LLNL scientists confirm thermonuclear fusion in a sheared-flow Z-pinch (2024)

In findings that could help advance another “viable pathway” to fusion energy, research led by Lawrence Livermore National Laboratory (LLNL) physicists has proven the existence of neutrons produced through thermonuclear reactions from a sheared-flow stabilized Z-pinch device.

The researchers used advanced computer modeling techniques and diagnostic measurement devices honed at the Lab to solve a decades-old problem of distinguishing neutrons produced by thermonuclear reactions from ones produced by ion beam-driven instabilities for plasmas in the magneto-inertial fusion regime.

While the team’s previous research showed neutrons measured from sheared-flow stabilized Z-pinch devices were “consistent with thermonuclear production, we hadn’t completely proven it yet,” said LLNL physicist Drew Higginson, one of the co-authors of a paper recently published in Physics of Plasmas.

“This is direct proof that thermonuclear fusion produces these neutrons and not ions driven by beam instabilities,” said Higginson, principal investigator of the Portable and Adaptable Neutron Diagnostics (PANDA) team that is doing research under a Department of Energy Advanced Research Projects Agency-Energy (ARPA-E) cooperative agreement. “It’s not proven they’re going to get energy gain, but it is a promising result that suggests they are on a favorable path.”

LLNL physicist James Mitrani was the lead author on the paper, which demonstrates how the Lab’s broad range of research is benefiting the larger fusion community beyond the major advancements made by LLNL’s National Ignition Facility (NIF), the world’s most energetic laser system.

“The research only focused on this one device,” Mitrani said, “but the general techniques and concepts are applicable to a lot of fusion devices in this intermediate magneto-inertial fusion regime.” He noted that regime operates in the area between laser fusion facilities, such as NIF and the Omega Laser Facility at the University of Rochester, and fusion devices that confine plasmas in the purely magnetic regime, like ITER (a multinational project in southern France), SPARC (under construction near Boston) or other tokamak devices.

Since August, NIF has generated buzz throughout the global scientific community because an inertial confinement fusion (ICF) experiment yielded a record 1.35 megajoules (MJ) of energy. That milestone brought researchers to the threshold of ignition — defined by the National Academy of Sciences and the National Nuclear Security Administration as when a NIF implosion produces more fusion energy than the amount of laser energy delivered to the target. That shot was preceded by progress LLNL researchers made in achieving a burning plasma state in laboratory experiments (see “Nature: How Researchers Achieved Burning Plasma Regime at NIF”).

Fusion is the energy source found in the sun, stars and thermonuclear weapons. NIF’s ICF experiments focus 192 laser beams on a small target to compress and heat partially frozen hydrogen isotopes inside a fuel capsule, creating an implosion replicating the conditions of pressure and temperature found only in the cores of stars and giant planets and in exploding nuclear weapons. Z pinch machines accomplish fusion using a powerful magnetic field to confine and “pinch” the plasma.

The Z pinch concept is a relatively simple design that has existed as a theoretical model since the 1930s. But Higginson noted it had a long history of “terrible instabilities” that hindered the ability to generate the conditions needed to attain a net fusion energy gain.

In the 1990s, LLNL scientists began working with University of Washington (UW) researchers to advance another promising path toward ignition, the sheared-flow stabilized Z-pinch concept. Instead of powerful stabilizing magnets used in other Z-pinch devices, sheared-flow stabilized Z-pinch devices use pulsed electrical current to generate a magnetic field flowing through a column of plasma to reduce fusion-disrupting instabilities.

“The problem with instabilities is that they don’t create a viable path to energy production, whereas thermonuclear fusion does,” Higginson said. “It’s always been tricky to diagnose this difference, especially in a Z-pinch.”

In 2015, LLNL and UW researchers were awarded a $5.28 million ARPA-E cooperative agreement to test the physics of pinch stabilization at higher energies and pinch current under the university’s Fusion Z-Pinch Experiment (FuZE) project.

LLNL scientists confirm thermonuclear fusion in a sheared-flow Z-pinch (1)

The top photo shows one of the scintillator detectors used for neutron measurements on the FuZE device. The bottom simplified schematic shows the physical mechanism for pulse generation in the detector, where recoil protons produced by fast neutron interactions generate light via excitation and ionization of the scintillating medium. The scintillation light is converted to an electric signal using a photomultiplier tube (PMT).

