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Shuangxi Zhang

Publications and source records attributed to Shuangxi Zhang.

16 recordsLinked to original sources
arXiv2020

Gravity field modeling using space frequency signal transfer technique between satellites

Here we provide an alternative approach to determine the Earth's external gravitational potential field based on low-orbit target satellite (TS), geostationary satellites (GS), and microwave signal links between them. By emitting and receiving frequency signals controlled by precise clocks between TS and GS, we can determine the gravitational potential (GP) at the TS orbit. We set the TS with polar orbits, altitude of around 500 km above ground, and three evenly distributed GSs with equatorial orbits, altitudes of around 35000 km from the Earth's center. In this case, at any time the TS can be observed via frequency signal links by at least one GS. In this way we may determine a potential distribution over the TS-defined sphere (TDS), which is a sphere that best fits the TS' orbits. Then, based on the potential distribution over the TDS, an Earth's external gravitational field can be determined. Simulation results show that the accuracy of the potential filed established based on 30-days observations can achieve decimeter level if optical atomic clocks with instability of $1\times 10^{-17}τ^{-1/2}$ are available. The formulation proposed in this study may enrich the approachs for determining the Earth's external gravity field.

physics.geo-ph↗
arXiv2020

Unification of global height system at centimeter level using precise frequency signal links

The realization of International Height Reference System (IHRS) is one of the major tasks of the International Association of Geodesy (IAG). A main component of the IHRS realization is the global vertical datum unification, which requires the connection of the existing local vertical height reference systems (VHS). However, it is difficult to estimate the offsets between two local height systems by conventional approaches when they are far apart. In this paper, we formulate a framework for connecting two local VHSs using ultra-precise frequency signal transmission links between satellites and ground stations, which is referred to as satellite frequency signal transmission (SFST) approach. The SFST approach can directly determine the geopotential difference between two ground datum stations without location restrictions, and consequently determine the height difference of the two VHSs. Simulation results show that the China's VHS and the US's VHS can be unified at the accuracy of several centimeters, provided that the stability of atomic clocks used on board the satellite and on ground datum stations reach the highest level of current technology, about $4.8\times 10^{-17}/\sqrtτ$ for an averaging time τ (in seconds). The SFST approach is promising to unify the global vertical height datum in centimeter level in future, and it also provide a new way for the IHRS realization.

physics.geo-ph↗
arXiv2020

Gyrokinetic Vlasov-Poisson model derived by hybrid-coordinate transform of the distribution function

This paper points out that the full-orbit density obtained in the standard electrostatic gyrokinetic model is not truly accurate at the order $\varepsilon^{σ-1}$ with respect to the equilibrium distribution $e^{-αμ}$ with $μ\in (0, μ_{\max})$, where $\varepsilon$ is the order of the normalized Larmor radius, $\varepsilon^σ$ the order of the amplitude of the normalized electrostatic potential, and $α$ a factor of $O(1)$. This error makes the exact order of the full-orbit density not consistent with that of the approximation of the full-orbit distribution function. By implementing a hybrid coordinate frame to get the full-orbit distribution, specifically, by replacing the magnetic moment on the full-orbit coordinate frame with the one on the gyrocenter coordinate frame to derive the full-orbit distribution transformed from the gyrocenter distribution, it's proved that the full-orbit density can be approximated with the exact order being $\varepsilon^{σ-1}$. The numerical comparison between the new gyrokinetic model and the standard one was carried out using Selalib code for an initial distribution proportional to $\exp(\frac{-μB}{T_i})$ in constant cylindrical magnetic field configuration with the existence of electrostatic perturbations. In such a configuration, the simulation results exhibit similar performance between the two models.

physics.plasm-ph↗
arXiv2017

Two electrostatic gyrokinetic models derived by two different perturbative methods

This paper presents two different electrostatic gyrokinetic models derived through two different perturbative methods. One of the two models is just the conventional electrostatic gyrokinetic model, the derivation of which is repeated using the Lie transform perturbative method. One term is rectified in the derivation of the conventional model. To derive the other model, we use a new method, which is based on the covariant transform formula of the differential 1-form. The new method doesn't split the coordinate transform into the guiding-center transform and the gyrocenter transform. It carries out the coordinate transform up to the order equaling that of the amplitude of the perturbative wave. Compared with the conventional model, the finite Larmor radius terms are completely removed from the orbit equations of the new one, making it simpler for the numerical application.

