Good news! This could be a breakthrough! Are we close to reaching a burning plasma or the sun on Earth?
"Researchers working on China's fully superconducting Experimental Advanced Superconducting Tokamak (EAST) have experimentally accessed a theorized "density-free regime" for fusion plasmas, achieving stable operation at densities well beyond conventional limits. ...
By realizing a novel high-density operating scheme on EAST, the team demonstrated that plasma density, long constrained by empirical limits in tokamak operation, can be substantially extended without triggering disruptive instabilities. ...
For deuterium-tritium fusion reactions, plasmas must be heated to an optimal temperature of around 13 keV (150 million kelvin). Under these conditions, thermonuclear power scales with the square of fuel density.
However, in conventional tokamak operation, plasma density has long been restricted by an empirical upper limit. Exceeding this limit often leads to instabilities that disrupt plasma confinement and endanger tokamak operation, posing a major challenge to improving fusion performance.
The recent development of the plasma–wall self organization (PWSO) theory provides a novel perspective on understanding the disruptive density limit. ...The theory predicts that a new density-free regime could be accessed by achieving a delicate balance between the plasma and the metallic walls of the device, which are dominated by physical sputtering. ..."
"... While long-term international fusion research has indicated that the physical processes triggering the density limit occur at the plasma-wall boundary region, the underlying mechanisms have remained unclear.
In this study, the Chinese research team developed a self-organized plasma-wall interaction theoretical model. Through this model, they identified the critical role of radiation instability induced by boundary impurities in triggering the density limit, thereby elucidating the underlying mechanism.
Building on this theoretical insight, researchers experimentally controlled the plasma to exceed the density limit and successfully guided it into a new "density-free zone."
These results mark the first experimental confirmation of such a zone in tokamaks. ..."
From the abstract:
"High plasma density operation is crucial for a tokamak to achieve energy breakeven and burning plasma. However, there is often an empirical upper limit of electron density in tokamak operation, namely, the Greenwald density limit ng
, above which tokamaks generally disrupt.
Achieving high-density operation above the density limit has been a long-standing challenge in magnetic confinement fusion research.
Here, we report experimental results on the Experimental Advanced Superconducting Tokamak (EAST) achieving line-averaged electron density in the range of (1.3 to 1.65) ng, significantly above the typical EAST operational range of (0.8 to 1.0) ng. This is performed with electron cyclotron resonance heating (ECRH)–assisted ohmic start-up and sufficiently high initial neutral density.
These experiments are shown to operate in the density-free regime first predicted by a recent plasma-wall self-organization theory. These results suggest a promising scheme for substantially increasing the density limit in tokamaks, a critical advancement toward achieving burning plasma."
Tokamak experiments exceed plasma density limit, offering new approach to fusion ignition
