The acceleration of electrons with the help of laser light inside a photonic nanostructure represents a microscopic alternative to microwave-driven accelerators. The main advantage is that the much higher driving facilitates damage thresholds of dielectric materials reaching 10 GV/m. This means that acceleration gradients far in excess of 1 GeV/m should be attainable. Furthermore, the structure size of the optical accelerators lies in the nanometer range, meaning that nanofabrication methods can be employed to build the accelerator structures. In pursuit of these goals, we demonstrated a scalable nanophotonic linear electron accelerator that coherently combines particle acceleration and transverse beam confinement utilizing an alternating phase focusing (APF) scheme. It accelerates and guides electrons over a considerable distance of 500 μm in a channel just 225 nm wide. The highest energy gain observed was 43%, from 28.4 keV to 40.7 keV. We expect this work to pave the way for nanophotonic accelerators. These on-chip particle accelerators might enable transformative applications in medicine, industry, materials research and science. In this talk, we will give a status update of nanophotonics accelerators.

A Dielectric Disk Accelerator (DDA) is a metallic accelerating structure loaded with dielectric disks to increase coupling between cells, thus high group velocity, while still maintaining a high shunt impedance. This is crucial for achieving high efficiency high gradient acceleration in the short rf pulse acceleration regime. Research of these structures has produced traveling wave structures that are powered by very short (~9 ns), very high power (400 MW) RF pulses using two beam acceleration to produce these pulses. In testing, these structures have withstood more than 320 MW of power and produced accelerating gradients of over 100 MV/m. The next step of testing these structures will use a more conventional, klystron power source. A new standing wave DDA structure is being fabricated for testing on the Nextef2 test stand at KEK. Simulation results of this structure show that at 50 MW of input power, the DDA produces a 457 MV/m gradient. It also has a large shunt impedance of 160 MΩ/m and an r/Q of 21.6 kΩ/m. Cold testing of this structure will be conducted July 2024 with high power testing to be done in August.

A Dielectric Disk Accelerator (DDA) is a metallic accelerating structure loaded with dielectric disks to increase coupling between cells, thus high group velocity, while still maintaining a high shunt impedance. This is crucial for achieving high efficiency high gradient acceleration in the short rf pulse acceleration regime. Research of these structures has produced traveling wave structures that are powered by very short (~9 ns), very high power (400 MW) RF pulses using two beam acceleration to produce these pulses. In testing, these structures have withstood more than 320 MW of power and produced accelerating gradients of over 100 MV/m. The next step of testing these structures will use a more conventional, klystron power source. A new standing wave DDA structure is being fabricated for testing on the Nextef2 test stand at KEK. Simulation results of this structure show that at 50 MW of input power, the DDA produces a 457 MV/m gradient. It also has a large shunt impedance of 160 MΩ/m and an r/Q of 21.6 kΩ/m. Cold testing of this structure will be conducted July 2024 with high power testing to be done in August.

Corrugated waveguide based colinear wakefield accelerator development at Argonne National Laboratory has been ongoing, achieving significant progress in fabrication and testing of most principal components of the accelerator module. A few 30 cm long corrugated waveguides with a 2 mm ID and short transition sections which provide fundamental mode power extraction and beam offset diagnostics via the wakefield induced dipole mode have been fabricated. Several high field gradient quadrupoles envisioned for beam guidance and suppression of a beam breakup instability have been fabricated as well. The structures have been tested at mmWave frequencies and the quadrupoles were characterized via magnetic measurements. Electron beam testing was conducted at Brookhaven National Lab’s Accelerator Test Facility. The fundamental and dipole mode’s frequency and signal levels were measured and a good agreement with design parameters has been demonstrated.

