IRPSS: A Green’s Function Approach to Modeling Photoinjectors
Short Electron Pulses from RF Photoinjectors Massimo Ferrario INFN - LNF
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Short Electron Pulses from RF Short Electron Pulses from RF PhotoinjectorsPhotoinjectors
Massimo FerrarioMassimo FerrarioINFN - LNFINFN - LNF
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Schematic View of the Envelope Schematic View of the Envelope EquationsEquations
(HOMDYN model)(HOMDYN model)′ σ
′ γ γ
+σΩ2 ′ γ 2
γ2
I2I Aσγ3 +
εn,sl2
σ 3γ2
′ ϑ =−Ksol +pϑ ,o
mcβγR2
€
KzRF ϕ( )σ z
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KzSC
σ z
€
′ ′ σ
€
′ ′ σ z
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€
′ γ = 2
σ w
ˆ Ι
3I0γ
€
γ= 8
3
ˆ I
2Ioε th ′ γ
€
σ ' = 0
Emittance Compensation: Emittance Compensation:
Controlled Damping of Plasma OscillationControlled Damping of Plasma Oscillation
Brillouin FlowBrillouin Flow
Hokuto IijimaHokuto Iijima
L. Serafini, J. B. Rosenzweig, Phys. Rev. E 55 (1997)
100 A ==> 150 MeV
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0
0.5
1
1.5
2
2.5
3
3.5
0 2 4 6 8 10Z_[m]
GunLinac
rms beam size [mm]
rms norm. emittance [um]
-0.04
-0.02
0
0.02
0.04
0 0.001 0.002 0.003 0.004 0.005 0.006
z=0.23891
Pr
R [m]
-0.05
0
0.05
0 0.0008 0.0016 0.0024 0.0032 0.004
z=1.5
Pr
R [m]
-0.04
-0.02
0
0.02
0.04
0 0.0008 0.0016 0.0024 0.0032 0.004
z=10
pr_[rad]
R_[m]
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
-0.003 -0.002 -0.001 0 0.001 0.002 0.003
z=0.23891
Rs [m]
Zs-Zb [m]
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
-0.003 -0.002 -0.001 0 0.001 0.002 0.003
Z=10
Rs [m]
Zs-Zb [m]
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
-0.003 -0.002 -0.001 0 0.001 0.002 0.003
z=1.5
Rs [m]
Zs-Zb [m]
Final emittance = 0.4 m
Matching onto the Local Emittance Max.,
Example of an optimized matchingExample of an optimized matching
M. Ferrario et al., “HOMDYN Study For The LCLS RF Photo-Injector”, Proc. of the 2nd ICFA Adv. Acc. Workshop on “The Physics of High Brightness Beams”, UCLA, Nov., 1999, also in SLAC-PUB-8400
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Coherent Synchrotron Radiation in bending magnets
Coherent Synchrotron Radiation in bending magnets
Powerful radiation generates energy spread in bendsPowerful radiation generates energy spread in bends Powerful radiation generates energy spread in bendsPowerful radiation generates energy spread in bends
Causes bend-plane emittance growth (DESY experience)Causes bend-plane emittance growth (DESY experience) Causes bend-plane emittance growth (DESY experience)Causes bend-plane emittance growth (DESY experience)
Energy spread breaks achromatic systemEnergy spread breaks achromatic system Energy spread breaks achromatic systemEnergy spread breaks achromatic system
x = Rx = R1616((ss))E/EE/E
bend-plane emittance growthbend-plane emittance growth
ee––RR
σσzz
coherent radiation coherent radiation forfor σσzz
overtaking length:overtaking length: L L00 (24 (24σσzzRR22))1/31/3
ssxx
LL00
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Pulsed photodiodes
Ballistic bunching
Velocity bunching
Bunch slicing
Talk OutlineTalk Outline
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Q = 20-100 pC
σz < ~ 250 m ==> σz = 20 m
σx ~ 20-30 m ==> nx < 5 m
γγ < 1 %
γ ~ γ ~150 MeV
ee-- beam requirements beam requirements
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€
QMAX ∝ ′ γ σ 2
maximum amount of charge that can be extracted from a photocathode illuminated by a laser
€
γγ
∝Q′ γ σ 2
−σ φ cosϕ the induced rms energy spread on the electron bunch:
€
I ∝ ′ γ σ sinϕ ( )
2
f Al ,γ( )
the actual beam current at the gun exit will be almost
independent on the initial peak current
L. Serafini, “The Short Bunch Blow-out Regimein RF Photoinjectors”
Pulsed photodiode + femtoseconds laser
€
′ γ ≅ eE0
2mc2High gradient required !
