People have always been looking for cleaner and more sustainable energy sources, and nuclear fusion is one of the potential solutions.

According to the "Global Fusion Industry Report" by the Fusion Industry Association, "Investment in the global nuclear fusion industry has increased to $6.21 billion. Currently, there are about 43 companies worldwide engaged in the nuclear fusion business [1]."

Scientists are working hard to develop controllable nuclear fusion technology to achieve sustainable large-scale energy supply in the future. Recently, some commercial fusion companies have tried to advance the development of technology from neutron-free fusion or methods that reduce neutrons.

To understand neutron-free fusion, we must first talk about its function. Nuclear fusion is a nuclear reaction where two light nuclei combine to form a heavier nucleus.

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During the nuclear fusion process, the nuclei of light elements will fuse into heavier elements, releasing a tremendous amount of energy.In nuclear fusion reactions, hydrogen isotopes deuterium and tritium are commonly used as fuel. Since deuterium and tritium are isotopes of hydrogen, they undergo fusion reactions when subjected to sufficiently high temperatures and pressures.

At the same time, an excessive flux of neutrons is also produced in the process of nuclear fusion. Neutrons play a role in providing energy and promoting chain reactions in nuclear fusion reactions.

It is worth noting that controlling the release and capture of neutrons is crucial for achieving controllable nuclear fusion. In laboratories and future fusion reactors, it is necessary to effectively control and regulate the generation and release of neutrons to prevent neutron radiation from damaging the reactor wall and affecting infrastructure and nearby organisms.

Now, researchers in the field are working to solve the problem of neutrons. Their approach is to replace deuterium-tritium fuel with naturally occurring nuclides that release charged particles instead of high-energy neutrons when they fuse.

People who advocate for neutron-free fusion methods believe that these devices will eventually be easier to manufacture and more suitable for power generation systems, as it is easier to convert the energy of charged particles into electrical energy. In addition, they produce very little or almost no radioactive waste.Nuclear engineer and emeritus professor at the University of Wisconsin, Gerald Kulcinski, stated to the media: "From the 1960s to the 1980s, a lot of research was conducted in the field of advanced fuels."

He said that due to the difficulty of inducing this type of nuclear reaction being about ten times that of the deuterium-tritium reaction, this research became unpopular starting ten years ago.

"Taking into account the damage caused to the reactor walls by neutrons, people have started to pay more attention to advanced fuels again."

TAE: Hydrogen-boron nuclear fusionTAE Technologies is a nuclear fusion energy company located in California, USA. It was established in 1998 and has since obtained over 1,400 patents and more than 1.2 billion dollars in investment.

As of now, the company has built 5 national laboratory-scale devices and has successfully generated and confined fusion plasma more than 140,000 times.

In TAE's view, using hydrogen and boron (p-11B) as reaction fuels is not only clean but also has cost advantages. Boron is characterized by abundant resources and energy security. After the hydrogen-boron fusion reaction occurs, it releases three positively charged helium-4 nuclei, also known as alpha particles.

TAE designs to confine plasma through the Field Reversed Configuration (FRC), which can achieve very high reaction temperatures. In the FRC, the plasma is mainly confined by the internal magnetic field, rather than relying on externally applied magnetic fields.

However, it must also be seen that there has always been a voice that is not optimistic about FRC in history. Once the plasma is improperly operated and breaks the closed magnetic field, the plasma will also cool down.In recent years, TAE has been exploring methods to stabilize plasma through the development of real-time reshaping and repositioning techniques and hardware, utilizing AI and machine learning.

TAE Technologies CEO Michl Binderbauer stated to the media: "Now we can manipulate these currents and maintain their stability, and their behavior is completely consistent with predictions."

Additionally, there is another significant drawback to using hydrogen-boron as a fusion fuel, which is the extreme temperature conditions required, exceeding 300 million degrees Celsius.

It is important to understand that this temperature is 20 to 30 times the temperature required for deuterium-tritium reactions. Many physicists believe that under such temperature conditions, the cooling of plasma by electron radiation will be faster than the heating of the plasma.

In February 2023, a joint team of TAE and the National Institute for Fusion Science in Japan innovatively conducted a successful hydrogen-boron fusion experiment in magnetically confined plasma, with the only byproduct being helium.The research has demonstrated the feasibility of neutron-free fusion and its dependence on hydrogen-boron, with the relevant paper published in Nature Communications[2].

