Beam Dynamics in a Spilt SRF-Gun
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Transcript of Beam Dynamics in a Spilt SRF-Gun
Beam Dynamics in a Spilt SRF-GunBeam Dynamics in a Spilt SRF-GunM. Ferrario, W. D. Moeller, J. B. Rosenzweig, J. Sekutowicz, M. Ferrario, W. D. Moeller, J. B. Rosenzweig, J. Sekutowicz,
G.TravishG.Travish
INFN, UCLA, DESYINFN, UCLA, DESY
Meeting on “ Superconducting RF Gun Simulations“EUROFEL Work Package 52.-3. June 2005 at BESSY
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Main Advantage: Low RF Power Losses & CW OperationLow RF Power Losses & CW Operation
SUPERCONDUCTING RF PHOTO-SUPERCONDUCTING RF PHOTO-INJECTORSINJECTORS
Main Questions/ConcernsMain Questions/Concerns
• Emittance Compensation ? Emittance Compensation ? • Q degradation due to Magnetic Q degradation due to Magnetic Field ?Field ?• High Peak Field on Cathode ?High Peak Field on Cathode ?• Cathode Materials and QE ?Cathode Materials and QE ?• Laser System ?Laser System ?
Before Cool-DownBefore Cool-Down
B
After Cool-DownAfter Cool-Down
B
Schematic View of the Envelope Schematic View of the Envelope EquationsEquationsHOMDYNHOMDYN
′ σ ′ γ γ
+σ Ω2 ′ γ 2
γ2
I2I Aσγ3 + εn,sl
2
σ 3γ2
′ ϑ =−Ksol +pϑ ,o
mcβγR2
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KzRF ϕ( )σ z
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KzSC
σ z
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Projected Phase Space Slice Phase Spaces
Emittance Oscillations and Growth are driven Emittance Oscillations and Growth are driven by space charge differential defocusing by space charge differential defocusing
in core and tails of the beamin core and tails of the beam
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′ γ = 2σ w
ˆ Ι 3I0γ
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γ= 83
ˆ I 2Ioε th ′ γ
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σ ' = 0
Emittance Compensation: Controlled Emittance Compensation: Controlled Damping of Plasma Oscillation (LS-JBR)Damping of Plasma Oscillation (LS-JBR)
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enxT_[um]enxT+_[um]enxCore_[um]enxH-_[um]enxH_[um]enx_[um]enxT_[um]
Z_[m]
Gun Working PointGun Working Point
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enxT_[um]enxT+_[um]enxCore_[um]enxH-_[um]enxH_[um]enx_[um]enxT_[um]
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Linac Working PointLinac Working Point
The emittance compensation occuring in the booster The emittance compensation occuring in the booster when the invariant envelope matching conditions are when the invariant envelope matching conditions are satisfied is actually limited by the head and tail slice satisfied is actually limited by the head and tail slice
behavior behavior
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Homdyn movie
Head and tail slices carry the most pronounced Head and tail slices carry the most pronounced energy spreadenergy spread
ks = qB2mcβγ
Simple Case: Transport in a Long Simple Case: Transport in a Long SolenoidSolenoid
σ'' +ks2σ =K
σ
σeq ξ( ) = K ξ( )ks
σ'' =0 ==> Equilibrium solution ? ==>==> Equilibrium solution ? ==>
0 0.0005 0.001 0.0015 0.002 0.0025metri
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g K = 2Ig ξ( )Io βγ( )3g(
σ =σ eq+δσ δσ'' +2ks2δσ =0
Small perturbations around the Small perturbations around the equilibrium solutionequilibrium solution
Same Plasma Same Plasma FrequenciesFrequencies
σ ξ( )=σ eq ξ( )+ σ ξ( )−σ eq ξ( )( )cos 2ksz( )σ' ξ( ) =− 2ks σ ξ( ) −σ eq ξ( )( )sin 2ksz( )
Different AmplitudesDifferent Amplitudes
ε z( )= σr2 σr
' 2 − σrσ r' 2 ÷sin 2ksz( )
0 1 2 3 4 5metri
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envelopes
