Generation of ultralow-emittance electron beams with high brightness is critical for several applications such as ultrafast electron diffraction, microscopy, and advanced accelerator techniques. By leveraging the differences in work function and electronic structure between different materials, we enabled spatially localized photoemission, resulting in picometer-scale emittance from a flat photocathode. We also investigated space charge effects by measuring how the emission spot size, as measured in a photoemission electron microscope, changes with the number of electrons emitted per laser pulse. When more than one electron is emitted simultaneously, Coulomb repulsion causes a substantial broadening of the observed source size, enabling us to investigate the limitations imposed by vacuum space charge forces during pulsed photoemission. Our results highlight the potential of nanoscale photoemitters as high-brightness electron sources and offer new insights into electron correlations that emerge after ultrafast photoemission.

Generation of ultralow-emittance electron beams with high brightness is critical for several applications such as ultrafast electron diffraction, microscopy, and advanced accelerator techniques. By leveraging the differences in work function and electronic structure between different materials, we enabled spatially localized photoemission, resulting in picometer-scale emittance from a flat photocathode. We also investigated space charge effects by measuring how the emission spot size, as measured in a photoemission electron microscope, changes with the number of electrons emitted per laser pulse. When more than one electron is emitted simultaneously, Coulomb repulsion causes a substantial broadening of the observed source size, enabling us to investigate the limitations imposed by vacuum space charge forces during pulsed photoemission. Our results highlight the potential of nanoscale photoemitters as high-brightness electron sources and offer new insights into electron correlations that emerge after ultrafast photoemission.

The continuing development of radio-frequency (RF) amplifier technology has paved the way for RF electron accelerators in which each cavity is independently powered, allowing the amplitude and phases to be individually tunable. In this work we study the potential benefits provided by this flexibility in maximizing the capture efficiency in a ≈2 MeV compact accelerator suitable for a wide variety of industrial and medical applications, as well as traditional roles in research and education. Simulations demonstrate capture efficiencies > 90%, far surpassing typical capture efficiencies which are on the 50% scale.

A distributed-drive linac consists of individually powered and phased single- cell cavities. In this paper, we evaluate options for coupling RF power into the linac cavities, and present an initial design for a cavity frequency tuning mechanism.

Recent simulation work has indicated that next generation photoinjectors will be capable of delivering beams with emittances below 100 nm for bunch charges of a few hundred pico-Coulombs. Experimentally validating these results by measuring such emittances is challenging due to the high resolution required. Additionally, in some cases it is desirable for these characterization measurements to be non-destructive, and to have the capability of selecting subsets of the beam. One technique that has been considered is the use of inverse Compton scattering (ICS) spectra to measure the emittance. Here we present simulation results on the use of ICS to measure 50 nm – 500 nm emittances for a 250 pC bunch charge electron beam.

The performance of solid-state amplifiers, across a range of metrics, has improved to the point where it is possible to construct a compact accelerator from individually phased and powered single-cell cavities. This distributed drive linear accelerator (DDL) architecture can provide significant advantages over conventional architectures in terms of power efficiency, redundancy, modularity, flexibility of operation, and fault tolerance. Compact DDL accelerators can fill increasing needs for medical and commercial applications, as well as more traditional roles in research, education and security. We have been studying how to advance this concept at Los Alamos National Laboratory, with a specific focus on a few-MeV, high-average-power concept, and overview our efforts and key results on power requirements, beam transport, and structure design.

We present an optimization of a novel compact accelerator configuration, where each accelerating cell is individually driven by an emerging high-power, solid-state RF amplifier. This architecture, first developed at LANL for space applications, has the potential to produce a high-power electron beam with reduced footprint. Optimizing the size, weight, and cost of construction and operation of such an accelerator, while ensuring redundancy, requires a detailed particle simulation model. In this work, the design of a 2 MeV compact electron linac with 1.5 kW average beam power was optimized using a simulation model of the linac created using the software package General Particle Tracer (GPT). The accelerator consists of a 20 kV DC electron gun, a pre-buncher cavity and five 4-cell modules containing S-band cavities that accelerate the beam to 2 MeV, as well as provide transverse focusing. Additional transverse focusing is provided by solenoids along the beamline to maximize transmission. The cavity phases and the solenoid currents were optimized to maximize transmission through the accelerator. The design of the compact electron linac and its optimization will be presented at the conference.