Transport of Particles, Electron Energy, and Turbulence in Strong Interchange-Type Turbulence

The Helimak is an approximation to the infinite cylindrical slab with a size large compared with turbulence transverse scale lengths, but with open field lines of finite length. A pressure gradient in unfavorable magnetic curvature is unstable to interchange-type modes, leading to large amplitude nonlinear fluctuations similar to those in a tokamak SOL. A novel magnetically-baffled probe cluster permits full characterization of the turbulence, including density, temperature, and true plasma potential fluctuations as well as radial transport of all quantities across the full plasma profiles. Despite the short coherence lengths, the level of saturated turbulence and transport cannot be inferred from local parameters. The fluxes of density and temperature turbulence (quadratic in the dimensionless fluctuation amplitudes) are generally small, less than 10m/s, less than 25% of those of the density/thermal fluxes themselves and insufficient in both magnitude and sign to explain the large turbulent amplitudes seen in linearly stable regions of the pressure profile. The transport statistics of the turbulence are unusual. The Helimak is now at Shenzhen University.