杜报-等离子体物理-墙报-精品文档资料整理.ppt

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1、Numerical calculation：By making , an electrons motion is seen in the following figures: Influence of an External Axial Magnetic Field on Betatron Radiation from the Interaction of a Circularly Polarized Laser with PlasmaBao Du and Xiao-Fang WangDepartment of Modern Physics, University of Science and

2、 Technology of ChinaTheoretical analyses and numerical calculations are carried out to investigate the influence of an externally applied axial constant magnetic field on electrons betatron radiation when an circularly polarized laser pulse of 5e19 W/cm2 propagates in plasma of density 1e20/cm3. The

3、 applied magnetic field can modulate the resonance process between the electrons betatron oscillation and the laser electric field. When B0=3e3 T, the maximum electron energy and the total radiation energy are increased by 11.0% and 41.1%.Background: Great progress has been made in laser-plasma wake

4、field electron acceleration since it was proposed1. In addition to being an electrons longitudinal accelerator, the wakefield can also act as a wiggler for an ultra-relativistic electron, resulting in an oscillation in the transverse direction. Such an oscillating electron will emit x-rays, which is

5、 also called the betatron radiation2. Direct laser acceleration (DLA) would further enhance an electrons energy gain when a resonance is reached between the electrons betatron frequency and the laser frequency3. When the laser is circularly polarized, an trapped electron will move along a helical tr

6、ajectory4. It is possible to modulate the resonance by an externally applied axial magnetic field, which will result in a change to the electron energy and the betatron radiation.Theoretical analyses: The motion of a trapped electron in the presence of the wakefield and the laser pulse together with

7、 an externally applied axial magnetic field can be described bywhere the expressions of can be referenced from Ref. 5. The left hand of Eq. 1 describes a betatron motion with an oscillation frequency , the right hand describes an oscillation driven by the Doppler-shifted laser electric field of freq

8、uency. The electrons transverse motion then can be derived as whereClearly, when approaches , the electrons betatron motion will get closer to the state of resonance with the laser electric field, leading to a sharp increase of the electrons energy. At the same time, when the external magnetic field

9、 is applied in the opposite direction to the self-generated axial magnetic field, is decreased and the resonance process will be enhanced. Thus, the electron will gain energy from the laser and more radiation energy will be emitted. ,zEb002424,1,10/,rmIWmmMulti electrons：1e4 electrons randomly place

10、d on a circular plane of the radius are sampled, with a temperature of 5 keV. We find that electrons trapping efficiency gets an increased of 15% from the stronger transverse confining force brought by the external axial magnetic field.Reference:1 E. Esarey, C. Schroeder, et al. Rev. Mod. Phys. 81,

11、1229 (2009). 2 S. Corde, K.Ta Phuoc, et al. Phys. Rev. Lett. 107, 255003 (2011). 3 A. Pukhov, Z.-M. Sheng, and J. Meyer-ter-Vehn, Phys. Plasmas 6, 2847 (1999);4 B. Liu, X.-Q. Yan, X.-T. He, et al. Phys. Rev. Lett. 110, 045002 (2013).5 B. Qiao, S. P.-Zhu, C.-Y. Zheng, et al. Phys. Plasmas 12, 083102

12、(2005). E-mail：Published: Physics of Plasmas 24, 093106 (2017)222002222002(1)(1)sin()(1)(1)cos()xzzxLeppyzzyLeppd peQpeEkztdtm d peQpeEkztdtm 2222222200020002/exp(/ 2) /+1exp(,/)/ /exp()eEzezBLzQBeQm brrBrrrrrrre m ( 1 )L=sin(),=cos()22LLxypPtpPt 222/ 2cos()1/1()()/ ()LLzpezpLPeEteQmL30000.1,3 10,30

13、,40,1.01ecnnTmBLm z Fig. 1. Electron motion in the first 40 ps. (a) . (b) Transverse momentum. (c) Relativistic factor. (d) Orbit radius.LFig. 2. The betatron radiation. (a) Angular distribution. (b) Radiation spectra. 1 mFig.3. (a) Electrons scattergram and (b) Angular distribution of the radiation. ( 2 )