High Brightness Electron Beam Diagnostics and their ... - CASA

High Brightness Electron Beam Diagnostics and their ... - CASA High Brightness Electron Beam Diagnostics and their ... - CASA

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1000 900 800 700 Figure4.4:SteadystatetemperatureversusaveragebeamcurrentforthreedierentTRradiator thicknessandabeamequivalentradiusof2mm. 600 distribution): 500 00000 11111 00000 11111 00000 11111 00000 11111 400 2 m 00000 11111 0.5 micron 00000 11111 00000 11111 2 1micron m 00000 11111 00000 11111 RewritingtheaboveequationintheFourierspaceyieldsthescatteringdistributionfunctionofthe whereistheconvolutionproduct. S()=(TB)() (4.18) 00000 11111 1 0.5 micron m 00000 11111 00000 11111 300 0 100 200 300 400 500 600 700 Average Beam Current ( A) Fromthisgurewecanseethatthelargerthethicknessis,thelargerthermsscatteringangle(i.e. varianceofthescatteringdistribution)is. ComparisonwiththeTheory TheF1istheinverseFouriertransformation.Wehavenumericallyperformedthisdeconvolution, andthecalculatedscatteringfunctionsforthreedierentfoilthicknessareshowningure4.6. Itisusefultocomparethepreviousresultswiththetheory,inordertoseehowaccuratelyweare abletopredicttheeectsofanOTRradiatoronthebeam.Thereareseveraltheoreticalmodel Temperature ( o K) Melting point foil: T=F1SB (4.19)

Wire Scanner Readback (mV) 1200 1000 Foil out 800 600 400 whichdependsonthemeanaverageofcollisionanelectronexperiencesasitpassthroughthe foil:simplescattering(1), beamismeasuredusingawirescannerlocateddownstreamthefoil. describingscatteringinsideverythintargetseachofthemhavetheirowndomainofapplicability Figure4.5:Anexampleoftheeectofa0:8mthickaluminumfoilonthebeamprole.The 0.8 m Foil in 200 0 0 10 20 30 40 50 60 pluralscattering(1 20), Position (mm) thatdescribesmultiplescattering.ThedetailedstudyofKeilmodelisoutofthescopeofthis thesis.Inbrief,KeilusedtheFouriertransformofthescatteringdistributionderivedbyMoliere Inthecaseofaluminumfoilwiththicknessthinnerthan5m,themeannumberofcollisionbeing lessthen20weareinthepluralscatteringregime.Thistypeofscatteringiswelldescribedby thesemi-empiricalmodelelaboratedbyKeil[30]whichisanextrapolationoftheMolieremodel multiplescattering(20). andonlyconsideredthetworsttermsofthisseries,avalidapproximationifthemeannumber ofcollisionisbelow20.Hethenempiricallycalculatedthenumericalcoecientoftheseriesusing theexperimentalmeasurementsperformedbyLeisegang[31]ashewasexperimentallystudying scatteringthroughverythingoldfoils.Therelationthatgivestheangularscatteringdistribution

1000<br />

900<br />

800<br />

700<br />

Figure4.4:SteadystatetemperatureversusaveragebeamcurrentforthreedierentTRradiator thickness<strong>and</strong>abeamequivalentradiusof2mm.<br />

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11111 0.5 micron<br />

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11111 2 1micron m 00000<br />

11111<br />

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RewritingtheaboveequationintheFourierspaceyieldsthescatteringdistributionfunctionofthe whereistheconvolutionproduct. S()=(TB)() (4.18)<br />

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11111 1 0.5 micron m 00000<br />

11111<br />

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300<br />

0 100 200 300 400 500 600 700<br />

Average <strong>Beam</strong> Current ( A)<br />

Fromthisgurewecanseethatthelargerthethicknessis,thelargerthermsscatteringangle(i.e. varianceofthescatteringdistribution)is. ComparisonwiththeTheory TheF1istheinverseFouriertransformation.Wehavenumericallyperformedthisdeconvolution, <strong>and</strong>thecalculatedscatteringfunctionsforthreedierentfoilthicknessareshowningure4.6.<br />

Itisusefultocomparethepreviousresultswiththetheory,inordertoseehowaccuratelyweare abletopredicttheeectsofanOTRradiatoronthebeam.Thereareseveraltheoreticalmodel<br />

Temperature ( o K)<br />

Melting point<br />

foil: T=F1SB (4.19)

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