Superconducting planar coils for magnetic field shaping in the Helios Stellarator

The “Helios” fusion power plant, developed by Thea Energy, Inc., utilizes a novel planar coil magnet system to resolve the manufacturing complexity of traditional stellarators. This system comprises twelve large planar encircling coils and an array of 324 smaller, individually-controllable superconducting planar shaping coils for precise magnetic field correction. This paper details the pre-conceptual design and analysis of the shaping coils, which is critical for achieving high-performance plasma confinement. The large number of individually controlled coils necessitates a low-current, high-inductance design. Manufacturability at this scale is enabled by making shaping coils out of a modular, standardized double-pancake, each circular, planar, and identical in size and wound under tension. Maintenance and installation are simplified by grouping shaping coils together into Field Shaping Units (“FSUs”), that also centralize cryogenic and electrical interfaces. A coil architecture is presented for the most extreme shaping coil in the array, and electromagnetic and thermal simulations provide a technical basis for this design to apply to the entire shaping coil array. The proposed architecture features parallel wound (“PW”) and no-insulation (“NI”) technologies to make intrinsically defect tolerant and quench self-protecting coils. Double-pancakes are connected in series using remountable joints, and the shaping coils are conduction cooled – design decisions that allow rapid removal and replacement without disrupting a cryogenic fluid line. A mechanical structure is proposed to withstand hoop stresses and the 40 MN·m overturning moment with 554 kN peak force on structural bolts from the background field generated by encircling coils. Collectively, the design and multiphysics analysis presented here validates the technical feasibility of the Helios planar coil architecture. This supports a compelling new path for stellarator power plant development, offering significant advantages in manufacturability, serviceability, and economic efficiency.