Scientists want to create a “star in a jar” by discovering an efficient way of eliminating instabilities in fusion plasma.

Replication of the physical process, fusion, that occurs naturally in stars has been investigated on Earth for decades. Scientists created Tokamak in an attempt to replicate the conditions found inside the Sun, on Earth. Confined by its own strong gravitational field, the sun’s burning plasma is a sphere of fusing particles, producing the heat and light that makes life possible on our planet. However, creating a commercially viable fusion reactor, capable of providing a virtually endless source of clean energy, is easier said than done.

The working mechanism discussed in the study focuses on a device that heats and confines turbulent plasma fuel, in a donut-shaped chamber, long enough to create fusion called the Tokamak. Cocooned by magnets, the plasma torus responds to magnetic fields guiding the fusing plasma particles around the toroidal chamber and away from its walls. Having said that, these reactions are sustainable only in short pulses because making a practical energy source requires a constant steady state.

Fusion produces near unlimited energy in a star. Scientists seek to replicate the process of fusion found in stars that merges light elements in the form of hot, charged plasma composed of free electrons and atomic nuclei, to create a virtually inexhaustible supply of power to generate electricity. The ultimate goal of the researchers is to create a “star in a jar” by making use of the Tokamak reactors. However, there are several challenges to be met on this road and one of them is Edge Localized Modes (ELMs). For viable fusion on Earth, ELMs is a common instability in plasma which must be lessened or eliminated. Flare-like bursts of ELMs can slam into and damage walls of doughnut-shaped Tokamak reactors.

Scientists disturb the plasma using tiny Resonant Magnetic perturbations (RMPs) which distorts the torus plasma. This, in turn, prevents ELMs due to reducing pressure lessening. In order to counter this situation, the experts need to come up with the precise quantum of 3D distortion to eliminate the ELMs, avoiding triggering other instabilities, or releasing too much energy. All in all, researchers must evade disruptions that terminate the plasma. It has been a difficult challenge to overcome because the number of magnetic distortions associated with the plasma is limitless.

Jong-Kyu Park, a Physicist from the Princeton Plasma Physics Laboratory (PPPL), collaborated with the National Fusion Research Institute (NFRI) of Korea and a researching team of the United States to find a group of beneficial 3D distortions that govern ELMs without additional problems. Using the Superconducting Tokamak Advanced Research (KSTAR), South Korean facility researchers validated the predictions. KSTAR provided advanced magnet controls for generating precise distortions in torus plasma that were ideal for testing the predictions. Without the team’s predictive model, identifying beneficial distortions among the innumerable distortions possible within KSTAR, was impossible. Park praised this outstanding achievement in the following words:

“We show for the first time the full 3D field operating window in a tokamak to suppress ELMs without stirring up core instabilities or excessively degrading confinement. For a long time, we thought it would be too computationally difficult to identify all beneficial symmetry-breaking fields, but our work now demonstrates a simple procedure to identify the set of all such configurations.”

The realization that the plasma’s range of distortion is significantly less than that of the 3D fields that can be applied to it greatly simplified the calculations researchers needed to make. The team worked from distortions to 3D fields finding ones that effectively eliminated ELMs. The predictions were validated by the KSTAR experiments. The team of Park said, 

“The method and principle adopted in this study can substantially improve the efficiency and fidelity of the complicated 3D optimizing process in tokamaks.”

Therefore, the KSTAR findings back the ability to predict optimal 3D fields for ITER, the international Tokamak being constructed in France. It will control ELMs utilizing special magnets to produce 3D distortions. A close monitoring and control of ITER will be necessary as it aims to produce 10 times more energy than what is required to heat the plasma.