arXiv subjects

H. Y. Wang

Publications and source records attributed to H. Y. Wang.

34 records · Page 2Linked to original sources

arXiv2017

Direct detection of a break in the teraelectronvolt cosmic-ray spectrum of electrons and positrons

High energy cosmic ray electrons plus positrons (CREs), which lose energy quickly during their propagation, provide an ideal probe of Galactic high-energy processes and may enable the observation of phenomena such as dark-matter particle annihilation or decay. The CRE spectrum has been directly measured up to $\sim 2$ TeV in previous balloon- or space-borne experiments, and indirectly up to $\sim 5$ TeV by ground-based Cherenkov $γ$-ray telescope arrays. Evidence for a spectral break in the TeV energy range has been provided by indirect measurements of H.E.S.S., although the results were qualified by sizeable systematic uncertainties. Here we report a direct measurement of CREs in the energy range $25~{\rm GeV}-4.6~{\rm TeV}$ by the DArk Matter Particle Explorer (DAMPE) with unprecedentedly high energy resolution and low background. The majority of the spectrum can be properly fitted by a smoothly broken power-law model rather than a single power-law model. The direct detection of a spectral break at $E \sim0.9$ TeV confirms the evidence found by H.E.S.S., clarifies the behavior of the CRE spectrum at energies above 1 TeV and sheds light on the physical origin of the sub-TeV CREs.

astro-ph.HE↗

arXiv2017

Enhanced laser-driven ion acceleration by superponderomotive electrons generated from near-critical-density plasma

We report on the experimental studies of laser driven ion acceleration from double-layer target where a near-critical density target with a few-micron thickness is coated in front of a nanometer thin diamond-like carbon foil. A significant enhancement of proton maximum energies from 12 to ~30 MeV is observed when relativistic laser pulse impinge on the double-layer target under linear polarization. We attributed the enhanced acceleration to superponderomotive electrons that were simultaneously measured in the experiments with energies far beyond the free-electron ponderomotive limit. Our interpretation is supported by two-dimensional simulation results.

physics.plasm-ph↗

arXiv2017

Spatial resolution measurement of Triple-GEM detector and diffraction imaging test at synchrotron radiation

A triple-GEM detector with two-dimensional readout is developed. The detector provides high position resolution for powder diffraction experiments at synchrotron radiation. Spatial resolution of the detector is measured in the lab using a 55Fe X-ray source. A resolution of about 110 um FWHM is achieved. The energy resolution is better than 27% for 5.9 keV X-rays. The detector's validity under illumination of photons in particular energy range is verified using a Cu X-ray tube. Imaging of the head of a wire stripper with X-ray tube demonstrates its imaging ability. A diffraction imaging experiment using the sample of powder SiO2 is successfully carried out at 1W2B laboratory of Beijing Synchrotron Radiation Facility (BSRF). Different diffraction rings are clearly seen under various X-ray energies.

physics.ins-det↗

arXiv2016

Effect of ion mass on pair production in the interaction of an ultraintense laser with overdense plasmas

The effect of ion mass on pair production in the interaction of an ultraintense laser with overdense plasmas has been explored by particle-in-cell (PIC) simulation. It is found that the heavier ion mass excites the higher and broader electrostatic field, which is responsible for the enhancement of backward photon number. The pair yields are also reinforced due to the increase of head-on collision of backwards photon with incoming laser. By examining the density evolution and angle distribution of each particle species the origin of pair yields enhancement has been clarified further.

physics.plasm-ph↗

arXiv2014

The silicon matrix for the prototype for the Dark Matter Particle Explorer

A new generation detector for the high energy cosmic ray - the DAMPE(DArk Matter Particle Explorer) is a satellite based project. Its main object is the measurement of energy spectrum of cosmic ray nuclei from 100GeV to 100TeV, the high energy electrons and gamma ray from 5GeV to 10TeV. A silicon matrix detector described in this paper, is employed for the sea level cosmic ray energy and position detection while the prototype testing of the DAMPE. This matrix is composed by the 180 silicon PIN detectors, which covers an area of 32*20 cm2. The primary testing results are shown including MIPs energy spectrum and the position sensitive map.

physics.ins-det↗

arXiv2014

Relativistic plasma optics enabled by near-critical density nanostructured material

The nonlinear optical properties of a plasma due to the relativistic electron motion in an intense laser field are of fundamental importance for current research and the generation of brilliant laser-driven sources of particles and photons1-15. Yet, one of the most interesting regimes, where the frequency of the laser becomes resonant with the plasma, has remained experimentally hard to access. We overcome this limitation by utilizing ultrathin carbon nanotube foam16 (CNF) targets allowing the strong relativistic nonlinearities at near- critical density (NCD) to be exploited for the first time. We report on the experimental realization of relativistic plasma optics to spatio-temporally compress the laser pulse within a few micrometers of propagation, while maintaining about half its energy. We also apply the enhanced laser pulses to substantially improve the properties of an ion bunch accelerated from a secondary target. Our results provide first insights into the rich physics of NCD plasmas and the opportunities waiting to be harvested for applications.