Muons, Inc is developing Compact Electron Linacs to meet the increasing demand for modern solutions to address diverse applications including Co60 replacement, isotope production, industrial uses, and sterilization of medical devices, food and water. The designs employ the Muons, Inc. – Richardson Electronics Limited 1497 MHz magnetrons that were designed, built, and being tested to replace the klystrons at the Jefferson Lab CEBAF superconducting RF recirculating Linac. The key features of the new designs are a single Linac that is powered by a high efficiency magnetron and permanent magnet systems that recirculate the beam through the Linac to enable compactness and efficiency. Future directions include integrating Nb3Sn-based superconducting cavities with cryocoolers for higher beam energies and scalability. We believe that these Compact Electron Linacs offer a cost-effective, versatile solution to revolutionize electron beam applications across industries.

Distributed coupling linear accelerators (DCLs) represent a revolutionary approach to accelerator design, offering significant advantages over traditional standing-wave and traveling-wave linacs. DCLs achieve record-breaking efficiency and gradient while remaining highly reliable, even under extreme operating conditions. These advancements make them ideal for a wide range of applications, including: Novel FELs, C3 collider concepts, medical radiotherapy, and Inspection and imaging technologies. This presentation delves into the theoretical underpinnings of DCLs and their latest development. We will explore how the technology has evolved from its initial pi-mode configuration to the even more efficient 3 pi/4-mode structure.

Observation of ultrafast structural dynamics is very important for elucidating functions and creating new materials. We have been promoting research and development of ultrafast electron microscopes by generating relativistic femtosecond electron beam pulses using radio frequency (RF) accelerator technology. So far, we have fabricated the world's first ultrafast electron microscope using a normal-conducting S-band RF electron gun and demonstrated its feasibility in demonstration experiments. However, the normal-conducting RF electron gun uses high-power RF pulses, which causes limitations of low beam repetition rate and pulse-by-pulse energy stability. In this study, we have devised an L-band Nb3Sn superconducting RF electron gun that breaks through these limitations and are aiming to develop an ultrafast electron microscope using this gun. We will report the design of the Nb3Sn superconducting RF electron gun, beam simulation results, and conceptual design of an ultrafast electron microscope using the gun.

We recently demonstrated generation of very high charge (1+ nC), very high energy (10 GeV) electron bunches from a nanoparticle-assisted laser wakefield accelerator [1]. While the experiment did yield record breaking results, the statistics were quite poor due to the very slow repetition rate of the Texas Petawatt Laser system. We are currently on a campaign to repeat and improve upon these results. Here we will report on our improved understanding of the nanoparticle-assist effect as well as the planned experimental program we have laid out. [1] C. Aniculaesei et al. “The Acceleration of a High-Charge Electron Bunch to 10 GeV in a 10-cm Nanoparticle-Assisted Wakefield Accelerator”, Matter Radiat. Extremes 9, 014001 (2024) https://doi.org/10.1063/5.0161687

We have designed a tapered dielectric-lined waveguide for the acceleration of sub-relativistic electron bunches with THz-frequency electromagnetic pulses. We consider an example design based on a commercial 100keV electron gun and a THz generation scheme driven by a mJ-level regenerative amplifier laser system. With a 12μJ THz pulse we simulated acceleration of a 100keV electron bunch to 162keV with very low energy spread. A second example design shows energy doubling from 100keV to 205keV using a 22.5μJ pulse. The former of these two designs has been assembled for experimental testing. We also discuss methods to improve the efficiency of the design process using 1D particle tracking to provide better estimates of the initial geometry before optimization.

We have designed a tapered dielectric-lined waveguide for the acceleration of sub-relativistic electron bunches with THz-frequency electromagnetic pulses. We consider an example design based on a commercial 100keV electron gun and a THz generation scheme driven by a mJ-level regenerative amplifier laser system. With a 12μJ THz pulse we simulated acceleration of a 100keV electron bunch to 162keV with very low energy spread. A second example design shows energy doubling from 100keV to 205keV using a 22.5μJ pulse. The former of these two designs has been assembled for experimental testing. We also discuss methods to improve the efficiency of the design process using 1D particle tracking to provide better estimates of the initial geometry before optimization.