The institute’s chief scientist, Chen Jiming, hailed the achievement as “a substantial breakthrough after thousands of experiments and 18 years of hard work”, and another example of China “fulfilling its commitments to ITER”.
China, one of seven members of the ITER project, is responsible for producing 54 of the 440 panels needed for the reactor. Together they will form the so-called “first wall”, a crucial part of ITER designed to protect the rest of the reactor by absorbing most of the radiation and heat from the plasma.
The panels, each measuring 1 x 1.5 metres (3.2 x 4.9ft), are composed of layers of beryllium, copper alloy and stainless steel, and must be able to withstand a heat load of 4.7 megawatts per square metre.
“By comparison, the solar radiation hitting Earth is about 0.001 megawatts per square metre. That is the heat we feel on our body while standing under the sun at the equator in summer at mid-day,” said ITER director-general Pietro Barabaschi.
Removing a heat load 4,700 times more than that amount of solar radiation requires “an unprecedented engineering effort to develop suitable technologies,” he said.
The panels also had to be designed to last the entire 20-year lifespan of ITER, meaning they will have to endure about 30,000 plasma pulses of various durations.
While plasma can reach temperatures of more than 100 million degrees Celsius, the surface of the first wall will not exceed more than a few hundred degrees, Barabaschi noted, since the plasma is confined within a strong magnetic field and will not touch the first wall directly.
“All these require the development of cutting-edge technologies – a multi-year development and qualification programme that China has carried out successfully and on time,” he said.
The most difficult part of the development process was joining the panel’s different layers, especially beryllium and copper alloy, Chen told Sichuan Online. “If the joint does not work properly, materials can easily melt and fall into the plasma.”
“We failed so many times. Eventually we came up with an innovative approach to laser welding and solved the problem,” Chen said.
The first wall of the reactor is also responsible for stopping or slowing down the neutrons produced from the fusion reactions, as well as controlling the flow of those particles in the chamber.
“The panels from China are critically important, since they are the ones dedicated to form the limiting surface for defining the plasma boundary,” said Barabaschi.
China, the European Union and Russia are said to be making good progress in developing the first wall panels of reactors. The EU is producing 215 panels – about half of the total – which must withstand a heat load of 2 megawatts per square metre. A full-scale prototype was completed and tested last year and is awaiting production approval.
India, Japan, Korea and the United States are also helping to build the ITER reactor, which will be located in southern France.
Once completed, the ITER reactor, which was first conceived in 1978, will contain nearly a million components and is expected to start producing plasma in 2025.