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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ε x (mm−mrad)<br />
Nominal<br />
6<br />
4<br />
2<br />
cryounitexitversustheemittancesolenoidmagneticeld.<br />
10<br />
Misaligned<br />
9<br />
Phase-PhaseCorrelationMeasurement Figure6.8:Measured(squares)<strong>and</strong>predictedtransverseemittances(solid<strong>and</strong>dashlines)atthe<br />
8<br />
7<br />
6<br />
5<br />
4<br />
Nominal<br />
3<br />
2<br />
RF-inducedsteeringwhich,inturn,dependsontheinjectionofthebuncheswithrespecttothe<br />
3000 3200 3400 3600 3800<br />
RFacceleratingeldinthecryounit.Henceatthepickupcavitylocation,theTOFofthebunch SimilarlytothebunchcompressioneciencydiagnosticsdescribedintheChapter3,theinjectoris instrumentedwithapickupcavitythatcanbeusedtomeasurethetimeofarrivalofabunch<strong>and</strong> consequentlydeterminephase-phasecorrelationbymodulatingtheRF-phaseofthephotocathode drivelaser.UnfortunatelyinthecaseoftheFELinjector,thepickupcavityislocatedinadispersive regionwhichrendersthetime-of-ight(TOF)dependentonotherparameters4,inparticularto<br />
Solenoid Magnetic Field (Gauss cm)<br />
centroidemittedatthephotocathodesurfacewithinitialphaseiwithrespecttothe\zerocrossing"bunch(i.e.thebunchforwhichtheTOFiszerobydenition)is: whereRFistheTOFcontributionduetotheRF-inducedsteering:RF=Rc!f ;c,i,<strong>and</strong>farerespectivelythelocationofthecryounitexit,thephotocathodesurface,<strong>and</strong>the pickupcavity. TheRFsteeringisdueto(1)theRFtransverseequationofmotioninanacceleratingcavity,<strong>and</strong> (2)theforwardpower<strong>and</strong>highordermodecouplerinducedkicks.Toquantifythecontribution oftheRF-steeringinthephase-phasecorrelationmeasurement,wehavecomparedphase-phase f=RF+Ri!f 55i+Ri!f 56i 51xc+Rc!f 52x0c (6.15)<br />
correlationmapsgeneratedvianumericalsimulationusingparmelawithtwodistinctmodelsof 4ThenecessityofstudyingcarefullythispointwasbroughttomyattentionbyD.R.Douglas<br />
ε y (mm−mrad)<br />
12<br />
10<br />
8<br />
Misaligned
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