TJ-II Stellarator

The TJ-II Stellarator is a medium-sized, flexible heliac-type magnetic confinement research facility located at the Laboratorio Nacional de Fusión within the Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT) in Madrid, Spain. Characterized by a major radius of $R = 1.5\text{ m}$, a minor radius of $a = 0.2\text{ m}$, and a magnetic field strength approaching $B = 1.0\text{ T}$, it represents the second-largest operational stellarator in Europe, surpassed only by the Wendelstein 7-X device in Germany. TJ-II's unique design features a central conductor coil system wrapped by helical windings, allowing for an exceptionally high degree of rotational transform adjustability and magnetic shear variation. This structural flexibility allows researchers to explore transport barriers, turbulence mitigation, and plasma stability thresholds across varying magnetic topologies. Experimental operations frequently require advanced diagnostics and support hardware, interfacing with high-energy pulsed systems and dedicated Capacitor Bank networks for field energization and heating control. Computational modeling of its 3D kinetic and transport dynamics often leverages high-performance simulation tools related to architectures like VPIC (Vector Particle-in-Cell), enabling predictive benchmarking of particle confinement against legacy toroidal and field-reversed configurations across the broader international fusion ecosystem.