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In a comprehensive experimental study, an international team of researchers has confirmed that the calculations of a leading turbulence simulation program match experimental data to an unprecedented degree. This marks an important breakthrough in understanding turbulent transport processes in nuclear fusion reactors.

The simulation study has now been published in the journal Nature Communications. It lays out a crucial foundation for predicting the performance of fusion power plants.

Future fusion power plants will generate usable energy efficiently by fusing light atomic nuclei. Magnetic confinement fusion is the most advanced approach to confining a plasma. A gas is heated to millions of degrees Fahrenheit, within a magnetic field. This plasma is suspended inside a donut-shaped vacuum chamber without touching the wall of the reactor.

The energy released from the nuclear fusion reaction is intended for two purposes. It not only generates electricity but also maintains plasma temperature. To sustain the fusion reaction, the plasma must retain as much energy as possible. This is what researchers refer to as achieving a high-energy confinement time.

To reach this goal, physicists must first understand the extremely complex turbulent processes in plasmas and, ideally, find ways to regulate them. To some extent, turbulence is actually beneficial because it helps transport the helium nuclei, which are byproducts of the fusion reaction, out of the plasma while bringing fresh fuel into the core. However, excessive turbulence decreases the energy confinement time because the energy escapes from the plasma center too quickly.

Dr. Klara Höfler is a physicist who studied this phenomenon at the Max Planck Institute for Plasma Physics (IPP) in Garching near Munich. “You can compare this to a drop of milk in a cup of coffee: if you stir with a spoon, turbulent eddies form, and the liquids mix much faster than without stirring.”

Working with colleagues from IPP and five other research institutions in Europe and the United States, she has made a significant breakthrough in understanding turbulence in fusion plasmas. For the first time, the researchers achieved a comprehensive agreement between experimental results and computer simulations. The team simultaneously compared seven key plasma turbulence parameters which are significantly more than the parameters examined in previous studies.

For the new study, Höfler employed the world’s unique diagnostic equipment at the IPP fusion device Axially Symmetric Divertor Experiment (ASDEX) Upgrade. ASDEX Upgrade is a divertor tokamak at the Max-Planck-Institut für Plasmaphysik, Garching that went into operation in 1991. At present, it is Germany’s second largest fusion experiment after stellarator Wendelstein 7-X. The current purpose of the facility is to make experiments under reactor-like conditions possible, essential plasma properties. They are focused on measuring the plasma density and pressure and the wall load. The ASDEX Upgrade has been adapted to replicate the conditions that will be present in a future fusion power plant.

This equipment allowed her to precisely measure the properties of the multi-million-degree plasma during two discharges with different settings. Her team compared plasma measurement data from two discharges at ASDEX Upgrade with the results of GENE simulations.

ASDEX Upgrade

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