“The United States currently produces about 7% of its electricity from wind energy,” said Sara Pryor, professor in the Department of Earth and Atmospheric Sciences. “This research shows that a quadrupling of the installed capacity of wind turbines from 2014 levels will allow us to attain the goal of 20% of electricity from the wind, without requiring additional land, or negative impacts on systemwide efficiency or local climates.”

Pryor worked with Rebecca Barthelmie, professor in the Sibley School of Mechanical and Aerospace Engineering, and postdoctoral researcher Tristan Shepherd to develop scenarios for how wind energy can expand from current levels to one-fifth of the entire U.S. electricity supply by 2030, as outlined by the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) in 2008.

Called the “20% Wind Scenario,” the NREL report noted that generating 20% of U.S. electricity from wind could eliminate approximately 825 million metric tons of carbon dioxide emissions in the electrical energy sector in 2030.

From 2016 to 2017, wind-generated electricity in the U.S. grew by 12% to 254 terawatt hours — then increased another 8.3% to 275 terawatt hours in 2018, the researchers said. In context, the U.S. currently uses approximately 310 to 320 terawatt hours of electricity each month — generated from coal, natural gas, nuclear and renewable energy power plants.

“Wind energy is already playing a key role in decarbonizing the global energy system,” Pryor said. “Wind turbines repay the lifetime carbon emissions associated with their deployment and fabrication in three to seven months of operation and provide nearly 30 years of virtually carbon-free electricity generation.”

But, the researchers asked, does quadrupling the number of wind turbines reduce the efficiency of turbine fleets that gather energy? And can that generation negatively affect the local climate?

In high-density arrays of large wind turbines, the researchers examined possible declines in systemwide efficiency associated with a phenomenon called “wind turbine wakes,” where the wind speed is slowed by extraction of momentum by wind turbines. This wake is eroded by mixing with undisturbed air in the atmosphere, but can reduce the wind speed that impinges on downstream wind turbines.

“The ‘theft’ of wind by upstream wind turbines reduces the overall power produced by the total ensemble of wind turbines and the enhanced mixing (turbulence) can alter local climate conditions close to wind turbines,” said Barthelmie.

The researchers offered scenarios — such as repowering turbines with improved technology — for expanding the installed capacity of wind turbines without using additional land. The researchers demonstrated that expansion of the installed capacity has a tiny influence on systemwide efficiency and very small impacts on local climate that are reduced by deploying large, state-of-the-art turbines.

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Materials provided by Cornell University. Original written by Blaine Friedlander. Note: Content may be edited for style and length.

The work, led by Yuping Huang, director of the Center for Quantum Science and Engineering at Stevens, addresses a decades old problem with LIDAR, which fires lasers at distant targets, then detects the reflected light. While light detectors used in these systems are sensitive enough to create detailed images from just a few photons — miniscule particles of light that can be encoded with information — it’s tough to differentiate reflected fragments of laser light from brighter background light such as sunbeams.

“The more sensitive our sensors get, the more sensitive they become to background noise,” said Huang, whose work appears in the Feb. 17 advanced online issue of Nature Communications. “That’s the problem we’re now trying to solve.”

The technology is the first real-world demonstration of single-photon noise reduction using a method called Quantum Parametric Mode Sorting, or QPMS, which was first proposed by Huang and his team in a 2017 Nature paper. Unlike most noise-filtering tools, which rely on software-based post-processing to clean up noisy images, QPMS checks light’s quantum signatures through exotic nonlinear optics to create an exponentially cleaner image at the level of the sensor itself.

Detecting a specific information-bearing photon amid the roar of background noise is like trying to pluck a single snowflake from a blizzard — but that’s exactly what Huang’s team has managed to do. Huang and colleagues describe a method for imprinting specific quantum properties onto an outgoing pulse of laser light, and then filtering incoming light so that only photons with matching quantum properties are registered by the sensor.

The result: an imaging system that is incredibly sensitive to photons returning from its target, but that ignores virtually all unwanted noisy photons. The team’s approach yields sharp 3D images even when every signal-carrying photon is drowned out by 34 times as many noisy photons.

