Microinstabilities in the Wendelstein VII A Stellarator Observed by CO2-Laser-Light Scattering

Homodyne detection of scattered C${\mathrm{O}}_2$-laser light demonstrates a close relation between microturbulence level and energy confinement in the Wendelstein VII A stellarator during both Ohmic and neutral-beam heating experiments. With the onset of neutral injection an abrupt order of magnitude decrease in ${\left(\frac{\delta n}{n}\right)}^2$ accompanied by a broadening of the fluctuation spectra is observed, indicating an almost immediate improvement of containment time.