Scientists measure laser-heated plasma using the Doppler weather forecasting technique

Scientists used a popular weather forecasting technique to gain insight into how powerful lasers turn clumps of solids into a soup of electrically charged particles known as plasma.

Using this time-tested technique in a new context could help researchers make important measurements in self-entrapment fusion devices, a concept that is being explored as a way to harness fusion energy. This process, which powers the sun and stars, could be a green way to generate electricity on Earth without producing greenhouse gases or long-lived radioactive waste.

Scientists from PPPL, a US Department of Energy (DOE) national laboratory run by Princeton University, measured the dense cloud of plasma generated by a powerful laser striking a solid target. The intense heat caused atoms to vaporize from the surface and emit energetic X-rays.

He measured the speed of light using the Doppler effect – the same phenomenon that causes ambulance sirens to soar as they approach and then fall as they move away. Meteorologists rely on this effect to measure the speed of thunderstorms.

Physicists want to gain a better understanding of dense plasma in part because it is produced by self-entrapment fusion devices — facilities such as the Department of Energy’s Lawrence Livermore National Laboratory’s National Ignition Facility that last year produced more fusion energy than it took to heat the plasma. The more physicists can understand the behavior of the resulting dense plasma, which is 10 billion times denser than the plasma inside doughnut-shaped magnetic tokamak, the more likely they will be able to form fusions more efficiently.

Scientists have found evidence of a barrier, or sheath, between the outer and inner layers of the dense plasma cloud. This observation indicates that the laser-produced dense plasma behaves similarly to the less dense plasma. This discovery marks the first time that scientists have used the Doppler technique to measure very dense plasma. The experiment was performed using the Advanced Laser for Extreme Photonics (ALEPH) facility of Colorado State University.

The results show that dense plasma behaves like other types of plasma, a behavior scientists haven’t been able to directly observe until now, according to Frances Krause, lead author of a paper reporting the findings in Physical review letters.

Prior to this discovery, the researchers didn’t know if they could precisely measure X-rays in the dense plasma, which can obscure such observations. “Scientists didn’t think you could identify X-ray behavior among all the other signals,” Krause said. “But our diagnosis shows that you can.”

Invented in 1960, the laser is used for a wide variety of tasks, including surgery, welding, and printing. Lasers — the term stands for “light amplification by stimulated emission of radiation” — consist of beams of light that are all composed of light rays of the same frequency. In addition, the photon particles that make up the laser light all move in the same direction and direction. As lasers have become more powerful, the need to understand their basic properties has increased.

“You have to understand what these lasers create before you find uses for them,” Krause said. “These are key things. These ultra-powerful lasers will have a lot of applications in the future. We don’t know yet what they will be.”