Under a subsequent ARPA-E “capability team” cooperative agreement, LLNL researchers focused on diagnostics that measured the neutron emissions produced during the fusion process, including the spatial locations and time profiles of those emissions. Combining the plasma diagnostic expertise of national laboratories and the agile operation of private companies draws on each of their individual strengths and is a key objective of the ARPA-E fusion capability team program.

As the radius of the FuZE cylinder narrowed to increase compression, it also would create dips in the plasma that generated much stronger magnetic fields that would cause the plasma to pinch inwards more in certain spots than in others. Like the pinched ends of a popular tubular minced meat, those undesired “sausage” instabilities would create beams of faster ions that produced neutrons that could be confused with desired thermonuclear-produced neutrons.

LLNL researchers placed two plastic scintillator detectors outside of the device to measure traces of neutrons as they emerged in just a few microseconds from different points and angles outside the Z-pinch chamber.

“We showed that emitted neutron energies were equal at different points around this device, which is indicative of thermonuclear fusion reactions,” Mitrani said.

The analysis included creating histograms of the neutron pulses detected by the two scintillators and comparing them using methods such as Monte Carlo computerized simulations that examine all possible outcomes.

The diagnostics aren’t new, Higginson said, but “the idea of usinghistograms of individual neutron pulse energiesto measure the anisotropy — the difference in energieswhen you look in different directions — isanewtechniqueand is something we thought of, developed and implemented here. In addition, we have been working with UC Berkeley, which has helped us to develop the modeling capability to iron out the uncertainties in the measurements and completely understand the data we’re seeing. We’re not just looking through raw data.”

The paper, “Thermonuclear neutron emission from a sheared-flow stabilized Z-pinch,” was published in November and stemmed from an invited talk Mitrani presented at the American Physical Society-Division of Plasma Physics annual meeting in 2020.

Mitrani and Higginson were joined by LLNL colleague Harry McLean; Joshua Brown and Thibault Laplace of UC Berkeley; Bethany Goldblum of UC Berkeley and Lawrence Berkeley National Laboratory; and Elliot Claveau, Zack Draper, Eleanor Forbes, Ray Golingo, Brian Nelson, Uri Shumlak, Anton Stepanov, Tobin Weber and Yue Zhang of the University of Washington.

The research spun off a privately funded Seattle startup named Zap Energy in 2017.

Research is continuing under new grants, with more detailed measurements taken by 16 detectors as Zap Energy continues experiments.

“We want to be involved because we don’t know what surprises might arise,” Higginson said. “It could turn out that as you go to a higher current, all of a sudden you start driving instabilities again. We want to be able to prove as the current goes up that it is possible to maintain a high quality and stable pinch.”

—Benny Evangelista

LLNL scientists confirm thermonuclear fusion in a sheared-flow Z-pinch (2024)

FAQs

What was significant about the recent fusion experiment conducted at Lawrence Livermore Labs? ›

The demonstrated level of target gain of 1.5 times was the first time that fusion target gain was unambiguously achieved in the laboratory in any fusion scheme,” the researchers said.

What is the theory of thermonuclear fusion? ›

Thermonuclear fusion is the process of atomic nuclei combining or "fusing" using high temperatures to drive them close enough together for this to become possible.

Why are thermonuclear fusion reactions so difficult to carry out? ›

On earth, we need temperatures exceeding 100 million degrees Celsius and intense pressure to make deuterium and tritium fuse, and sufficient confinement to hold the plasma and maintain the fusion reaction long enough for a net power gain, i.e. the ratio of the fusion power produced to the power used to heat the plasma.

How does a pinch work? ›

A pinch (or: Bennett pinch (after Willard Harrison Bennett), electromagnetic pinch, magnetic pinch, pinch effect, or plasma pinch.) is the compression of an electrically conducting filament by magnetic forces, or a device that does such. The conductor is usually a plasma, but could also be a solid or liquid metal.

What is the pinch effect in nuclear fusion? ›

When current flows in the same direction through two parallel wires, they will be pulled toward each other due to the Lorentz force. The plasma can be thought of as many parallel wires, so when a current flows through the plasma, a magnetic field begins to arise and compresses the plasma. The effect is called a pinch.

