LLNL, Livermore, California, USA
SLAC, Menlo Park, California, USA
We present an optimized 5 + ½ cell, X-band photoinjector designed to produce 7 MeV, 250 pC, sub-micron emittance electron bunches for the LLNL Mono-Energetic Gamma-Ray (MEGa-Ray) light source. This LLNL/SLAC collaboration modifies a design previously demonstrated to sustain 200 MV/m on-axis accelerating fields*. We discuss the photoinjector operating point, optimized by scaling beam dynamics from S-band photo-guns and by evaluation of the MEGa-Ray source requirements. The RF structure design is presented along with the current status of the photoinjector construction and testing.
*A.E. Vlieks, et al., High Energy Density and High Power RF: 6th Workshop, AIP, CP691, p. 358 (2003).
UCLA, Los Angeles, California, USA
LLNL, Livermore, California, USA
Instituto Superior Tecnico, Lisbon, Portugal
IPFN, Lisbon, Portugal
A series of laser wakefield accelerator experiments leading to electron energy exceeding 1 GeV are described. Theoretical concepts and experimental methods developed while conducting experiments using the 10 TW Ti:Sapphire laser at UCLA were implemented and transferred successfully to the 100 TW Calisto Laser System at the Jupiter Laser Facility at LLNL. To reach electron energies greater than 1 GeV with current laser systems, it is necessary to inject and trap electrons into the wake and to guide the laser for more than 1 cm of plasma. Using the 10 TW laser, the physics of self-guiding and the limitations in regards to pump depletion over cm-scale plasmas were demonstrated. Furthermore, a novel injection mechanism was explored which allows injection by ionization at conditions necessary for generating electron energies greater than a GeV. The 10 TW results were followed by self-guiding at the 100 TW scale over cm plasma lengths. The energy of the self-injected electrons, at 3x1018 cm-3 plasma density, was limited by dephasing to 720 MeV. Implementation of ionization injection allowed extending the acceleration well beyond a centimeter and 1.4 GeV electrons were measured.
LLNL, Livermore, California, USA
UCLA, Los Angeles, California, USA
Oxford University, Physics Department, Oxford, Oxon, United Kingdom
UCSD, La Jolla, California, USA
A two-stage Laser Wakefield Accelerator (LWFA) has been developed, which utilizes the ionization induced injection mechanism to produce high energy, narrow energy spread electron beams when the electron density is equal in both stages. However, when the densities are not equal these high quality beams are not observed. As the electron density varies across the interface between the adjacent stages the size of the ion cavity is expected to change; this results in either a reduction of the peak electron energy (for a density decrease), or in the exclusion of previously trapped charge from the first wake period (for a density increase). The latter case can be overcome if the interaction length before the density interface exceeds a threshold determined by the densities in each stage, and may provide a mechanism for enhanced energy gain.
LLNL, Livermore, California, USA
This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
LLNL, Livermore, California, USA
SLAC, Menlo Park, California, USA
A new class of gamma-ray light source based on Compton scattering is made possible by recent progress in accelerator physics and laser technology. Mono-energetic gamma-rays are produced from collisions between a high-brightness, relativistic electron beam and a high intensity laser pulse produced via chirped-pulse amplification (CPA). A precision, tunable gamma-ray source driven by a compact, high-gradient X-band linac is currently under development and construction at LLNL. High-brightness, relativistic electron bunches produced by an X-band linear accelerator designed in collaboration with SLAC will interact with a Joule-class, 10 ps, diode-pumped CPA laser pulse to generate tunable gamma-rays in the 0.5-2.5 MeV photon energy range via Compton scattering. The source will be used to conduct nuclear resonance fluorescence experiments and address a broad range of current and emerging applications in nuclear photoscience. Users include homeland security, stockpile science and surveillance, nuclear fuel assay, and waste imaging and assay. The source design, key parameters, and current status are presented, along with important applications.
LLNL, Livermore, California, USA
A Mono-energetic Gamma-Ray (MEGa-Ray) source, based on Compton scattering of a high-intensity laser beam off a highly relativistic electron beam, requires highly specialized laser systems. To minimize the bandwidth of the gamma-ray beam, the scattering laser must have minimal bandwidth, but also match the electron beam depth of focus in length. This requires a ~1 J, 10 ps, fourier-transform-limited laser system. Also required is a high-brightness electron beam, best provided by a photoinjector. This electron source in turn requires a second laser system with stringent requirements on the beam including flat transverse and longitudinal profiles and fast rise times. Furthermore, these systems must be synchronized to each other with ps-scale accuracy. Using a novel hyper-dispersion compressor configuration, advanced fiber amplifiers, and diode-pumped Nd:YAG amplifiers, we have designed laser systems that meet these challenges for the x-band photoinjector and Compton-scattering source being built at Lawrence Livermore National Laboratory.