  Turbulence, produced by an impulsive spin-down from angular velocity Omega to
rest of a cube-shaped container, is investigated in superfluid 4He at
temperatures 0.08 K - 1.6 K. The density of quantized vortex lines L is
measured by scattering negative ions. Homogeneous turbulence develops after
time t of approximately 20 \Omega and decays as L proportional to t^(-3/2). The
corresponding energy flux epsilon = nu' (kappa L)^2, which is proportional to
t^(-3), is characteristic of quasi-classical turbulence at high Re with a
saturated energy-containing length. The effective kinematic viscosity in the
T=0 limit is nu' = 0.003 kappa, where kappa=10^(-3) cm^2 / s is the circulation
quantum.
