Speaker
Description
The preliminary design of the Thomson Scattering(TS) system devoted to the measurement of the
electron density and temperature in the pedestal region of DTT ( Divertor Test Tokamak) is
described. The evaluation of the DTT pedestal width based on the presently elaborated models
tested on JET and DIIID leads to a pedestal width Δ=15mm , assuming maximum temperature
Te=20keV and density ne=5 10 20 m -3 . The pedestal region to be measured could be evaluated in
75mm ( 5 times the pedestal width). The geometry considered for the installation of the TS is the
DTT equatorial port #17 : both the laser focusing optics and the collection optics are installed
inside the port , thus realizing a compact backscattering design. The evaluation of numerical
aperture of the collection optics is F#/5 ( optics clear aperture ≈ 20cm , distance of the optics to the
plasma ≈100cm) leading to a feasible spatial resolution on the pedestal δr≈5mm, with accuracy of
10% in the electron temperature measurement and 5% in density measurements. These numbers are
consistent with the measurements technical specifications of the ITER EDGE TS . The number of
the spatial points object of measurement is 75. The minimum laser energy per pulse is 2J at a
100Hz repetition rate . Given the neutron flux evaluated for DTT scenarios, a collection optics
made by rhodium coated molibdenum mirrors can be considered, together with collimating lenses
while the collecting fibres are placed outside the port exit window.
