arXiv subjects

Y. H. Li

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

10 recordsLinked to original sources

arXiv2023

Colliding of two high Mach-number quantum degenerate plasma jets

Colliding of two high Mach-number quantum degenerate plasmas is one of the most essential components in the double-cone ignition (DCI) inertial confinement fusion scheme, in which two highly compressed plasma jets from the cone-tips collide along with rapid conversion from the colliding kinetic energies to the internal energy of a stagnated isochoric plasma. Due to the effects of high densities and high Mach-numbers of the colliding plasma jets, quantum degeneracy and kinetic physics might play important roles and challenge the predictions of traditional hydrodynamic models. In this work, the colliding process of two high Mach number quantum degenerate Deuterium-plasma jets with sizable scale ($\sim 1000\ \si{μm}$, $\sim 300\ \si{ps}$, $\sim 100\ \si{g/cc}$, $\sim 300\ \si{km/s}$) were investigated with first-principle kinetic simulations and theoretical analyses. In order to achieve high-density compression, the colliding kinetic pressure should be significantly higher than the pressure raised by the quantum degeneracy. This means high colliding Mach numbers are required. However, when the Mach number is further increased, we surprisingly found a decreasing trend of density compression, due to kinetic effects. It is therefore suggested that there is theoretically optimal colliding velocity to achieve the highest density compression. Our results would provide valuable suggestions for the base-line design of the DCI experiments and also might be of relevance in some violent astrophysical processes, such as the merger of two white dwarfs.

physics.plasm-ph↗

arXiv2023

Pinch effect of self-generated magnetic fields in the quantum degenerate plasmas on the heating process of the double-cone ignition scheme

In the double-cone ignition scheme, compressed fuels in two head-on cones are ejected to collide, forming a colliding plasma with an isochoric distribution for rapid heating by high flux fast electrons from picosecond petawatt laser beams in the perpendicular direction from the cone axis. In this work, we investigate the effects of quantum degeneracy on the transport of fast electrons in the colliding plasma, which rapidly evolves from the quantum degenerate in the outer region of the plasma to the classical state in the concentric core region heated by the colliding fronts of the plasma jets. With large scale particle-in-cell simulations, it is found that the self-generated magnetic field generated by the transport of fast electrons in the quantum degenerate state at the outer region is much stronger than in the corresponding classical state with the same fuel density in the core region. Theoretical analysis of the growth of the self-generated magnetic field is developed to explain the simulation results. Such strong self-generated magnetic fields in the quantum degenerate states can pinch the axially injected fast electrons to deposit their energy in the concentric core region, improving the heating efficiency for fast ignition.

physics.plasm-ph↗

arXiv2021

A fourth-order finite difference scheme with accurate dispersion and adaptive dissipation for computational aeroacoustics

For computational acoustics, schemes need to have low-dispersion and low-dissipation properties in order to capture the amplitude and phase of the wave correctly. To improve the spectral properties of the scheme, the authors have previously proposed a scale sensor to automatically adjust the numerical dissipation. In consequence, a fourth-order finite difference scheme with minimized dispersion and adaptive dissipation (MDAD) has been proposed [1]. In this study, we further investigate this method for the high-fidelity numerical simulation of the acoustic problems and a new dispersion control method is proposed which is different from the traditional dispersion relation preserving (DRP) approach. Firstly, the scale sensor, which quantifies the local length scale of the solution as the effective scaled wavenumber, is modified for better performance on composite waves. Then the scale sensor is applied to control both the dispersion and dissipation of the scheme. The relationships between the dispersion/dissipation parameter and the effective scaled wavenumber are analytically and artificially constructed respectively. Thus, a fourth-order finite difference scheme with accurate dispersion and adaptive dissipation (ADAD) is constructed. The approximate dispersion relation (ADR) shows that the ADAD scheme achieves accurate dispersion property at k < 2.5. The dissipation is negligible at low wave number and gradually increases after k = 1 to suppress non-physical oscillations. Several benchmark cases of computational acoustics are presented to verify the high resolution of the proposed scheme compared with the conventional spectral optimized schemes.

physics.comp-ph↗

arXiv2021

A sixth-order finite difference scheme with the minimized dispersion and adaptive dissipation for solving compressible flow

The dispersion and dissipation properties of a scheme are important to realize high-fidelity simulations of the compressible flow, especially the cases with broadband length scales. It has been recognized that the minimization of dispersion error is an effective method to improve the precision. In addition, the proper dissipation of a scheme is important to restrain the non-physics oscillations and reserve details of flows simultaneously. The authors have previously proposed a scale sensor to adjust the numerical dissipation of a fourth-order finite difference scheme according to the local scale of the flow. In this paper, the scale sensor is further modified for the sixth-order finite difference scheme to achieve minimized dispersion and adaptive dissipation properties. Firstly, the scale sensor quantifies the local length scale of the numerical solution as the effective scaled wavenumber. Then, the dispersion-dissipation condition is used to construct the relationship between the dissipation/dispersion parameter and the effective scaled wavenumber. Therefore, a sixth-order finite difference scheme with minimized dispersion and adaptive dissipation (MDAD6th) is proposed. Several benchmark test cases with broadband length scales are presented to clarify the high resolution of the new scheme.

physics.flu-dyn↗

arXiv2021

Picosecond creation of switchable optomagnets with giant photoinduced Kerr rotations in polar antiferromagnetic (Fe$_{1-x}$Zn$_{x}$)$_{2}$Mo$_{3}$O$_{8}$

