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

Abstract

Three-dimensional spatiotemporal dynamics of detached helium plasma parameters along time, radius, and magnetic field were revealed in the linear device NAGDIS-II. To measure plasma parameters before and after the radial plasma ejection that was enhanced around the volume-recombining region, the conditional averaging technique was applied. The radial ejection was found to correlate with low-frequency changes of plasma-column parameters, which seemed to suppress the axial movement of the recombining region. Moreover, an azimuthal charge separation inside the ejected structure was observed, similar to the typical edge transport phenomenon: blobby plasma transport. The neutral flow effect was suggested as a candidate of the driving force.

Effects from the Target Plate Geometry on Fluctuations of Helium Plasma in the Linear Divertor Simulator Magnum-PSI

“…Stronger oscillations in the ionization zone and/or recombination front region were observed in hydrogen plasmas in Pilot-PSI in earlier studies of linear divertor plasmas [6,7]. In an area that was axially localized and where pure He plasmas in NAGDIS-II experienced high volume recombination, the cross-field transport was enhanced [9][10][11]. The cross-field transport appeared to be enhanced in the region between the TS axial location and the target plate (Z tgt = 200 mm) at 1.4 Pa gas pressure [15].…”

“…The radiation zone, ionization region, recombination region, and momentum loss region are thought to make up the plasma conditions along the magnetic field to the diverter plate [1][2][3][4]. In addition, in some linear plasma simulators, including NAGDIS-II, Pilot-PSI, and Magnum-PSI [5][6][7][8][9][10][11][12][13][14][15], and the SOL of the tokamak plasma of ASDEX Upgrade [16], low-frequency fluctuations around the recombination front region have been observed in the detached plasma conditions. These fluctuations result in radial particle losses across the magnetic field.…”

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

“…The correlation between the detachment [1] and the non-diffusive cross-field plasma transport in the boundary layer has been reported in various magnetic confinement devices. These are tokamak [2,3], helical [4] and linear [5,6,7,8,9,10,11,12] devices. Such a correlation is expected to expand the width of the heat flux to the divertor target, i.e., λ q .…”

“…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.…”

Plasma Potential Measurement in Detached Plasmas by Emissive Probe Considering Space-Charge-Limited Effect

“…By using the T e estimated by DP and the floating potential V f measured with SP at the vicinity, V s can be also measured in the detached plasma (hereafter called "DSP" technique) [6]. Furthermore, by using the statistical analysis technique called the conditional averaging (CA), time evolution of V s during the intermittent plasmaejection event was revealed with high-temporal resolution (∼µs) [7]. This reported that V s has important roles for determining azimuthal and radial motions of coherent structures.…”