垂直激波加速中粒子动量变化的数值模拟研究
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摘要
利用测试粒子数值模拟的方法统计研究了电子在垂直激波附近每次穿越过程中的动量增量随粒子速度的变化规律.模拟采用的磁场模型是由均匀的背景磁场和"slab+2D"形式的三维湍流磁场叠加构成的.数值结果表明,粒子穿越激波面前后的相对动量变化和粒子动量的相对变化率均随速度的增加而减小,当速度大于2×10~8m/s时,粒子动量的相对变化率随速度呈现更加显著的衰减趋势,明显反映出相对论参数γ=1/■所引起的物理效应.模拟结果在较大的湍流强度范围内都与理论给出的变化关系较为一致.
Using test particle simulations,we have studied the change of electronparticle momentum increment during crossing the shock front with varying electronparticle velocity for electronacceleration at perpendicular shocks.We adopted a magnetic field model that is composed of a mean background field and a three-dimensional"slab+2D"turbulent field.The simulation results show that both the relative variation of particle momentum in the process of crossing shock front and the rate of particle momentum relative change decrease with increasing particle velocity.When the velocity is larger than 2×10~8m/s,the rate of particle momentum relative change displays a more noticeable decreasing tendency with particle velocity,which reflects the physical effect caused by the relativistic parameter r=1/■.Our simulation results agree,in a wide range of magnetic turbulence level,(b/B_0)~2=0.01-1.0,with the relationships given by the theorytheoretical results.
Using test particle simulations,we have studied the change of electronparticle momentum increment during crossing the shock front with varying electronparticle velocity for electronacceleration at perpendicular shocks.We adopted a magnetic field model that is composed of a mean background field and a three-dimensional"slab+2D"turbulent field.The simulation results show that both the relative variation of particle momentum in the process of crossing shock front and the rate of particle momentum relative change decrease with increasing particle velocity.When the velocity is larger than 2×10~8m/s,the rate of particle momentum relative change displays a more noticeable decreasing tendency with particle velocity,which reflects the physical effect caused by the relativistic parameter r=1/■.Our simulation results agree,in a wide range of magnetic turbulence level,(b/B_0)~2=0.01-1.0,with the relationships given by the theorytheoretical results.
引文
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[17]ZANK G P,LI G,FLORINSKI V,et al.Particle acceleration at perpendicular shock waves:Model and observations[J].J Geophys Res,2006,111(A6):A06108.
[18]QIN G,KONG F J,ZHANG L H.Effects of shock and turbulence properties on electron acceleration[J].Astrophys J,2018,860(1):3-11.
[19]QIN G,MATTHAEUS W H,BIEBER J W.Subdiffusive transport of charged particles perpendicular to the large scale magnetic field[J].Geophys Res Lett,2002a,29(4):1048.
[20]QIN G,MATTHAEUS W H,BIEBER J W.Perpendicular transport of charged particles in composite model turbulence:Recovery of diffusion[J].Astrophys J,2002b,578(2):L117-L120.
[2]AXFORD W I,LEER E,SKADRON G.Acceleration of cosmic rays at shock fronts[C]//Proc15th Int Cosmic Ray Conf.[s.l.]:[s.n.],1977:273.
[3]KRYMSKY G F.A regular mechanism for the acceleration of charged particles on the front of a shock wave[J].Dokl Akad Nauk SSSR,1977,234(6):1306-1308.
[4]BELL A R.The acceleration of cosmic rays in shock fronts.I[J].Mon Not R Astron Soc,1978,182(1):147-156.
[5]BLANDFORD R D,OSTRIKER J P.Particle acceleration by astrophysical shocks[J].Astrophys J,1978,221(1):L29-L32.
[6]JOKIPII J R.Particle drift,diffusion,and acceleration at shocks[J].Astrophys J,1982,255(2):716-720.
[7]AXFORD W I.Modulation of galactic cosmic rays in interplanetary medium[J].Planet Space Sci,1965,13(2):115-130.
[8]MORFILL G E,VOLK H J,DRURY L,et al.The Gamma-ray source CG-353+16-A super-nova shock interacting with the cloud rho ophiuchi[J].Astrophys J,1981,246(3):810-816.
[9]DRURY L O’C.An introduction to the theory of diffusive shock acceleration of energetic particles in tenuous plasmas[J].Rep Prog Phys,1983,46(8):973-1027.
[10]JOKIPII J R.Rate of energy gain and maximum energy in diffusive shock acceleration[J].Astrophys J,1987,313(2):842-846.
[11]DECKER R B,VLAHOS L.Numerical studies of particle acceleration at turbulent,oblique shocks with an application to prompt ion acceleration during solar flares[J].Astrophys J,1986,306(2):710-729.
[12]KONG F J,QIN G,ZHANG L H.Numerical simulations of particle acceleration at interplanetary quasi-perpendicular shocks[J].Astrophys J,2017,845(1):43.
[13]MATTHAEUS W H,GOLDSTEIN M L,ROBERTS D A.Evidence for the presence of quasi-two-dimensional nearly incompressible fluctuations in the solar wind[J].J Geophys Res,1990,95(A12):20673-20683.
[14]ZANK G P,MATTHAEUS W H.Waves and turbulence in the solar wind[J].J Geophys Res,1992,97(A11):17189-17194.
[15]BIEBER J W,WANNER W,MATTHAEUS W H.Dominant two-dimensional solar wind turbulence with implications for cosmic ray transport[J].J Geophys Res,1996,101(A2):2511-2522.
[16]GRAY P C,PONTIUS D H JR,MATTHAEUS W H.Scaling of field-line random walk in model solar wind fluctuations[J].Geophys Res Lett,1996,23(9):965-968.
[17]ZANK G P,LI G,FLORINSKI V,et al.Particle acceleration at perpendicular shock waves:Model and observations[J].J Geophys Res,2006,111(A6):A06108.
[18]QIN G,KONG F J,ZHANG L H.Effects of shock and turbulence properties on electron acceleration[J].Astrophys J,2018,860(1):3-11.
[19]QIN G,MATTHAEUS W H,BIEBER J W.Subdiffusive transport of charged particles perpendicular to the large scale magnetic field[J].Geophys Res Lett,2002a,29(4):1048.
[20]QIN G,MATTHAEUS W H,BIEBER J W.Perpendicular transport of charged particles in composite model turbulence:Recovery of diffusion[J].Astrophys J,2002b,578(2):L117-L120.