On-demand spin orientation with long polarized lifetime and easily detectable signal is an ultimate goal for spintronics. However, there still exists a trade-off between controllability and stability of spin polarization, awaiting a significant breakthrough. Here, we demonstrate switchable optomagnet effects in (Fe$_{1-x}$Zn$_{x}$)$_{2}$Mo$_{3}$O$_{8}$, from which we can obtain tunable magnetization, spanning from -40$\%$ to 40$\%$ of a saturated magnetization that is created from zero magnetization in the antiferromagnetic state without magnetic fields. It is accomplishable via utilizing circularly-polarized laser pulses to excite spin-flip transitions in polar antiferromagnets that have no spin canting, traditionally hard to control without very strong magnetic fields. The spin controllability in (Fe$_{1-x}$Zn$_{x}$)$_{2}$Mo$_{3}$O$_{8}$ originates from its polar structure that breaks the crystal inversion symmetry, allowing distinct on-site $d$-$d$ transitions for selective spin flip. By chemical doping, we exploit the phase competition between antiferromagnetic and ferrimagnetic states to enhance and stabilize the optomagnet effects, which result in long-lived photoinduced Kerr rotations. The present study, creating switchable giant optomagnet effects in polar antiferromagnets, sketches a new blueprint for the function of antiferromagnetic spintronics.

cond-mat.mtrl-sci↗

arXiv2020

Tunable microwave absorption performance of nitrogen and sulfur dual-doped graphene by varying doping sequence

Sulfur and nitrogen dual doped graphene have been extensively investigated in the field of oxygen reduction reaction, supercapacitors and batteries, but their magnetic and absorption performance have not been explored. Besides, the effects of doping sequence of sulfur and nitrogen atoms on the morphology, structural property and the corresponding microwave absorption performance of the dual doped graphene remain unexplored. In this work, nitrogen and sulfur dual doped graphene with different doping sequence were successfully prepared using a controllable two steps facile thermal treatment method. The first doping process played a decisive role on the morphology, crystal size, interlayer distance, doping degree and ultimately magnetic and microwave absorption properties of the dual doped graphene samples. Meanwhile, the second doping step affected the doping sites and further had a repairing or damaging effect on the final doped graphene. The dual doped graphene samples exhibited two pronounced absorption peaks which intensity was decided by the order of the doping elements. This nitrogen and sulfur dual doped graphene with controlled doping order provides a strategy for understanding of the interaction between nitrogen and sulfur as dual dopants in graphene and further acquiring microwave absorbing materials with tunable absorption bands by varying the doping sequence.

physics.app-ph↗

arXiv2013

Generation of correlated photon pairs in micro/nano-fibers

We study the generation of correlated photon pairs via spontaneous four wave mixing in a 15 cm long micro/nano-fiber (MNF). The MNF is properly fabricated to satisfy the phase matching condition for generating the signal and idler photon pairs at the wavelengths of about 1310 and 851 nm, respectively. Photon counting measurements yield a coincidence-to-accidental ratio of 530 for a photon production rate of about 0.002 (0.0005) per pulse in the signal (idler) band. We also analyze the spectral information of the signal photons originated from the spontaneous four wave mixing and Raman scattering. In addition to discovering some unique feature of Raman scattering, we find the bandwidth of the individual signal photons is much greater than the calculated value for the MNF with homogeneous structure. Our investigations indicate the MNF is a promising candidate for developing the sources of nonclassical light and the spectral property of photon pairs can be used to non-invasively test the diameter and homogeneity of the MNF.

quant-ph↗

arXiv2013

Spectral characterization of third-order harmonic generation assisted by two-dimensional plasma grating in air

A dramatic spectral modulation of third-order harmonic (TH) emission generated in a near in- frared femtosecond (fs) pulse filamentation, assisted by a two-dimensional plasma grating formed by two pump femtosecond pulses, is experimentally demonstrated when their spatiotemporal overlap is achieved. It is mainly attributed to strong cross-phase modulation induced by the fundamental wave of the probe pulse and two pump ones. The delay dynamic of TH spectra indicates the influence of two retarded nonlinear responses on the TH generation. The dependences of TH generation on the energies of probe and pump pulses, relative field polarization angle are also studied.

physics.optics↗

arXiv2012

Ballistic spin filtering across the ferromagnetic-semiconductor interface

The ballistic spin-filter effect from a ferromagnetic metal into a semiconductor has theoretically been studied with an intention of detecting the spin polarizability of density of states in FM layer at a higher energy level. The physical model for the ballistic spin filtering across the interface between ferromagnetic metals and semiconductor superlattice is developed by exciting the spin polarized electrons into n-type AlAs/GaAs superlattice layer at a much higher energy level and then ballistically tunneling through the barrier into the ferromagnetic film. Since both the helicity-modulated and static photocurrent responses are experimentally measurable quantities, the physical quantity of interest, the relative asymmetry of spin-polarized tunneling conductance, could be extracted experimentally in a more straightforward way, as compared with previous models. The present physical model serves guidance for studying spin detection with advanced performance in the future.

cond-mat.mes-hall↗

arXiv1999

Two-phase behavior in strained thin films of hole-doped manganites

We present a study of the effect of biaxial strain on the electrical and magnetic properties of thin films of manganites. We observe that manganite films grown under biaxial compressive strain exhibit island growth morphology which leads to a non-uniform distribution of the strain. Transport and magnetic properties of these films suggest the coexistence of two different phases, a metallic ferromagnet and an insulating antiferromagnet. We suggest that the high strain regions are insulating while the low strain regions are metallic. In such non-uniformly strained samples, we observe a large magnetoresistance and a field-induced insulator to metal transition.

cond-mat.str-el↗