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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

€

KzSC

σ z

€

′ ′ σ

€

′ ′ σ z

3

€

′ 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

4

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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QuickTime™ and aCinepak decompressor

are needed to see this picture.

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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QuickTime™ and aCinepak decompressor

are needed to see this picture.

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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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are needed to see this picture.

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).