Operators of China’s HT-7U reactor, known as EAST (Experimental Advanced Superconducting Tokamak), have claimed a new fusion record, representing an incremental step in the long road to commercial energy production.

According to the official Xinhua news agency, the EAST reactor was able to maintain stable plasma at high temperatures for 1,056 seconds (17.6 minutes). That represents a significant improvement above the previous record of 101 seconds set last year. EAST operates on deuterium, a stable hydrogen isotope abundant in nature.

The experiment at Hefei, the capital of Anhui Province in eastern China, was directed by Gong Xianzu, a researcher at the Chinese Academy of Sciences’ Institute of Plasma Physics. Details are here.

EAST is among the nuclear fusion reactors located at the Chinese research institute. The doughnut-shaped tokamak produces a high-temperature plasma controlled by powerful electromagnets operating at hundreds of degrees below zero.

Magnetic coils are wrapped around the doughnut to keep the plasma suspended and away from the tube’s interior walls. The design allows the reactor to reach temperatures required for controlled thermonuclear fusion, which involves fusing the nuclei of light atoms to extract the resulting energy.

According to EAST researchers, the experimental design accomplished three goals: an operational period of more than 1,000 seconds; a temperature of 160 million degrees; and a current of 1 million amperes. Those goals were achieved on Dec. 30, the researchers said.

By May, the reactor had achieved a record temperature of 160 million °C, exceeding that of the Sun by a factor of about 10. The duration record was achieved at the end of the year, maintaining continuous plasma operation at about 70 million °C for 17.6 minutes.

Temperatures in the hundreds of millions of degrees are required, but not sufficient, to initiate nuclear fusion processes. Acceptable plasma density and a sufficiently long confinement period are two additional requirements. The nuclei of the elements (positive charges) must be sufficiently close for the strong nuclear force to overcome the repulsion of the Coulombian potential barrier. Appropriate plasma conditions can be achieved by increasing the pressure due to plasma heating. Temperatures in the tens or hundreds of millions of degrees are required to achieve such pressure and density levels.

The ultimate objective of the EAST experiment is achieving nuclear fusion in the same way as does the Sun, utilizing abundant deuterium in the ocean to provide a constant stream of energy.

Unlike finite fossil fuels such as coal, oil and natural gas that produce greenhouse gases, the raw elements required for the “artificial sun” are plentiful. As a result, fusion energy is seen by promoters as the “ultimate energy” source.

However, nuclear fusion requires astronomically high temperatures. Fifteen million degrees on the Sun is sufficient given the enormous pressure. This ignition energy is physically feasible at severe temperatures rather than at the excessive pressures on the Sun’s surface. In a fusion reactor, the “magic number” required is roughly 100 million degrees Celsius.

The Chinese experiment represent an incremental step toward a fusion reactor that produces more energy than it consumes. Among the obstacles to nuclear reactions is finding ways to manage the extremely high temperatures. Plasma confinement is one such technique since there are no natural “containers” for sustaining extreme temperatures. Another technique under development, magnetic confinement, entails spiraling the particles around a field’s lines of force, keeping particles away from the container’s walls, thereby preventing their destruction.

Several countries are spearheading nuclear fusion research, including China, the European Union, India, Japan, Russia, South Korea and the U.S. Still, according to the most optimistic forecasts, commercial nuclear fusion technology is not expected to be available until the middle of this century.

By: DocMemory
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