The Quest for Fusion Energy | Daniel Jassby | Inference

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Original Article: The Quest for Fusion Energy | Daniel Jassby | Inference Convert your long form article to podcast? Visit SendToPod Follow me on Twitter to find out more. ---- In recent years, a steady flow of press releases from nuclear fusion research projects has hailed breakthrough advances and new record yields. Despite the relentlessly optimistic tone of these announcements and the repeated claims that the prospects for commercialization have never looked brighter, the stark reality is that practical fusion-based electric power remains a distant prospect. It is likely unachievable anytime in the next half a century. Even then, it may still remain beyond our grasp. The most readily accessible nuclear fusion process combines the hydrogenic isotopes deuterium and tritium to release energy in the form of energetic neutrons and helium ions. There are two broad approaches toward achieving terrestrial fusion. In magnetic confinement fusion (MCF), magnetic fields are used to confine the hot fusion fuel in the form of a fully ionized gas or plasma that persists for seconds or longer. In inertial confinement fusion (ICF), laser or particle beams are used to compress and heat a tiny capsule of fusion fuel to generate a micro-explosion of a nanosecond duration. The most advanced MCF device currently in operation is the Joint European Torus (JET) tokamak located at the Culham Centre for Fusion Energy in the United Kingdom.1 Commissioned almost 40 years ago, JET is one of the world’s two largest tokamaks and the only MCF device presently equipped to use tritium fuel. The ICF approach is exemplified by the laser-induced micro-explosions at the National Ignition Facility (NIF) near Livermore, California.2 Completed in 2009 at a cost of around US$5 billion, NIF is the world’s most powerful laser-driven fusion facility. This essay is concerned with scientific feasibility, a basic prerequisite that the reacting fusion medium must satisfy before it can be developed as the basis for a commercial fusion power reactor. A demonstration of scientific feasibility is usually taken as the achievement of fusion energy breakeven. This condition is met when the fusion energy produced during a pulse is equal to or greater than the energy applied from external sources to heat the plasma during that pulse. During the last 12 months, a clear disparity in relative performance between MCF and ICF has emerged. This was evident from the results of the near-simultaneous deuterium-tritium (D-T) experiments that took place at the NIF and JET facilities during 2021. These were the most important ICF and MCF experiments undertaken in the last quarter of a century. Taken together, the two sets of results have arguably the greatest significance for the development of the field since the T-3 tokamak results were presented in the summer of 1968 at an international fusion energy conference in the Soviet Union.3 This essay compares the backgrounds and outcomes of the recent D-T campaigns at the JET and NIF facilities, shows why inertial confinement has established a clear lead over magnetic confinement in attaining reactor-relevant fusion conditions, and examines the future directions of both approaches. While there is a strong argument that the scientific feasibility of ICF has been demonstrated in recent experiments, the status and prospects for MCF are far less favorable. Scientific Feasibility and Ignition The fusion energy gain, Q, of a reacting plasma configuration is commonly described as the ratio of the fusion energy output released in a pulse, Ef, to the external heating energy deposited in the plasma during that pulse, Eh. In MCF devices, the dominant heating energy is injected into the plasma by neutral particle beams and radio-frequency waves. In ICF devices with indirect drive, such as the NIF, a D-T fuel capsule is emplaced inside a tiny box, known as a hohlraum, from the German for “cavity.” The fuel capsule is then imploded and heated by x-rays gene...