physics.plasm-ph↗

arXiv2014

Bright subcycle XUV pulse from a single dense relativistic electron sheet

Relativistic electrons are prodigious sources of photons. Beyond classical accelerators, ultra-intense laser interactions are of particular interest as they allow the coherent motion of relativistic electrons to be controlled and exploited as sources of radiation. Under extreme laser conditions theory predicts that isolated free relativistic electron sheets (FRES) can be produced and exploited for the production of a new class of radiation - unipolar extreme ultraviolet(XUV) pulses. However, the combination of extremely rapid rise-time and highest peak intensity in these simulations is still beyond current laser technology. We demonstrate a route to isolated FRES with existing lasers by exploiting relativistic transparency to produce an ultra-intense pulse with a steep rise time. When such an FRES interacts with a second, oblique target foil the electron sheet is rapidly accelerated ('kicked'). The radiation signature and simulations demonstrate that a single, nanometer thick FRES was produced. The experimental observations together with our theoretical modeling suggest the production of the first unipolar (half-cycle) pulse in the XUV - an achievement that has so far only been realized in the terahertz spectral domain.

physics.plasm-ph↗

arXiv2013

Bright gamma-rays from betatron resonance acceleration in near critical density plasma

We show that electron betatron resonance acceleration by an ultra-intense ultra-short laser pulse in a near critical density plasma works as a high-brightness gamma-ray source. Compared with laser plasma X-ray sources in under-dense plasma, near critical density plasma provides three benefits for electron radiation: more radiation electrons, larger transverse amplitude, and higher betatron oscillation frequency. Three-dimensional particle-in-cell simulations show that, by using a 7.4J laser pulse, 8.3mJ radiation with critical photon energy 1MeV is emitted. The critical photon energy $E_c$ increases with the incident laser energy %faster than a linear relation. $W_I$ as $E_c \propto W_I^{1.5}$, and the corresponding photon number is proportional to $W_I$. A simple analytical synchrotron-like radiation model is built, which can explain the simulation results.

physics.acc-ph↗

arXiv2013

Ultrasmall divergence of laser-driven ion beams from nanometer thick foils

We report on experimental studies of divergence of proton beams from nanometer thick diamond-like carbon (DLC) foils irradiated by an intense laser with high contrast. Proton beams with extremely small divergence (half angle) of 2 degree are observed in addition with a remarkably well-collimated feature over the whole energy range, showing one order of magnitude reduction of the divergence angle in comparison to the results from micrometer thick targets. We demonstrate that this reduction arises from a steep longitudinal electron density gradient and an exponentially decaying transverse profile at the rear side of the ultrathin foils. Agreements are found both in an analytical model and in particle-in-cell simulations. Those novel features make nm foils an attractive alternative for high flux experiments relevant for fundamental research in nuclear and warm dense matter physics.

physics.plasm-ph↗

arXiv2012

Pressure dependence of elastic and dynamical properties of zinc-blende ZnS and ZnSe from first principle calculation

The density-functional theory (DFT) and density-functional perturbation theory (DFPT) are employed to study the pressure dependence of elastic and dynamical properties of zinc-blende ZnS and ZnSe. The calculated elastic constants and phonon spectra from 0 GPa to 15 GPa are compared with the available experimental data. Generally, our calculated values are overestimated with experimental data, but agree well with recent other theoretical values. The discrepancies with experimental data are due to the use of local density approximation (LDA) and the effect of temperature. In this work, in order to compare with experimental data, we calculated and discussed the pressure derivatives of elastic constants, the pressure dependence of dynamical effect charge, and mode Grüneisen parameter at Γ.

cond-mat.mtrl-sci↗

arXiv2011

High-quality proton bunch from laser interaction with a gas-filled cone target

Generation of high-energy proton bunch from interaction of an intense short circularly polarized(CP) laser pulse with a gas-filled cone target(GCT) is investigated using two-dimensional particle-in-cell simulation. The GCT target consists of a hollow cone filled with near-critical gas-plasma and a thin foil attached to the tip of the cone. It is observed that as the laser pulse propagates in the gas-plasma, the nonlinear focusing will result in an enhancement of the laser pulse intensity. It is shown that a large number of energetic electrons are generated from the gas-plasma and accelerated by the self-focused laser pulse. The energetic electrons then transports through the foil, forming a backside sheath field which is stronger than that produced by a simple planar target. A quasi-monoenergetic proton beam with maximum energy of 181 MeV is produced from this GCT target irradiated by a CP laser pulse at an intensity of $2.6\times10^{20}W/cm^2$, which is nearly three times higher compared to simple planar target(67MeV).