0 1 2 3 4 5metri
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emi
σr(z)
(z)
Envelope oscillations drive Emittance oscillations
δγγ
=00.5≤g ξ( )≤1
′ σ =0
Bunch with a Linear Bunch with a Linear Energy SpreadEnergy Spread CorrelationCorrelation
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γ+ =γo 1+δγ( )
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γ−=γo 1−δγ( )
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δγ =δγγo
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σ+ =σeq+ +δσ+ cos 2k+z( )
′ σ + = − 2k+δσ+ sin 2k+z( )
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σ−=σeq− +δσ − cos 2k−z( )
′ σ − = − 2k−δσ − sin 2k−z( )
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n =γ2
ko σ eqo 2δσ o +δγ( ) sinΔk2
z ⎛ ⎝ ⎜
⎞ ⎠ ⎟cos k z( ) +δσ o
2 sin Δkz( )
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k =12
k+ + k−( ) = 2ko
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Δk = 2 k− − k+( ) = 2 2koδγ
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δσo = σ c − σ eqo
A Spread in Plasma Frequencies drives A Spread in Plasma Frequencies drives a a BeatingBeating in Emittance Oscillations in Emittance Oscillations
On a longer time scaleOn a longer time scale
increasing the initial envelope offset the emittance evolution is increasing the initial envelope offset the emittance evolution is dominated by the beating term and the original minimum is dominated by the beating term and the original minimum is
recovered only after a longer periodrecovered only after a longer period
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Movable Emittance-Movable Emittance-MeterMeter
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HBUNCH.OUT
sigma_x_[mm]enx_[um]
Bz_[T]
sigma_x_[mm] Bz_[T]
z_[m]
emittance envelope
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E0 ∝ λ rf−1 120-140 MV/m==> 52-60 MV/m
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λ1.3 GHz
λ 3 GHz= 2.33
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σ i ∝ λ rf
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Bz ∝ λ rf−1
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Q∝ λ rf 1 nC ==> 2.33 nC
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Q1 nC
Q2.33 nC3 = 0.75
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σ i ∝Q1 / 3
Scaling the LCLS design from S-band to L-bandScaling the LCLS design from S-band to L-band
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charge_scaling
enx_[mmmrad]
Q [nC]
Q^2/3
Q^4/3
TTF VUV-FEL PhotoinjectorTTF VUV-FEL Photoinjector
1.3 GHz, 1.5 cell RF Gun
Main SolenoidBucking Solenoid
Y. KimY. Kim RPPT008 RPPT008 Emittance Damping in TTF2 Booster Linac with Gaussian Longitudinal Laser Beam Profile
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EzBz
z [m]
Splitting Acceleration and Splitting Acceleration and FocusingFocusing
• The Solenoid can be placed downstream the cavity The Solenoid can be placed downstream the cavity • Switching on the solenoid when the cavity is cold Switching on the solenoid when the cavity is cold prevent any trapped magnetic fieldprevent any trapped magnetic field
36 cm
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HBUNCH.OUT
sigma_x_[mm]enx_[um]
sigma_x_[mm]
z_[m]
Q =1 nCQ =1 nCR =1.69 mmR =1.69 mmL =19.8 psL =19.8 psthth = 0.45 mm-mrad = 0.45 mm-mrad
EEpeakpeak = 60 MV/m (Gun) = 60 MV/m (Gun)
EEacc acc = 13 MV/m (Cryo1)= 13 MV/m (Cryo1)B = 3 kG (Solenoid)B = 3 kG (Solenoid)
I = 50 AI = 50 A
E = 120 MeVE = 120 MeV
nn = 0.6 mm-mrad = 0.6 mm-mrad
nn
[mm-mrad][mm-mrad]
Z [m]
HOMDYN Simulation
6 MeV6 MeV
3.3 m
PARMELA PARMELA simulationssimulations
µ-metal shield
solenoid
stainless steelniobiumHe tank
