Large amplitude drift wave fluctuations have been investigated in a 1=2 stellarator with very low shear (Ls/Ln>or=600). Considerable broadening and decorrelation of the linear unstable modes omega k approximately omega e*(k) ( omega e*(k)=kperpendicular to (kBTe/eB). Del ne/ne being the diamagnetic drift frequency) due to nonlinear wave-wave coupling is observed ( Delta omega k approximately= omega k). The resulting saturated turbulent spectrum shows some evidence for an inverse cascade process transferring wave energy from the most unstable modes to lower kperpendicular to (kperpendicular to rho s approximately=0.1 according to linear theory, rho s=(kTe/mi)12// omega ci being the effective ion gyroradius). A rather high saturation level ( delta n/n)2<or=0.2 of the turbulent spectrum is found. An estimate of the test particle diffusion coefficient Dperpendicular to t= Sigma k Delta omega k(kperpendicular to Phi k/B omega k)2 accounting for the E*B convection of the particles is given. The observed electron energy confinement time is shown to be in reasonable agreement with the estimated convective loss rate.
Dispersion relation for a large-orbit gyrotron