physics.plasm-ph↗
arXiv2017

A multi-parameter Lie transform method applied to the transform of the Lagrangian differential one-form

In this paper, to fit the multi-scale perturbations, the single-parameter Lie transform perturbation theory given in [Ann Phys, 151 1 (1983)] is generalized to a multi-parameter case, which provides a formal solution of the new Lagrangian differential 1-form transformed from the old one. In the new method, the generators and their orders are appropriately chosen under the purpose of reducing the fast variables from the new Lagrangian differential 1-form order by order. As for the application, this multi-parameter Lie transform method is applied to deriving the gyrokinetic model with the presentation of low-frequency electrostatic perturbations. Compared with the conventional model, the Finite Larmor Radius terms in the Lagrangian 1-form of the new model are perfectly cancelled, without using any gauge function.

physics.plasm-ph↗
arXiv2017

Guiding-center kinetic model based on the assumption of homogeneous distribution over gyrophase

The purpose of this paper is to develop a simplified model as the modeling of the magnetized plasmas. The starting point is an assumption that the distribution of the ensemble of charged particles in the same species is homogeneous over gyrophase. The particles in this ensemble are located at the same guiding-cneter position $(\mathbf{X},μ,U)$. Then, a fundamental Lagrangian differential 1-form is developed. It contains all particles in the magnetized plasma system as well as the Coulomb pair force between particles instead of field-particle interaction used in conventional gyrokinetic models. By transforming the Lagrangian 1-form to the new one on guiding-center coordinate with the ensemble summation over gyrophase, the new fundamental 1-form is naturally independent of gyrophase of each particle based on the homogeneous distribution over gyrophase, and it determines the dynamics of all particles on the new coordinates. By using a coarse-grained scheme, this new 1-form can be modeled by the guiding-center kinetic model.

physics.plasm-ph↗
arXiv2017

Deriving the trajectory equations of gyrocenter with a multi-parameter Lie transform method

It's pointed out that the values of the generators derived by the modern gyrokinetic theory are inappropriately amplified by the pullback transform with the existence of electromagnetic perturbation, and the trajectory equations of the gyrocenter include terms containing the perturbative magnetic vector potential not in the form of its curl. These terms are not physical ones, as the perturbative magnetic vector potential could include an arbitrary gauge term. In this paper, instead of the single-parameter Lie transform method utilized by the modern gyrokinetic theory, a multi-parameter Lie transform method is utilized. All characteristic scales of the system can be taken into account. With the assistance of a kind of linear cancellation rule, the new method can decouple the gyroangle $θ$ from the remaining degrees of freedom up to the second order of the parameter as the ratio between the Larmor radius and the transverse length scale of the equilibrium magnetic field. With this new method, those nonphysical terms don't appear anymore in the trajectory equations.

physics.plasm-ph↗
arXiv2017

Resonant terms on gyrocenter coordinates introduced by resonant electromagnetic perturbations

It's pointed out that the treatment of the resonant electromagnetic perturbation with the Lie transform method adopted in the gyrokinetic theory generates some nonphysical terms in the trajectory equations. By utilizing a modified application of this transform method, the resonant terms in the trajectory equations satisfying each resonant condition are found out up to the second harmonic resonance. Through separating the fast-dynamic terms from the slow-dynamic ones, the slow-dynamic trajectory equations including the resonant terms are derived for various resonant conditions. The slow-dynamic evolution equation of gyroangle reveals that the real gyrating frequency of the charged particle around the magnetic field line under driving by the resonant wave has a shift from the cyclotron frequency without the wave driving. To study the effect caused by the frequency shift, a simple example for the fundamental-frequency cyclotron resonance is presented.

physics.plasm-ph↗
arXiv2017

Modelling the Lagrangian of magnetized plasmas with low-frequency magnetic perturbations by a gyrokinetic Ampere-Poisson model

Following the method in Ref.(1), this paper introduces a fundamental Lagrangian 1-form on the particle's coordinates, which determines the dynamics of all ions and electrons of the magnetized plasma with low-frequency magnetic perturbations. An Ampere-Vlasov model is utilized to model this fundamental Lagrangian 1-form based on a kind of coarse-grained scheme. With the Cary-Littlejohn single-parameter Lie transform method, a new fundamental Lagrangian 1-form on the gyrocenter coordinates is derived through transforming the one on particle's coordinates. This new 1-form determines the dynamics of all ions and electrons on the gyrocenter coordinates. A new Ampere-Vlasov model totally defined on the gyrocenter coordinates is developed to model the new Lagrangian 1-form. By incorporating the electrostatic perturbation into the Lagrangian 1-form, we eventually derived an Ampere-Poisson-Vlasov model defined on the gyrocenter coordinates.

