Abstract
Many new applications for electron accelerators require high-brightness, high-average power beams, and most rely on photocathode-based electron injectors as a source of electrons. To achieve such a photoinjector, one requires both a high-power laser system to produce the high average current beam, and also a system at reduced repetition rate for electron beam diagnostics to verify high beam brightness. Here we report on two fiber laser systems designed to meet these specific needs, at 50 MHz and 1.3 GHz repetition rate, together with pulse pickers, second harmonic generation, spatiotemporal beam shaping, intensity feedback, and laser beam transport. The performance and flexibility of these laser systems have allowed us to demonstrate electron beam with both low emittance and high average current for the Cornell energy recovery linac.
Highlights
Intense electron beams are key to a large number of scientific endeavors, including electron cooling of hadron beams, electron-positron colliders, secondary-particle beams such as photons and positrons, and new highgradient accelerators that use electron-driven plasmas
Detailed simulations show that the final beam emittance is not affected by the longitudinal profile modulations of the laser if they remain within 50% so that both temporal profiles shown in Fig. 14 are acceptable to generate bunches with nearly identical low emittance [17]
The electro-optic modulator used for power stability has 20% loss, the longitudinal shaping crystals have 10% loss, clipping the laser beam on the pinhole aperture can have huge losses depending on the size of the aperture, but is typically 30% or more
Summary
Intense electron beams are key to a large number of scientific endeavors, including electron cooling of hadron beams, electron-positron colliders, secondary-particle beams such as photons and positrons, and new highgradient accelerators that use electron-driven plasmas. The high-power fiber amplifiers and second harmonic generation that delivers the necessary average power will be described first, followed by a number of the key ingredients necessary for efficient beam shaping, diagnostics, and control These components include optical pulse pickers, 50 MHz & 1.3 GHz High-power fiber lasers. Thanks to the larger mode area and shorter fiber length in the rod amplifier, we could substantially reduce the nonlinear phase shift accumulation, and boost the pulse energy by 10 times without important spectral distortion. Frequency doubling of amplified pulses yields 70 W green power with 70% efficiency This higher power laser can be used for Compton scattering nondestructive diagnostics of the electron beam [12,13].
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