pulsed-ionstudyofultrasonicallygeneratedturbulenceinsuperfluid4he》

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1、Volume82A,number5PHYSICSLETTERS30March1981PULSED-IONSTUDYOFULTRASONICALLYGENERATEDTURBULENCEINSUPERFLUID4HeK.W.SCHWARZandC.W.SMITH1IBMThomasJ.WatsonResearchCenter,YorktownHeights,NY10598,USAReceived8January1981Apulsed-ionmethodisusedtoinvestigatetheturbulentfieldgeneratedbyabeamofultrasound

2、.Basicinformationabouthowionsinteractwiththevortextangleisobtained.Globalline-densityprofileswhichshowhowtheturbulencecon-vectsawayfromtheexcitedregionarealsopresented.AccordingtothemodelproposedbyFeynman[1]vortextangle,andthentomapoutthedistributionofandelaboratedbyVinen[2],thesuperfluidco

3、mpo-turbulenceinageometrydesignedtobeparticularlynentof~Hecanbecometurbulentbydevelopingasuitedfortheoreticalanalysis.randomtangleofquantizedvortices.AgreatdealofOurapproachisbasedonthewell-knownfact[7]efforthasbeendevotedtotheexperimentalstudyofthatnegativeions(electronbubbles)inthesuperfl

4、uidsuperfluidturbulenceinvariouskindsofchannelflowcanbecometrappedonquantizedvortices.Theex-andmanyfascinatingqualitativefeatureshavebeenperimentutilizesastandarddriftcell[8],withawell-identifiedandinvestigated.Arecenttheoreticaltreat-definedregionilluminatedbyultrasoundofsufficientment[3]o

5、fthemicrostructureoffullydeveloped,inteiisitytogenerateturbulence[9](fig.1).Sincethehomogeneousturbulencehasprovidedsomeunder-ultrasoundhasawavelengthoforder10—2cm,thestandingofafewoftheobservedphenomena,andof-experimentalregionliesintheextremeFresnellimitferspromiseoffurtherprogress.Astheb

6、estmodernexperiments[4—6]show,however,thequantitativeaspectsofthesephenomenaoftendependmarkedlySGH~SG2FGonchannelgeometry,onendeffects,andonwallef-Ifects,implyingthatturbulenceinchannelsismacro-scopicallyinhomogeneousandhencemoredifficulttooe___onregionssmallenoughtobeeffectivelyhomogeneous

7、.SConversely,onewouldliketobeabletoobtainglobalIImapsofturbulentfieldsinordertostudythenature~ofthemacroscopicinhomogeneities.Inthepresentpaperatechniquecapableofmakinglocalmeasure-mentsontheturbulentfieldisdescribed.Thistech-niqueisusedfirst,tostudyhowi