Image of the first plasma as captured by a Fast Camera (Right)

Institute of Plasma Research has commissioned India’s first Small-Scale Spherical TOKAMAK (SS-ST), adding to its existing TOKAMAKs and marking a notable milestone in compact fusion research. The spherical design features a significantly smaller horizontal footprint compared to conventional TOKAMAKs, yet it can confine very hot plasma efficiently.

The SS-ST is designed to operate with less powerful magnets, potentially reducing construction costs, while presenting integration challenges due to tight space around the central column and the need for very precise tolerances in sub-assemblies. At IPR, the project aims to address manufacturing and assembly challenges specific to this configuration and to explore the associated plasma physics.

All SS-ST components were designed and developed indigenously and fabricated with the support of domestic industries. After assembling the subsystems and conducting initial tests, first plasma experiments were conducted on 11 December 2025.

The vacuum vessel achieved a base pressure below 2 × 10^-7 mbar, and all subsystems—hydrogen gas feed, magnetic coil power supplies, 2.45 GHz electron cyclotron resonance system, machine diagnostics, front-end electronics, and the central triggering and ST Control System (STCS)—were individually evaluated for performance and reliability.

During the campaign, the STCS operated in pre-programmed mode, delivering 99.999% pure hydrogen gas into the vessel and sequentially applying currents to the magnetic field coils. Plasma was successfully produced on the very first attempt.

High-speed visible imaging captured the plasma formation, revealing filamentary structures aligned with the toroidal magnetic field. All diagnostic signals acted as expected, confirming plasma breakdown and the presence of excited impurity lines, with detailed data analysis underway.

A photograph of the first plasma is provided in the report, illustrating the successful ignition and initial plasma behaviour in this pioneering small-scale spherical TOKAMAK. This milestone demonstrates both the feasibility of indigenously developed components and the viability of SS-ST for continued fusion research and physics investigations in this unique toroidal configuration.