等离子体物理学导论L7(1).ppt

,IntroductiontoPlasmaPhysics等离子体物理学导论主讲:陈耀第七讲山东大学威海空间天气物理与探测研究中心2009.32009.6,2.3曲率漂移,粒子被洛仑兹力约束在磁力线上,导心沿着力线平行运动;若磁力线是弯曲的，则在导心坐标系中，粒子将感受到惯性离心力，并产生曲率漂移。惯性离心力可表示为,漂移速度：,曲率半径,考虑势场(无旋场)或无力场(电流与磁场平行)情况,证明:磁力线是弯曲的,则磁场必然是非均匀的.,小结：由磁场不均匀性造成的效应：(1)磁镜效应由平行方向受到与梯度反向的作用力(2)梯度漂移垂直方向受力产生梯度漂移(3)曲率漂移弯曲力线中,粒子沿磁力线运动时，受离心力作用，产生曲率漂移两种漂移运动,通常同时存在:漂移方向一致,但大小与动能及电荷有关产生电荷分离与电场,Q：给出具Maxwell分布（温度T）的等离子体粒子的两种漂移速度！,2.4缓变系统的绝热不变量(AdiabaticInvariants)（1）磁矩守恒（请验证这一组等式！）,磁矩守恒迴旋轨道包围的磁通是守恒的,在强场区，磁通/矩(角动量)守恒要求粒子回旋轨道收缩和垂直动能增加,（2）纵向不变量J(LongitudinalInvariant)证明该纵向不变量.该不变量在地磁场中约束的粒子运动中有重要应用.（3）第三绝热不变量:漂移面总磁通守恒：磁通不变量,在地磁场中的应用：在地磁场中，粒子的运动是三种不同时间尺度的运动形式的叠加：1.迴旋运动磁矩守恒2.两极间的磁镜反射之往返运动地磁场基本对称时，粒子漂移一周后将回到同一根磁力线上3.漂移时间尺度太长、系统不满足缓变条件因此地球磁场中漂移面所含磁通一般不守恒,回旋往返漂移,WEST,In1990,thesatelliteCombinedReleaseandRadiationEffectsSatellite(CRRES)discoveredathirdradiationbeltlocatedbetweentheinnerandouterVanAllenbelts.Also,aroundMay8,1998,therewereaseriesoflarge,solardisturbancesthatcausedanewradiationbelttoformintheso-called“slotregion”betweentheinnerandoutervanAllenbelts.Thenewbelteventuallydisappearedoncethesolaractivitysubsided.Nucleartestsinspaceartificialradiationbelts.StarfishPrime,damagedordestroyedasmanyasonethirdofthesatellitesinlowearthorbitatthetime(1962?).,VanAllen辐射带的稳定存在反映了纵向不变量的近似守恒,Innerandouterradiationbelts:Theouterbelt:mainlyelectrons(0.110MeV)(3to10Re)Theinnerbelt:mainlyprotons(0.1to1.5Re)100MeV&electrons(hundredsofkev).Therelativedriftbetweentheionsandelectronsproducestheringcurrentinthegeomagnetosphere.AgapbetweentheinnerandouterVanAllenbelts,sometimescalledsafezoneorsafeslot,iscausedbytheverylowfrequency(VLF)waveswhichscatterparticlesinpitchanglewhichresultsinthelossofparticlestotheatmosphere,Duringthedevelopmentofso-calledgeomagneticstorms,chargedparticlesareinjectedintotheVanAllenbeltsfromtheoutermagnetosphere,givingrisetoasharpincreaseintheringcurrent,andacorrespondingdecreaseintheEarthsequatorialmagneticfield.Thefielddecreaseismeasuredbytheso-calledDstindex,whichisbasedonhourlyaveragesofthenorthwardhorizontalcomponentoftheterrestrialmagneticfield.TheaboveFigureshowstheDstindexforthemonthofMarch1989.Theverymarkedreductionintheindex,centredaboutMarch13th,correspondstooneofthemostseveregeomagneticstormsexperiencedinrecentdecades.Infact,thisparticularstormwassoseverethatittrippedoutthewholeHydroQuebecelectricdistributionsystem,plungingmorethan6millioncustomersintodarkness.MostofHydroQuebecsneighbouringsystemsintheUnitedStatescameuncomfortablyclosetoexperiencingthesamecascadingpoweroutagescenario.NotethatareductionintheDstindexby600nTcorrespondstoareductionintheterrestrialmagneticfieldattheequator.,2.5不均匀电场的影响假定电场具弱空间不均匀，将电场Taylor展开至二阶小：,运动主体仍为迴旋运动，叠加上电场漂移、电场不均匀性导致的速度扰动,运动方程化为：,新的扰动力项,则总的电场力写为：,相