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
Funding: This work is supported by the DOE Contract No. DE-FG03-92ER40727.
Over the last several years, the Target Normal Sheath Acceleration (TNSA) mechanism in solid density plasmas produced by a laser pulse has achieved proton energies up to 10’s of MeV and quasi-monoenergetic beams at lower energies. Although solid-target experiments have demonstrated high-charge and low-emittance proton beams, little work has been done with gaseous targets which in principle can be operated at a very high repetition frequency. At the Neptune Laboratory, there is an ongoing experiment on CO2 laser driven proton acceleration using a rectangular (0.5x2mm) H2 gas jet as a target. The main goal is to study the coupling of the laser pulse into a plasma with a well defined density in the range of 0.5 to 2 times critical density and characterize the corresponding spectra of accelerated protons. Towards this end, the Neptune TW CO2 laser system is being upgraded to produce shorter 1-3ps pulses. These high-power pulses will allow us to investigate acceleration of protons via the TNSA and Direct Ponderomotive Pressure mechanisms as well as their combination. The current status of the proton source experiment will be presented.