Galaxy clusters possess turbulent magnetic fields with a dominant scale length l _ { B } \simeq 1 - 10 kpc .
In the static-magnetic-field approximation , the thermal conductivity \kappa _ { T } for heat transport over distances \gg l _ { B } in clusters is \simeq \kappa _ { S } l _ { B } / L _ { S } ( \rho _ { e } ) , where \kappa _ { S } is the Spitzer thermal conductivity for a non-magnetized plasma , the length L _ { S } ( r _ { 0 } ) 
is a characteristic distance that a pair of field lines separated by a distance r _ { 0 } < l _ { B } at one location must be followed before they separate by a distance l _ { B } , and \rho _ { e } is the electron gyroradius .
We introduce an analytic Fokker-Planck model and a numerical Monte Carlo model of field-line separation in strong magnetohydrodynamic ( MHD ) turbulence to calculate L _ { S } ( r _ { 0 } ) .
We also determine L _ { S } ( r _ { 0 } ) using direct numerical simulations of MHD turbulence with zero mean magnetic field .
All three approaches , like earlier models , predict that L _ { S } asymptotes to a value of order several l _ { B } as r _ { 0 } is decreased towards l _ { d } in the large- l _ { B } / l _ { d } limit , where l _ { d } is the dissipation scale , which is taken to be the proton gyroradius .
When the turbulence parameters used in the Fokker-Planck and Monte Carlo models are evaluated using direct numerical simulations , the Fokker-Planck model yields L _ { S } ( \rho _ { e } ) \simeq 4.5 l _ { B } and the Monte Carlo model yields L _ { S } ( \rho _ { e } ) \simeq 6.5 l _ { B } in the large- l _ { B } / l _ { d } limit .
Extrapolating from our direct numerical simulations to the large- l _ { B } / l _ { d } limit , we find that L _ { S } ( \rho _ { e } ) \simeq 5 - 10 l _ { B } , implying that \kappa _ { T } \simeq 0.1 \kappa _ { S } -0.2 \kappa _ { S } in galaxy clusters in the static-field approximation .
We also discuss the phenomenology of thermal conduction and particle diffusion in the presence of time-varying turbulent magnetic fields .
Under the questionable assumption that turbulent resistivity completely reconnects field lines on the time scale l _ { B } / u , where u is the rms turbulent velocity , we find that \kappa _ { T } is enhanced by a moderate amount relative to the static-field estimate for typical cluster conditions .