Compton X-Ray Source Development
A.E. Vlieks, D. Martin, G. Caryotakis
Stanford Linear Accelerator Center
D. Price
Lawrence 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
Solenoid and
Photoinjector
Solenoid and
Photoinjector
Waveguide
from Klystron
Laser Feedthru / Electron
Beam Diagnostics
Waveguide
Window
Electron Beam Diagnostics
Camera
Quadrupole
Magnets
Linac
Linac
Quadrupole
Magnets
Dipole Corrector
Magnet
Gate Valve
Vacuum
Pumpout
6 ft
SLAC Compact X-band Accelerators and Microwave Power Sources
Compton X-Ray Source Beamline
•
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
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•
X-band klystrons
developed for the Next
Linear Collider
11.424 GHz
1.5 ms pulsewidth
60 MW output power
420 kV, 327 A
Two klystrons used for
CXS-10; however, the
clinical device will use a
single source
•
•
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•
X-band 1.05 m long accelerator structure
Processing accelerator structure to 75 MV/m
Before
aperture
What is a
photoinjector?
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
UV Laser light
eCu
• Ultrashort optics techniques are
utilized to synchronize and shape
the laser for optimum electron
beam and x-ray production
Photoelectric Effect + RF Acceleration
1. Emission of electrons from surface is characterized by laser
pulse shape and intensity
Cathode parameters:
Interaction parameters:
• Ultraviolet laser 266 nm
• Energy spread g/g < 1%
• Flat-top duration 800 fs
• Energy tunable 25 – 60 MeV
• Electron bunch charge 500 pC
• Quantum efficiency 2 x
10-5
• Uniform emission radius 0.25 mm
TW pulse compressor
2. Pulse can be very short. ( 0.1-1 ps)
• Peak current 630 Amperes
• Emittance 1 p mm-mrad
• Focal spot 20 micron diameter
3. Current can be high. ( 0.5 nC charge630 A for an 800 fs
pulse)
4. Beam size can be small. Size is determined by laser pulse
shape.
12 fs laser oscillator
5. RF fields can be very high. ( 200 MeV/m)
Successful Initial X-Band
Photoinjector Electron Beam
Production Experiment
Trigger Photodiode
Laser Energy Meter
Faraday Cup
1.55 MeV
250
   3
Cathode Quantum
0

q  q 0 e xp  
-5
Efficiency
=

 2 x10

20
15
C h a rg e (a .u .)
Phosphor Screen
1.50
270
25
Solenoids
1.45
290
Bu n c h Ch a rg e (p C)
Operation of the First Xband Photoinjector (8.6
GHz)
First Implementation of an
Ultrashort Pulse Laser into a
Photoinjector
Production of Low Emittance
and Low Energy Spread
Electron Beams
Energy (MeV)
1.40
Before aperture
230
210
190
170
10
150
5
130
1.47 MeV sub-picosecond electron
P ixe l Numbe r
bunch produced with
an energy spread
of 1.8% at a gradient of over 100
MeV/m
850
0
0
60
120
180
240
300
o
Laser Injection Phase ( )
360
After aperture
Normalized rms emittance = 1.63 p mmmrad
855
860
865
870
875
880
885
The X-Band Photoinjector:
A New Source of High Brightness Electron Beams
Electromagnetic Simulations
Pre-bonding
RF gun with new cell 6
Qext ~ 4900
Pi mode field profile
0.4
T = 22.8 C
1
0.35
string added
0.8
E-field (relative)
RF Gun 2D Electric Field Profile from
SUPERFISH
S11 Magnitude
0.3
0.25
0.2
0.6
11414.6 MHz
0.4
0.15
0.1
0.2
0.05
11.440
11.435
11.430
200
11.425
150
11.420
100
Position in z
11.415
50
11.410
0
11.405
0
0
11.400
11424.3 MHz
3D HFSS modeling to adjust Q ext and frequency
Freq GHz
Post-bonding
0.35
1
0.3
0.9
0.25
0.8
0.2
0.7
Cold test photoinjector
cavity
Cold Tests
11.41350 GHz
8.7 MHz
0.15
0.6
0.1
0.5
0.4
0.05
11.4222 GHz
0
0
50
100
150
200
0.3
11.4
11.41
11.41
11.42
11.42
11.43
11.43
11.43
11.44
Bead-pull apparatus for
cold testing of field
profiles
Field flatness maintained and frequency change
quantified
Emittance
Compensation
Solenoid Magnet
6
5
4
3
2
1
0
2
4
6
8
12
10
14
16
18
20
Z (cm)
Individual Tuning of Final Cells
Frequency Sensitivity:
F
r
 29 MHz / mil
Waveguide Assembly
Components
Input waveguide
Coax.
antenna
Ceramic Window
Power Splitter
Endcaps
Cathode
Cells 2-5
Beam
Exit
Cell 1
Pump-out port
Cell 6
Structure
Bonding
Photoinjector cells
in bonding furnace
Water-cooling
Final
Mechanical
Design
and
Fabrication
Waveguide
Assembly
Final Bonded Photoinjector Cavity
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