Connection to tuner
RT
2K
≤4K
Coupler port
130 mmR
=125
mm
500 mm
20 mGauss(2G wo )
166 mG 320 mG
Table 1 – SRF gun parameters f MHz] 1300 Epeak at cathode MV/m] 60 < Eacc> MV/m] 32 Bpeak/< Eacc> mT/(MV/
m) 4.47
Epeak/< Eacc> - 1.87 Specification for Qo
- 8*109
Pd at nom. gradient W ~20
L-band SC gun design with coaxial couplerL-band SC gun design with coaxial coupler
SCRF GUN
Scaling with Scaling with γγ
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B ∝ γ
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σr
σ l
∝ γ
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J ∝ γ 3
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σ l ∝ γ −5 3
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σr ∝ γ −2 3
BNL All-Niobium SC GunBNL All-Niobium SC Gun
T. Srinivasan-Rao et al., PAC 2003
1/2 cell, 1.3 GHzMaximum Field: 45 MV/m
Q.E. of Niobium @ 248 nmwith laser cleaningbefore: 2 x 10-7
after: 5 x 10-5
I. Ben-Zvi, Proc. Int. Workshop, Erlangen, 2002
No contamination from cathode particlesNo contamination from cathode particles
2 10-5
4 10-5
6 10-5
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0.0001
0.00012
0.00014
0.00016
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0 10 20 30 40 50 60 70
BNL_SCRF_CAT
QE
QE
G [MV/m]
SCRF GUN
Measured
Limited by the available voltageLimited by the available voltage
Measurements at room T Measurements at room T on a dedicated DC on a dedicated DC
systemsystem
Extrapolation to Extrapolation to Higher Field Higher Field
Cs (WF=2 .1 eV)
Is Nb the best superconductor for the photoemission ?
a /pm b /pm c /pm 330 330 330 α / ° β / ° γ / ° 90 90 90
Pb (WF= 4.2 eV) Nb (WF= 4.9 eV)
a /pm b /pm c /pm 495 495 495 α / ° β / ° γ / ° 90 90 90
a /pm b /pm c /pm 614 614 614 α / ° β / ° γ / ° 90 90 90
Very preliminary results measured @ BNL
Quantum Efficiency of Pb
248 nm
213 nm
Puv= ƒ * (Q/ )*(h) = 4 W4 W laser @ 213 nm (V harmonic of 1064 nm laser) can
generate 1nC @ 1MHz nominal beam
1•10- 4
1.5•10-3
Conceptual All Fiber System
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Lots of development in Erbium and Ytterbium doped fiber systemsCommercially available 20W, 2MHz systemsProgress should be very rapid over next 1-2 years
Example: for UV lithographyx7 and x8 of 1.5 µmPicture stolen from Nikon
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sigma_x_[mm]
Z_[m]
Q =0.35 nCQ =0.35 nCR =1. mmR =1. mmL =19.8 psL =19.8 psthth = 0.7 mm-mrad = 0.7 mm-mrad
EEpeakpeak = 60 MV/m (Gun) = 60 MV/m (Gun)
EEacc acc = 11 MV/m (Cryo1)= 11 MV/m (Cryo1)B = 2.9 kG (Solenoid)B = 2.9 kG (Solenoid)
I = 18 AI = 18 A
E = 100 MeVE = 100 MeV
nn = 0.76 mm-mrad = 0.76 mm-mrad
3.2 m
HOMDYN Simulation
nn
[mm-mrad][mm-mrad]
σσxx
[mm][mm]
Z [m]
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Velocity bunching optionVelocity bunching option
CONCLUSIONSCONCLUSIONS
• Emittance compensation by external solenoid is Emittance compensation by external solenoid is possiblepossible• 60 MV/m peak field in SC cavity have been 60 MV/m peak field in SC cavity have been already demonstratedalready demonstrated• Work in progress @ BNL to demonstrate Work in progress @ BNL to demonstrate Pb QE ~10Pb QE ~10-3 -3 @ 200 nm@ 200 nm• Laser System: progress should be very rapid Laser System: progress should be very rapid over next 1-2 yearsover next 1-2 years
The following workshop was approved by ICFA at its meeting Feb 10-11,2005 in Vancouver:
Physics and Applications Physics and Applications of High Brightness Electron Beamsof High Brightness Electron Beams
Erice, Sicily, Italy, October 9-14, 2005Erice, Sicily, Italy, October 9-14, 2005Organizers: L. Palumbo (Univ. Roma), J. Rosenzweig (UCLA), L. Serafini(INFN-Milano).