The scientists found a way to build high-temperature superconducting magnets that are made of material that conducts electricity with little or no resistance at temperatures warmer than before. Such powerful magnets would more easily fit within the tight space inside spherical tokamaks, which are shaped more like a cored apple than the doughnut-like shape of conventional tokamaks, and are being explored as a possible design for future fusion power plants.

Since the magnets could be positioned apart from other machinery in the spherical tokamak’s central cavity to corral the hot plasma that fuels fusion reactions, researchers could repair them without having to take anything else apart. “To do this, you need a magnet with a stronger magnetic field and a smaller size than current magnets,” said Yuhu Zhai, a principal engineer at PPPL and lead author of a paper reporting the results in IEEE Transactions on Applied Superconductivity. “The only way you do that is with superconducting wires, and that’s what we’ve done.”

Fusion, the power that drives the sun and stars, combines light elements in the form of plasma — the hot, charged state of matter composed of free electrons and atomic nuclei — that generates massive amounts of energy. Scientists are seeking to replicate fusion on Earth for a virtually inexhaustible supply of safe and clean power to generate electricity.

High-temperature superconducting magnets have several advantages over copper magnets. They can be turned on for longer periods than copper magnets can because they don’t heat up as quickly, making them better suited for use in future fusion power plants that will have to run for months at a time. Superconducting wires are also powerful, able to transmit the same amount of electrical current as a copper wire many times wider while producing a stronger magnetic field.

The magnets could also help scientists continue to shrink the size of tokamaks, improving performance and reducing construction cost. “Tokamaks are sensitive to the conditions in their central regions, including the size of the central magnet, or solenoid, the shielding, and the vacuum vessel,” said Jon Menard, PPPL’s deputy director for research. “A lot depends on the center. So if you can shrink things in the middle, you can shrink the whole machine and reduce cost while, in theory, improving performance.”

These new magnets take advantage of a technique refined by Zhai and researchers at Advanced Conductor Technologies, the University of Colorado, Boulder, and the National High Magnetic Field Laboratory, in Tallahassee, Florida. The technique means that the wires do not need conventional epoxy and glass fiber insulation to ensure the flow of electricity. While simplifying construction, the technique also lowers costs. “The costs to wind the coils are much lower because we don’t have to go through the expensive and error-prone epoxy vacuum-impregnation process,” Zhai said. “Instead, you’re directly winding the conductor into the coil form.”

Moreover, “high-temperature superconducting magnets can help spherical tokamak design because the higher current density and smaller windings provide more space for support structure that helps the device withstand the high magnetic fields, enhancing operating conditions,” said Thomas Brown, a PPPL engineer who contributed to the research. “Also, the smaller, more powerful magnets give the machine designer more options to design a spherical tokamak with geometry that could enhance overall tokamak performance. We’re not quite there yet but we’re closer, and maybe close enough.”

This research was supported by the U.S. Department of Energy (Small Business Innovation Research and Laboratory Directed Research and Development).

Story Source:

Materials provided by DOE/Princeton Plasma Physics Laboratory. Original written by Raphael Rosen. Note: Content may be edited for style and length.

About 565 million years ago, however, the magnetic field’s strength decreased to 10 percent of its strength today. Then, mysteriously, the field bounced back, regaining its strength just before the Cambrian explosion of multicellular life on Earth.

What caused the magnetic field to bounce back?

According to new research from scientists at the University of Rochester, this rejuvenation happened within a few tens of millions of years — rapid on geological timescales — and coincided with the formation of Earth’s solid inner core, suggesting that the core is likely a direct cause.

“The inner core is tremendously important,” says John Tarduno, the William R. Kenan, Jr., Professor of Geophysics in the Department of Earth and Environmental Sciences and dean of research for Arts, Sciences & Engineering at Rochester. “Right before the inner core started to grow, the magnetic field was at the point of collapse, but as soon as the inner core started to grow, the field was regenerated.”

In the paper, published in Nature Communications, the researchers determined several key dates in the inner core’s history, including a more precise estimate for its age. The research provides clues about the history and future evolution of Earth and how it became a habitable planet, as well as the evolution of other planets in the solar system.

Unlocking information in ancient rocks

Earth is composed of layers: the crust, where life is situated; the mantle, Earth’s thickest layer; the molten outer core; and the solid inner core, which is, in turn, composed of an outermost inner core and an innermost inner core.

Earth’s magnetic field is generated in its outer core, where swirling liquid iron causes electric currents, driving a phenomenon called the geodynamo that produces the magnetic field.

Because of the magnetic field’s relationship to Earth’s core, scientists have been trying for decades to determine how Earth’s magnetic field and core have changed throughout our planet’s history. They cannot directly measure the magnetic field due to the location and extreme temperatures of materials in the core. Fortunately, minerals that rise to Earth’s surface contain tiny magnetic particles that lock in the direction and intensity of the magnetic field at the time the minerals cool from their molten state.

To better constrain the age and growth of the inner core, Tarduno and his team used a CO₂ laser and the lab’s superconducting quantum interference device (SQUID) magnetometer to analyze feldspar crystals from the rock anorthosite. These crystals have minute magnetic needles within them that are “perfect magnetic recorders,” Tarduno says.

By studying the magnetism locked in ancient crystals — a field known as paleomagnetism — the researchers determined two new important dates in the history of the inner core:

• 550 million years ago: the time at which the magnetic field began to renew rapidly after a near collapse 15 million years before that. The researchers attribute the rapid renewal of the magnetic field to the formation of a solid inner core that recharged the molten outer core and restored the magnetic field’s strength.
• 450 million years ago: the time at which the growing inner core’s structure changed, marking the boundary between the innermost and outermost inner core. These changes in the inner core coincide with changes around the same time in the structure of the overlying mantel, due to plate tectonics on the surface.

“Because we constrained the inner core’s age more accurately, we could explore the fact that the present-day inner core is actually composed of two parts,” Tarduno says. “Plate tectonic movements on Earth’s surface indirectly affected the inner core, and the history of these movements is imprinted deep within Earth in the inner core’s structure.”

Avoiding a Mars-like fate

Better understanding the dynamics and growth of the inner core and the magnetic field has important implications, not only in uncovering Earth’s past and predicting its future, but in unraveling the ways in which other planets might form magnetic shields and sustain the conditions necessary to harbor life.

Researchers believe that Mars, for example, once had a magnetic field, but the field dissipated, leaving the planet vulnerable to solar wind and the surface ocean-less. While it is unclear whether the absence of a magnetic field would have caused Earth to meet the same fate, “Earth certainly would’ve lost much more water if Earth’s magnetic field had not been regenerated,” Tarduno says. “The planet would be much drier and very different than the planet today.”

In terms of planetary evolution, then, the research emphasizes the importance of a magnetic shield and a mechanism to sustain it, he says.

“This research really highlights the need to have something like a growing inner core that sustains a magnetic field over the entire lifetime — many billions of years — of a planet.”