Before aperture
description
Transcript of Before aperture
Before aperture After aperture
Faraday Cup
Trigger Photodiode
Laser Energy Meter
Phosphor ScreenSolenoids
Successful Initial X-Band Photoinjector Electron Beam Production Experiment
Energy (MeV)
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Pixel Number
Cha
rge
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.)
1.40 1.45 1.50 1.55 MeV
1.47 MeV sub-picosecond electron bunch produced with an energy spread of 1.8% at a gradient of over 100 MeV/m
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Bun
ch C
harg
e (p
C)
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00 e x pq q
Cathode Quantum Efficiency = 2 x 10-5 Normalized rms emittance = 1.63
mm-mrad
Compton X-Ray Source Development
A.E. Vlieks, D. Martin, G. CaryotakisStanford Linear Accelerator Center
D. PriceLawrence Livermore National Laboratory
C. DeStefano, J.P. Heritage, E.C. Landahl, B. Pelletier, N.C. Luhmann, Jr.Departments of Applied Science and Electrical and Computer Engineering, University of
California, Davis
Linac
QuadrupoleMagnets
Laser Feedthru / Electron Beam Diagnostics
Waveguide from KlystronSolenoid and
Photoinjector
Linac
QuadrupoleMagnets
Electron Beam Diagnostics Camera
Waveguide Window
Solenoid and Photoinjector
Vacuum Pumpout
Gate Valve
Dipole Corrector Magnet
Before aperture
6 ft
Compton X-Ray Source Beamline
Interaction parameters:
• Energy spread < 1%
• Energy tunable 25 – 60 MeV
• Peak current 630 Amperes
• Emittance 1 mm-mrad
• Focal spot 20 micron diameter
Cathode parameters:
• Ultraviolet laser 266 nm
• Flat-top duration 800 fs
• Electron bunch charge 500 pC
• Quantum efficiency 2 x 10-5
• Uniform emission radius 0.25 mm
What is a photoinjector?
Cue-
UV Laser light
Photoelectric Effect + RF Acceleration
1. Emission of electrons from surface is characterized by laser pulse shape and intensity
2. Pulse can be very short. ( 0.1-1 ps)
3. Current can be high. ( 0.5 nC charge630 A for an 800 fs pulse)
4. Beam size can be small. Size is determined by laser pulse shape.
5. RF fields can be very high. ( 200 MeV/m)
• X-band klystrons developed for the Next Linear Collider
• 11.424 GHz• 1.5 s pulsewidth• 60 MW output power• 420 kV, 327 A• Two klystrons used
for CXS-10; however, the clinical device will use a single source
• X-band permits high gradients of up to 75 MV/m
• Four times smaller than conventional technology
• Focusing of ~ kA beam to 30 microns in < 2 meters
• Opens up a new energy and intensity frontier to the medical community
Processing accelerator structure to 75 MV/m
X-band 1.05 m long accelerator structure
SLAC Compact X-band Accelerators and Microwave Power Sources
Table-Top Terawatt Laser • The same high field conditions
that exist inside a synchrotron x-ray source are generated at the interaction point for only 5 x 10-14 seconds
• Ultrashort optics techniques are utilized to synchronize and shape the laser for optimum electron beam and x-ray production
12 fs laser oscillator
TW pulse compressor
Operation of the First X-band Photoinjector (8.6 GHz)First Implementation of an Ultrashort Pulse Laser into a PhotoinjectorProduction of Low Emittance and Low Energy Spread Electron Beams
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RF gun with new cell 6Qext ~ 4900
S11 M
agnitude
Freq GHz
11414.6 MHz
11424.3 MHz
string added
T = 22.8 C
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Pi mode field profile
E-f
ield
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lative
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Position in z
Pre-bonding
The X-Band Photoinjector: A New Source of High Brightness Electron Beams
Electromagnetic Simulations
Structure Bonding
Final Mechanical Design and Fabrication
Cold Tests
Emittance Compensation Solenoid Magnet
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Z (cm)
Bz
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3D HFSS modeling to adjust Qext and frequency
Bead-pull apparatus for cold testing of field profiles
Waveguide Assembly
Cold test photoinjector cavity
Photoinjector cells in bonding furnace
Individual Tuning of Final Cells
Frequency Sensitivity:
milMHzr
F/29
Cells 2-5
Cell 6Cell 1
Endcaps
Coax. antenna
Waveguide Assembly Components
Ceramic Window
Power Splitter
Pump-out port
Cathode
Water-cooling
Input waveguide
Beam Exit
1. RF Design.
2. Beam dynamics design.
3. Manufacture of cold-test parts.
4. Diffusion bonding of cold-test Injector.
5. Re-measurement of cold-test Injector.
6. Coupler redesign.
7. Manufacture of final Gun parts
8. Cold testing/tuning of final gun parts.
9. Assembly/diffusion bonding
10. High Power tests underway
RF Gun 2D Electric Field Profile from SUPERFISH
Post-bonding
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8.7 MHz
11.4222 GHz
11.41350 GHz
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Field flatness maintained and frequency change quantified
Final Bonded Photoinjector Cavity