傅立叶质谱教程

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1、文档来源为：从网络收集整理.word版本可编辑.欢迎下载支持PartI-FTMSTutorialMotionofaChargedParticleinaUniformMagneticField:Thebasicprinciplesofcyclotronmotionarebasedonthefactthattheionsofinterestaresituatedinauniformmagneticfield.Anion'sflightpathmayormaynotbe3cteddependingonwhichdirectiontheparticleistravelinginrelati

2、ontothedirectionofthemagneticfield.Case1demonstratesasituationwhereanion'svelocity,shownbythevectorinred,andthemagneticfield,shownbythevectoringreen,aremovingparalleltoeachotherinthez-direction.Inthiscasethedirectionoftheionisnotaffectedinanywaybythemagneticfield.InCase2theion,shownagaininred,

3、ismovingperpendiculartothedirectionofthemagneticfield.Whenthissituationoccursthereisaforcethatisexertedontheionwhichcausesittobedeflectedintocircularorbits.Thisforceisgivenbythefollowingequation:F=q(vXB)F=forceontheionq=chargeontheionv=velocityoftheionB=magneticfieldNoticethatintheexpressionwe

4、aretakingthecrossproductofthevelocityandthemagneticfield.Whencalculatingacrossproductafactorofsin二(where-istheanglebetweenthevelocityvectorandthemagneticfieldvector)isintroduced.Sincethevelocityandmagneticfieldvectorsareperpendicularinthiscase,thefinalcrossproductwillbeperpendiculartovandB,and

5、itsmagnitudethesimplytheproductqvB.Thisforceisshownbythevectorinblue.Apositivelychargedparticlewillbedeflectedintoanorbitintheclockwisedirection,whileanegativelychargedparticlewillbedeflectedintoacounterclockwisedirection.CyclotronMotion:Inthediagramabovewearelookingdownthemagneticfieldinthebo

6、reofourhorizontalmagnet.Insidethisboreisachargedparticlemovingperpendiculartothemagneticfield,whichisdirectedstraightoffthepageatyou.Thetwocomponentswhichmakeupthisforcearethemagneticforce,theinwardforceontheion(F1),andthecentrifugeforce,theoutwardforceontheion(F2).Inordertokeeptheioninastable

7、circularorbitthemagneticforceandthecentrifugeforcemustexactlyequaleachother.Byequatingthetwoforceswecanderivethattheangularfrequency(0)ofanionwithmassmandchargeq:Thisangularfrequencyiscalledthecyclotronfrequencyintheseapplications.Itisi