Chinese researchers claim merger stage
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Operators of China’s HT-7U reactor, known as EAST (Experimental Advanced Superconducting Tokamak), have claimed a new fusion record, which represents a further step in the long road to commercial energy production.
According to the official Xinhua press, the EAST reactor was able to maintain stable plasma at high temperature for 1056 seconds (17.6 minutes). This is a significant improvement over the previous record of 101 seconds set last year. EAST works on deuterium, a stable isotope of hydrogen abundant in nature.
The experiment in Hefei, the capital of eastern China’s Anhui Province, was led by Gong Xianzu, a researcher at the Institute of Plasma Physics of the Chinese Academy of Sciences. Details are here.
EAST is one of the nuclear fusion reactors located at the Chinese research institute. The donut-shaped tokamak produces high-temperature plasma controlled by powerful electromagnets operating at hundreds of degrees below zero.
Magnetic coils are wound around the donut to keep the plasma suspended and away from the interior walls of the tube. The design allows the reactor to reach the temperatures required for controlled thermonuclear fusion, which involves fusing the nuclei of light atoms to extract the resulting energy.
According to the EAST researchers, the experimental design achieved three goals: an operational period of more than 1000 seconds; a temperature of 160 million degrees; and a current of 1 million amperes. These goals were met on Dec. 30, according to the researchers.
By May, the reactor had reached a record temperature of 160 million ° C, exceeding that of the Sun by a factor of about 10. The record for duration was reached at the end of the year, maintaining continuous operation of the plasma at around 70 million ° C. for 17.6 minutes.
Temperatures of several hundred million degrees are necessary, but not sufficient, to initiate nuclear fusion processes. An acceptable plasma density and a sufficiently long confinement period are two additional requirements. The nuclei of the elements (positive charges) must be close enough for the strong nuclear force to overcome the repulsion of the Coulomb potential barrier. Appropriate plasma conditions can be obtained by increasing the pressure due to heating of the plasma. Temperatures on the order of tens or hundreds of millions of degrees are required to achieve such levels of pressure and density.
The ultimate goal of the EAST experiment is to achieve nuclear fusion in the same way as the Sun, using the deuterium abundant in the ocean to provide a constant flow of energy.
Unlike finite fossil fuels such as coal, oil and natural gas which produce greenhouse gases, the crude elements necessary for “artificial sun” are plentiful. As a result, fusion energy is viewed by promoters as the “ultimate source of energy”.
However, nuclear fusion requires astronomically high temperatures. Fifteen million degrees on the Sun is sufficient given the enormous pressure. This ignition energy is physically achievable at severe temperatures rather than excessive pressures on the Sun’s surface. In a fusion reactor, the required “magic number” is around 100 million degrees Celsius.
The Chinese experiment represents a further step towards a fusion reactor that produces more energy than it consumes. Among the obstacles to nuclear reactions is finding ways to deal with extremely high temperatures. Containment of plasma is one such technique because there are no natural “vessels” to withstand extreme temperatures. Another technique under development, magnetic confinement, involves spiraling particles around the lines of force of a field, pushing the particles away from the walls of the container, thus preventing their destruction.
Several countries are at the forefront of nuclear fusion research, including China, the European Union, India, Japan, Russia, South Korea and the United States. Yet, according to the most optimistic forecasts, commercial nuclear fusion technology is not expected to be available until the middle of this century.