FLUID SIMULATIONS OF NONLOCAL DISSIPATIVE DRIFT-WAVE TURBULENCE

A two-dimensional [2d(x,y)] fluid code has been developed to explore nonlocal dissipative drift-wave turbulence and anomalous transport. In order to obtain steady-state turbulence, the y-averaged fluctuating density 〈n〉 has been forced to be zero in simulations, thus the difficulty of choosing proper sources and sinks in turbulence simulation codes has been avoided. If Ln≫Lc or Lαlc ≫ Lc, where Ln is the density gradient scale length, Lc the turbulence correlation length Lc, and Lαlc the adiabaticity-layer width, it has been shown that "local" turbulence simulations give reasonable results. However, for Ln∼L c, or Lαlc∼Lc "local" turbulence codes are found to overestimate the flux. For a family of hyperbolic tangent background density profiles, n0(x) = nm-n 1 tanh[(2x-Lx/2Δn] with n 1<0.5nm, it has been demonstrated that the nonlocality of the turbulence leads to a transition from local gyro-Bohm (Dlocal ≃ 7.6(Te/eB) x[ρs/Ln(x)] [αlc(x)/0.01]-1/3), where αlc(x) = α(x)/κ(x) < 1, to nonlocal gyro-Bohm transport scaling [D nonlocal≃7.6(Te/eB)(n1ρs/ nmΔn)(αnlc/0.01) -1/3(Δn/40ρs)2/5 for αnlc(x) = α/κmax>1, κ(x) = ρs/Ln(x) and α=k∥ 2χe]. For the case Φ0(x) = n 0(x) with the model hyperbolic tangent density profiles n 0(x), velocity shear increases the turbulence flux by 230% and the root-mean-square (RMS) fluctuating density by 36%. Otherwise, for Φ0(x) = n0(x), the turbulence flux is reduced by 71% and the RMS value of fluctuating density is decreased by 31% by velocity shear effects. © 1995 American Institute of Physics.