Optimizing disc dynamo

J. Priede^1,2 - R. A. Avalos-Zúñiga³

¹ Fluid and Complex Systems Research Centre, Coventry University, Coventry, CV1 5FB, United Kingdom
² Department of Physics, University of Latvia, Riga, LV-1004, Latvia
³ Research Centre in Applied Science and Advanced Technology (CICATA - Querétaro), Instituto Politécnico Nacional, Cerro Blanco 141, Colinas del Cimatario, Querétaro, Mexico

Abstract
We present an optimized design of our recently realized disc dynamo. Like the original set-up, the optimized dynamo consists of a flatmulti-arm spiral coil and a co-axially placed disc which is connected to the former by sliding liquid metal contacts. In contrast to the original set-up, the disc and the coil in the optimized design have different sizes. This allows the disc to capture more of the high-density magnetic flux generated in the inner part of the coil and to avoid the reverse flux in the outer part of the coil. By optimizing the coil and dics radii, the critical magnetic Reynolds number can be reduced from ≈ 34.6 when the disc and the coil have equal inner and outer radii with the ratio r_i/r_o ≈ 0.36 to Rm ≈ 11.6. This lowest possible disc dynamo threshold is attained when the disc and the coil have relatively narrow widths. Using a slightly suboptimal but more practical set-up with the inner and outer radii of the disc and coil equal to to (0.3,0.9) and (0.74,1), respectively, self-excitationis expected at Rm ≈ 14.6. Figs 7, Refs 10.