Picosecond Electron Bunches Research Articles

Overall comparison of subpicosecond electron beam diagnostics by the polychromator, the interferometer and the femtosecond streak camera

Measurements of longitudinal bunch length of subpicosecond and picosecond electron beams have been performed by three methods with three radiation sources at the 35 MeV S-band twin liner accelerators at Nuclear Engineering Research Laboratory, University of Tokyo. The methods we adopt are the femtosecond streak camera with a nondispersive reflective optics, the coherent transition radiation (CTR) Michelson interferometer and the 10 ch polychromator that detects the spectrum of CTR and coherent diffraction radiation (CDR). The measurements by the two CTR methods were independently done with the streak camera and their results were consistent with one another. As a result, the reliability of the polychromator for the diagnostics of less than picosecond electron bunch and the usefulness of the diagnostics for the single shot measurement were verified. Furthermore, perfect nondestructive diagnostics for subpicosecond bunches was performed utilizing CDR interferometry. Then the good agreement between CDR interferometry and the streak camera was obtained.

Measurements of harmonic wake fields excited by rough surfaces.

An experiment has been carried out at the TESLA Test Facility linac to investigate the wake fields generated by picosecond electron bunches in narrow beam pipes with an artificially roughened inner surface. The energy structure imposed on the bunches by the wake fields has been analyzed with a magnetic spectrometer. Strong harmonic-wake-field effects are observed as expected from simulations in which the rough surface is modeled by a dielectric layer.

Can coherent Smith–Purcell radiation be used to determine the shape of an electron bunch?

Recent measurements at Frascati of the Smith–Purcell radiation emitted from the interaction of a 2.3 MeV (total) electron beam with a 2.5 mm grating show clear evidence of coherent enhancement of the radiation, with power levels exceeding 100 mW at emission angles around 90° relative to the beam direction. The experimental results are in reasonable agreement with theoretical predictions and suggest that Smith–Purcell radiation may offer a simple way of determining the shape and duration of short (picosecond) electron bunches.

Experimental investigation of wake fields excited by a rough surface

An experiment has been carried out at the TESLA Test Facility (TTF) linac to investigate the wake fields generated by picosecond electron bunches in narrow beam pipes with artificially roughened inner surface. Two methods were employed: (a) the energy structure imposed on the bunches by the wake fields was analysed with a magnetic spectrometer, and (b) the generated THz radiation was directly recorded in an interferometer equipped with Golay cell detectors. Both methods indicate the presence of strong wake field effects as expected from simulations in which the rough surface is modelled by a dielectric layer.

A diffusion model for picosecond electron bunches from negative electron affinity GaAs photocathodes

Even though theoretical estimates predict response times for the photoemission process of electrons from a negative electron affinity GaAs photoemitter in excess of hundreds of picoseconds, recent measurements found electron bunch durations of 40 ps or less. This work presents precise measurements of picosecond electron bunches from a negative affinity bulk GaAs photocathode and develops a model which explains the measured bunch durations as well as the observed bunch shapes. The bunch shape turns out to be independent from the quantum efficiency of the photoemitter.

Picosecond polarized electron bunches from a strained layer GaAsP photocathode

At the Mainz electron accelerator MAMI a facility has been set up that allows the measurement of the bunchlength, the energy spread and the averaged and phase resolved polarization of picosecond electron bunches from a source of polarized electrons for MAMI. Electron bunches of typically 10 to 30 ps duration are generated by illuminating a strained layer GaAsP photocathode with femtosecond laser pulses.

Comment on "Measurement of coherent Cherenkov radiation from an intense beam of a picosecond electron bunch"

A Comment on the Letter by J. Ohkuma, S. Okuda, and K. Tsumori, Phys. Rev. Lett. 66, 1967 (1991).

Measurement of coherent Cherenkov radiation from an intense beam of a picosecond electron bunch.

High-intensity Cherenkov radiation (CR), emitted in air from a high-current 30-MeV electron bunch (2\ifmmode\times\else\texttimes\fi{}${10}^{11}$ electrons/bunch) of the linear accelerator at the Institute of Scientific and Industrial Research was observed at wavelengths from 0.4 to 3 mm. The radiation was emitted at an angle of 38 mrad, with some spread, from the beam axis. The radiation measured was about ${10}^{11}$ times as intense as that calculated for ordinary CR. Such enhancement is attributed to the coherence which appears in CR emitted from electron bunches of relatively short length.