Microscopic Eddys don’t imply gyroBohm Scaling Scan device size while keeping all other dimensionless parameters fixed Turbulence eddy size remains small when device size increases radial correlation length ~ 7  i consistent with D-IIID measurement [Mckee et al, Nuclear Fusion, 2001] Probability density functions (PDF) decay exponentially fluctuating potential Implies gyroBohm scaling? Bohm scaling for device size corresponding to present day machine Gyro-Bohm scaling for larger machine Device size for scaling transition larger than most theoretical predictions Hahm-Diamond-Lin-Itoh-Itoh

Turbulence Spreading into Linearly Stable Zone Radial profile of fluctuation intensity broader for smaller devices  radial spreading of fluctuation into stable region Nonlinearity of ExB drift yields two types of terms: local turbulence damping and radial diffusion   turbulence intensity   r  local linear growth rate   : local nonlinear damping   i =  0 I: diffusivity proportional to intensity [Lin, et al.,PRL,(1999)]  Hahm-Diamond-Lin-Itoh-Itoh

Turbulence Spreading affects Transport Scaling Near region  (r 0 )=0 and I <<1, nonlinear diffusion yields a front-like solution  front r 0 +  =(24Q   r 0 t+r 0 3 ) 1/3 Balancing radial spread of front and local radial damping:  ~17  i Compares favorably with simulation estimate of  ~25  i, Deviation from GyroBohm Scaling I r r0r0 r0+r0+