Home > Timetable > Session details > Contribution details

Contribution Invited Oral

Budker INP - Conference Hall
X-ray structural analysis

Status of dynamic diagnostics of plasma material interaction based on synchrotron radiation scattering at the VEPP-4 beamline 8


  • Dr. Aleksey ARAKCHEEV

Primary authors



The residual mechanical deformation and stress were measured in the preliminary experiments carried out at synchrotron radiation (SR) scattering stations at VEPP-3 in the Siberian Center of Synchrotron and Terahertz Radiation (“Precision diffractometry and anomalous scattering”, “Diffractometry in hard X-rays”). The deformation and stress were calculated on the basis of the dependence of the scattering angle on the inclination of the irradiated tungsten sample. Significant changes in the SR diffraction are found as the result of material recrystallization or irradiation of the material by plasma. It implies that the SR scattering diagnostics may be an informative instrument for in-situ observations of the state of the plasma facing components.

The next stage of the SR scattering diagnostics development at the VEPP-4 beamline 8 is the dynamic measurements during pulsed heat loads. Currently a 1J Nd:YAG laser is used for the 0.2ms heat load simulation and a 100J laser is under development. The parameters of the heating are sufficient for simulation of the expected pulsed heat load in ITER. The destructive effect of pulsed heat loads is caused by mechanical stresses that occurs in highly non-uniformly heated materials. The main aim of the current development of diagnostics based on SR scattering is the dynamic measurements of the mechanical deformation and stress dependences on the depth below the surface. It looks like the rotation of crystallographic planes due to mechanical deformations is the dominant effect in the SR scattering. So the deformation and stress distributions may be calculated using measurements of the diffraction peak parameters of SR passed through the sample. The set of requirements (the pass through material, dynamical measurements of pulsed processes) determines restrictions on SR brightness and energy. The SR from VEPP-4 with energy 69keV will be used for experiments with tungsten. Also a single crystal samples are necessary for increasing of the diffraction peak brightness. Currently, the one-dimensional gas X-ray detector DIMEX is used for measurements. The development of the silicon detector for increasing of the sensitivity is in progress.

The first dynamical measurements of the diffraction peak of SR passed through the 250µm thick single crystal tungsten were carried using the one-dimensional detector. The inclination of the sample to the initial SR beam was about 45° in order to result in the diffraction peak shift. The change of the SR scattering angle about 0.1° during the laser irradiation and the subsequent fast return during the comparable time were found out. The behavior could be explained by the bending of the initially plane sample. The bending moment is proportional to the difference of the temperature at the heated and opposite sides. The moment disappears while the temperature distribution flattens across the thin sample. Conversely the temperature propagation along the sample surface takes more time. Thus the expected effect of the crystal planes rotation could be estimated as the diffraction peak shift after the temperature flattening across the sample. The measured shift was about 0.03°. The measurements of deformation and stress distributions across the sample requires the analysis of the diffraction peak shape during the laser irradiation.