Plasma heating efficiency in fusion devices boosted by metal screens

To address this problem, scientists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) conducted computer simulations and demonstrated a technique that prevents the generation of unwanted waves, called slow-wave modes, that increase entry into the plasma. of heat.

“This is the first time scientists have used 2D computer simulations to explore how to reduce slow modes,” said Eun-Hwa Kim, principal research physicist at PPPL and lead author of the paper reporting the results. plasma physics. “The results could lead to more efficient plasma heating and potentially easier access to fusion energy.”

The team, which included researchers from General Atomics using the DIII-D Tokamak Fusion Facility, determined that a metal grid, also known as a Faraday screen, would be tilted slightly 5 degrees relative to the antenna that generates the heat waves. Spiral waves, stopping the generation of slow modes. The researchers wanted to avoid creating slow modes because, unlike spiral waves, they cannot penetrate the magnetic field lines that confine the plasma to heat the core, where most fusion reactions occur. Furthermore, slow modes are easily attenuated or eliminated by the plasma itself. Therefore, any energy used to create the slow mode is energy not used to heat the plasma and promote the fusion reaction.

The researchers simulated the generation of spiral waves and slow-wave patterns using Petra-M computer code, a powerful and versatile program used to model electromagnetic waves in fusion devices and space plasmas. The simulation replicated conditions in the DIII-D tokamak, a toroidal plasma facility operated by General Atomics for the U.S. Department of Energy. The team conducted a series of virtual experiments to test which of the following has the greatest influence on the generation of slow modes: the alignment of the antenna, the alignment of the Faraday screen, or the density of small particles called electrons in front of the antenna. The simulations confirmed suggestions by previous researchers that when the Faraday screen is aligned at an angle of five degrees or less to the direction of the antenna, the screen actually short-circuits the slow modes, causing them to disappear before they appear. .

Slow mode suppression depends largely on how far the Faraday screen is tilted to one side. “We found that when the screen orientation exceeds just a little more than 5 degrees, the slow mode grows substantially,” said Masayuki Ono, co-author of the paper and principal research physicist at PPPL. “The development of the slow mode has important implications for screen alignment.” The sensitivity surprised us. “Scientists can use this information to adjust the design of new fusion facilities to make their heating more powerful and efficient.

In the future, the scientists plan to deepen their understanding of how to prevent slow modes by running computer simulations that take more into account the properties of the plasma and take into account more information about the antenna.

This research was supported by the Department of Energy’s Office of Science (Fusion Energy Science) (Contract Nos. DE-AC20-09CH11466 and DE-FC02-04ER54698) and by the Department of Energy’s Scientific Discovery through Advanced Computing Program (Contract No. for DE-SC0024369). Simulations were performed using the National Energy Research Scientific Computing Center, a U.S. Department of Energy user facility at Lawrence Berkeley National Laboratory, under Contract DE-AC02-05CH11231 and Contract FES-ERCAP0027700.