The Czech Republic’s high-field compact tokamak, designed to study ITER- and DEMO-relevant plasma–wall interactions at magnetic fields above 5 T in a device small enough to iterate quickly and affordably.
The original COMPASS tokamak, a small D-shaped device transferred from the Culham Centre for Fusion Energy to the Institute of Plasma Physics of the Czech Academy of Sciences (IPP Prague) in 2007, served for over a decade as a versatile tool for edge-plasma and H-mode studies. COMPASS-U is its successor: a purpose-built, high-field compact tokamak designed from the outset to operate at toroidal fields exceeding 5 T, placing it among the highest-field tokamaks in the European fusion programme.1
COMPASS-U features a major radius of approximately 0.89 m, a minor radius of 0.27 m, and copper toroidal-field coils capable of producing up to 5 T on axis. Plasma current is designed to reach 2 MA, yielding edge safety-factor profiles relevant to ITER and DEMO scrape-off-layer studies. The device is equipped with an ITER-like divertor geometry, including the option for alternative advanced divertor configurations such as the Super-X and snowflake topologies.2 Heating systems include neutral-beam injection and electron-cyclotron resonance heating, providing the power density needed to access high-performance regimes in a compact volume.
The primary scientific focus of COMPASS-U is the plasma boundary: the scrape-off layer, divertor, and first wall. At high field, the machine can match the dimensionless parameters—collisionality, normalised pressure, and Larmor-radius-to-machine-size ratio—of the ITER edge, making it a direct testbed for divertor heat-exhaust solutions.3 Planned experiments include liquid-metal plasma-facing components, advanced divertor geometries, and real-time detachment control, all areas where ITER and DEMO require validated solutions before construction commitments can be finalised.
COMPASS-U is a flagship project of the Czech national fusion programme, co-funded through the EUROfusion consortium. Detailed engineering design was largely completed by the mid-2020s, with magnet and vacuum-vessel fabrication progressing in parallel. The project benefits from strong institutional continuity: IPP Prague has operated tokamaks continuously since the 1970s and maintains one of Europe’s deepest benches in edge-plasma diagnostics.4
When operational, COMPASS-U will complement the Italian DTT and the upgraded WEST and ASDEX-Upgrade programmes, forming a network of medium-scale European tokamaks dedicated to solving the exhaust problem before DEMO’s final design review.