Abstract
An amplitude modulation reflectometry system is in operation at thestellarator TJ-II. Recently, the first electron density profiles wereobtained, showing good agreement with profiles measured by Thomsonscattering and lithium beam diagnostics. In order to measure densityprofiles from the plasma edge, the extraordinary mode of polarization isused. A hyper-abrupt varactor-tuned oscillator used in combination withactive multipliers generate two frequency segments: 25-36 and 36-50etc GHz sharing a unique common wave-guide system (Ka band). The signalis amplitude modulated at 200 MHz and the phase demodulation is done atlower intermediate frequency. The time evolution of the electron densityprofile was measured under different experimental conditions. In thispaper, we present the temporal evolution of the profiles obtained duringa transition to an enhanced confinement mode and during cold pulsepropagation experiments. We also report the modification in the shape ofthe density profile measured during a magnetic configuration scan inwhich a low-order rational surface is moved from the scrape-off layerinto the plasma confinement region.
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