China’s reactor pushes density limit; widens path to power, PgII

Key Highlights:

• Chinese scientists at the EAST fusion reactor exceeded the Greenwald density limit by 65%, achieving a stable plasma state.
• The team combined Electron Cyclotron Resonance Heating (ECRH) with increased deuterium gas to cool the divertor.
• Experiments achieved densities of 5.6 × 10^19 particles per cubic meter, significantly higher than the reactor's normal limit.
• The findings align with the plasma-wall self-organisation (PWSO) theory, suggesting a path to higher density limits in tokamaks.

Detailed Insights:

• The Greenwald limit has long constrained tokamak reactors, causing plasma collapse and potential damage.
• The EAST reactor team used ECRH during start-up and increased deuterium gas to lower the divertor temperature.
• Coating the reactor's tungsten surfaces with lithium reduced impurities and improved plasma-wall interaction.
• The PWSO theory predicts stable states beyond the Greenwald limit, dependent on divertor temperature.
• Lower divertor temperatures result in fewer impurities and cleaner plasma, allowing for higher hydrogen atom density.
• Repeated ECRH shots improved wall conditions, reducing sputtering and enabling higher densities over time.
• The advance could allow reactors to achieve ignition at lower temperatures or with shorter confinement times.
• The findings are relevant to ITER, the international fusion experiment in France, potentially overcoming density limits.

Scientific/Technical Concepts Involved:

• Nuclear Fusion: The process of combining hydrogen atoms to form helium, releasing energy.
• Plasma Density: The number of fuel particles squeezed into a reactor.
• Tokamaks: Donut-shaped magnetic vessels designed to contain superhot plasma.
• Greenwald Limit: A density threshold beyond which plasma collapses in a disruption.