­Permanent Magnet Stellarator Design

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Novel Stellarator Design

Princeton Docket # 21-3827 / 3821 / 3822

Procedure for Designing Arrays of Permanent Magnets
PPPL inventors have developed a novel procedure for designing an array of magnets for confining stellarator plasmas using a small number of unique magnet parts. The parts consist of identically shaped cubes, each of which is polarized along one of as few as three unique orientations. The procedure has been shown to arrive at solutions in which the surface-averaged relative normal component of the magnetic field on the plasma boundary is well below 1%, satisfying physics requirements for field accuracy. An additional distinguishing feature of this procedure is that the polarization directions of the magnets need not be pre-specified; rather, they can be optimized in such a way as to make more efficient use of the available space for magnets.

All Planar Coil Stellarator
Given an optimized plasma target and a large field coil array that produces a predominantly toroidal field, the surface dipole distribution that produces the required fields for the plasma can be determined using the virtual casing theorem. This continuous distribution can then be discretized using numerous numerical techniques. This will give the field requirements for a series of small, discrete circular coils that will be distributed on the surface. The number of small coils is chosen to minimize cost and complexity while meeting the field accuracy requirements. The plasma can then be reconstructed using a free-boundary plasma solver and the plasma properties compared to the original target. The procedure above can be solved iteratively to optimize the target plasma properties and magnetic field coil requirements, including optimizing the properties of the planar toroidal array. Mechanical supports can then be designed to react to the forces on the coils. Minimizing force is another possible optimization parameter. The large number of free coil current parameters will enable the precise control of the 3D equilibrium as plasma parameters vary. This enables a wide operating window of plasma parameters for the stellarator.

Stellarator Neutron Source
Modern stellarators use numerical optimization to improve the confinement properties. Because of this, the magnetic field coils are designed to make the fields that provide this optimized behavior. Recently schemes have been developed to improve the fast particle confinement of stellarators. The concept is to use negative ion neutral beams to accelerate deuterium to energies near the peak of the D-D fusion cross-section and to inject this beam into a stellarator that has been optimized for fast ion confinement. The scale and operating parameters of the stellarator will be set by the required path length to fully absorb the neutral beam energy. Counter streaming beams will be beneficial, but not required. The electron temperature will be adjusted (using, e.g. electron cyclotron heating) so that the beam slowing down time is long enough for the fast ions to create sufficient neutron flux.


  • Magnetically confining stellarator plasmas


  • Drastically simplifies the design of a stellarator by removing the need for complex 3D coils
  • Enables designs of magnet arrays consisting of a small number of unique parts—as few as three—allowing for efficient bulk fabrication of the magnets
  • Makes more efficient use of the available magnet volume and/or enables confinement of plasmas with higher overall magnetic field strengths


David Gates is the Head of Advanced Projects and Stellarator Physics Leader at the Princeton Plasma Physics Laboratory. After receiving his Ph. D. in plasma physics from Columbia University in 1993 he spent four years at the Culham Laboratory near Oxford, England. Since then he has worked at PPPL in various roles including managing the development of the control system for the National Spherical Torus Experiment (NSTX). He is an expert in Magneto-HydroDynamics (the study of magnetized conducting fluids) and is the author of 187 scholarly papers, and was elected a fellow of the American Physical Society in 2013. In his role as Stellarator Physics Leader he manages the US contributions to a multi-institutional international collaboration on Wendelstein 7-X, located in Greifswald, Germany. He has also been heavily involved with the ITER fusion reactor that is currently under construction in southern France. His current research interests are focused on establishing the stellarator device as a viable solution to fusion energy.

Intellectual Property Status

Patent protection is pending.

Princeton is currently seeking commercial partners for the further development and commercialization of this opportunity.


Chris Wright

Princeton University Office of Technology Licensing • (609) 258-6762• cw20@princeton.edu

Laurie Bagley

Princeton Plasma Physics Laboratory • (609) 243-2425• lbagley@pppl.gov

Patent Information:
Energy and CleanTech
For Information, Contact:
Chris Wright
Licensing Associate
Princeton University
David Gates
Caoxiang Zhu
Kenneth Hammond