“By cleaning up initial photon detection, we’re pushing the limits of accurate 3D imaging in a noisy environment,” said Patrick Rehain, a Stevens doctoral candidate and the study’s lead author. “We’ve shown that we can reduce the amount of noise about 40,000 times better than the top current imaging technologies.”

That hardware-based approach could facilitate the use of LIDAR in noisy settings where computationally intensive post-processing isn’t possible. The technology could also be combined with software-based noise reduction to yield even better results. “We aren’t trying to compete with computational approaches — we’re giving them new platforms to work in,” Rehain said.

In practical terms, QPMS noise reduction could allow LIDAR to be used to generate accurate, detailed 3D images at ranges of up to 30 kilometers. It could also be used for deep-space communication, where the sun’s harsh glare would ordinarily drown out distant laser pulses.

Perhaps most excitingly, the technology could also give researchers a closer look at the most sensitive parts of the human body. By enabling virtually noise-free single-photon imaging, the Stevens imaging system will help researchers create crisp, highly detailed images of the human retina using almost invisibly faint laser beams that won’t damage the eye’s sensitive tissues.

“The single-photon imaging field is booming,” said Huang. “But it’s been a long time since we’ve seen such a big step forward in noise reduction, and the benefits it could impart to so many technologies.”

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Materials provided by Stevens Institute of Technology. Note: Content may be edited for style and length.

Cutting-edge facility

The cutting-edge facility, built and housed at the Max Planck Institute for Plasma Physics with PPPL as the leading U.S. collaborator, is designed to improve the performance and stability of the plasma — the hot, charged state of matter composed of free electrons and atomic nuclei, or ions, that makes up 99 percent of the visible universe. Fusion reactions fuse ions to release massive amounts of energy — the process that scientists are seeking to create and control on Earth to produce safe, clean and virtually limitless power to generate electricity for all humankind.

Recent research on the W7-X aimed to determine whether design of the advanced facility could temper the leakage of heat and particles from the core of the plasma that has long slowed the advancement of stellarators. “That is one of the most important questions in the development of stellarator fusion devices,” said PPPL physicist Novimir Pablant, lead author of a paper describing the results in Nuclear Fusion.

His work validates an important aspect of the findings. The research, combined with the findings of an accepted paper by Max Planck physicist Sergey Bozhenkov and a paper under review by physicist Craig Beidler of the institute, demonstrates that the advanced design does in fact moderate the leakage. “Our results showed that we had a first glimpse of our targeted physics regimes much earlier than expected,” said Max Planck physicist Andreas Dinklage. “I recall my excitement seeing Novi’s raw data in the control room right after the shot. I immediately realized it was one of the rare moments in a scientist’s life when the evidence you measure shows that you’re following the right path. But even now there’s still a long way to go.”

Common problem

The leakage, called “transport,” is a common problem for stellarators and more widely used fusion devices called tokamaks that have traditionally better coped with the problem. Two conditions give rise to transport in these facilities, which confine the plasma in magnetic fields that the particles orbit.

These conditions are:

• Turbulence. The unruly swirling and eddies of plasma can trigger transport;
• Collisions and orbits. The particles that orbit magnetic field lines can often collide, knocking them out of their orbits and causing what physicists call “neoclassical transport.”

Designers of the W7-X stellarator sought to reduce neoclassical transport by carefully shaping the complex, three-dimensional magnetic coils that create the confining magnetic field. To test the effectiveness of the design, researchers investigated complementary aspects of it.

Pablant found that measurements of the behavior of plasma in previous W7-X experiments agreed well with the predictions of a code developed by Matt Landreman of the University of Maryland that parallels those the designers used to shape the twisting W7-X coils. Bozhenov took a detailed look at the experiments and Beidler traced control of the leakage to the advanced design of the stellarator.

“This research validates predictions for how well the optimized design of the W7-X reduces neoclassical transport,” Pablant said. By comparison, he added, “Un-optimized stellarators have done very poorly” in controlling the problem.

Further benefit

A further benefit of the optimized design is that it reveals where most of the transport in the W7-X stellarator now comes from. “This allows us to determine how much turbulent transport is going on in the core of the plasma,” Pablant said. “The research marks the first step in showing that high-performance stellarator designs such as W-7X are an attractive way to produce a clean and safe fusion reactor.”

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