BNL Photocathode R&D - UCLA Physics &...
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C-AD electron-cooling BNL Photocathode R&D BNL Photocathode R&D An overview of research on high An overview of research on high quantum efficiency photocathodes quantum efficiency photocathodes and associated laser systems and associated laser systems Andrew Burrill HPHB Workshop Nov 9, 2004
Transcript of BNL Photocathode R&D - UCLA Physics &...
C-AD electron-cooling
BNL Photocathode R&DBNL Photocathode R&DAn overview of research on highAn overview of research on high
quantum efficiency photocathodesquantum efficiency photocathodesand associated laser systemsand associated laser systems
Andrew BurrillHPHB WorkshopNov 9, 2004
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High Quantum EfficiencyHigh Quantum Efficiency 0.5 A at 351 MHz (1/2 RF frequency) = 1.3nC/bunch0.5 A at 351 MHz (1/2 RF frequency) = 1.3nC/bunch
Uniform emission surfaceUniform emission surface Long lifetimeLong lifetime RobustRobust Reproducible preparation techniqueReproducible preparation technique Photoemission at convenient laserPhotoemission at convenient laser
wavelengthwavelength
Photocathode CriteriaPhotocathode Criteria
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Research GoalsResearch Goals
Establish deposition system with a reproducibleEstablish deposition system with a reproducibleoptimized recipeoptimized recipe
Study Lifetime related issues: Dependence onStudy Lifetime related issues: Dependence on laser intensity and wavelengthlaser intensity and wavelength
current densitycurrent density
ContaminantsContaminants
Vacuum conditionsVacuum conditions
Integration into load lock or diamond capsuleIntegration into load lock or diamond capsule
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Cathode OptionsCathode Options
YesYesNoNoYesYesYesYesPrompt emissionPrompt emission
NoNoMaybeMaybeNoNoYesYesCommercial LaserCommercial Laseravailableavailable
2300 W2300 W15 W15 W77 W77 W38W/17W38W/17WLaser power toLaser power toachieve .5Aachieve .5A
.1%.1%5-10%5-10%3%3%3%/10%3%/10%QEQE
266 nm266 nm800 nm800 nm266 nm266 nm532/355532/355Laser wavelengthLaser wavelength
MgMgGaAsGaAsCsCs22TeTeCsKCsK22SbSbPhotocathodePhotocathode
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Photocathode Deposition SystemPhotocathode Deposition System
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Fabrication ProcedureFabrication Procedure
Chemical DepositionChemical Depositionsystemsystem
Polished 1Polished 1”” Molybdenum Molybdenumsubstratesubstrate
Multi-stage depositionMulti-stage depositionprocessprocess 200 200 ÅÅ Sb, 150 Sb, 150 ÅÅ K, ~200 K, ~200 ÅÅ
CsCs
Current is monitored as aCurrent is monitored as afunction of Cs depositionfunction of Cs deposition
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Current vs. Cs Deposition timeCurrent vs. Cs Deposition time
0
2
4
6
8
10
12
14
16
18
20
0 50 100 150 200 250 300 350 400
time (sec)
Cur
rent
(uA
)
0
0.5
1
1.5
2
2.5
3
QE
(%
)
Current
QE %
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Surface UniformitySurface Uniformity
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 5 10 15 20 25 30
Position
curr
en
t (u
A)
545 nm
365 nm
Position for Cs/Kdeposition
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ReproducibilityReproducibility
0
5
10
15
20
25
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
curr
ent
in u
A
2.6%
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Lifetime StudiesLifetime Studies
0
5
10
15
20
25
0 10 20 30 40 50 60
Days
Cu
rre
nt
(uA
)
normal laser lifetime
focused laser
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Cathode Gun InterfaceCathode Gun Interface
Load-lock to attach deposition system toLoad-lock to attach deposition system toSCRF gunSCRF gun
Capsule design with diamond windowCapsule design with diamond windowsealed onto photocathodesealed onto photocathode
Outcome of SEY program will determineOutcome of SEY program will determinefinal course takenfinal course taken
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Laser System RequirementsLaser System Requirements
351.875 MHz351.875 MHz
532 nm, 355 nm532 nm, 355 nm
10 ps pulse length10 ps pulse length
Synchronized toSynchronized tomaster RF clockmaster RF clock
Adjustable outputAdjustable outputpowerpower
Variety of amplifierVariety of amplifiersystemssystems
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Laser RequirementsLaser Requirements
9%9%
9%9%
3%3%
3%3%
CsKCsK22SbSbQEQE
0.35 W0.35 W0.5 A0.5 A5050355 nm355 nm
17 W17 W0.5 A0.5 A00355 nm355 nm
38 W38 W0.5 A0.5 A00532 nm532 nm
0.7 W0.7 W0.5 A0.5 A5050532 nm532 nm
LaserLaserPower toPower toCathodeCathode
DesiredDesiredCurrentCurrent
SEYSEYLaserLaserWavelengthWavelength
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Laser Layout optionsLaser Layout options
Oscillator → multi-pass Amplifier Chain → Harmonic Conversion
CsK2Sb cathode in SCRF gun
CsK2Sb cathode with diamond secondary emitter
Oscillator → Amplifier → Harmonic Conversion
1064 nm351 MHzFew watts
Multi-passMulti-stageAdjustable output power to 80 W
2nd or 3rd Harmonic40 W green20 W UV
1064 nm351 MHzFew watts
Single pass(Optional)
2nd or 3rd Harmonic1 W green0.5 W UV
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ConclusionsConclusions
Cathode researchCathode research Moderate QE obtainedModerate QE obtained Good surfaceGood surface
uniformityuniformity Lifetime and currentLifetime and current
density studies aredensity studies arepromisingpromising
Reproducibility needsReproducibility needsto be betterto be better
Different SubstrateDifferent Substratematerials will bematerials will bestudiedstudied
Laser SystemLaser System Commercial oscillatorsCommercial oscillators
are availableare available Outcome of SEYOutcome of SEY
experiments willexperiments willdetermine amplifierdetermine amplifierneedsneeds
Cathode-GunCathode-Guninterface beinginterface beingaddressedaddressed
