Inertial Confinement Fusion

Inertial confinement fusion (ICF) is a method to achieve nuclear fusion by compressing and heating fuel with high-intensity laser. (click here for my article about petawatt laser)

Nuclear fusion is the opposite of nuclear fission where heavy nuclei split into lighter ones. Nuclear fission provides about 9-10% of global power from about 440 reactors (end of 2025), but faces challenges like cost, safety and the radioactive waste.

Nuclear fusion is a way to set free energy by binding atoms. Stars like the sun fuse elements like hydrogen as their energy source. Nuclear fusion requires extreme conditions as the atoms only fuse under extreme pressure and temperature like the one in the sun that brings them close enough together to overcome a certain repulsive barrier. This barrier is called Coloumb barrier caused by electrostatic repulsion between positively charged nuclei. After overcoming this barrier, the strong nuclear force outweighs the repulsive electrostatic force and fuses the atoms.

The challenge of generating energy through nuclear fusion has been achieving extreme conditions to overcome the Coloumb barrier.

How exactly does ICF work?

A high-intensity laser pulse is fired on a millimetre-sized capsule designed like a hollow spherical shell. The actual fuel lies inside the capsule and consist of Deuterium and Tritium, two isotopes (more neutrons than hydrogen).

When the high-intensity laser pulse hits the capsule (shell around the actual fuel), it explodes. This process is called ablation. The electric field of the laser pulse is strong enough to ionize the atoms of the capsule, turning it into a high-temperature plasma. The shell explodes outward due to the extreme heat.

This outward explosion creates an equal an opposite reaction according to Newtons Third Law. It pushes the fuel inward at a speed of hundreds of kilometres per second. The deuterium and tritium fuel is compressed more than 1000 times, creating sun-like conditions and a temperature of approximately 100.000.000 degree Celsius.

Those conditions allow the atoms to overcome the Coloumb barrier and fuse, releasing energy. This energy is usually in form of kinetic energy of the fusion products such as high-speed neutrons.

A barrier, for instance a lithium-containing blanket, surrounding the reactor chamber absorbs high-speed neutrons, converting their kinetic energy into thermal energy. Then, certain materials extract the thermal energy to drive turbines or generate electricity.

What has been achieved?

The concept of ICF was proposed in 1972 by several scientists. But the major breakthrough for nuclear fusion occurred on December 5, 2022, when ICF achieved scientific breakeven, meaning that the fusion reaction released more energy than the input laser energy. Specifically, 2.1 MJ of laser energy resulted in 3.15 MJ of fusion energy.

The review „Future for internal-fusion energy in Europe: a roadmap “from 2023 stated „a recent experiment in August 2023 provided an even larger yield: about 170% of the input laser energy “(5)

What are prospects for the future?

The review „Future of internal-fusion energy in Europe: a roadmap “published in 2023 by Cambridge University Press proposes the development of a fusion power plant based on the ICF concept. „This project aims to create a scientific basis and a technological readiness that will enable future commercialisation of laser fusion energy. The goal is to demonstrate direct drive ignition of fusion reactions with lasers and high repetition rate (HRR) high-gain laser operation using frontier laser technology and sustainable materials. This goal will be achieved on a time scale of 20–30 years. It will be facilitated by creating a European Laser Fusion Research Centre – a joint venture of several major stakeholders – including research laboratories, universities, governmental organisations and private companies. “(5)