Construction of experimental facilities on controlled thermonuclear fusion at the RFX consortium in Padova, Italy. Credit: Dino Fracchia / Alamy Stock Photo
On 5 December at the National Ignition Facility in Livermore, in the US, 192 laser beams hit a small capsule filled with deuterium and tritium housed in a golden cylinder, causing what physicists call ‘ignition’. For the first time, the amount of energy produced by a controlled nuclear fusion reaction was larger than the energy carried by the lasers used to initiate it. The target absorbed 2.05 megajoules of energy, emitting 3.15 megajoules in return, a 54% energy gain.
Why does it matter?
The potential to exploit this experimental scheme, called inertial fusion, to produce clean energy is still decades away. In fact, to deliver 2.05 megajoules on to the target, the laser system absorbed nearly 322 megajoules of electric energy from the grid.
Nevertheless, the result is big news to scientists. “It was 10 years in the making”, says Stefano Atzeni, an expert in inertial fusion at Sapienza university in Rome. “NIF was supposed to reach ignition a few years after its launch in 2009, but the first round of experiments yielded just a few kilojoules.”
NIF was not originally built to produce energy, but to maintain the US thermonuclear weapon stockpile, offering an alternative way to test them after underground nuclear tests were banned in 1996. But the latest results expanded its mission from national security to energy programmes, with the inclusion of the inertial approach in the 10-year plan for commercial fusion energy launched by the White House in March.
Until now the production of energy from fusion has been mainly attempted through another approach, called magnetic confinement. In the most studied configuration, a deuterium-tritium plasma is held at high temperatures in large doughnut-shaped chambers, called tokamak, thanks to fine-tuned magnetic fields. This is the idea behind ITER, the project under construction in the south of France, financed by the European Union, and six countries, including the US. ITER should start operations in 2025 and plans to reach ignition in 2035.
Who is doing fusion research in Italy?
Magnetic confinement is also the most studied approach in Italy. Starting in the 1970s, the National Agency for New Technologies, Energy and Sustainable Development (ENEA) has built and operated a tokamak in Frascati that was then upgraded and eventually shut down in 2019. ENEA now leads the DTT project, a compact tokamak under construction designed to test the exhaust gas systems that will be required by DEMO, ITER’s successor and the first experimental fusion power plant.
In 2020, the energy company ENI (controlled by the Italian government) joined DTT, financing nearly 25% of its operational costs. ENI is also involved in another magnetic confinement experiment called SPARC, a spin-off of MIT which is building a tokamak using high temperature superconducting magnets. Another tokamak that uses a different magnetic field configuration is located in Padova in the laboratories of the RFX consortium co-financed by the National Research Council, ENEA, INFN, Università di Padova and Acciaierie Venete.
ENEA also maintains an inertial fusion experiment in Frascati. It is much smaller than NIF, consisting of two laser beams with 100 joules of energy each, and explores a different approach to inertial fusion, called direct drive. Here, the fuel capsule is hit directly by the laser beams and not by the X-rays emerging from the internal walls of the golden cavity, as at NIF. Since a lot of energy is lost in this conversion, the direct-drive approach is the most promising for inertial fusion reactors. At the CNR Intense Laser Irradiation Laboratory (ILIL) in Pisa, director, Leonida Gizzi, and his collaborators also study aspects of laser-plasma interactions that may help develop direct-drive inertial fusion.
“The NIF result is good news for the whole fusion research community”, says Marco Ciotti, director of the plasma division at ENEA. “It will speed up the solution of problems common to both [magnetic and inertial] approaches, for example the research of materials capable of withstanding the intense flux of high energy neutrons produced by fusion.”
What will change for fusion research in Europe?
The world’s largest facility studying direct-drive inertial fusion is the Laboratory for Laser Energetics at the University of Rochester, in the US, with a laser capable of delivering up to 60 kilojoules of energy split in 60 beams. In Europe inertial fusion researchers proposed the construction of a similar facility, called HiPER. A preliminary design was completed in 2008, but the project went nowhere.
EURATOM and EUROfusion (the two programmes that fund fusion research in Europe) have devoted much of their investments and coordination efforts towards magnetic confinement.
“Concentrating funds on a single project was necessary to demonstrate as soon as possible that producing energy from fusion is feasible”, says Luca Zabeo, scientific officer of the science division at ITER. “Magnetic confinement offered the highest chances for success.”
Zabeo thinks that the “NIF result is of the utmost importance, but more from a scientific [than from an application] standpoint.” He says that “ignition has never been achieved in the direct-drive scheme, the most promising for an inertial fusion reactor”. Achieving a symmetric compression is a much bigger challenge when the fuel capsule is hit directly, and symmetry is crucial to reach ignition since it minimizes instabilities that hinder fusion reactions.
According to Atzeni, Europe’s attitude towards inertial fusion is shortsighted. “Since August 2021 things are changing in the US also with the involvement of the private sector,” he says. “We tried to restart a dialogue with EURATOM and EUROfusion1, but with no results. They are overly committed to ITER, and they say they have no money to invest elsewhere.”
Representatives of EUROfusion say that its main mission is to pursue magnetic confinement, and that it still supports some inertial fusion research through additional funding schemes. “The inertial fusion research community should seek funding opportunities from the European Commission”, says Tony Donné, EUROfusion programme manager. “I would encourage them to think about what an inertial fusion reactor would look like, and start from there to understand what are the next steps”.
Gizzi thinks that the construction of an inertial fusion facility in Europe would advance European research in several fields beyond fusion, such as high-power lasers and laser-plasma interaction2. “Inertial fusion research has long been considered only as military research” he says, “and this has limited the willingness of European nuclear energy agencies to pursue it, but this vision is now outdated and it’s time to move ahead.”
