arXiv subjects

William S. Graves

Publications and source records attributed to William S. Graves.

3 recordsLinked to original sources

arXiv2025

Characterization of Spatiotemporal Overlap of Femtosecond Lasers and Electron Beam With Ce:YAG Screens

Interactions between short laser pulses and electron bunches determine a wide range of accelerator applications. Finding spatiotemporal overlap between few-micron-sized optical and electron beams is critical, yet there are few routine diagnostics for this purpose. We present a method for achieving spatiotemporal overlap between a picosecond laser pulse and a relativistic sub-ps electron bunch. The method uses the transient change in optical transmission of a Ce:YAG screen upon irradiation with a short electron bunch to co-time the electron and laser beams. We demonstrate and quantify the performance of this method using an inverse Compton source comprised of a 30 MeV electron beam from an X-band linac focused to a 10 $μ$m spot, overlapped with a joule-class picosecond Yb:YAG laser system. This method is applicable to electron beams with few-microjoule bunch energies, and uses standard scintillator screens common in electron accelerators.

physics.acc-ph↗

arXiv2017

Nano-modulated electron beams via electron diffraction and emittance exchange for coherent x-ray generation

We present a new method for generation of relativistic electron beams with current modulation on the nanometer scale and below. The current modulation is produced by diffracting relativistic electrons in single crystal Si, accelerating the diffracted beam and imaging the crystal structure, then transferring the image into the temporal dimension via emittance exchange. The modulation period can be tuned by adjusting electron optics after diffraction. This tunable longitudinal modulation can have a period as short as a few angstroms, enabling production of coherent hard x-rays from a source based on inverse Compton scattering with total accelerator length of approximately ten meters. Electron beam simulations from cathode emission through diffraction, acceleration and image formation with variable magnification are presented along with estimates of the coherent x-ray output properties.

physics.acc-ph↗

arXiv2015

Aberration Corrected Emittance Exchange

Full exploitation of emittance exchange (EEX) requires aberration-free performance of a complex imaging system including active radio-frequency (RF) elements which can add temporal distortions. We investigate the performance of an EEX line where the exchange occurs between two dimensions with normalized emittances which differ by multiple orders of magnitude. The transverse emittance is exchanged into the longitudinal dimension using a double dog-leg emittance exchange setup with a five cell RF deflector cavity. Aberration correction is performed on the four most dominant aberrations. These include temporal aberrations that are corrected with higher order magnetic optical elements located where longitudinal and transverse emittance are coupled. We demonstrate aberration-free performance of an EEX line with emittances differing by four orders of magnitude, \textit{i.e.} an initial transverse emittance of 1~pm-rad is exchanged with a longitudinal emittance of 10~nm-rad.

physics.acc-ph↗