PRINCETON — Tucked away from major roadways and nestled amid more than 80 acres of forest sits a massive warehouse-like building where inside, a device that can produce temperatures hotter than the sun has sat cold and quiet for more than two years.

But the wait is almost over for the nuclear fusion reactor to get back up and running at the Princeton Plasma Physics Laboratory.

“We’re very excited and we’re all anxious to turn that machine back on,” said Adam Cohen, deputy director for operations at PPPL.

The National Spherical Torus Experiment (NSTX) has been shut down since 2012 as it underwent a $94 million upgrade that will make it what officials say will be the most powerful fusion facility of its kind in the world. It is expected to be ready for operations in late winter or early spring, Cohen said.

The NSTX is used to study the physics of plasma, and scientists said that the data they collect from the device now could ultimately lead to a clean, sustainable and possibly limitless energy source — fusion energy.



The 15-year-old reactor, when in operation, creates and controls super-hot plasma gas. Laser beams are shot into the doughnut-shaped cabin of the device to heat the plasma to temperatures about 10 times hotter than the sun's core while magnets down the center and around the sphere confine the plasma, ultimately creating fusion energy.

The upgrade (NSTX-U) will essentially double the power of the reactor by increasing the heat, electrical current and magnetic field. A second laser device that helps heat the plasma was added, and the center magnet, which resembles the core of an apple, was rebuilt to create a stronger magnetic field.

“We may reach several hundred million degrees Celsius in the new machine,” said Masa Ono, a research physicist and head of the NSTX department.

At these high temperatures the electrons are detached from the nuclei of the atoms, and the heat and magnetic field cause the particles to quickly bounce around until ultimately fusing together, creating nuclear fusion. During each fusion of particles, a small amount of energy is released, which scientists hope to one day be able to capture and convert into electricity.

“There’s a lot of technology that has to be done to learn how to make that electricity,” said Jonathan Menard, principal research physicist and program director for NSTX. He added that NSTX-U could be the prototype for bigger, more powerful machines that can produce commercial fusion power.

The scientists said that they hope to be working on a conceptual design for a reactor capable of harnessing fusion energy in the next decade. Commercial application is still a long way off. Ono said it could be 50 years before fusion energy is actually contributing to the grid.

In a building adjacent to the one housing NSTX, about a half a dozen engineers can be found at any time during the day tinkering with the center magnet, which is the final phase of the upgrade and nearing completion after two years and roughly $25 million.

The new column features rows of magnets wrapped in a heating coil and a cooling tube through the center to release the heat.

“This is really the heart of NSTX and I think it’s the best magnet that we’ve ever built for this machine in terms of capability, quality, workmanship and physics. It’s going to deliver,” Menard said.

The center magnet is expected to be dropped back into the reactor around Thanksgiving.

Once the NSTX-U is operational, scientists will gauge how much more powerful the capabilities of the machine are. Data from pulses of fusion activity will be collected and analyzed.

Pulses in the former NSTX reactor lasted up to a second, but will last five seconds in NSTX-U, according to Michael Williams, associate director for engineering and infrastructure. He explained that they have the ability to make the pulses last much longer, but it’s unnecessary for the purpose of their experiment.

“The physics that happens on that five-second scale is the same physics that will happen on a long time scale,” he said.

Similar experiments are also underway in other countries including France and England.

Kelly Johnson may be reached at kjohnson@njtimes.com. Follow The Times of Trenton on Twitter @TimesofTrenton. Find The Times of Trenton on Facebook.