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2 MV HV 1 ns pulse on a 2 mm diode gap:1 GV/m , 100 pC ==> 200 fs bunch,
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Provide a correlated energy spread enough to produce, in a drift of length Ldrift a path difference equal to half the bunch length Lo
Ldrift =γ 2L0
2Δγ γ ΔL =
Ldrift
γ 2⎡
⎣ ⎢
⎤
⎦ ⎥ Δγγ
Δγ
L0
z
γ γ
zΔγ
Lfin=εzΔγ
Bullistic Bunching
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Bullistic Bunching experiment at UCLA (Rosenzweig)
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Velocity bunching conceptVelocity bunching concept
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Quarter wavelength synchrotron oscillation
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Limitation: longitudinal emitance growth induced Limitation: longitudinal emitance growth induced by RF non-linearitiesby RF non-linearities
Limitation: longitudinal emitance growth induced Limitation: longitudinal emitance growth induced by RF non-linearitiesby RF non-linearities
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Average current vs RF compressor phase
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
-95 -90 -85 -80 -75 -70 -65 -60
RF compressor phase (deg)
Average current (A)
LOW COMPRESSION
MEDIUM COMPRESSION
HIGH COMPRESSION
OVER-COMPRESSION
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20B. Spataro et al, PAC05 ==>B. Spataro et al, PAC05 ==>
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<I> = 860 A<I> = 860 A
nxnx = 1.5 = 1.5 mm
C. Ronsivalle et al. , “C. Ronsivalle et al. , “Optimization of RF compressor in the SPARX injector”, Optimization of RF compressor in the SPARX injector”, PAC05PAC05
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To be published on JJAP
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Streak Images of Electron BunchStreak Images of Electron Bunch
Injected Phase -70O
Minimum!
200 psec range 50 psec range
Injected Phase -1O
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Stability of Velocity Bunching (-1 degree)Stability of Velocity Bunching (-1 degree)
Streak images at injection phase of –1 degree. Fluctuation is 0.4 ps (rms) for 30 shots. Streak images at injection phase of –1 degree. Fluctuation is 0.4 ps (rms) for 30 shots.
1.1 psec 1.4 psec 0.9 psec
0.5 psec 1.1 psec 0.8 psec
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Current sensitivity for 1 degree error in Current sensitivity for 1 degree error in the RF compressor phase with IV harmonic the RF compressor phase with IV harmonic
cavitycavity
D. Alesini, PAC05D. Alesini, PAC05
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Rectilinear Bunching Experiments Rectilinear Bunching Experiments SummarySummary
BNLBNL UCLAUCLA BNL-DUVFELBNL-DUVFEL UTNL-18LUTNL-18L LLNLLLNL
MethodeMethode Ballistic BallisticVelocity Bunching
Velocity Bunching
Velocity Bunching
Acc. Acc. StructureStructure
S-band PWT 4 S-band 1 S-band 4 S-band
MeasurementMeasurement
zero-phasing method
CTRzero-phasing
methodFemotsecond
Streak CameraCTR
ChargeCharge 0.04 nC 0.2 nC 0.2 nC 1 nC 0.2 nC
Bunch Bunch widthwidth
0.37 ps(rms)
0.39 ps(rms)
0.5 ps(rms)
0.5 ps (rms) < 0.3 ps
Comp. Comp. RatioRatio
6 15 > 3 > 13 10
Solenoid Solenoid fieldfield No No No Yes Yes
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==> D. Giulietti talk tomorrow
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Exercise for this workshopExercise for this workshop
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 2 4 6 8 10 12 14 16
HBUNCH.OUT
Bz_[T]
Bz_[T]
Z_[m]
σz = 200 m ==> < 25 m
σx =175 m ==> < 20 m
γγ = 0.2% , nx < 0.3 m
Q = 20 pC
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HOMDYN movieHOMDYN movie
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0
0.1
0.2
0.3
0.4
0.5
0.6
0 2 4 6 8 10 12 14 16
HBUNCH.OUT
sigma_z_[mm]sigma_x_[mm]
sigma_z_[mm]
Z_[m]
0
0.5
1
1.5
2
2.5
3
0 2 4 6 8 10 12 14 16
HBUNCH.OUT
enx_[um]dg/g_[%]
enx_[um]
Z_[m]
0
50
100
150
200
0 2 4 6 8 10 12 14 16
HBUNCH.OUT
I_[A]T_[MeV]
I_[A]
Z_[m]
0
0.5
1
1.5
2
2.5
0 2 4 6 8 10 12 14 16
HBUNCH.OUT
elz_[KeVmm]
elz_[KeVmm]
Z_[m]
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C. Vaccarezza et al., EPAC_04
Bunch slicingBunch slicing
Q = 1nC ==> 25pCQ = 1nC ==> 25pC
LLbb=10 ps ==> 100 fs=10 ps ==> 100 fs
σσxx = 0.5 mm ==> 5 = 0.5 mm ==> 5 mm
γγ γγ < 0.2%< 0.2%
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Short pulses delivered by RF photoinjectors could meet the plasma acceleretor requirements
Within a quite short time more experimental data will be available on RF compression in optimized layout
ConclusionsConclusions
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Physics and Applications Physics and Applications of High Brightness Electron of High Brightness Electron
BeamsBeams
Organizers: L. Palumbo (Univ. Roma), J. Rosenzweig (UCLA), L. Serafini (INFN-Milano).