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1、直流辉光放电与射频辉光放电directcurrent(DC)andradiofrequency(RF)glowdischargesByWenQiLU9/21/20061.气体放电规律电极间的气体放电glow-to-arctransition电源dc/acVi1.DarkDischargeTheregimebetweenAandEonthevoltage-currentcharacteristicistermedadarkdischargebecause,exceptforcoronadischargesandthebreakdownitsel
2、f,thedischargeremainsinvisibletotheeye.A-BThebackgroundionizationstageDuringthebackgroundionizationstageoftheprocesstheelectricfieldappliedalongtheaxisofthedischargetubesweepsouttheionsandelectronscreatedbyionizationfrombackgroundradiation.Backgroundradiationfromcosmicrays,
3、radioactiveminerals,orothersources,producesaconstantandmeasurabledegreeofionizationinairatatmosphericpressure.Theionsandelectronsmigratetotheelectrodesintheappliedelectricfieldproducingaweakelectriccurrent.Increasingvoltagesweepsoutanincreasingfractionoftheseionsandelectron
4、s.B-CThesaturationregionHereradiationinducessaturationcurrentchangeIfthevoltagebetweentheelectrodesisincreasedfarenough,eventuallyalltheavailableelectronsandionsaresweptaway,andthecurrentsaturates.Inthesaturationregion,thecurrentremainconstantwhilethevoltageisincreased.This
5、currentdependslinearlyontheradiationsourcestrength,aregimeusefulinsomeradiationcounters.(e.g.盖革计数器)C-DElectronavalancheandtheTownsenddischargeIfthevoltageacrossthelowpressuredischargetubeisincreasedbeyondpointC,thecurrentwillriseexponentially.Theelectricfieldisnowhighenough
6、sotheelectronsinitiallypresentinthegascanacquireenoughenergybeforereachingtheanodetoionizeaneutralatom.Astheelectricfieldbecomesevenstronger,thesecondaryelectronmayalsoionizeanotherneutralatomleadingtoanavalancheofelectronandionproduction.Theregionofexponentiallyincreasingc
7、urrentiscalledtheTownsenddischarge.D-ECoronadischargesCoronadischargesoccurinTownsenddarkdischargesinregionsofhighelectricfieldnearsharppoints,edges,orwiresingasespriortoelectricalbreakdown.Ifthecoronalcuurentsarehighenough,coronadischargescanbetechnically“glowdischarges”,v
8、isibletotheeye.Forlowcurrents,theentirecoronaisdark,asappropriateforthedarkdischar
