Laser fusion has become a parallel pathway to magnetic confinement fusion in controlled thermonuclear fusion research since 1972, when the principle of centripetal burst fusion was proposed by the American scientist J. Nachols and others.

The target pellet in laser fusion is spherically symmetric. The central region of the sphere (with a radius of about 3 mm) is filled with low density (≤1 g/cm3) deuterium and tritium gases. The spherical shell consists of an ablative layer and a fuel layer: the thickness of the ablative layer is 200-300 µm and the material is a low Z (atomic number) material such as silica; the thickness of the fuel layer is about 300 µm and the material is liquid deuterium and tritium, whose mass is about 5 mg. Some target pellets have a vacuum in the central region, and the spherical shell consists of plastic containing deuterium and tritium elements. In some cases, solid deuterium and tritium fuel is used and the spherical shell is made of glass.

The ultimate goal of nuclear fusion research is to provide future energy for humanity. The hydrogen bomb was a demonstration of the power of nuclear fusion energy in an uncontrollable form. Great efforts are being made to achieve controlled nuclear fusion. Currently, research on nuclear fusion reactors is on the eve of achieving high gains.

The principle of laser fusion

The principle of nuclear fusion is that the electrons outside the nucleus can be released from the bondage of the nucleus only at very high temperature and pressure, so that two nuclei can be attracted to each other and collide together to produce a new nucleus with a heavier mass (e.g., helium).

The release of a large number of electrons and neutrons shows up as a huge release of energy. This is a form of nuclear reaction. Atomic nuclei contain enormous amounts of energy, and changes in the nucleus (from one type of nucleus to another) are often accompanied by a release of energy. Nuclear fusion is the opposite form of nuclear reaction to nuclear fission.

Milestones in nuclear fusion technology

At 10:00 on the 13th of 2022, the United States announced a breakthrough scientific achievement: for the first time, mankind has achieved the successful ignition of laser fusion. Successful ignition for nuclear fusion actually means that the input energy is less than the output energy, a process known as ignition. Scientists used 192 powerful laser beams to irradiate a rice-sized deuterium-tritium plasma target with an input energy of 2.05 MJ and a fusion output energy of 3.15 MJ, for a final energy gain of 153%. After decades, nuclear fusion technology has finally reached a milestone. There is still a long way to go before it is commercially available, but at least it is a huge success.

One of the important military uses of laser fusion is the development of new nuclear weapons, especially new hydrogen bombs. Because the fusion reaction is achieved by replacing the atomic bomb with a high-energy laser as the ignition device for the hydrogen bomb, the same plasma conditions can be generated as for the hydrogen bomb explosion, providing physics data for nuclear weapon design, testing computational procedures, and thus developing new nuclear weapons.

With the technological maturity of laser fusion, the cost of manufacturing a "clean hydrogen bomb" has been greatly reduced. This is because the fuel for nuclear fusion, deuterium, is almost inexhaustible and makes thermonuclear fusion reactions much easier. Laser fusion can simulate the physical processes and effects of nuclear weapon explosions in the laboratory, providing a basis for research into nuclear weapon physics, allowing for the possession of safe and reliable nuclear weapons without nuclear testing, modifying existing nuclear warheads, and maintaining the research and development capabilities of nuclear weapons. Laser fusion can be repeated many times, is easy to test, and saves money.

What are the issues facing laser fusion

Key challenges and issues facing laser fusion.

1) The efficiency of converting the total incident laser energy into implosion energy of the target pellet is too low, reaching only about 1-2%. How to improve the conversion efficiency is the key to the success of ICF.

(2) the existing ICF implosion compression process in the density compression and temperature increase is coupled together, can the compression process and the heating process are separated and controlled separately?

(3) laser plasma interaction instability not only causes scattering of laser energy, but also may lead to compression difficulties due to the preheating of superheated electrons, can the instability and inter-beam energy transfer in the laser plasma interaction process be effectively controlled?

4) Can the nonlinear growth of plasma hydrodynamic instability be effectively controlled in the implosion process?

5) How to achieve the pressure of ablation pressure?

6) How to avoid fuel mixing?

7) How to improve the target quality and other key technologies?

From a long-term perspective, the successful realization of laser fusion will solve the human energy problem once and for all, bringing us unprecedentedly huge economic and social benefits. Meanwhile, laser fusion can be used to simulate nuclear weapons-related processes, which is of great significance for national security.