QUADCOIL Promises to Reshape Stellarator Design

A major challenge in stellarator design is calculating the precise shapes of the coils that produce the magnetic field responsible for confinement. But a newly developed computational software called QUADCOIL, described in the journal Nuclear Fusion earlier this year, promises to streamline that process. QUADCOIL designs stellarator coils by optimizing against both physics and engineering constraints, promising simpler, more efficient fusion reactor designs.

A standout feature of QUADCOIL is its ability to incorporate coil force and stress considerations directly into the design. This is a major advantage for the structural stability of the magnet system. By designing coils whose currents run parallel to the field where possible, QUADCOIL can dramatically reduce net transverse forces (Lorentz forces) on the coils, meaning less mechanical strain and simpler support structures. This is especially important for modern high-field stellarators that use brittle high-temperature superconductors—aligning currents with fields can help such coils carry higher current without quenching​.

QUADCOIL’s ability to directly incorporate coil physics and engineering criteria stands in sharp contrast to NESCOIL, a coil design tool used in developing the Wendelstein 7-X (W7-X) and the National Compact Stellarator Experiment (NCSX) stellarators. While NESCOIL excels at producing a magnetic field that conforms to a target plasma shape, it treats coil design as abstract mathematics and ignores practical engineering constraints. The resulting coils can be extremely contorted and tightly spaced, pushing the limits of advanced manufacturing. In practice, designers have had to add ad-hoc smoothing or iterate on coil geometry to make these designs more feasible to build.

Another key advantage of QUADCOIL is its speed. The software can evaluate a candidate magnet configuration in about 10 seconds, compared to 20 minutes to several hours for traditional methods​. This ~100x faster processing time blurs the line between designing the plasma shape and designing the coils. For example, scientists can pick a candidate plasma shape and run QUADCOIL to see what kind of coils it demands. If the coils look overly complex, they can adjust the plasma shape immediately and try again​. 

This iterative feedback loop would be impractical with slower tools. In this way, QUADCOIL could empower teams to consider both physics and engineering constraints from the beginning, avoiding designs that are great on paper but unbuildable​. Simplified coil shapes and reduced mechanical strain also mean lower construction and maintenance costs–a crucial consideration for any future fusion power plant.