physics.plasm-ph↗
arXiv2016

Gyrokinetic resonant theory of low frequency electromagnetic perturbation

It's pointed out that the traditional gyrokinetic theory dealing with low frequency electromagnetic perturbation violates the near identity transformation, which is supposed to be obeyed by Lie perturbed transformation theory, if resonance happens between ωand k\cdot v. A modification is given to overcome this problem by not requiring all components in the first order Lagrangian 1-form equaling zero. A numerical example is given as an application of the new theory.

physics.plasm-ph↗
arXiv2014

The dispersion modification of electrostatic geodesic acoustic mode by electron geodesic drift current

The past studies treated the perturbed distribution of circulating electrons as adiabatic one when studying the dispersion relation of electrostatic geodesic acoustic mode(GAM). In this paper, the flow of electron geodesic current (FEGC) is added to modify this adiabatic distribution. Based on the drift kinetic theory, it is found that FEGC obviously increases the magnitude of the standard GAM's frequency and reduces its damping rate. The increase of frequency results from the contribution of FEGC to the radial flow. The reason for the reduction of damping rate is that when the effect of FEGC counts, the new resonant velocity becomes much larger than ions thermal velocity with equilibrium distribution obeying Maxwellian distribution, compared with unmodified Landau resonant velocity. Especially, FEGC changes the characters of the frequency and damping rate of low-frequency GAM as functions of safety factor $q$ .

physics.plasm-ph↗
arXiv2009

High efficiency Four-Wave Mixing in a five-level atomic System based on the two electromagnetically induced transparency

We have analyzed a five-level $\wedge$-configuration Four-Wave Mixing (FWM) scheme for obtaining a high-efficiency FWM based on the two electromagnetically induced transparency. We find that the maximum FWM efficiency is nearly 30%, which is orders of magnitude larger than previous schemes based on the two electromagnetically induced transparency. Our scheme may provide a new possibility for technological applications such as nonlinear spectroscopy at very low light intensity, quantum single-photon nonlinear optics and quantum information science.

physics.atom-ph↗
arXiv2009

Weyl correspondence method to construct multipartite entangled quantum state

Via the Weyl correspondence approach, we construct multipartite entangled state which is the common eigenvector of their center-of-mass coordinate and mass-weighted relative momenta. This approach is concise and effective for setting up the Fock representation of continuous multipartite entangled states. The technique of integration within an ordered product (IWOP) of operators is also essential in our derivation.

quant-ph↗
arXiv2009

A new Coherent-Entangled state generated by an asymmetric beam splitter and its applications

A new kind of tripartite non-symmetric coordinate coherent-entangled state (TNCCES) $ | β,γ,x >$ is proposed which exhibits the properties of both coherence and entanglement and makes up a new quantum mechanical representation.We investigate some properties of TNCCES such as completeness and orthogonality which prove it is just a tripartite complete continuous coordinate base. A protocol for generating TNCCES is proposed using asymmetric beam splitter. And in application of TNCCES, we find its corresponding Wigner operator and carry out its marginal distribution form; further a new tripartite entangled squeezed operator is also presented. The multipartite CES and its generation are also disussed.

quant-ph↗
arXiv2009

Higher-order properties and Bell-inequality violation for the three-mode enhanced squeezed state

By extending the usual two-mode squeezing operator $S_{2}=\exp [ iλ(Q_{1}P_{2}+Q_{2}P_{1}) ] $ to the three-mode squeezing operator $S_{3}=\exp {iλ[ Q_{1}(P_{2}+P_{3}) +Q_{2}(P_{1}+P_{3}) +Q_{3}(P_{1}+P_{2}) ]} $, we obtain the corresponding three-mode squeezed coherent state. The state's higher-order properties, such as higher-order squeezing and higher-order sub-Possonian photon statistics, are investigated. It is found that the new squeezed state not only can be squeezed to all even orders but also exhibits squeezing enhancement comparing with the usual cases. In addition, we examine the violation of Bell-inequality for the three-mode squeezed states by using the formalism of Wigner representation.

quant-ph↗