EAST, WEST and KSTAR Progress

January 2, 2017

Progress on EAST

In November, China celebrated the 10th anniversary of physics operations, of EAST (Experimental Advanced Superconducting Tokamak) campaign and reached a milestone in the exploration of advanced operation scenarios—achieving over 60s fully non inductive steady-state long-pulse H-mode plasmas under radio-frequency heating and ITER-like tungsten divertor operations, which marked the first minute-scale steady-state H-mode operation obtained on past and existing tokamaks around the world. This is a major advance beyond the achievement of a record 32s long-pulse H-mode discharge in 2012. Since then, the EAST team has made great efforts to develop the steady-state H-mode scenario on EAST.

The auxiliary heating system, tungsten divertor and plasma diagnostic system have been upgraded continuously to enhance the capacity for long-pulse, high-performance operations. High power NBI and LHCD systems were developed to further extend the current drive capability and access high β regimes. Tremendous efforts were dedicated to research involving RF power coupling, L-H transition, control of MHD instabilities, plasma-wall interactions, and impurity transport and control to develop advanced integrated operation scenarios, especially in the RF-dominated heating low-torque input conditions. Research results have been presented on various international conferences and journals like Nature Physics, Physical Review Letters and Nuclear Fusion and attracted interest from the world fusion community, which fostered a great many of international collaborations.

The achievement is based on domestic and international collaboration, especially the joint experiment with DIII-D team of General Atomics, USA. As an open international platform, EAST attracts scientists home and abroad who have made great contribution to the experiment.

Progress on WEST

On 14 December WEST, the rejuvenated Tore Supra tokamak designed to serve as a test bench for ITER, achieved first plasma after four years that involved stripping out the 30-year-old machine, adding magnetic coils to change the originally circular plasma into a D shape, and trading its carbon-carbon fiber (CFC) "limiter" for an ITER-like tungsten divertor.

Operators at the French Institute for Magnetic Fusion Research (IRFM) are now confident that they can move forward to the first experimental campaign, set to be launched in March 2017. The first phase of the campaign will explore heat load patterns and H mode transition; the second in October-December 2017 will focus on testing plasma-facing components under the high heat loads of ITER-grade plasmas. On the very same day that the IRFM team was celebrating WEST's first plasma, another team, at the other end of the world, also had an achievement to announce: a record 70-second H-mode plasma had just been recorded by the Korean superconducting tokamak KSTAR. One month earlier, in mid-November, the Chinese tokamak EAST had achieved a similar but slightly shorter 60-second steady-state high energy plasma.

Since its construction in the 1980s, the Tore Supra tokamak has continued to evolve in order to improve plasma performances, even setting a world record with a stationary plasma lasting over six minutes for an extracted energy of 1 gigajoule (GJ). The WEST project (Tungsten (W) Environment in Steady-state Tokamak) aims to transform Tore Supra into a test bed for ITER or, more precisely, to test a "divertor" using ITER technology. The divertor, which is situated on the floor of the vacuum chamber, is a fundamental component as it receives most of the heat and particle fluxes coming from the central plasma. Its function is to extract the "ash" (helium) and part of the heat produced by the fusion reaction, whilst minimising the contamination of the plasma by the other impurities.

WEST makes it possible to: (1) minimize risks (costs and deadlines) linked to the industrialization of the high-tech components of the ITER divertor. (Prototypes produced by the suppliers selected for the manufacture of the ITER divertor are already in place, and industrial pre-series are under preparation); (2) obtain initial experimental findings on the functioning of this divertor and to prepare the teams for its scientific exploitation in ITER; and (3) test, in an accelerated manner, the durability and ageing of this plasma-facing component during extended discharges.

Progress on KSTAR

The National Fusion Research Institute (NFRI) in Korea achieved a world record of more than 1 minute (70 seconds) of high performance (H-mode) operation in its superconducting tokamak, KSTAR. The achievement was made using high power neutral beams and various techniques including a rotating 3D field to alleviate accumulated heat fluxes on plasma facing components.

In addition to the above results, the KSTAR researchers succeeded in achieving alternative advanced plasma operation with the Internal Transport Barrier (ITB). This is the first ITB operation achieved in a superconducting device at the lowest heating power. Such operation can avoid harmful ELM-crash at the plasma edge.

KSAR is now focusing on issues essential for the operation of a fusion reactor beyond ITER, including a new efficient divertor concept for the Korean Fusion Demonstration Reactor (K-Demo), which is envisioned to produce electricity.