Before aperture After aperture

Faraday Cup

Trigger Photodiode

Laser Energy Meter

Phosphor ScreenSolenoids

Successful Initial X-Band Photoinjector Electron Beam Production Experiment

Energy (MeV)

130

150

170

190

210

230

250

270

290

850 855 860 865 870 875 880 885

Pixel Number

Cha

rge

(a.u

.)

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

0

5

1 0

1 5

2 0

2 5

0 6 0 1 2 0 1 8 0 2 4 0 3 0 0 3 6 0L a s e r I n je c t i o n P h a s e ( o )

Bun

ch C

harg

e (p

C)

3

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

0

0.2

0.4

0.6

0.8

1

11.4

00

11.4

05

11.4

10

11.4

15

11.4

20

11.4

25

11.4

30

11.4

35

11.4

40

RF gun with new cell 6Qext ~ 4900

S11 M

agnitude

Freq GHz

11414.6 MHz

11424.3 MHz

string added

T = 22.8 C

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 50 100 150 200

Pi mode field profile

E-f

ield

(re

lative

)

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

6

5

4

3

2

1

2 4 86 100 14 16 201812

Z (cm)

Bz

(kG

)

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

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

11.4 11.41 11.41 11.42 11.42 11.43 11.43 11.43 11.44

8.7 MHz

11.4222 GHz

11.41350 GHz

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 50 100 150 200

Field flatness maintained and frequency change quantified

Final Bonded Photoinjector Cavity