STEP (Spherical Tokamak for Energy Production)

STEP (Spherical Tokamak for Energy Production) is the UK's flagship fusion energy program, representing one of the largest government-funded fusion energy initiatives in the world. The program is managed by the UK Atomic Energy Authority (UKAEA) and was announced in 2019 with initial government funding of £220 million for the concept design phase.

The STEP program aims to deliver a prototype fusion power plant that demonstrates the full cycle of fusion energy generation, including tritium breeding, power extraction, and grid connection. The target for first plasma is the early 2040s, with the goal of demonstrating net energy production and establishing the technical and commercial viability of fusion energy.

STEP uses a spherical tokamak design, a variant of the conventional tokamak where the plasma is more compact and spherical rather than toroidal. The spherical tokamak concept was pioneered at the Mega Amp Spherical Tokamak (MAST) at Culham, and offers several potential advantages:

• Higher plasma beta (ratio of plasma pressure to magnetic pressure), allowing more efficient use of magnetic field
• More compact reactor size, potentially reducing cost
• Better confinement at lower magnetic fields

However, spherical tokamaks also present engineering challenges, particularly in the narrow central column where space for shielding and magnets is extremely limited.

In October 2022, the UK government selected West Burton, a former coal-fired power station site in Nottinghamshire, as the location for the STEP prototype. This choice reflects the government's 'levelling up' agenda and the goal of transitioning from fossil fuel to fusion energy generation at the same site. The site selection was followed by the announcement of £2.5 billion in funding for the program over the period 2025-2030.

The STEP program is structured in phases:

• Phase 1 (2019-2024): Concept design and site selection
• Phase 2 (2024-2032): Detailed design and regulatory framework
• Phase 3 (2032-2040): Construction
• Phase 4 (early 2040s): Commissioning and first plasma

The UK government's Fusion Strategy, published in 2023 and updated in 2026, positions STEP as the centerpiece of the UK's fusion energy ambition. The strategy also includes regulatory reform (the Fusion Energy Act), international partnerships, and support for private fusion companies. The UK's departure from EURATOM and the ITER program has made STEP even more critical as the UK's primary government-funded fusion energy pathway.

STEP connects to the broader UK fusion ecosystem at Culham, which includes the MAST Upgrade (MAST-U) experiment, the JET facility (now decommissioned), various materials and technology test facilities, and private fusion companies. The program also connects to international fusion research through bilateral agreements and the UK's continued participation in some European fusion programs.