When Japan lost the bid to host ITER, a landmark agreement with Europe created JT-60SA and IFMIF/EVEDA — ensuring that both partners advanced toward fusion energy.
The Broader Approach (BA) Agreement emerged from one of the most contentious negotiations in the history of international science: where to build ITER. By the early 2000s, two candidate sites remained — Cadarache in southern France and Rokkasho-mura in northern Japan. Both sites had strong technical credentials, and the decision became as much a matter of geopolitics and prestige as engineering suitability.[1]
In June 2005, the ITER parties agreed that Cadarache would host the machine. To secure Japan's continued participation and recognise its substantial technical contributions, the parties negotiated a package of compensatory measures. This package was formalised as the Agreement between the Government of Japan and the European Atomic Energy Community (Euratom) for the Joint Implementation of the Broader Approach Activities in the Field of Fusion Energy Research, signed on 5 February 2007.[2]
The Broader Approach Agreement established three major projects, each addressing a gap between ITER and a future demonstration fusion power plant (DEMO):
JT-60SA (Super Advanced): A large superconducting tokamak built by upgrading and replacing Japan's existing JT-60U device at the Naka Fusion Institute. JT-60SA was designed to explore advanced plasma operating scenarios — particularly steady-state, high-beta plasmas — that ITER would not fully address. With a plasma volume of approximately 132 cubic metres and superconducting coils capable of long-pulse operation, JT-60SA became the largest operational tokamak in the world when it achieved first plasma in October 2023.[3]
IFMIF/EVEDA (International Fusion Materials Irradiation Facility / Engineering Validation and Engineering Design Activities): A programme to design and validate key technologies for a high-intensity neutron source that would test candidate structural materials under the extreme radiation conditions expected in a fusion power plant. The centrepiece was the development and testing of a prototype deuterium-lithium accelerator at Rokkasho, which would validate the beam technology needed for the full IFMIF facility.
IFERC (International Fusion Energy Research Centre): A centre at Rokkasho dedicated to DEMO design coordination, computational simulation of fusion plasmas, and remote experimentation techniques. IFERC provided a framework for Japan and Europe to jointly develop the conceptual design of a demonstration power plant that would follow ITER.
The BA Agreement was structured as a bilateral arrangement between Japan and Euratom, operating in parallel with but legally separate from the ITER Agreement. Costs were shared roughly equally, with Japan providing the host facilities and a larger share of in-kind contributions, and Europe contributing components, expertise, and funding.[1]
Implementation faced significant challenges. The 2011 Tohoku earthquake and tsunami disrupted the Japanese nuclear establishment and delayed construction timelines. The complexity of manufacturing superconducting coils for JT-60SA across multiple European countries introduced coordination difficulties. Budget pressures on both sides periodically strained the partnership. Nevertheless, the agreement held together, and all three projects progressed to completion or near-completion.
JT-60SA achieved its first plasma on 23 October 2023, marking the culmination of over a decade of construction and assembly. The device demonstrated that a large superconducting tokamak could be built through genuine international collaboration, with major components fabricated in France, Italy, Spain, and other European nations before being shipped to Japan for assembly. The operational programme aims to explore plasma scenarios directly relevant to ITER and DEMO, including high-confinement and steady-state regimes.
The Broader Approach Agreement demonstrated that international science diplomacy could transform a potentially divisive competition into a productive partnership. By creating substantial fusion research infrastructure in Japan, it maintained Japanese engagement in the global fusion programme at a level commensurate with the country's technical capabilities and ambitions. The model of compensatory "satellite" projects has been studied by other large-scale international collaborations as a template for managing site-selection disputes.