Divergence angle consideration in energy spread measurement for high-quality relativistic electron beam in laser wakefield acceleration

The thorough exploration of the transverse quality represented by divergence angle has been lacking yet in the energy spread measurement of the relativistic electron beam for laser wakefield acceleration(LWFA). In this work, we fill this gap by numerical simulations based on the experimental data, which indicate that in a C-shape magnet, magnetic field possesses the beam focusing effect, considering that the divergence angle will result in an increase in the full width at half maxima(FWHM) of the electron density distribution in a uniformly isotropic manner, while the length-to-width ratio decreases. This indicates that the energy spread obtained from the electron deflection distance is smaller than the actual value, regardless of the divergence angle. A promising and efficient way to accurately correct the value is presented by considering the divergence angle(for instance, for an electron beam with a length-to-width ratio of 1.12, the energy spread correct from 1.2% to 1.5%), providing a reference for developing the high-quality electron beam source.

Prospect of ultrahigh-resolution fast neutron absorption spectroscopy based on a laser plasma electron accelerator

Fast neutron absorption spectroscopy is widely used in the study of nuclear structure and element analysis. However,due to the traditional neutron source pulse duration being of the order of nanoseconds, it is difficult to obtain a high-resolution absorption spectrum. Thus, we present a method of ultrahigh energy-resolution absorption spectroscopy via a high repetition rate, picosecond duration pulsed neutron source driven by a terawatt laser. The technology of single neutron count is used, which results in easily distinguishing the width of approximately 20 keV at 2 MeV and an asymmetric shape of the neutron absorption peak. The absorption spectroscopy based on a laser neutron source has one order of magnitude higher energy-resolution power than the state-of-the-art traditional neutron sources, which could be of benefit for precisely measuring nuclear structure data.

Study of the internal characteristics of the stall in a centrifugal pump with a cubic non-linear SGS model

The stall in a centrifugal pump impeller under a quarter-load condition is investigated by using a third-order SGS model named the DCNM, for a better understanding of the rotation effect on the stall phenomenon. The study of the distributions of the Reynolds stresses, the production tei*m and the rotation term reveals that the production and the rotation jointly result in the non-uniform Reynolds stress distribution. Further study of the two components of the production and the rotation shows that they jointly transport a certain energy from the Reynolds component R、to Ruu.

Spatial differences of ice volume across High Mountain Asia

Advanced knowledge of glacier ice volume is vital for water resource assessment.Previous studies have focused on the estimation of ice volume,but the quantitative understanding of the spatial variability of ice volume across High Mountain regions is currently lacking.Here,we used global-scale ice thickness,debris cover and equilibrium line data to analyse ice-volume differences at various scales across High Mountain Asia(HMA).The results showed that 6.3%of the HMA glaciers are covered by debris,with debris area and volume accounting for 9%and 13.8%of the total glacier area and volume,respectively.An average debris-cover volume ratio of 13%was observed.The spatial distribution of ice volume across the HMA varies considerably from region to region.The ice volume is predominately distributed on north-facing slopes and accounts for approximately 38%of the total.It is very common in Altay and Sayan,East Tian Shan,West Kunlun,East Kunlun and Qilian Shan.Meanwhile,ice volumes in the Himalayas and Hengduan Shan are mainly distributed on the southeast aspect.Relative weight functions showed that glacier area,maximum length and average thickness are closely related to ice volume,with average relative weights of 63.7%,22.5%and 9.8%,respectively.This study is important for the evolution of glacier volume and water resource assessment.

Investigation on the stall types in impellers with different blade numbers

Stall is a complex flow phenomenon and its existence usually shows significant differences in different impeller forms.In this paper,the flow field characteristics and mechanism of stall types in impellers with different blade numbers were studied through the combination of experiment and numerical simulation at stall inception stage.In the experiments,it was observed that the five-blade impeller entered the rotating stall stage from a relatively stable flow field within a small flow rate interval.For the six-blade impeller,the root cause that stall vortices appeared in channels alternately rather than each one evenly was also reasonably explained.The validated numerical simulation method was utilized to reveal the three-dimensional flow field in impeller channels.The results indicate the swirling vortex near the impeller shroud was periodically sucked in and escaped from region near the blade suction side,which was the fundamental driving force of rotating stall.The sudden change of flow field caused by the fusion of the separation vortex at the channel inlet and the vortex induced by the swirling vortex near shroud is the essential reason for the formation of alternating stall.What’s more,the stall inception flow field is clearly defined in impellers,which is of great significance for the further analysis of stall characteristics.Based on the distribution characteristics of vortex structure near impeller shroud with different blade numbers at different flow rate conditions,this paper deeply investigated the formation mechanism of different stall types in impellers.