High-repetition-rate few-attosecond high-quality electron beams generated from crystals driven by intense X-ray laser

Advances in X-ray laser sources have paved the way to relativistic attosecond X-ray laser pulses and opened up the possibility of exploring highenergy-density physics with this technology.With particle-in-cell simulations,we investigate the interaction of realistic metal crystals with relativistic X-ray laser pulses of parameters that will be available in the near future.A wakefield of the order of TV/cm is excited in the crystal and accelerates trapped electrons stably even though the wakefield is locally modulated by the crystal lattice.Electron injection either occurs at the sharp crystal-vacuum boundary or is controlled by coating the crystal with a high-density film.High-repetition-rate attosecond(20 as)monoenergetic electron beams of energy 125 MeV,charge 100 fC,and emittance 1.6310−9mrad can be produced by shining MHz X-ray laser pulses of energy 2.1 mJ onto coated crystals several micrometers thick.Such a miniature crystal accelerator,which has high reproducibility and allows sufficient control of the parameters of the electron beams,greatly expands the applications of X-ray free electron lasers.For example,it could serve as an ideal electron source for ultrafast electron diffraction and ultrafast electron microscopy to achieve attosecond resolution.

Economic Evaluation for 5G Planning of a Distribution Network Considering Network Coupling and Important Node Identification

The rapid development of communication services in the power distribution network poses challenges for existing wireless communications,and the deployment of a fiber optic network is costly and difficult.The emerging 5G technology has been piloted in power distribution networks,though the cost-effectiveness of its large-scale deployment remains unclear.This paper proposes an economic evaluation method for 5G planning in power distribution networks,considering the coupling relationship between power distribution and communication networks and the identification of important network nodes.First,the objective function to solve the planned number of 5G base stations is established.This is solved using the adaptive particle swarm algorithm and K-means algorithm.Second,the coupling relationship between the distribution and communication networks is discussed and quantified.The node importance of the coupling network is analyzed to identify the important nodes,and micro base stations or optical fibers are added to improve the reliability of the distribution network at the communication level.Finally,an economic evaluation index of 5G planning of the distribution network is established.The paper compares the economic solutions of 5G and 4G communications in city and town scenarios using the IEEE 123-node network as an example,and concludes that the economics of 5G are better than those of 4G.

Grounding fault location method of overhead line based on dual-axis magnetic field trajectory

To address the challenges in fault location in distribution networks,the distribution of magnetic field under overhead line and its relationship with three-phase currents are explored in this paper.At the same time,considering the influ-ence of sensor installation position,line sag and galloping on magnetic field,a grounding fault location method of an overhead line based on dual-axis magnetic field trajectory is proposed.The analytical expressions of the magnetic field on the x-axis and y-axis under the overhead line are obtained by least squares fitting.The Lissajous figure synthe-sized by dual-axis is then compared with the general equation of an ellipse,and the characteristic quantity expression characterizing the magnetic field trajectory structure is obtained.Finally,a fault location criterion is constructed using the difference of the characteristic quantities of the ellipses synthesized by x-axis and y-axis magnetic fields upstream and downstream of the fault point,i.e.,the difference of the length of the major axis and the minor axis,and the sign for the ratio of the cosine value of the inclination angle.Compared with other location methods based on electrical quantity,the principle of this method is simpler and it can locate faults more quickly and accurately.A large number of simulation results show that the proposed method is suitable for different types of fault conditions.