Researchers find new ways to control fusion using lasers and magnetic fields

Imagine that you are trying to summon the sun to your research lab.

Yes, you big bright star! Bring with you your searing heat, the drama of your core’s constant nuclear fusion, and incredible levels of energy. We want to know how to make this fusion energy happen here on Earth – at will and efficiently – so that we can permanently cross “power supply” off our list of worries.

But of course the sun can’t get into the lab. It lives too far away – about 93 million miles – and too big (about 864,000 miles in diameter). In addition, it is too hot and denser than anything on Earth. That’s why it can support the reactions that generate all the energy that powers life on Earth.

Of course, this did not stop scientists from continuing their search for nuclear fusion.

Instead, they found unusual ways – using powerful lasers and hydrogen fuel – to create extreme conditions similar to those that exist in the core of the Sun, producing nuclear fusion in tiny 1mm plastic capsules. This approach is called “inertial containment synthesis”.

The challenge is to create a system that generates more fusion energy than is required to create it.

This is exceptionally difficult because it requires highly precise experiments under extreme conditions, but researchers have made significant advances in the science and technology needed to produce controlled laboratory synthesis over the past decades.

Now University of Delaware researcher Arijit Bose and his collaborators are working on a promising variation on this approach. Their work was recently published in Physical Review Letters.

They have applied powerful magnetic fields to laser-controlled implosion, which could allow them to control fusion reactions in ways not previously explored in experiments.

Bose, assistant professor of physics and astronomy at UD, began his research on nuclear fusion in graduate school at the University of Rochester.

After visiting the Laser Energy Laboratory in Rochester, where lasers are used to explode spherical capsules and create a plasma known as “inertial confinement fusion”, he found a direction for his own research.

“Confluence is what powers everything on Earth,” he said. “To have a miniature sun on Earth – a millimeter-sized sun – that’s where a thermonuclear reaction could take place. And it struck me.”

According to Bose, research in the field of thermonuclear fusion using a laser has been going on for several decades.

It started at Lawrence Livermore National Laboratory in the 1970s. Livermore now houses the world’s largest laser system, the size of three football fields. The fusion research conducted there uses an indirect approach. The lasers are directed into a small 100mm gold jar. They hit the inner surface of the jar and emit X-rays, which then hit the target – a tiny sphere of frozen deuterium and tritium – and heat it up to a temperature close to the core of the Sun.

“Nothing can survive this,” Bose said. “The electrons are ripped off the atoms, and the ions are moving so fast that they collide and merge.”

The target explodes in a nanosecond – a billionth of a second – first under the influence of a laser, and then continues to shrink under its own inertia. Finally, it expands due to the increase in central pressure caused by compression.

“Starting a chain reaction of self-heating fusion is called ignition,” Bose said. “We’re surprisingly close to igniting.”

On August 8, Livermore researchers reported exciting new advances in this area.

The OMEGA laser facility in Rochester is smaller and is being used to test the direct drive approach. This process does not use a gold can. Instead, the lasers hit the target sphere directly.

The new part is a powerful magnetic field – in this case up to 50 Tesla – that is used to manipulate charged particles. In comparison, a typical magnetic resonance imaging (MRI) uses magnets around 3 tesla. According to Bose, the magnetic field that protects the Earth from the solar wind is many orders of magnitude smaller than 50 T.

“You want the nuclei to fuse,” Bose said. “Magnetic fields trap charged particles and make them move around the lines of force. This helps create collisions and speed up synthesis. This is why the addition of magnetic fields has advantages for producing fusion energy.”

According to Bose, fusion requires extreme conditions, but they have been achieved. The challenge is to get more energy out than in, and magnetic fields provide the push that can transform this approach.

Experiments published in Physical Review Letters were made while Bose was doing postdoctoral research at MIT’s Center for Plasma Science and Fusion. This collaboration continues.

Bose said he was attracted to the University of Delaware in part because of the Physics and Astronomy Department’s focus on plasma physics, including William Matthäus, Michael Shay and Ben Maruka.

“They do research and analyze data coming from the NASA solar program and all of its missions,” he said. “We are conducting laboratory astrophysical experiments in which these phenomena are scaled in space and time for the laboratory. This gives us an opportunity to unravel some of the complex physics questions posed by NASA missions.”

According to Bose, students are important drivers of this work, and their careers can advance significantly in this new field of study.

“This is a fascinating part of science and students are a very important part of developing the workforce for national laboratories,” he said. “Students with experience in this science and technology often become scientists and researchers in national laboratories.”

There is still a lot of work to be done, he said.

“Tomorrow we will not have a decision. But we are doing our part to solve the problem of clean energy.”