Error Field Physics Constraints on SPARC Assembly Tolerances

A statistical likelihood model of SPARC construction asymmetries provides error field expectations that, together with a model of the mode locking threshold, constrain tolerances for device construction and assembly. The combination of high field and compact geometry in SPARC means slight asymmetries in the coils can potentially produce deleterious 3D error fields (EFs) that lead to mode locking. To ensure that the EFs do not compromise the SPARC mission, a model including the intrinsic asymmetries of the primary coil windings as well as a statistical model of the shaping (construction) and location (installation) tolerances for each coil is used to produce an EF probability density function (PDF) for the fully assembled machine. This, together with a PDF of mode locking taken from the empirical ITPA EF threshold scaling, provides the risk of locking for any set of given coil designs and tolerances. The full device model enables fast iterative assessment of interconnected coil geometries and assembly plans, examples of which will be shown in this presentation. The EF and locking PDFs it provides also enable efficient mapping of the EF risk across scenarios, providing maps of safe operating regimes for SPARC.