Millimeter-wave imaging technology is widely used in airborne radar¹（机载雷达）, automotive sensors² and full-body scanners for passenger screening at airports. A new, quasi-optical radar technique images millimeter-wave radiation reflected from fusion³ plasmas in 2D, time-resolved images. This novel application lets researchers image waves in fusion plasmas in startling detail, and provides vital information to devise strategies to avoid instabilities which can reduce fusion（融合，熔化） power output. This enhanced imaging diagnostic of the tokamak interior was developed by a collaboration⁵ of fusion scientists from the University of California at Davis and the U.S. Department of Energy's Princeton Plasma⁴ Physics Laboratory.

 

Fusion experiments burn far hotter than the surface of our sun, too hot even to emit visible light. This renders typical photographic techniques all but useless. However, just as millimeter-waves penetrate⁶ the light clothing of passengers screened at airports and reflect from denser⁷, concealed⁸ objects, millimeter-wave imaging reflectometry (MIR) illuminates⁹ the plasma with radio waves that penetrate the thin outer layers and reflect off small density¹⁰ fluctuations¹¹ within the plasma interior. In plasma, waves can eject particles that ride the waves like surfers to the shore. Or the particles can grow uncontrollably until the entire discharge is lost. On the DIII-D tokamak at General Atomics in San Diego, MIR is paired with an Electron Cyclotron Emission¹² Imaging (ECE-I) camera that radiometrically detects small variations in electron temperature.

 

In this way, both the density and temperature fluctuations caused by waves can be imaged in the same place and at the same time. Furthermore, because these diagnostics do not rely on an energetic particle beam, they can take 2D pictures continuously during the discharge without perturbing¹³ the plasma conditions. The results are images that help scientists understand how and why the waves grow and how to maintain plasma stability.

 

"The 2D and 3D structure of plasma fluctuations are important components¹⁴ of the magnetohydrodynamic（磁流体动力的） (MHD) theory that allows us to predict the behavior of a future burning plasma fusion power plant," said physicist¹⁵ Benjamin Tobias who participated in the research.

 

"With this new visualization¹⁶ capability¹⁷, we can perform the kinds of ambitious experiments that will accelerate our progress toward a viable¹⁸ new energy resource."

点击收听单词发音