Before aperture After aperture Faraday Cup Trigger Photodiode Laser Energy Meter Phosphor Screen Solenoids 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 P ixel Num ber Charge (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 10 15 20 25 0 60 120 180 240 300 360 L a s e r In je c tio n P h a s e ( o ) Bunch Charge (pC) 3 0 0 exp q 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. 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 Linac Quadrupole Magnets Laser Feedthru / Electron Beam Diagnostics Waveguide from Klystron Solenoid and Photoinject or Linac Quadrupole Magnets Electron Beam Diagnostics Camera Waveguide Window Solenoid and Photoinjecto r 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? Cu e - 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 Photoinjector Production of Low Emittance and Low Energy Spread Electron Beams