Conservation of Magnetic Helicity and Its Constraint on $α$-Effect of Dynamo Theory
| dc.creator | Chou, Hongsong | |
| dc.creator | Field, George B. | |
| dc.date | 2000-11-29 | |
| dc.date | 2001-04-23 | |
| dc.date.accessioned | 2026-07-07T01:56:45Z | |
| dc.date.available | 2026-07-07T01:56:45Z | |
| dc.description | Dynamical studies of MHD turbulence on the one hand, and arguments based upon magnetic helicity on the other, have yielded seemingly contradictory estimates for the $α$ parameter in turbulent dynamo theory. Here we show, with direct numerical simulation of three-dimensional magnetohydrodynamic turbulence with a mean magnetic field, $\OB$, that the constraint on the dynamo $α$-effect set by the magnetic helicity is time-dependent. A time-scale $t_c$ is introduced such that for $t<t_c$, the $α$-coefficient calculated from the simulation is close to the result of Pouquet et al and Field et al, $-\frac{τ_{cor}}{3}(< \v \cdot \nabla \times \v > - < \b \cdot \nabla \times \b >)$; for $t>t_c$, the classical result of the $α$-coefficient given by the Mean-Field Electrodynamics is reduced by a factor of $1/({R_m |\OB|^2/v_{rms}^2})$, as argued by Gruzinov & Diamond, Seehafer and Cattaneo & Hughes. Here, $R_m$ is the magnetic Reynolds number, $v_{rms}$ the rms velocity of the turbulence, $τ_{cor}$ the correlation time of the turbulence, and $\overline B$ is in velocity unit. The applicability of and connection between different models of dynamo theory are also discussed. | |
| dc.description | 31 pages, 5 figures, submitted to ApJ | |
| dc.identifier | https://arxiv.org/abs/astro-ph/0011548 | |
| dc.identifier | http://arxiv.org/abs/astro-ph/0011548 | |
| dc.identifier.uri | http://salesiana.dossiersoluciones.com/handle/123456789/2113 | |
| dc.subject | Astrophysics | |
| dc.title | Conservation of Magnetic Helicity and Its Constraint on $α$-Effect of Dynamo Theory | |
| dc.type | text |