LIDAR Thomson Scattering for the ITER Core Plasma

Diagnostics for steady state plasmas

“…Important for calibration is the fact that different spatial points are measured by the same set of detectors. Localization is accomplished by a time-of-flight measurement [120].…”

“…Allowing 0.1% absorption, a 4 cm optical path length double window made of KU1 quartz could be used at a neutron fluence of 8×10 20 n m −2 at the window location for ∼50000 ITER discharges of 1000 s (∼12500 h) duration, i.e. it would most likely not even be necessary to heat the window in order to anneal created colour centres [120]. By pre-irradiating the KU1 windows with doses of ∼20 MGy at 200 • C one could remove any potential problem of ionizing radiation induced laser absorption since this has been observed to result in a reduction of optical absorption at 500 nm by at least a factor of 10 [222].…”

“…Fortunately, recent experiments with stainless steel (310 SS) sputtered onto KU1 quartz windows showed a much more favourable behaviour [233], with the damage probability increasing with layer thickness and with window failures for the largest investigated film thickness of 200 nm only occurring at laser power densities of ∼10 15 W m −2 , which are a factor 100-1000 higher than, e.g. the power densities at the vacuum windows of the JET Thomson scattering system [234] or those foreseen for the ITER systems [120,[235][236][237]. A problem which could potentially become important at required power densities is the observed increase in damage probability with increasing window temperature observed for layer thicknesses of 70 nm at 400 • C [233], but only if it would increase significantly with layer thickness (not yet investigated).…”

“…A problem which could potentially become important at required power densities is the observed increase in damage probability with increasing window temperature observed for layer thicknesses of 70 nm at 400 • C [233], but only if it would increase significantly with layer thickness (not yet investigated). This is of no concern for the ITER Thomson diagnostics since there the vacuum windows will be located deep inside the labyrinths where they are not subjected to high heat loads and where the neutron fluence is sufficiently reduced so that annealing of created colour centres through high window temperatures will not be required [120].…”