This experiment has provided us with a wealth of data to utilize, and it indicates that hydrogen-boron fusion reactions have a place in large-scale fusion power generation.

"We can address the current physical challenges and provide the world with a revolutionary new carbon-free energy source that relies on this non-radioactive, abundant fuel," Bendall said to the media.

Public information shows that TAE's goal is to establish the first hydrogen-boron fusion power plant and connect it to the grid in the 2030s.

TAE is advancing a modular, easy-to-maintain design through FRC, which will have a compact footprint and the potential to utilize more efficient magnetic confinement methods. Compared to the tokamak, the output power of this method is expected to increase by 100 times.Helion Energy: Utilizing Deuterium and Helium-3 as Fuel

Helion Energy is a nuclear fusion company based in Washington State, USA, that employs deuterium and helium-3 as fuels. Helium-3 is a helium isotope gas, accounting for only 0.0001% of the available helium on Earth, and its production cost is extremely high.

There is approximately 1.1 million tons of helium-3 on the surface of the moon. One perspective suggests that people may eventually mine helium-3 on the lunar surface. However, Helion Energy's method of helium-3 reserves is unrelated to the moon; they plan to utilize the by-products of deuterium-deuterium reactions.

The charged particles produced by the fusion of deuterium and helium-3 can be directly recaptured as electrical energy. This helps maintain the compactness and efficiency of Helion Energy's system, enabling them to construct the system at a lower cost and more quickly.This fuel cycle also reduces the emission of neutrons, significantly reducing many of the engineering challenges faced by researchers in deuterium-tritium fusion fuel.

So far, Helion Energy has not produced a large amount of helium-3. However, they have obtained a patent for an efficient closed fuel cycle and are trying to increase the production of helium-3 through this patented technology.

Due to the non-negligible high-temperature conditions, Kusinski said to the media: "Deuterium and helium-3 may be a temporary transition for deuterium-tritium and p-11B."

It is worth noting that the reaction of deuterium and helium-3 releases about 5% of its energy in the form of fast neutrons, and it is not entirely a neutron-free reaction. That is to say, they cannot completely eliminate the harm of radiation, but only significantly reduce the associated hazards.

Helion's strategy is not to continuously produce reactions, but to generate a stable FRC at the center through the device in the form of a pulse once per second, and compress the plasma with a magnetic field until its temperature and density reach fusion.When fusion releases energy, the confining magnetic field is pushed outward by the plasma, and the nuclear fusion system receives charged energy through magnetic coils.

Some other attempts

Australian startup HB11 Energy aims to create a clean, safe, and reliable new source of energy. The company combines high-power lasers with magnetic confinement to fuse hydrogen and boron.

This method utilizes the ultra-short pulses of a chirped pulse amplification laser (a technology that won the 2018 Nobel Prize in Physics) to rapidly accelerate hydrogen through boron fuel within a captured magnetic field, generating nuclear fusion upon their collision.Marvel Fusion is a German startup company in the field of nuclear fusion energy, established in 2019. The company is pursuing laser-induced inertial confinement fusion using high-energy lasers and p-11B fuel in nanostructured targets.

Recently, Marvel Fusion has partnered with Colorado State University in the United States and is currently constructing one of the world's most powerful laser facilities in Fort Collins, Colorado.

Princeton Fusion Systems is a company focused on developing compact, clean fusion reactors for terrestrial and space applications.

The company's Field-Reversed Configuration (FRC) reactor is based on more than 15 years of research and experience at the Princeton Plasma Physics Laboratory, primarily funded by the U.S. Department of Energy and NASA.

They utilize deuterium and helium-3, and employ radio frequency heating to form FRC and heat the plasma. The company provides compact systems for mobile and portable power generation for spacecraft and fusion propulsion through the use of superconducting magnet technology.On the other hand, the Princeton Plasma Physics Laboratory reported on the Princeton Field-Reversed Configuration (PFRC) nuclear fusion reactor in the Journal of Fusion Energy [3].

This concept is an innovative method of fusion power generation that prioritizes reducing neutron yield and small size. The combination of analytical modeling and numerical simulation indicates that the novel heating method can generate a Field-Reversed Configuration (FRC) with closed field lines.

Regardless of the outcome of future development, fusion with or without neutrons, in today's global efforts to address the climate crisis, this undoubtedly provides a new possibility.