Spatial and temporal measurement of recombining detached plasmas by laser Thomson scattering

Abstract

Elucidation and control of the low temperature recombining plasmas under fusion relevant conditions are crucial issues. In this study, we applied a conditional average for laser Thomson scattering technique to measure the temporal evolution of the plasma instability in detached recombining plasmas in the divertor simulator NAGDIS-II. In recombining plasmas, it is shown that the electron energy distribution function has a non-Maxwellian component, and the fraction of the low electron temperature component increases with the gas pressure. It is found that one of the major reasons to cause the non-Maxwellian distribution function is in the temporal variations of the electron temperature. By using the conditional averaging method, the temporal evolutions of the spatial (vertical and radial) profiles of the electron density and temperature are revealed for different frequency ranges.

Spatiotemporal dynamics of cross-field ejection events in recombining detached plasma

“…By using measured T e and n e , an effective recombination rate coefficient ⟨σv⟩ rec can be deduced by the collisional radiative (CR) model [21]. Furthermore, ion particle loss rate S rec , which corresponds to the production rate of ground-state neutrals, can be estimated from S rec = ⟨σv⟩ rec n 2 e , where n e = n i is assumed to be equal to the ion density [8,16].…”

“…In this study, we applied conditional averaging (CA) method to two-dimensional (2D) movable multi-pin Langmuir probe consisting of double probe and an additional single probe in a steady-state detached helium plasma in NAGDIS-II. The CA is a powerful statistical tool and has been applied to electrostatic probes [14] and LTS measurements as well [15,16] in several devices. Reference signal for CA was acquired in the periphery to detect ejected plasma structures.…”

Atomic nitrogen density measurements by actinometry method in the toroidal device NAGDIS-T

“…34) Two temperature Gaussian fitting is a reasonable method used in various situations, for ex., I-V characteristics of probe in a magnetron sputtering device 35) and laser Thomson scattering in a linear plasma device. 36) Figures 5(a), 5(b) shows the pressure dependences of the electron density and temperature, respectively. The probe measurement was performed at the first loop of the plasma.…”

Linear analysis of cross-field dynamics with feedback instability on detached divertor plasmas

“…Such a correlation is expected to expand the width of the heat flux to the divertor target, i.e., λ q . Thus, the observation and analysis regarding the correlation phenomena have been actively performed in linear devices, e.g., the NAGDIS-II [5,6,7,8,13,14,15,16,17,18,19,20]. However, the physical dynamics of the correlation has not been revealed sufficiently.…”

“…Thus, the observation and analysis regarding the correlation phenomena have been actively performed in linear devices, e.g. the NAGDIS-II [5][6][7][8][13][14][15][16][17][18][19][20]. However, the physical dynamics of the correlation has not been * Author to whom any correspondence should be addressed.…”