China’s Huanliu-3 (HL-3) tokamak in Chengdu, the largest and most advanced magnetic confinement tokamak device in China, has heated plasma to over 100m degrees for the first time. The temperature of the ions in its plasma exceeded 100m degrees Celsius (10.1 keV), and the efficiency of energy retention approached the levels required to start a thermonuclear fusion reactor.
These values were achieved in a special mode of operation in which the ions inside the plasma are heated two times more than the electrons. Even when the plasma entered a calmer state (the so-called L-mode), the temperature was kept at 9.4 keV, which shows the stability of the system.
The progress was made possible by improvements in plasma heating and confinement systems. The HL-3 used a neutral particle injection (NBI) system of beams of accelerated atoms that fly into the plasma and transfer energy to it. In the experiment, beams with a power of up to 5 megawatts heated the substance to record temperatures.
At the same time, engineers used a special configuration – a shift of magnetic field lines – which helps stabilise the plasma and hold it longer. Within such a field, areas are formed where heat losses are sharply reduced. These are called transport barriers. The HL-3 managed to create two at once: internal and external, which made it possible to retain energy longer than usual.
The tokamak itself has an improved geometry: the plasma inside it is not just annular but elongated and slightly triangular. This shape improves stability and allows you to store more energy with the same magnetic field. To control the parameters, the scientists used charge exchange spectroscopy to measure the speed and temperature of ions and Thomson scattering. This is a method in which a laser is directed into the plasma and the temperature and density of electrons are determined from the scattered light.
Further HL-3 experiments will address two key challenges: how to efficiently remove excess heat and how to prevent instability during long-term operation. For this purpose, it is planned to test new types of diverters – special magnetic configurations that bring plasma to the cooled walls of the reactor, protecting its elements. Among these are “snowflake” and “tripod” configurations, which have already shown good results in other tokamaks.
In November 2024, HL-3 launched a new series of physical experiments, incorporating for the first time a digital twin system developed by China National Nuclear Corporation (CNNC). A key aspect of the device’s operation is the “baking” of the vacuum chamber, with the digital twin system acting as a “super eye” for this process This creates a digital model in virtual space that is identical to the physical entity, allowing for real-time and precise monitoring of the vacuum chamber baking process.