physics.plasm-ph↗

arXiv2011

Determination of Carrier-Envelope Phase of Relativistic Few-Cycle Laser Pulses by Thomson Backscattering Spectroscopy

A novel method is proposed to determine the carrier-envelope phase (CEP) of a relativistic few-cycle laser pulse via the central frequency of the isolated light generated from Thomson backscattering (TBS). We theoretically investigate the generation of a uniform flying mirror when a few-cycle drive pulse with relativistic intensity ($I > 10^{18} {\rm{W} \mathord{/ {\vphantom {\rm{W} {\rm{cm}^{\rm{2}}}}}. \kern-\nulldelimiterspace} {\rm{cm}^{\rm{2}}}}$) interacts with a target combined with a thin and a thick foil. The central frequency of the isolated TBS light generated from the flying mirror shows a sensitive dependence on the CEP of the drive pulse. The obtained results are verified by one dimensional particle in cell (1D-PIC) simulations.

physics.plasm-ph↗

arXiv2011

Generating sub-TeV quasi-monoenergetic proton beam by an ultra-relativistically intense laser in the snowplow regime

Snowplow ion acceleration is presented, using an ultra-relativistically intense laser pulse irradi- ating on a combination target, where the relativistic proton beam generated by radiation pressure acceleration can be trapped and accelerated by the laser plasma wakefield. The theory suggests that sub-TeV quasi-monoenergetic proton bunches can be generated by a centimeter-scale laser wakefield accelerator, driven by a circularly polarized (CP) laser pulse with the peak intensity of 10^23W/cm^2 and duration of 116fs.

physics.plasm-ph↗

arXiv2008

Reconstructing the cosmic density field with the distribution of dark matter halos

We develop a new method to reconstruct the cosmic density field from the distribution of dark matter haloes above a certain mass threshold. Our motivation is that well-defined samples of galaxy groups/clusters, which can be used to represent the dark halo population, can now be selected from large redshift surveys of galaxies, and our ultimate goal is to use such data to reconstruct the cosmic density field in the local universe. Our reconstruction method starts with a sample of dark matter haloes above a given mass threshold. Each volume element in space is assigned to the domain of the nearest halo according to a distance measure that is scaled by the virial radius of the halo. The distribution of the mass in and around dark matter haloes of a given mass is modelled using the cross-correlation function between dark matter haloes and the mass distribution within their domains. We use N-body cosmological simulations to show that the density profiles required in our reconstruction scheme can be determined reliably from large cosmological simulations, and that our method can reconstruct the density field accurately using haloes with masses down to $\sim 10^{12}\msun$ (above which samples of galaxy groups can be constructed from current large redshift surveys of galaxies). Working in redshift space, we demonstrate that the redshift distortions due to the peculiar velocities of haloes can be corrected in an iterative way. We also describe some applications of our method.

astro-ph↗

arXiv2006

Environmental Dependence of Cold Dark Matter Halo Formation

We use a high-resolution $N$-body simulation to study how the formation of cold dark matter (CDM) halos is affected by their environments, and how such environmental effects produce the age-dependence of halo clustering observed in recent $N$-body simulations. We estimate, for each halo selected at redshift $z=0$, an `initial' mass $M_{\rm i}$ defined to be the mass enclosed by the largest sphere which contains the initial barycenter of the halo particles and within which the mean linear density is equal to the critical value for spherical collapse at $z=0$. For halos of a given final mass, $M_{\rm h}$, the ratio $M_{\rm i}/M_{\rm h}$ has large scatter, and the scatter is larger for halos of lower final masses. Halos that form earlier on average have larger $M_{\rm i}/M_{\rm h}$, and so correspond to higher peaks in the initial density field than their final masses imply. Old halos are more strongly clustered than younger ones of the same mass because their initial masses are larger. The age-dependence of clustering for low-mass halos is entirely due to the difference in the initial/final mass ratio. Low-mass old halos are almost always located in the vicinity of big structures, and their old ages are largely due to the fact that their mass accretions are suppressed by the hot environments produced by the tidal fields of the larger structure. The age-dependence of clustering is weaker for more massive halos because the heating by large-scale tidal fields is less important.

astro-ph↗

arXiv2005

The phase-space distribution of infalling dark matter subhalos

We use high-resolution numerical simulations to study the physical properties of subhalos when they merge into their host halos. An improved algorithm is used to identify the subhalos. We then examine their spatial and velocity distributions in spherical and triaxial halo models. We find that the accretion of satellites preferentially occurs along the major axis and perpendicular to the spin axis of the host halo. Furthermore, the massive subhalos show a stronger preference to be accreted along the major axis of the host halo than the low-mass ones. Approximate fitting formulae are provided for the physical properties of subhalos. Combined with analytical and semi-analytic techniques, these empirical formulae provide a useful basis for studying the subsequent evolution of subhalos and satellite galaxies in their hosts. Future studies should however account for satellites that may not be undergoing the first infall in their evolution.

astro-ph↗