Advances in laser-plasma interactions using intense vortex laser beams

Low-intensity light beams carrying orbital angular momentum(OAM),commonly known as vortex beams,have garnered significant attention due to promising applications in areas ranging from optical trapping to communication.In recent years,there has been a surge in global research exploring the potential of high-intensity vortex laser beams and specifically their interactions with plasmas.This paper provides a comprehensive review of recent advances in this area.Compared with conventional laser beams,intense vortex beams exhibit unique properties such as twisted phase fronts,OAM delivery,hollow intensity distribution,and spatially isolated longitudinal fields.These distinct characteristics give rise to a multitude of rich phenomena,profoundly influencing laser-plasma interactions and offering diverse applications.The paper also discusses future prospects and identifies promising general research areas involving vortex beams.These areas include low-divergence particle acceleration,instability suppression,high-energy photon delivery with OAM,and the generation of strong magnetic fields.With growing scientific interest and application potential,the study of intense vortex lasers is poised for rapid development in the coming years.

Using the physical decomposition method to study the effects of Arctic factors on wintertime temperatures in the Northern Hemisphere and China

The physical decomposition method separates atmospheric variables into four parts, correlating each with solar radiation, land-sea distribution, and inter-annual and seasonal internal forcing, strengthening the anomaly signal and increasing the correlation between variables. This method was applied to the reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research （NCEP/NCAR）, to study the effects of Arctic factors （Arctic oscillation （AO） and Arctic polar vortex） on wintertime temperatures in the Northern Hemisphere and China. It was fotmd that AO effects on zonal average temperature disturbance could persist for 1 month. In the AO negative phase in wintertime, the temperatures are lower in the mid-high latitudes than in normal years, but higher in low latitudes. When the polar vortex area is bigger, the zonal average temperature is lower at 50N. Influenced mainly by meridional circulation enhancement, cold air flows from high to low latitudes; thus, the temperatures in Continental Europe and the North American continent exhibit an antiphase seesaw relationship. When the AO is in negative phase and the Arctic polar vortex larger, the temperature is lower in Siberia, but higher in Greenland and the Bering Strait. Influenced by westerly troughs and ridges, the polar air disperses mainly along the tracks of atmospheric activity centers. The AO index can be considered a predictor of wintertime temperature in China. When the AO is in negative phase or the Asian polar vortex is intensified, temperatures in Northeast China and Inner Mongolia are lower, because under the influence of the Siberia High and northeast cold vortex, the cold air flows southwards.

Factors Affecting Small Axial Cooling Fan Performance

Many factors such as outer diameter, hub ratio, blade numbers, shape and stagger angle affect the performance of small cooling fans. A small cooling fan was simulated using CFD software for three blade stagger angles （30.5°, 37.5°, 44.5°）and obtained the internal flow field and the static characteristics. Research indicated that the stagger angle has an obvious effect on the static characteristics of a fan. For flow rates below 0.0104 mVs, total pressure is the greatest when the stagger angle is 37.5°; flow rates higher than 0.0104 m^3/s, the total pressure is greatest when the stagger angle is 44.5° For the same flow rates, the velocity at inlet of pressure surface increases with in- creasing stagger angle, but the change of velocity on the suction surface is very small. For one model, vortices and the speed of revolution surfaces decrease with tip clearance increasing. But for other three models, increasing the stagger angle, the vortex intensity and speed of revolution surfaces at same height tip clearance increases, simultaneously, the position of vortex offset from the top of the rotor blade to the suction surface.

A Climatological Investigation of the Activity of Summer Subtropical Vortices

By applying a new vortex detection method to the ECMWF 40-yr reanalysis （ERA40） data from 1985 to 2002, the climatology of summer vortices has been investigated in five subtropical regions, i.e., the northwestern Pacific, northeastern Pacific, northwestern Atlantic, northeastern Atlantic, and Australia- South Pacific, followed by validation with NCEP/NCAR reanalysis data. Results are as follows： （1） The spatial distributions of ERA40 vortex activities （VAC） were well consistent with those of NCEP/NCAR reanalysis （NRA） results in all regions, especially in northwestern Pacific. （2） Because of different model resolutions, both the number and intensity of vortices obtained from NRA were significantly weaker than ERA40＇s. （3） Vortices mainly cruised in coasts and the adjacent seas, from where to the land or the open sea vortex activities were gradually decreased. （4） There were two active centers in the northwestern Pacific： one was located in South China Sea and the other, as the largest center of the five regions, spread from the east side of the Philippines to Japan. （5） Over the northwestern Atlantic, most vortices occurred in Panama and its west-side offshore. （6） The spatial distributions of vortices were alike between the northeastern Pacific and northeastern Atlantic, both spreading from coasts to the west-side sea at 5°-20°N. （7） In the Australia-South Pacific, vortices were not as active as those in the other four regions, and mostly took place in the equator-side of near ocean areas. （8） Except the northwestern Pacific and northwestern Atlantic, the VAC interannual variations in the other three regions were different between ERA40 and NRA data. （9） In the northwestern Pacific and northwestern Atlantic, the VAC interannual variation could be separated to several distinct stages. （10） Since the mid 1980s, mean vortex intensity was getting increased in the northwestern Pacific, which was most significant in the subtropical areas on a global basis. In the western North Atlantic, there was a decreasing （increasing） trend of the mean vortex intensity before （after） the mid 1990s.