Achievements at EAST and WEST
In the past weeks, two superconducting tokamaks—EAST in China and WEST in France—have announced new performance records. What relevance to ITER?
On 20 January, EAST plasma shot #150425 became the first to break the barrier of 1,000 seconds in steady-state high-confinement mode operating with a W divertor and lithium injection. Maintaining plasma operation at these conditions for 1,066 seconds at a temperature of nearly 70 million °C represents a significant milestone for the EAST team, which has improved the device’s auxiliary heating, diagnostics and plasma control systems over time to increase performance. The record builds on two prior milestones—the achievement of 100 seconds in 2017 and 403 seconds in 2023.
At WEST—which also operates with a tungsten divertor to help prepare for ITER operation—discharge #60947 was maintained for 824 seconds—approximately double the duration and the ratio of energy injected/extracted compared to the record of the device when it operated with a carbon limiter (former Tore Supra tokamak). This builds on a former record last year of 364 seconds.
Successful operation of tokamaks with very long pulses, in the range of those foreseen in ITER, demonstrates that our knowledge to control high temperature plasmas is mature, explains Alberto Loarte, head of the ITER Science Division. “Successful long pulse tokamak operation requires a high degree of integration and control to ensure that neither physics processes nor technological limitations limit the pulse duration," he explains. "Important issues in this respect are: the control of the magnetic field configuration, since sensors signals may drift over long timescales and the profile of the plasma current relaxes in these timescales and can become unstable; maintaining good power exhaust from the plasma facing components by water cooling leading to a constant component temperature; and avoiding the contamination of the plasma by tungsten that can terminate it due to excessive radiation losses. While not all the systems used in EAST and WEST to demonstrate long-pulse tokamak operation are included in the ITER baseline, their experience is very valuable for us to identify where the key issues are, in practice, so that we can tackle them with our systems.”
These achievements at EAST and WEST add to the broad body of work carried out by tokamak teams around the globe who are working to address key physics and technology issues for ITER, in particular those linked to the new baseline, and to test advanced scenarios for the nuclear fusion reactors of the future.