arXiv subjects

Avraham Gover

Publications and source records attributed to Avraham Gover.

21 records · Page 2Linked to original sources

arXiv2017

Relativistic electron beam acceleration in a zero-slippage terahertz-driven Inverse Free Electron Laser scheme

THz radiation promises breakthrough advances in compact advanced accelerators due to the high frequency and GV/m fields achievable, orders of magnitude larger than in conventional radiofrequency (RF) based accelerators. Compared to laser-driven schemes, the large phase acceptances of THz-driven accelerators are advantageous for operation with sizable charge. Despite burgeoning research, THz sources, particularly laser-based ones, cannot yet compete with the efficiency of RF amplifiers for high average current accelerators. Nevertheless, THz-based phase space manipulation is of immediate interest for a variety of applications, including generation and diagnostics of ultrashort bunches for electron diffraction/microscopy and compact free-electron laser applications. The challenge of maintaining overlap and synchronism between an electron beam and short laser-generated THz pulse has so far limited interactions to the few mm scale. We discuss a novel scheme for simultaneous group and phase velocity matching of nearly single-cycle THz radiation with a relativistic electron beam for meter-scale interaction. We demonstrate energy modulations of up to 150 keV using modest THz pulse energies (up to 1 uJ). We apply this large and efficient energy exchange for beam compression and time-stamping of a relativistic beam, paving the way towards realizing the unique opportunities enabled by laser-based THz accelerators.

physics.acc-ph↗

arXiv2012

Self accelerating electron Airy beams

We report the first experimental generation and observation of Airy beams of free electrons. The electron Airy beams are generated by diffraction of electrons through a nanoscale hologram, that imprints a cubic phase modulation on the beams' transverse plane. We observed the spatial evolution dynamics of an arc-shaped, self accelerating and shape preserving electron Airy beams. We directly observed the ability of electrons to self-heal, restoring their original shape after passing an obstacle. This electromagnetic method opens up new avenues for steering electrons, like their photonic counterparts, since their wave packets can be imprinted with arbitrary shapes or trajectories. Furthermore, these beams can be easily manipulated using magnetic or electric potentials. It is also possible to efficiently self mix narrow beams having opposite signs of acceleration, hence obtaining a new type of electron interferometer.

physics.optics↗

arXiv2008

Virtual dielectric waveguide mode description of a high-gain free-electron laser I: Theory

A set of mode-coupled excitation equations for the slowly-growing amplitudes of dielectric waveguide eigenmodes is derived as a description of the electromagnetic signal field of a high-gain free-electron laser, or FEL, including the effects of longitudinal space-charge. This approach of describing the field basis set has notable advantages for FEL analysis in providing an efficient characterization of eigenmodes, and in allowing a clear connection to free-space propagation of the input (seeding) and output radiation. The formulation describes the entire evolution of the radiation wave through the linear gain regime, prior to the onset of saturation, with arbitrary initial conditions. By virtue of the flexibility in the expansion basis, this technique can be used to find the direct coupling and amplification of a particular mode. A simple transformation converts the derived coupled differential excitation equations into a set of coupled algebraic equations and yields a matrix determinant equation for the FEL eigenmodes. A quadratic index medium is used as a model dielectric waveguide to obtain an expression for the predicted spot size of the dominant system eigenmode, in the approximation that it is a single gaussian mode.

physics.optics↗