What elements were discovered at LLNL? ›

Lawrence Livermore teamed with the Joint Institute for Nuclear Research in Dubna, Russia (JINR) in 2004 to discover elements 113 and 115. LLNL worked again with JINR in 2006 to discover element 118.

Have scientists confirmed fusion experiments have broken even? ›

The new papers detail the progress that made 'breaking even' possible, including tinkering with the fuel mix, eliminating defects in the capsule walls, increasing the mass of the pea-sized capsule, boosting laser energies, and upping the volume of fuel used.

What type of fusion reactor is Lawrence Livermore? ›

The National Ignition Facility (NIF) is a laser-based inertial confinement fusion (ICF) research device, located at Lawrence Livermore National Laboratory in Livermore, California, United States.

What are the disadvantages of thermonuclear fusion? ›

A long-recognized drawback of fusion energy is neutron radiation damage to exposed materials, causing swelling, embrittlement and fatigue.

Is thermonuclear fusion possible on Earth? ›

On Earth, we need temperatures of over 100 million degrees Celsius to make deuterium and tritium fuse, while regulating pressure and magnetic forces at the same time, for a stable confinement of the plasma and to maintain the fusion reaction long enough to produce more energy than what was required to start the ...

Why is nuclear fusion impossible? ›

Fusion is very hard to get going: the atomic nuclei of the hydrogen isotopes are positively charged, and we know that like charges repel each other. And so it's very hard to get those nuclei close enough together that the attractive interactions can take over, and that they can actually undergo this reaction.

Is fusion energy actually possible? ›

A breakthrough in December 2022 resulted in an NIF experiment demonstrating the fundamental scientific basis for inertial confinement fusion energy for the first time. The experiment created fusion ignition when using 192 laser beams to deliver more than 2 MJ of ultraviolet energy to a deuterium-tritium fuel pellet.

Is it legal to build a fusion reactor? ›

Twelve states currently have restrictions on the construction of new nuclear power facilities: California, Connecticut, Hawaii, Illinois, Maine, Massachusetts, Minnesota, New Jersey, New York, Oregon, Rhode Island and Vermont.

What is the biggest obstacle for scientists trying to create a nuclear fusion reactor? ›

Recreating the conditions in the centre of the Sun on Earth is a huge challenge. “We need to heat up isotopes of hydrogen gas so they become the fourth state of matter, called plasma. “In order for the nuclei to fuse together on Earth, we need temperatures 10 times hotter than the Sun – around 100 million Celsius."

Thermonuclear Fusion - an overview ...ScienceDirect.comhttps://www.sciencedirect.com ›

The fusion reaction that requires the lowest energy and, hence, the most readily attainable fusion process on Earth, is the combination of a deuterium nucleus w...
Thermonuclear reaction, fusion of two light atomic nuclei into a single heavier nucleus by a collision of the two interacting particles at extremely high temper...
Controlling nuclear fusion for power production is expected to require large and expensive magnetic coils or laser systems to create, heat, confine, and control...

How does the pinch effect work? ›

pinch effect, self-constriction of a cylinder of an electrically conducting plasma. When an electric current is passed through a gaseous plasma, a magnetic field is set up that tends to force the current-carrying particles together.

How does a pinch sensor work? ›

A pinch sensor is designed to measure the force on a rolling window. These sensors are "trained" to not interfere with operation up to a certain point of force, but will immediately activate if the standard amount of force is exceeded.

Top Articles
Latest Posts
Recommended Articles
Article information

Author: Delena Feil

Last Updated:

Views: 6616

Rating: 4.4 / 5 (45 voted)

Reviews: 92% of readers found this page helpful

Author information

Name: Delena Feil

Birthday: 1998-08-29

Address: 747 Lubowitz Run, Sidmouth, HI 90646-5543

Phone: +99513241752844

Job: Design Supervisor

Hobby: Digital arts, Lacemaking, Air sports, Running, Scouting, Shooting, Puzzles

Introduction: My name is Delena Feil, I am a clean, splendid, calm, fancy, jolly, bright, faithful person who loves writing and wants to share my knowledge and understanding with you.