文档介绍：该【1.4975855参考论文参考论文资料 】是由【学习好资料】上传分享，文档一共【6】页，该文档可以免费在线阅读，需要了解更多关于【1.4975855参考论文参考论文资料 】的内容，可以使用淘豆网的站内搜索功能，选择自己适合的文档，以下文字是截取该文章内的部分文字，如需要获得完整电子版，请下载此文档到您的设备，方便您编辑和打印。,,,,J.,,:AIPConferenceProceedings1812,040008(2017);doi::http://dx./:http://aip./toc/apc/1812/1PublishedbytheAmericanInstituteofPhysicsArticlesyoumaybeinterestedinFree-eleratorsAIPConferenceProceedings1812,020002020002(2017);,020003020003(2017);-monoenergeticelectronbeamsfromlaser-eleratorsAIPConferenceProceedings1812,040005040005(2017);-spacemanipulationoflaser-eleratedelectronbeamsusingactiveplasmalensesAIPConferenceProceedings1812,040006040006(2017);-induceddensitydownrampinjectionAIPConferenceProceedings1812,040004040004(2017);,040013040013(2017);.Daniels1,2,,a),,3,,,,LawrenceBerkeleyNationalLaboratory,1CyclotronRd,94720BerkeleyCA,USA2CoherenceandQuantumTechnologyDepartment,EindhovenUniversityofTechnology,DenDolech2,5600MBEindhoven,herlands3NuclearEngineeringDepartment,UniversityofCalifornia-Berkeley,94720BerkeleyCA,USAa)Correspondingauthor:******@-of-the-artofcapillary-elerators(LPAs),-,,demonstratingaheatingeffectontheplasmachannelasevidencedfromnanosecond-,,(LPAs)elerateelectronbunchestoenergiesbeyond4GeVandtoachievebunchchargesof30pCandover[1,2].TheseachievementsillustratetheadvancementoftheLPAfield,munity-wide,application-targetedapproach,withimplicationsforbasicenergyscience,medicaltechnologyandnationalsecurity,,aworkshophostedbyLawrenceBerkeleyNationalLab(LBNL)waschargedbytheUSDepartmentofEnergyOfficeofHighEnergyPhysics(DoE,HEP)todevelopR&Droadmapswithaseriesofmilestonesandcriteriatowardsthegoalofconstructingamulti-TeVelectron-,elerators,withoneofthemosteleratormodule[3].Inlinewiththistarget,,thefirstofwhichdiscussesplasmadensitydiagnosticsemployedoncapillary--axisdensity,leadingtothedevelopmentofalaser---classelectronenergieswiththeBELLAlaser,,040008-1–040008-5;doi:.978-0-7354-1480-8/$-1DENSITYDIAGNOSTICSPlasmachannelscreatedthroughhighvoltagedischargeofgas-filledcapillariescanbedescribedashavinga
parabolicradialdensitydistribution
=
+
/(π
),withanon-axisminimumdensity
andamatchedspotsize
,where
-axisdensityisacriticalparameter,asitgovernsthegroupvelocityofthelaser,through
β==1?
?
