TJ-II

Intelligence Summary: TJ-II Flexible Heliac Stellarator

Node Identity: TJ-II is a flexible, medium-size stellarator of the heliac type located at the Laboratorio Nacional de Fusión (LNF) at CIEMAT in Madrid. It is the second-largest operational stellarator in Europe after W7-X and serves as Spain's flagship magnetic confinement fusion experiment. Key parameters: major radius R₀ = 1.5 m, averaged minor radius ⟨a⟩ = 0.2-0.25 m, magnetic field B₀ = 1 T. Heating is via microwave ECRH (800 kW at 53 GHz) and neutral beam injection (1.6 MW, 30 keV). The device features 92 access windows for diagnostics and a rotational transform range of 0.96 < ι₀ < 2.5, making it unique for studying magnetic configuration effects on transport.

Strategic Relevance: TJ-II's strategic relevance to the FRC/plasma weapons landscape is defined by its 25+ years of continuous operation and its unique flexibility in magnetic configuration. The heliac design allows variation of the rotational transform, enabling systematic studies of how magnetic geometry affects plasma confinement, turbulence, and transport — knowledge directly transferable to compact toroid and FRC concepts where magnetic configuration optimization is critical. The device was designed in collaboration with Oak Ridge National Laboratory (ORNL, USA) and IPP Garching (Germany), connecting Spanish stellarator research directly to US fusion programs. The liquid metals research program (Li and alloys for power exhaust) is directly relevant to plasma-facing component technology with dual-use implications. Spain's stellarator expertise represents a genuine, long-term plasma physics capability that contributes to W7-X operations and broader stellarator optimization.

Technical Focus / Capabilities: TJ-II research focuses on: (1) turbulence and zonal flow physics; (2) isotope effect studies; (3) power exhaust physics with liquid metals (Li and alloys); (4) stellarator optimization using swarm strategy; (5) Alfvén eigenmode control and stability; (6) support for W7-X operations. The device achieved L-H transition in 2008 using NBI and lithium wall conditioning. Leading researcher Carlos Hidalgo (h-index 52, 10,209 citations) has published extensively on model validation of plasma flow asymmetries, plasma fuelling physics, Alfvén eigenmodes, neoclassical-turbulence interplay, and liquid metals. TJ-II is the third device in a series: TJ-I tokamak (1983-1995), TJ-IU torsatron (1994, later transferred to Germany as TJ-K), and TJ-II.

Network Linkage: TJ-II maintains 1 documented connection: CIEMAT operates TJ-II (at Laboratorio Nacional de Fusión, Madrid). TJ-II was designed with ORNL (USA) and IPP Garching (Germany). It is funded through EUROfusion Spain and supports W7-X operations. The device received EURATOM preferential support for Phase I (Physics) in 1986 and Phase II (Engineering) in 1990. Construction completed October 1996, with 60% of investments reverting to Spanish companies.