FIR Collective Scattering from the UCLA Microtor Tokamak

The anomalous transport and energy loss observed in present toroidal magnetic fusion confinement devices may be due to low frequency microturbulence [1]. One way of studying such turbulence has been to scatter microwave or CO2 laser radiation from small-scale density fluctuations [2-8]. As long as the scattering parameter α = 1/kλD ≃ λO/4Πλ sin(θ/2) ≳ 1, one obtains information about collective fluctuations. The problem with both CO2 and microwave scattering is that if one satisfies the abovementioned criterion it is not possible to simultaneously provide a localized scattering measurement and good wavenumber resolution. On the other hand, FIR laser scattering is ideally suited to magnetic fusion parameters and easily provides spatial resolution Δx ≃ 1.5-3 cm while providing wavenumber resolution Δk ≳ 3 cm−1 FWHM. An additional bonus arises from the ease of changing incident laser wavelength, thereby increasing the range of instability wavenumbers which can be investigated (k ≃ 4Πsin(θ/2)/λO).