nuclear fusion

nuclear fusion
Name	Nuclear fusion
Field	Nuclear physics, Plasma physics
Related	Nuclear fission, Thermonuclear weapon

nuclear fusion is a fundamental physical process where two light atomic nuclei combine to form a heavier nucleus, releasing a tremendous amount of energy in accordance with Einstein's mass–energy equivalence principle. This process powers stars like the Sun and is the basis for thermonuclear weapons. Achieving controlled, energy-producing fusion on Earth remains a monumental scientific and engineering challenge pursued by major international projects like the ITER facility under construction in France.

Overview

The quest to harness the power that fuels the Sun and other stars has driven decades of research in plasma physics and nuclear engineering. Pioneering work at institutions like the Lawrence Livermore National Laboratory and the Joint European Torus has laid the groundwork for current efforts. The potential for a nearly limitless, clean energy source has motivated global collaborations, most notably the ITER project, which involves members from the European Union, the United States, Russia, China, India, Japan, and South Korea.

Fundamental principles

The process requires overcoming the strong electrostatic repulsion, known as the Coulomb barrier, between positively charged nuclei. This is achieved at extremely high temperatures, on the order of tens to hundreds of millions of degrees Celsius, creating a state of matter called a plasma. Under these conditions, nuclei can tunnel through the barrier due to the quantum tunneling effect. The most studied reaction for energy production is between the hydrogen isotopes deuterium and tritium, which yields a helium nucleus, a neutron, and significant kinetic energy.

Approaches and confinement methods

Two primary approaches dominate research: magnetic confinement and inertial confinement. The leading magnetic confinement device is the tokamak, a toroidal design pioneered by Soviet scientists like Igor Tamm and Andrei Sakharov. Major examples include the Joint European Torus in the United Kingdom and the upcoming ITER in France. The alternative, inertial confinement, uses powerful lasers or ion beams, such as those at the National Ignition Facility at the Lawrence Livermore National Laboratory, to rapidly compress and heat a small fuel pellet.

Fuel cycles and reactions

While the deuterium-tritium (D-T) cycle is the primary focus due to its high cross-section, other fuel cycles are also researched. The deuterium-deuterium (D-D) reaction offers the advantage of abundant fuel but has a lower reaction rate. More advanced cycles, like the proton–boron-11 (p–¹¹B) reaction, are aneutronic, producing primarily charged particles instead of neutrons, which could simplify reactor design. Research into these alternatives is conducted at facilities worldwide, including the Wendelstein 7-X stellarator in Germany.

History and development

The theoretical foundation was laid in the 1920s with the work of Arthur Eddington on stellar energy. The first human-made, uncontrolled release was demonstrated in the Ivy Mike thermonuclear test in 1952. The pursuit of controlled fusion began in earnest during the 1950s, with early devices like the ZETA in the United Kingdom and the secretive Project Sherwood in the United States. A pivotal moment was the 1968 announcement of breakthrough results from the Soviet T-3 tokamak, which redirected global research toward the tokamak design.

Challenges and current status

The central challenge is achieving and sustaining the extreme conditions required for a net energy gain, a milestone known as scientific breakeven or ignition. Key hurdles include maintaining plasma stability, managing immense heat flux on reactor walls, and breeding tritium fuel. Recent progress includes record plasma performance at the Joint European Torus and achieving ignition at the National Ignition Facility. The international ITER project aims to demonstrate a tenfold energy gain, serving as a precursor to a demonstration power plant like the proposed DEMO.

Applications and future prospects

The primary application is the generation of baseload electricity with minimal long-lived radioactive waste and no direct greenhouse gas emissions. Successful development could significantly impact global energy security and climate goals, as envisioned in studies by the International Atomic Energy Agency. Beyond power, fusion technology has niche applications, such as producing neutrons for research or medical isotope production. The roadmap beyond ITER involves constructing prototype power plants, with design efforts underway by entities like the United Kingdom Atomic Energy Authority and various private companies such as TAE Technologies and Commonwealth Fusion Systems.

Category:Nuclear physics Category:Energy Category:Plasma physics