THE SPECTRUM OF RANDOM MAGNETIC-FIELDS IN THE MEAN FIELD DYNAMO THEORY OF THE GALACTIC MAGNETIC-FIELD

被引:399
作者
KULSRUD, RM
ANDERSON, SW
机构
[1] PRINCETON UNIV,PLASMA PHYS LAB,PRINCETON,NJ 08544
[2] PLASMA PHYS LAB,PRINCETON,NJ 08544
关键词
ISM MAGNETIC FIELDS; MHD; TURBULENCE;
D O I
10.1086/171743
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We consider the fluctuation spectrum that must arise in a mean field dynamo generation of galactic fields if the initial field is weak. We derive and solve a kinetic equation for its evolution. The spectrum evolves by transfer of energy from one magnetic mode to another by interaction with turbulent velocity modes. This kinetic equation is valid in the limit that the rate of evolution of the magnetic modes is slower than the reciprocal decorrelation time of the turbulent modes. This turns out to be the case by a factor greater than 3. Most of the fluctuation energy concentrates on small scales, shorter than the hydrodynamic turbulent scales. The fluctuation energy builds up to equipartition with the turbulent energy in times that are short compared to the e-folding time of the mean field. The turbulence becomes strongly modified before the dynamo amplification starts. Thus, the kinematic assumption of the mean dynamo theory is invalid. It seems very difficult to build up magnetic fields from very weak seed fields on the galactic scale by dynamo action. Thus, the galactic field must have a primordial origin, although it may subsequently be modified by dynamo action.
引用
收藏
页码:606 / 630
页数:25
相关论文
共 11 条
[1]  
ANDERSON S, 1991, THESIS PRINCETON U
[3]   GROWTH OF TURBULENT MAGNETIC FIELDS [J].
KRAICHNAN, RH .
PHYSICS OF FLUIDS, 1967, 10 (04) :859-+
[4]   EFFECT OF WAVE-PARTICLE INTERACTIONS ON PROPAGATION OF COSMIC RAYS [J].
KULSRUD, R ;
PEARCE, WP .
ASTROPHYSICAL JOURNAL, 1969, 156 (2P1) :445-&
[5]  
Moffatt H. K., 1978, MAGNETIC FIELD GENER
[6]  
PARKER EN, 1979, COSMICAL MAGNETIC FI
[7]  
PETSCHEK HE, 1964, P AAS NASA C PHYSICS
[8]  
Ruzmaikin A., 1988, MAGNETIC FIELDS GALA
[9]   THE DYNAMICS OF MAGNETIC-FIELDS IN A HIGHLY CONDUCTING TURBULENT MEDIUM AND THE GENERALIZED KOLMOGOROV-FOKKER-PLANCK EQUATIONS [J].
VAINSHTEIN, SI ;
KITCHATINOV, LL .
JOURNAL OF FLUID MECHANICS, 1986, 168 :73-87
[10]   ON TURBULENT-DIFFUSION OF MAGNETIC-FIELDS AND THE LOSS OF MAGNETIC-FLUX FROM STARS [J].
VAINSHTEIN, SI ;
ROSNER, R .
ASTROPHYSICAL JOURNAL, 1991, 376 (01) :199-203