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A compressible large eddy simulation (LES) is performed to study a pulsed jet actuator that is used to control a turbulent axisymmetric bluff body wake. The actuator is driven at low-frequency (
$f = 200$Hz, 
$S{t_\theta } = 0.029$) and high amplitude (
${C_\mu } = 0.034$). The numerical scheme and a suitable boundary condition for the pulsed jet are validated, showing good agreement with experimental results. A comparison of the velocity boundary condition and the moving boundary condition shows that, in the vicinity of the orifice/slot and in the downstream region, the results from these two methods are identical, while the fluid behaviour inside the cavity shows difference. An analysis of the pulsed jet actuator shows that the phase lag of the cavity pressure is determined by the integration of the diaphragm motion and the pulsed jet. The mean total pressure distribution shows that the total pressure loss is concentrated in the vicinity of the slot. Dynamic mode decomposition (DMD) on the pressure field is used to extract coherent structures which oscillate with the same frequency as that of the diaphragm motion. Some small-scale high-frequency structures are also apparent.
Competition among the two-plasmon decay (TPD) of backscattered light of stimulated Raman scattering (SRS), filamentation of the electron-plasma wave (EPW) and forward side SRS is investigated by two-dimensional particle-in-cell simulations. Our previous work [K. Q. Pan et al., Nucl. Fusion 58, 096035 (2018)] showed that in a plasma with the density near 1/10 of the critical density, the backscattered light would excite the TPD, which results in suppression of the backward SRS. However, this work further shows that when the laser intensity is so high (
$>{10}^{16}$ W/cm2) that the backward SRS cannot be totally suppressed, filamentation of the EPW and forward side SRS will be excited. Then the TPD of the backscattered light only occurs in the early stage and is suppressed in the latter stage. Electron distribution functions further show that trapped-particle-modulation instability should be responsible for filamentation of the EPW. This research can promote the understanding of hot-electron generation and SRS saturation in inertial confinement fusion experiments.
Over the last 25 years, radiowave detection of neutrino-generated signals, using cold polar ice as the neutrino target, has emerged as perhaps the most promising technique for detection of extragalactic ultra-high energy neutrinos (corresponding to neutrino energies in excess of 0.01 Joules, or 1017 electron volts). During the summer of 2021 and in tandem with the initial deployment of the Radio Neutrino Observatory in Greenland (RNO-G), we conducted radioglaciological measurements at Summit Station, Greenland to refine our understanding of the ice target. We report the result of one such measurement, the radio-frequency electric field attenuation length $L_\alpha$
. We find an approximately linear dependence of $L_\alpha$
on frequency with the best fit of the average field attenuation for the upper 1500 m of ice: $\langle L_\alpha \rangle = ( ( 1154 \pm 121) - ( 0.81 \pm 0.14) \, ( \nu /{\rm MHz}) ) \,{\rm m}$
for frequencies ν ∈ [145 − 350] MHz.
