Toroidal crystal spectrometer for time-resolved x-ray absorption diagnostic in dense plasmas

A toroidal crystal spectrometer was designed with the purpose of measuring the aluminum K-absorption edge shift, in the wavelength range around 7.9 Å, in strongly compressed matter. The expected shift is about 100 mÅ (∼20 eV). The x rays reflected from the crystal are focused onto a streak camera slit of 16 mm high and 100 μm width, to obtain a time-resolved spectrum. High resolution and dispersion of about 1-16 Å/mm on the detection window are obtained. A crystal with a toroidal surface is used to enhance the focusing power in the spatial dimension as in the spectral one. Numerical simulations are performed by means of one- and two-dimensional codes for the determination of the crystal characteristics like the dimension and the curvature radius with respect to the geometric constraints. Some experimental results are presented concerning the obtained spectra.