UCLA, Los Angeles, California
Funding: Office of Naval Research (US) Grant No. N000140711174
Longitudinal beam dynamics of the photoinjector "blowout" regime are investigated. A two beamlet macroparticle approach is first used to investigate the effects of S-Band RF photogun fields on a picosecond time scale. The beams' longitudinal phase spaces (LPS) are measured via an X-band RF deflecting cavity and dipole spectrometer. Lastly, the LPS of a single subpicosecond beam is investigated as a function of initial charge density at the cathode and compared to simulation.
UCLA, Los Angeles, California
We report on the use of a ultrashort high brigthness relativistic beam from the UCLA Pegasus laboratory RF photoinjector source for probing matter transformation at the atomic scale with sub-100 fs time resolution. The high accelerating gradient and the relativistic electron energy allow to pack more than 107 electrons in less than 100 fs bunch length, enabling the study of irreversible ultrafast phenomena by single-shot diffraction patterns. The experimental setup, and the initial results from the first ever relativistic electron diffraction time-resolved study will be discussed.
RadiaBeam, Marina del Rey
UCLA, Los Angeles, California
NCSU, Raleigh, North Carolina
INFN/LNF, Frascati (Roma)
Electron beam based additive fabrication techniques have been successfully applied to produce a variety of complex, fully dense, metal structures. These methods, collectively known as Solid Freeform Fabrication (SFF) are now being explored for use in radio frequency (RF) structures. SFF technology may make it possible to design and produce near-netshape copper structures for the next generation of very high duty factor, high gradient RF photoinjectors. The SFF process discussed here, Arcam Electron Beam Melting (EBM), utilizes an electron beam to melt metal powder in a layer-by-layer fashion. The additive nature of the SFF process and its ability to produce fully dense parts are explored for the fabrication of internal cooling passages in RF photoinjectors. Following an initial feasibility study of the SFF process, we have fabricated a copper photocathode, suitable as a drop-in replacement for the UCLA 1.6 cell photoinjector, with internal cooling channels using SFF. Material analysis of the prototype cathode and new designs for a high duty factor photoinjector utilizing SFF technology will be presented.
UCLA, Los Angeles, California
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
PSI, Villigen
The resonant harmonic interaction of an electron beam (e-beam) with an EM input field in a helical undulator is explored. The e-beam is coupled to the input radiation field at frequency harmonics through transverse gradients in the EM field, and helical micro-bunching of the e-beam is shown to occur naturally at the higher harmonics with the injection of a simple gaussian laser mode onto a cylindrically symmetric e-beam. This approach is under investigation as a method to generate a strongly pre-bunched e-beam seed for superradiant emission of light that carries orbital angular momentum in a downstream free-electron laser.
UCLA, Los Angeles, California
Funding: This work was supported by DOE grants DE-FG03-92ER40727 and DE-FG03-92ER40693
Many proposals and ongoing national projects exist worldwide to build a single-pass X-ray FEL amplifier in which a high-brightness, multi-GeV electron beam has a resonant energy exchange with radiation in an undulator. Because of the practical limit on the undulator period, the electron beam energy represents one of constraints on the shortest reachable wavelength. Recently the high-order harmonic FEL/IFEL interactions were considered theoretically as a technique that would allow the reduction of the beam energy without corresponding decrease in the undulator period and the magnetic field strength. We demonstrate microbunching of the 12.3 MeV electrons in a 7th order IFEL interaction, where the seed radiation frequency is seven times higher then the fundamental frequency. Strong longitudinal modulation of the beam is inferred from the observation of the first, second and third harmonics of the seed radiation in a Coherent Transition Radiation spectrum. The level of seed power is comparable to that required for microbunching at the fundamental frequency of the ten-period-long undulator. The implications of these results for the next generation of FELs will be explored.
UCLA, Los Angeles, California
INFN/LNF, Frascati (Roma)
ENEA C.R. Frascati, Frascati (Roma)
It has been suggested that an ultra-short, very low charge beam be used to drive short wavelength single-spike operation at the SPARC FEL. This paper explores the development and construction of a longitudinal diagnostic capable of completely characterizing the radiation based on the Frequency-Resolved Optical Gating (FROG) technique. In particular, this paper explores a new geometry based on a Transient-Grating (TG) nonlinear interaction and includes studies of start to end simulations for pulses at the SPARC facility using GENESIS and reconstructed using the FROG algorithm. The experimental design, construction and initial testing of the diagnostic are also discussed.
UCLA, Los Angeles, California
Funding: Office of Naval Research (US) Grant No. N000140711174
Electro-optic sampling (EOS) has been developed as a timing monitor at Pegasus photoinjector laboratory for 100-fs electron bunches. A geometrically simple 2-dimensional spatially encoding scheme is used to measure time-of-arrival (TOA) of these ultrashort electron bunches in a 20 ps window down to < 50 fs resolution. The setup described here has successfully observed EOS signals for low energy (~4 MeV) and low charge (< 10 pC) bunches, both parameters being lower than electro-optic TOA monitors currently used in other labs. Experimental 2-d EOS images are compared to particle-in-cell plasma simulations (OOPIC) of electron bunch transient electric fields in ZnTe and to theoretical field propagation in dielectric crystals.
UCLA, Los Angeles, California
Rome University La Sapienza, Roma
We present the status of development of a 1.5+0.5 cell photoinjector run in the blowout regime. LANL Parmela simulation results indicate a near uniform beam of slice energy spread on the order of 500 eV when neglecting thermal effects. We examine the use of an extra half cell to control longitudinal beam growth and compare the system in development with previous 1.6 cell photoinjector designs.