The proton spectral and angular distributions simultaneously within the target normal direction and laser propagation direction by using an angle-resolved proton energy spectrometer are studied.For the protons generated in the interactions of 100 fs,800nm laser pulses with aluminum foil targets,the deviations of proton beam centers of different energies from the target normal direction towards the laser propagation direction are different.This is probably because of the toroidal magnetic fields generated at the rear target surface,which deflect protons transversely.As a result,protons in low energy range have large deviation angles,protons in middle energy range have the smallest deviation angles,while protons in high energy tail have large deviation angles.
SU LuNingZHENG YiLIU MengHU ZhiDanWANG WeiMinYUAN XiaoHuiXU MiaoHuaSHENG ZhengMingSHEN ZhongWeiFAN HaiTaoLI YuTongMA JingLongLU XinCHEN LiMingWANG ZhaoHuaWEI ZhiYiZHANG Jie
A novel method of initiating nuclear fusion reactions in a full plasma environment was suggested, and a proof-of-concept experiment was carried out with the D t D ! n t3 He reaction. In this new approach, two plasma jets generated by high-intensity lasers collide headon-head. The center-of-mass energy of the nuclei increases accordingly, and therefore, reaction products can be significantly enhanced, especially in the sub-Coulomb barrier ranges. As a result of the fusion reaction, up to 7:6 105 neutrons had been observed. This new type of ‘‘plasma collider'' could provide an innovative tool to study nuclear reactions under astrophysical conditions.
A counter-streaming flow system is a test-bed to investigate the astrophysical collisionless shock（CS） formation in the laboratory. Electrostatic/electromagnetic instabilities, competitively growing in the system and exciting the CS formation, are sensitive to the flows parameters. One of the most important parameters is the velocity, determining what kind of instability contributes to the shock formation. Here we successfully measure the evolution of the counter-streaming flows within one shot using a multi-pulses imaging diagnostic technique. With the technique, the average velocity of the high-density-part（ne ≥ 8–9 × 10^19cm^-3） of the flow is directly measured to be of ～ 10^6cm/s between 7 ns and 17 ns.Meanwhile, the average velocity of the low-density-part（ne ≤ 2 × 10^19cm^-3） can be estimated as ～ 10^7cm/s. The experimental results show that a collisionless shock is formed during the low-density-part of the flow interacting with each other.
The first experimental measurements of intense(～7 × 1019 W cm-2) laser-driven terahertz(THz) radiation from a solid target which is preheated by an intense pulse of laser-accelerated protons is reported. The total energy of the THz radiation is found to decrease by approximately a factor of 2 compared to a cold target reference. This is attributed to an increase in the scale length of the preformed plasma, driven by proton heating, at the front surface of the target,where the THz radiation is generated. The results show the importance of controlling the preplasma scale length for THz production.
We present the particle-in-cell(PIC) simulation results of the interaction of a high-energy lepton plasma flow with background electron-proton plasma and focus on the acceleration processes of the protons. It is found that the acceleration follows a two-stage process. In the first stage, protons are significantly accelerated transversely(perpendicular to the lepton flow) by the turbulent magnetic field "islands" generated via the strong Weibel-type instabilities. The accelerated protons shows a perfect inverse-power energy spectrum. As the interaction continues, a shockwave structure forms and the protons in front of the shockwave are reflected at twice of the shock speed, resulting in a quasi-monoenergetic peak located near 200 Me V under the simulation parameters. The presented scenario of ion acceleration may be relevant to cosmic-ray generation in some astrophysical environments.
CUI YunQianSHENG ZhengMingLU QuanMingLI YuTongZHANG Jie
A bow shock is formed in the interaction of a high-speed laser-driven plasma cloud with a cylinder obstacle. Its temporal and spatial structures are observed by shadowgraphy and interferometry. The width of the shock transition region is - 50 μm, comparable to the ion–ion collision mean free path, which indicates that collision is dominated in the shock probably. The Mach-number of the ablating plasma cloud is ～ 15 at first, and decreases with time resulting in a changing shock structure. A two-dimension hydrodynamics code, USim, is used to simulate the interaction process. The simulated shocks can well reproduce the observed.
Thermodynamic and chemical properties of liquid carbon dioxide and nitrogen（CO_（2~–）N_2） mixture under the conditions of extremely high densities and temperatures are studied by using quantum molecular dynamic（QMD） simulations based on density functional theory including dispersion corrections（DFT-D）. We present equilibrium properties of liquid mixture for 112 separate density and temperature points, by selecting densities ranging from ρ = 1.80 g/cm^3 to 3.40 g/cm^3 and temperatures from T = 500 K to 8000 K. In the range of our study, the liquid CO_（2~–）N_2 mixture undergoes a continuous transition from molecular to atomic fluid state and liquid polymerization inferred from pair correlation functions（PCFs）and the distribution of various molecular components. The insulator–metal transition is demonstrated by means of the electronic density of states（DOS）.
The remarkable experimental progress in the studies of collisionless shockwave（CS） in laboratories employing highpower lasers is briefly reviewed. The results show that CS can be generated in laser-produced plasmas due to the microturbulence associated with instabilities. CS is one of the most important astronomical phenomena. It has been found in supernova remnants（SNRs）, Sun–Earth space, etc. This paper focuses on CS in ways relevant to SNRs. Laboratory astrophysics（LA）, a new interdisciplinary frontier of astrophysics, plasma and laser physics, has developed rapidly in recent years. As an accessory to the astronomical observation, LA experimenters can closely study some astronomical events scaled-down to controllable phenomena.
Terahertz （THz） radiation has attracted much attention due to its wide potential applications. Though radiation can be generated with various ways, it is still a big challenge to obtain strong tabletop sources. Plasma, with the advantage of no damage limit, is a promising medium to generate strong THz radiation. This review reports recent advances on strong THz radiation generation from low-density gases and high-density solid targets at different laser intensities.
