High Brightness Electron Beam Diagnostics and their ... - CASA
High Brightness Electron Beam Diagnostics and their ... - CASA High Brightness Electron Beam Diagnostics and their ... - CASA
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
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1000<br />
900<br />
800<br />
700<br />
Figure4.4:SteadystatetemperatureversusaveragebeamcurrentforthreedierentTRradiator thickness<strong>and</strong>abeamequivalentradiusof2mm.<br />
600<br />
distribution):<br />
500<br />
00000<br />
11111<br />
00000<br />
11111<br />
00000<br />
11111<br />
00000<br />
11111<br />
400<br />
2 m 00000<br />
11111 0.5 micron<br />
00000<br />
11111<br />
00000<br />
11111 2 1micron m 00000<br />
11111<br />
00000<br />
11111<br />
RewritingtheaboveequationintheFourierspaceyieldsthescatteringdistributionfunctionofthe whereistheconvolutionproduct. S()=(TB)() (4.18)<br />
00000<br />
11111 1 0.5 micron m 00000<br />
11111<br />
00000<br />
11111<br />
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)