Measurements of the longitudinal energy distribution of low energy electrons

The Transverse Energy Spread Spectrometer (TESS) is an ASTeC experiment designed to measure the energy of electrons from different cathode materials. It is a dedicated test stand for future light sources. A full particle tracking code has been developed in the QUASAR Group, which simulates particle trajectories through TESS. Using this code it is possible to simulate different operational conditions of the experiment and cathode materials. The simulation results can then be benchmarked against experimental data to test the validity of the emission and beam transport model. Within this paper, results from simulation studies are presented and compared against experimental data as a collaboration within the Cockcroft Institute between ASTeC and the QUASAR Group for the case of measuring the longitudinal velocity distribution of electrons emitted from a gallium arsenide cathode using a grid structure as an energy filter

Medium energy ion scattering (MEIS) study from the five-fold surface of icosahedral Ag-In-Yb quasicrystal

Medium energy ion scattering (MEIS) is employed to characterize the composition and structure of the five-fold surface of the icosahedral Ag42In42Yb16 quasicrystal. The composition of the surface after sputtering is dominated by Ag and In, and when the surface is annealed at temperatures approaching 430°C, Yb is restored at the surface. The composition is that expected from the bulk structure if the surface is formed at bulk planes involving the centre of rhombic triacontahedral clusters, the building blocks of the system. Structural analysis of MEIS results are also consistent with a surface after annealing that is in close agreement with bulk truncation intersecting the cluster centre

Characterisation of a Cs–Implanted Cu Photocathode

Abstract The generation of high-brightness electron beams is a crucial area of particle accelerator research and development. Photocathodes which offer high levels of quantum efficiency when illuminated at visible wavelengths are attractive as the drive laser technology is greatly simplified. The higher laser power levels available at longer wavelengths create headroom allowing use of manipulation techniques to optimise the longitudinal and transverse beam profiles, and so minimise electron beam emittance. Bi–alkali photocathodes which offer quantum efficiency ∼ 10 % under illumination at 532 nm are an example of this. Another solution is the use of modified photoemissive surfaces. Caesium has a low work function and readily photoemits when illuminated at green wavelengths (∼532nm). Caesium oxide has an even lower work function and emits at red wavelengths (∼635nm). We present data on our work to create a hybrid copper photocathode surface modified by implantation of caesium ions, measuring the surface roughness and probing its structure using MEIS. We measure the energy spread of photoemitted electrons, the QE as a function of illumination wavelength, and the practicality of this surface as a photocathode by assessing its lifetime on exposure to oxygen.</jats:p

Beam characterisation and machine development at VELA

An overview is presented of developments on VELA (Versatile Electron Linear Accelerator), an RF photoinjector with two user stations (beam areas BA1, and BA2) at Daresbury Laboratory. Numerous machine development, commissioning, beam characterisation and user experiments have been completed in the past year. A new beamline and a dedicated multi-purpose chamber have been commissioned in BA1 and the first experiments performed. A number of measures have been taken to improve the stability of machine by mitigating problems with a phase drift, laser beam transport drift and a coherent beam oscillation. The 6D phase space of the electron beam has been characterised through quadrupole scans, transverse tomography and with a transverse deflecting cavity