Beam Dynamics in a Spilt SRF-Gun

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Beam Dynamics in a Spilt SRF-Gun M. Ferrario, W.
D. Moeller, J. B. Rosenzweig, J. Sekutowicz,
G.Travish INFN, UCLA, DESY
Meeting on Superconducting RF Gun
Simulations EUROFEL Work Package 5 2.-3. June
2005 at BESSY
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SUPERCONDUCTING RF PHOTO-INJECTORS
Main Advantage
Low RF Power Losses CW Operation
Main Questions/Concerns

• Emittance Compensation ?
• Q degradation due to Magnetic Field ?
• High Peak Field on Cathode ?
• Cathode Materials and QE ?
• Laser System ?

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Schematic View of the Envelope Equations HOMDYN
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Emittance Oscillations and Growth are driven by
space charge differential defocusing in core and
tails of the beam
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Emittance Compensation Controlled Damping of
Plasma Oscillation (LS-JBR)
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Gun Working Point
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Linac Working Point
The emittance compensation occuring in the
booster when the invariant envelope matching
conditions are satisfied is actually limited by
the head and tail slice behavior
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Homdyn movie
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Head and tail slices carry the most pronounced
energy spread
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Simple Case Transport in a Long Solenoid
gt Equilibrium solution ? gt
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Small perturbations around the equilibrium
solution
Same Plasma Frequencies
Different Amplitudes
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Envelope oscillations drive Emittance oscillations
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Bunch with a Linear Energy Spread Correlation
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A Spread in Plasma Frequencies drives a Beating
in Emittance Oscillations
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On a longer time scale
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increasing the initial envelope offset the
emittance evolution is dominated by the beating
term and the original minimum is recovered only
after a longer period
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Movable Emittance-Meter
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Scaling the LCLS design from S-band to L-band
120-140 MV/mgt 52-60 MV/m
1 nC gt 2.33 nC
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TTF VUV-FEL Photoinjector
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Y. Kim RPPT008 Emittance Damping in TTF2 Booster
Linac with Gaussian Longitudinal Laser Beam
Profile
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Splitting Acceleration and Focusing
36 cm

• The Solenoid can be placed downstream the cavity
  
• Switching on the solenoid when the cavity is
  cold prevent any trapped magnetic field

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PARMELA simulations
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L-band SC gun design with coaxial coupler
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SCRF GUN
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Scaling with ?
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BNL All-Niobium SC Gun
No contamination from cathode particles
1/2 cell, 1.3 GHz Maximum Field 45 MV/m Q.E.
of Niobium _at_ 248 nm with laser cleaning before
2 x 10-7 after 5 x 10-5
T. Srinivasan-Rao et al., PAC 2003
I. Ben-Zvi, Proc. Int. Workshop, Erlangen, 2002
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Measurements at room T on a dedicated DC system
Extrapolation to Higher Field
SCRF GUN
Measured
Limited by the available voltage
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Is Nb the best superconductor for the
photoemission ?
Cs (WF2 .1 eV)
Nb (WF 4.9 eV)
Pb (WF 4.2 eV)
a /pm b /pm c /pm 330 330 330
a / ß / ? /   90 90
90
a /pm b /pm c /pm 495 495 495
a / ß / ? /   90 90
90
a /pm b /pm c /pm 614 614 614 a
/ ß / ? /   90 90
90
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Very preliminary results measured _at_ BNL
110- 4
1.510-3
Puv ƒ (Q/ ?)(h?) 4 W 4 W laser _at_ 213 nm (V
harmonic of 1064 nm laser) can generate 1nC _at_
1MHz nominal beam
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Conceptual All Fiber System
Lots of development in Erbium and Ytterbium doped
fiber systems Commercially available 20W, 2MHz
systems Progress 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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HOMDYN Simulation
Q 0.35 nC R 1. mm L 19.8 ps ?th 0.7
mm-mrad Epeak 60 MV/m (Gun) Eacc 11 MV/m
(Cryo1) B 2.9 kG (Solenoid)
I 18 A E 100 MeV ?n 0.76 mm-mrad
?n mm-mrad
?x mm
3.2 m
Z m
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Velocity bunching option
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• CONCLUSIONS
• Emittance compensation by external solenoid is
  possible
• 60 MV/m peak field in SC cavity have been
  already demonstrated
• Work in progress _at_ BNL to demonstrate
• Pb QE 10-3 _at_ 200 nm
• Laser System progress should be very rapid over
  next 1-2 years

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The following workshop was approved by ICFA at
its meeting Feb 10-11, 2005 in Vancouver Physics
and Applications of High Brightness Electron
Beams Erice, Sicily, Italy, October 9-14,
2005 Organizers L. Palumbo (Univ. Roma), J.
Rosenzweig (UCLA), L. Serafini (INFN-Milano).