Researchers at the Swiss Plasma Center (SPC) have detailed the design, construction, and initial plasma operations of Polaris, a new stellarator experiment. The device, characterized by a major radius of approximately 0.4 meters and a vacuum vessel volume of about 0.5 cubic meters, is engineered for high flexibility in magnetic configuration and plasma studies. Its primary goal is to serve as a testbed for various stellarator concepts and diagnostic techniques. The initial configuration uses a set of six identical, circular, water-cooled copper coils to generate the magnetic field. This simplified modular coil approach is a key design feature, aiming to create a large volume of magnetic surfaces with a significant rotational transform in vacuum. The successful achievement of first plasma marks the entry of a new experimental device into the global fusion research landscape. Source: arXiv

The Polaris magnet system produces an on-axis magnetic field of approximately 0.03 T with a total current of up to 5 kA in each of its six coils. This arrangement generates a vacuum rotational transform, or iota, of about 0.3. The design prioritizes diagnostic access, featuring a large vacuum vessel predominantly made of glass windows, which facilitates optical and probe-based measurements. Plasma is produced via an RF antenna delivering up to 2.5 kW of power, operating through inductive coupling and electron-impact ionization. This method is distinct from the high-power ECRH or NBI systems used in larger devices, reflecting Polaris's focus on fundamental plasma physics and experimental validation rather than high-performance targets. The preprint, published on arXiv, details the engineering solutions that enable this experimental versatility. Source: arXiv

The Polaris magnet system produces an on-axis magnetic field of approximately 0.03 T with a total current of up to 5 kA in each of its six coils.

Initial experiments have successfully produced plasma and performed preliminary characterization. The research team deployed probes at various toroidal locations to measure time-averaged values and fluctuations of key plasma parameters, including density, electron temperature, and floating potential. These first results confirm the operational status of the device and its diagnostic suite. The flexibility of the Polaris platform is a central theme; the design allows for the installation of different sets of magnetic coils within the same vacuum vessel, enabling direct comparisons between various stellarator configurations. This capability is valuable for benchmarking physics models and optimizing magnetic geometries for future, larger-scale fusion devices. Source: arXiv

Polaris joins a growing ecosystem of university-scale and national lab experiments aimed at refining the stellarator concept. While its parameters are modest compared to flagship programs like Wendelstein 7-X, its role is in rapid, low-cost exploration of novel configurations and control schemes. The emphasis on simple, modular coils addresses a key engineering challenge for stellarators: the manufacturing complexity and cost of non-planar coils. By demonstrating effective plasma confinement with a simplified coil set, Polaris provides valuable data for designers of future fusion power plants. The next phase of research will likely involve more detailed plasma studies and potentially the installation of alternative coil sets to explore different magnetic topologies. Source: arXiv