Magnetic helicity dissipation in an ideal MHD code
by
Axel Brandenburg(Nordita)
→
Europe/Stockholm
122:026
122:026
Description
We study a turbulent helical dynamo in a periodic domain by solving the ideal magnetohydrodynamic (MHD) equations with the FLASH code using the divergence-cleaning eight-wave method and compare our results with with direct numerical simulations (DNS) using the Pencil Code. At low resolution, FLASH reproduces the DNS results qualitatively by developing the large-scale magnetic field expected from DNS, but at higher resolution, no large-scale magnetic field is obtained. In all those cases in which a large-scale magnetic field is generated, the ideal MHD equations yield too little power at small scales. As a consequence, the small-scale current helicity is too small compared with the DNS. The resulting net current helicity has then always the wrong sign, and it also does not approach zero at late times, as expected from the DNS. Our results have implications for astrophysical dynamo simulations using ideal MHD codes.
arXiv:1910.06074
