Instabilities 3. Ignition and Burn Propagation C. Drivers 1. Lasers a. Nd.Glass Lasers b. Excimer Lasers c. Free Electron Lasers 2. Accelerators a. Light-Ion Accelerators for ICF b. Heavy-Ion Accelerators c. Radiofrequency Accelerators d. Induction Linacs D. Reactor Chambers
III.	Progress and Development of ICF
IV.	Contents and Scope of this Book
References

I. FUNDAMENTALS OF FUSION ENGINEERING

A. INTRODUCTION

In his article “Energy Production in Stars”,¹ published in the March, 1939 volume of Physical Review, Hans A. Bethe stated that “energy production of stars is then due entirely to the combination of four protons and two electrons into an alpha-particle.” Bethe was making use of the previous work by himself^2,3 and others (Atkinson and Houtermans,⁴ Gamow and Teller,⁵ Ladenburg and Hanner,⁶ Doolittle,⁷ Williams et al.,⁸ Landau,⁹ Eddington¹⁰) to demonstrate that some specific fusion reactions were the origin of the actual energy of the Universe. At that time, many cross-section measurements had been carried out^6,8 and it was possible to identify the fusion reactions that could be exploited in a man-made system, provided the formidable task of research and development be worked out.

It is a curious coincidence that at the same time of publication of Bethe’s paper on stellar energy, the first papers on the fission reaction had just been published.^11,12 The technological deployment of fission and fusion have followed very different pathways from then on, for well-known reasons related to the geopolitical circumstances of history. Of course, besides those external reasons, there are also some scientific or physical causes that explain such a different development: namely, neutrons do not suffer the coulombian repulsion when they approach a nucleus, unlike protons and other nuclei, which need a very high initial kinetic energy in order to overcome such repulsion. By the time of Bethe’s paper, a decade of fruitful research on accelerators^13,15 had permitted the study of nuclear reactions, particularly that of fusion. However, an accelerator is an energy-consuming device and the construction of an energy-producing fusion reactor based directly on accelerators seemed unlikely. Within the stars, the required kinetic energy of the nuclei to induce fusions is provided by the giant gravitational pull that produces internal temperatures of several tens of millions of degrees.

In later sections of this chapter, different methods to induce and confine fusion reactions will be discussed and the concept of inertial confinement fusion will be introduced. The term “confinement” does not come immediately from the consideration of a single fusion reaction, as a two-body interaction, but from the fact that an energy-producing system will need quadrillions of fusions per second. Within a star, ions and electrons are gravitationally confined. Hence, gravitation provides both the high kinetic energy of the nuclei (temperature) to induce fusions and the high density and confinement time needed to maintain those extraordinary powers for very long periods.

Two conditions are therefore essential for a fusion reactor: to reach very high temperature, and to confine the nuclear population. This double challenge, particularized to inertial confinement fusion, is the objective of this book.

B. FUSION REACTIONS

Bethe’s article¹ was primarily concerned with fusion reactions starting with protons like because hydrogen is the main constituent of stars. However, at that time some other reactions, like

$H+H=D+e^{+}$

(1)

$C^{12}+H=N^{13}+\text{γ}$

(2)

because hydrogen is the main constituent of stars. However, at that time some other reactions, like D + D reactions, had been identified,⁶ and it was clear that they could be easier to produce in a reactor, because they presented higher cross sections at lower temperatures (see Figures 1 to 3).

When the first programs of civilian applications of fusion were established in the 1950s,¹⁶ The DT $\left(\text{T}\equiv {}_1^3\text{H}\right)$ reaction was identified as the easiest approach to fusion exploitation. The reaction

${}_1^{2}D+{}_1^{3}H\to {}_2^{4}He+{}_0^{1}n(+17.6MeV)$

(3)

presents a very high mass defect (∼0.35% of the reactant’s mass), 80% of which is carried by the neutron (14.06 MeV of average energy, with a very narrow energy spectrum, depending on the conditions of the reacting particles).

Another reaction which was also considered from the beginning¹⁷ for civilian applications was that of D · D:

$\begin{array}{l}{}_1^{2}D+{}_1^{2}D\to {}_2^{3}He+{}_0{}^{1}n(+3.3MeV)\hfill \\ {}_1^{2}D+{}_1^{2}D\to {}_1^{3}H+{}_1^{1}H(+4.0MeV)\hfill \end{array}$

(4)

whose probabilities are 50% in each case. The potential advantage of these reactions is that only 33% of the output energy is carried by the neutron (of the first branch) while the rest is carried by charged particles, which deposit their energy in a very localized way (which is a positive feedback for the internal energy of the fusionable population) and which do not produce activation products. It is evident that one of the fundamental aspects of fusion is its radiological cleanliness. Radioactivity will be present if tritium is used as fuel or if it is produced in the reactions (see last case). Apart from tritium, the only inventory of radioactivity in a fusion reaction will be the neutron activation products, some of them long-lived ones. Of course, fusion reactors will not have fission products and actinides, which are the main source of concern in fission reactors. On the other hand, DT fusion produces more neutrons per total energy unit than fission, which means that in certain designs the activation inventory of fusion reactors can be very high. This is the reason why several studies have been focused on aneutronic fusion,^18,19 although the reactions involved are very difficult to induce because their...