Ellis, Robert | Search NASA

DOE OSTI2024

Simulation of a scintillator-based fast ion loss detector for steady-state operation in Wendelstein 7-X (invited)

A quantitative theoretical framework has been created to model neutral beam injection and fast ion losses in the Wendelstein 7-X (W7-X) stellarator, including a novel method to develop synthetic diagnostics for fast ion loss detectors (FILDs) of many types, such as scintillating and Faraday Cup FILDs. This is the first time that this has been done in stellarator geometry with this level of fidelity, providing a way for fast ion losses to be predicted more precisely in future stellarator experiments and in W7-X. Simulations of the signal seen by a Faraday Cup FILD have been completed for multiple W7-X plasmas and show close agreement with the measured signals. This method is now applied to an actively water-cooled, scintillator-based FILD, which is currently in development to measure the fast ion loss distribution in W7-X in greater detail. The design makes use of a double slit to measure energy-and-pitch-angle-resolved losses of both co-going and counter-going fast ions. The diagnostic, which can be inserted to different radial positions, has been designed to withstand steady-state heat fluxes of up to 120 kW/m 2 along with additional transient heat loads of 100 kW/m 2 lasting for up to 20 s at a time. Simulations of W7-X standard magnetic configuration show up to 8 × 10 13 (s –1 cm –2 ) ion fluxes onto the sensor from each neutral beam source and no signal from the counter-going slit. Finally, these simulations will help inform experimental proposals for future W7-X campaigns after installation of this diagnostic.

3D printing↗

DOE OSTI2023

Stellarator Simplification using Permanent Magnets (PM4Stell)

This Report describes the design and prototyping of an array of rare-Earth permanent magnets to form a stellarator. This effort was motivated by the hypothesis that the usage of permanent magnets, rather than electromagnetic coils with complex geometry, could reduce the cost of stellarator construction and thereby make increase the feasibility of the stellarator as a technology for a fusion-based power plant. In this project, we have developed novel methods for specifying the positions, shapes, and polarizations of the magnets in the array, and have developed designs for mounting structures and tooling for assembly. We have also performed detailed finite-element modeling to qualify the accuracy of the magnetic field produced by the magnet array as designed, and to confirm that the structure can withstand the forces between the magnets. We have also developed techniques for measuring the magnetic field produced by the array once constructed, as well as for correcting errors in the field arising from misalignments and offsets within the tolerances for mounting and fabrication. Finally, we have constructed a tabletop prototype of a section of the array to qualify the concept for assembling and mounting magnets within the array.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2023

Stellarator Simplification using Permanent Magnets (PM4Stell)

This Report describes the design and prototyping of an array of rare-Earth permanent magnets to form a stellarator. This effort was motivated by the hypothesis that the usage of permanent magnets, rather than electromagnetic coils with complex geometry, could reduce the cost of stellarator construction and thereby make increase the feasibility of the stellarator as a technology for a fusion-based power plant. In this project, we have developed novel methods for specifying the positions, shapes, and polarizations of the magnets in the array, and have developed designs for mounting structures and tooling for assembly. We have also performed detailed finite-element modeling to qualify the accuracy of the magnetic field produced by the magnet array as designed, and to confirm that the structure can withstand the forces between the magnets. We have also developed techniques for measuring the magnetic field produced by the array once constructed, as well as for correcting errors in the field arising from misalignments and offsets within the tolerances for mounting and fabrication. Finally, we have constructed a tabletop prototype of a section of the array to qualify the concept for assembling and mounting magnets within the array.

47 OTHER INSTRUMENTATION↗