Novel Radio-Frequency Gun Structures for Ultrafast Relativistic Electron Diffraction

Abstract

Radio-frequency (RF) photoinjector-based relativistic ultrafast electron diffraction (UED) is a promising new technique that has the potential to probe structural changes at the atomic scale with sub-100 fs temporal resolution in a single shot. We analyze the limitations on the temporal and spatial resolution of this technique considering the operating parameters of a standard 1.6 cell RF gun (which is the RF photoinjector used for the first experimental tests of relativistic UED at Stanford Linear Accelerator Center; University of California, Los Angeles; Brookhaven National Laboratory), and study the possibility of employing novel RF structures to circumvent some of these limits.

High quality single shot diffraction patterns using ultrashort megaelectron volt electron beams from a radio frequency photoinjector

“…18,19 These results increase the range of applicability of the UED technique to irreversible phase transformations, thick samples, or gas phase ultrafast processes which are out of reach or at the very edge of the capabilities of current UED sources. Possible pathways to further improve the temporal resolution to the sub-100 fs level include increasing the gun gradient, shortening the cathode-sample distance or recompression of the electron bunch.…”

Design and applications of an X-band hybrid photoinjector

“…The performance of the beam in this case has been studied in detail in previous analyses. Simulations concerning the performance of the low energy section alone concentrated on the possibility of using a low-charge, velocity bunched beam to extend the time resolution of ultra-relativistic electron diffraction (UED) [13]. They have also indicated that a beam of 1 nC can be strongly compressed, to less than 100 mm rms pulse length [14], while boosting the energy to 22 MeV with post-acceleration linacs.…”

“…The application of a highly compressed beam to ultra-fast electron diffraction (UED) has been examined in the context of the S-band hybrid previously [13]. While the UCLA program has shown excellent progress in UED, including the first demonstration of a time-resolved UED-based measurement [27], in order to obtain the 10 7 -10 8 electrons needed for a useful diffraction pattern, the beam is limited by longitudinal space-charge effects to 100 fs pulse lengths [28].…”

Generation and measurement of velocity bunched ultrashort bunch of pC charge

“…Wang et al discussed using the fields in the rf gun itself to compress the beam by launching the particle at a low injection phase [12]. Fukasawa et al developed a novel rf structure, the hybrid gun [13,14], where the beam passes through a traveling wave section at a compressing phase. The issue in these cases is that in order for the compression to effectively work the beam has to be relatively long in the region where the rf fields impart the energy chirp.…”