1+
,(1)
whereβ
isthenormalizedgroupvelocity,
isthelaserwavenumber,
isthespotsizeofthelaseratthechannelentrance,
and
aretheLaguerre-Gaussianmodenumbersofthelaser,and
istheplasmawavenumber,which
/
relatestotheon-axisdensityby
=4
/
,with
and
theelectronchargeandrestmass,respectively[4].Theimportanceofthisrelationshipistwofold;itallowsfordeterminingofthedensitybymeasuringthegroupvelocity[4],,inordertoreachhigherwakevelocities,(1)isvalidinthelow-power,low-intensitylimitonly;modificationofthegroupvelocityduetononlineareffectsisdescribedinRef.[5].MeasurementoftheOn-AxisDensityEquation(1)showsthatameasurementofthegroupvelocitycanprovideadiagnosticfortheon-,propagatingonlyoneofthepulsesthroughtheplasmawhiletheotherpassesthroughvacuum,biningthetwo,spectralinterferometrycanbeusedtomeasuretheminutedelayintroducedbytheplasma[6,7].ThiswasdoneforBELLA-stylecapillariesof500μmindiameteratvariouspre-dischargeneutralgaspressure,obtainingdelaymeasurementsdowntofs-level().Thelinearrelationshipbetweenon-:On-axiselectrondensityasafunctionofFigure2:Measuredmatchedspotsizeforvaryinginitialpressureforhydrogendischargesincylindricalneutralhydrogenpressure,-2MeasurementoftheMatchedSpotSizeTheplasmadensitydistribution,characterizedby
,
=
(definedbytheradiuswheretheintensitydropsto1/eofitson-axisvalue),wespeakofmatchedguiding,becausethetransversegradientinindexofrefractionassociatedwiththisdensityprofilewillresultinconfinementofthelasertoaconstantspotsizealongthelengthofthechannel,intheabsenceofnon--matchedguiding,,foraGaussianpulse,thisevolutionofthespotsize
alongthechannelaxis
isdescribedby[8]
=1+
+1?
cos
.(2)
Experimentally,thespotsizecanonlybereliablymeasuredneartheentranceandexitofthechannel;forknownchannellength,,previousliteraturecanprovideanindicationoftheexpectedmatchedspotsize[9–11].,describedby
=
cos
β
?os,(3)
/
where
=
+
istheoscillationamplitude,
=2/
,
istheinitialcentroidoffsetatthechannelentrance,
istheinputangle,and
istheoffsetfromthechannelaxisatlocation
.Now,bymeasuringtheoutputoffsetforknowninputoffset(eitherbymovingthecapillaryorthelaserposition),anothersetofsolutionsfor
-derivedsolutionscanthenyieldasinglemostprobablesolutionaswasdoneinRef.[2],-spotsizelasersystems,atrade-offmustbemadeinselectingacapillarypressure:near-matchedconditionsaredesiredtokeepthenormalizedvectorpotentialhigh,whilelargerelectronbeamenergiescanbe17-3reachedatloweron-,reaching10GeVrequires
~10cm[12].Atsuchlowdensity,however,thechannelwillbestronglymismatched(
?
),,implementationofans-scalelaserhasbeenproposedtolocallyheatthechannelthroughinverseBremsstrahlung[12,13].Thiswilleffectivelydeepenthechannelon-axis,-relevantparameters[14].Intheremainderofthisreport,wewilldiscusstherecentfindingsonaproof-of-principleexperiment,,whichisfedbyhydrogengasviatubes,--powerBELLAexperiments,,sub-μJ,,guidedthroughsingle-modefiber,,a12nsFWHM,,,camerasonastageprovidediagnosticsforbothbeamsseparately,whichareusedforinput/,consistingofslit,grating,imagingsystemandananosecondcamera,-,especiallyfromthen=3à2transition,emittingat656nm,knownastheH-,binationofhydrogenionsandfreeelectronsemitsacontinuumofradiation,;inthepresentcase,,::Schematiclayoutofthelaser-heatertheH-,theratiooftheH-αlineandtheunderlyingcontinuumcanyieldtheplasmatemperature[15,16].Wehaveusedthisrelationshiptoestimatetheradiallyaveragedtemperatureintheplasma,inthecaseofdischarge-onlyanddischarge+,-staticmodelpresentedinRef.[8],,:Radiallyaveragedelectrontemperature,basedonFigure6:Line/continuumratioinunitsoftheline/continuumratiomeasurements,-4Tostudytheeffectoftheheaterlaserontheplasmatemperature,theheaterwasthenintroducedat~-nssteps,,theH-αpeakhasdecreasedby~20%,-αtotheincreasedionizationdegreeon-axisunderinfluenceoftheheater,,thepeakhasreducedanother10%,–30ns,thecontinuumkeepsrising,,,whencontaminantlinesdonotshowanincrease,andforthedischarge-onlycase,,heatingandeliminatingneutralsfromthecore,introducingrelative