Milestones for several fusion reactors

22 December 2016

The Korean Superconducting Tokamak Advanced Research (KSTAR), a tokamak nuclear fusion reactor, achieved a world record of 70 seconds in high-performance plasma operation, South Korea's National Fusion Research Institute (NFRI) said in a statement on 14 December. NFRI said a fully non-inductive operation mode - a "high poloidal beta scenario" - had been used to achieve this long and steady state of operation using a high-power neutron beam. It said various techniques, including a rotating 3D field, had been applied to alleviate the accumulated heat fluxes on the plasma-facing components.

"This is a huge step forward for   realisation of the fusion reactor," NFRI said in a statement. While other reactors have managed to sustain plasma for longer than 70 seconds, KSTAR produced a "high performance" plasma, which is better suited for nuclear fusion. The researchers at the NFRI have also developed a new plasma "operation mode", which should enable reactions to handle greater pressures at lower temperatures.

The institute said KSTAR researchers had also succeeded in achieving an alternative advanced plasma operation mode with the internal transport barrier (ITB). This is a steep pressure gradient in the core of the plasmas due to the enhanced core plasma confinement. NFRI said this is the first ITB operation achieved in the superconducting device at the lowest heating power.

KSTAR, at the National Fusion Research Institute in Daejeon, is intended to study aspects of magnetic fusion energy which will be pertinent to the International Thermonuclear Experimental Reactor (Iter) fusion project under construction at Cadarache in the south of France. Iter, which will be the world’s biggest tokamak reactor, has been designed to produce 500MW output power for several seconds while needing 50MW to operate. The project is funded and run by sic countries (India, Japan, China, Russia, South Korea, the USA) and  the European Union (EU), which as host party, contributes 45% percent of the cost, with the other six parties each contributing some 9%.  

"With the progress of the Iter project, KSTAR research will focus on the mission essential for the fusion reactor beyond Iter," the institute said. "It includes a new efficient mode of operation and a new divertor concept suitable for the Korean fusion demonstration reactor, the K-DEMO device, which will lead the worldwide fusion energy development plan." Construction of KSTAR began in December 1995 and was completed in August 2007. The first experiment was conducted in 2009. KSTAR was the first tokamak to feature a fully superconducting magnet system with a central solenoid, toroidal and poloidal field coils.

China also announced a fusion breakthrough in December, Chinese media reported. Chinese researchers at the Experimental Advanced Superconducting Tokamak (EAST) at the Hefei-based Institute of Plasma Physics, claimed to have independently invented components to keep ionised gas burning steadily for twice the length of the previous record. This included a component for a fusion reactor core that can withstand extremely high temperatures. “The component we invented is one of the first of its kind in the world that has passed the international cyclic heat test,” Cheng Jiming of China National Nuclear Corporation told CCTV. The component is intended to be installed at Iter, and China said the new component is about 20% more heat-resistant than the reactor’s design requires.

EAST deputy director Professor Luo Guangnan  said some previous fusion experiments had lasted for more than 100 seconds, but they were “like riding a bucking bronco”, with plasma that was volatile and difficult to control. However, in an experiment conducted at EAST in August, the plasma was tamed in a high-performance steady state, known as H-mode. EAST is an experimental superconducting tokamak magnetic fusion energy reactor, which began operating in 2006. It was later put under control of Hefei Institutes of Physical Science. China said it was the first tokamak to employ superconducting toroidal and poloidal magnets. It aims for plasma pulses of up to 1000 seconds.

Meanwhile earlier in December, the Wendelstein 7-X (W7-X), the world’s largest and most sophisticated stellarator, began operating at the Max Planck Institute of Plasma Physics in Greifswald, Germany. It was completed in October 2015 and aims to evaluate the main components of a future fusion reactor built using stellarator technology. It plans to be able to operate with up to 30 minutes of continuous plasma discharge by 2021.

The W7-X aims to show that the earlier weaknesses in the stellarator concept have been addressed successfully, “and that the intrinsic advantages of the concept persist, also at plasma parameters approaching those of a future fusion power plant,” according to a report, by T. Sunn Pedersen and several of his colleagues from the Max Planck Institute published in the journal Nature Communications.

First plasma was also reported on 14 December for WEST, formerly known as Tore Supra, a plasma facility near Cadarache owned by France's Commissariat à l'Énergie Atomique (CEA). Tore Supra began operating in 1988 and upgrading it be become WEST required an extensive refit, beginning in 2013. The reactor was upgraded to undertake research to support Iter. WEST is the acronym for “'W Environment in a Steady-state Tokamak”, where W is the chemical symbol for tungsten, the material that will be used for the Iter divertor. CEA will WEST to minimise the cost and schedule risks of industrialising Iter's components by testing prototypes. It will also give initial findings on the functioning of the divertor and test the durability and ageing of tungsten materials.

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