A Dielectric Disk Accelerator (DDA) is a metallic accelerating structure loaded with dielectric disks to increase its shunt impedance. These structures use short RF pulses of 9 ns to achieve accelerating gradients of more than 100 MV/m. Single cell and multicell clamped structures have been designed and high power tested at the Argonne Wakefield Accelerator. During testing, the single cell clamped DDA structure achieved an accelerating gradient of 102 MV/m with no visible damage in the RF volume region. The minimal damage that was seen outside the RF volume was likely due to RF leakage from uneven clamping during assembly. Based on the success of that experiment, a clamped multicell DDA structure has been designed and tested at high power. Simulation results for this new structure show a 108 MV/m accelerating gradient with 400 MW of input power with high shunt impedance and group velocity. Engineering designs were improved from the single cell structure for a more consistent clamping over the entire structure. Up to this point in the high power experiments, the results show a peak input power of 222 MW correlating to an accelerating gradient of 80 MV/m. Testing of this structure will continue January 2024.

Dielectric-lined waveguides have been extensively studied for high-gradient acceleration in beam-driven dielectric wakefield acceleration (DWFA) and for beam manipulations, including the application of zero transverse force modes in the waveguides. In this paper, we investigate the zero transverse force modes excited by a relativistic electron bunch passing through a dielectric waveguide with a rectangular transverse cross section. Numerical simulations were performed to optimize the start-to-end beamline using Opal-t, ELEGANT, and WARPX. A Longitudinal Phase Space (LPS) measurement system is used to understand the interaction of the beam with the waveguide modes, and analysis of the resolution of the LPS system was conducted. We will discuss preliminary experimental data collected at the Argonne Wakefield Accelerator (AWA) benchmarked with the simulation results.

In the field of structure wakefield acceleration there is considerable interest in radiofrequency (RF) structures capable of producing high gradients. Structures in the sub-terahertz (sub-THz) regime are of note due to their high gradient and high efficiency, allowing for a low physical footprint. In the pursuit of this goal we have designed a metallic corrugated W-band structure using the CST Studio Suite. After optimizing for the maximum achievable gradient from a nominal Argonne Wakefield Accelerator (AWA) electron bunch at 65 MeV with a Gaussian distribution we attempted to achieve a higher transformer ratio using a shaped bunch. Shaped bunches such as these are achievable at the AWA emittance exchange (EEX) beamline. Preliminary results from the structure testing at AWA using shaped electron bunches will be presented. Further tests are planned, involving a comprehensive optimization of the beamline at AWA.

Metamaterial accelerators driven by nanosecond-long RF pulses show promise to mitigate RF breakdown. Recent high-power tests at the Argonne Wakefield Accelerator (AWA) with an X-band metamaterial structure have demonstrated to achieve a gradient of 190 MV/m, while we also observed a new acceleration regime, the breakdown-insensitive acceleration regime (BIAR), where the RF breakdown may not interrupt acceleration of a main beam. Statistical analysis between different breakdown types reveals that the characteristics of the BIAR breakdown are beneficial to high-gradient acceleration at short pulse lengths.

A corrugated waveguide based collinear wakefield accelerator is under development at Argonne National Laboratory. The accelerating mode is operating at 180 GHz with a high average power level up to 600 W compounding at the end of the 0.5 m long accelerator module. It is extracted by a dedicated coupler to prevent excessive heating of the corrugated structure of the next accelerator module downstream. Also, it is necessary to monitor beam offsets from the center of the corrugated structure. It is done by utilizing the offset beam’s induced wakefield dipole mode at 190 GHz and extracting it to diagnostic electronics via the second dedicated coupler. Both are contained in the transition section between the accelerator modules*. This paper presents the mechanical design, fabrication, and performance testing of the transition section. Testing included mmWave measurements at ANL and electron beam measurements at Brookhaven National Lab’s Accelerator Test Facility. Both tests involved characterizations of the wakefield modes and coupler’s performances.

The Accelerator Test Facility (ATF) at Brookhaven National Laboratory is a DOE Office of Science User Facility supported by the DOE Office of Accelerator R&D and Production. It provides its users with 3 major beam capabilities: 75 MeV high brightness electron beams, multi-terawatt long-wave infrared (LWIR) laser beams, and near infrared (NIR) laser beams. These capabilities can be used individually or in any combination by users. Over 20 active experimental efforts in advanced accelerator and laser research are presently underway. Recent progress and future plans for the ATF are described.

Dielectric laser acceleration (DLA) is a promising approach to accelerate single electrons at a high repetition rate to GeV energies, for indirect dark matter searches. Relevant concepts include the integration of the dielectric structure inside the laser oscillator. To efficiently use muons for high energy physics applications, they need to be accelerated rapidly, before they decay. Plasma acceleration achieves GV/m accelerating fields and could be ideal for accelerating to muon-collider energies. Single muons could also be accelerated in DLAs for dark matter searches. They could be injected from existing low-intensity muon sources, such as the one at PSI. A workshop organized in the frame of the EU project “Innovation Fostering in Accelerator Science and Technology” (I.FAST) focused on GHz Rate & Rapid Muon Acceleration for Particle Physics to address these topics. We report highlights and future research directions.

Space charge lenses are ion-optical devices that focus an ion beam by the intrinsic electric field of confined non-neutral plasmas, for example electron clouds. This was first proposed by Dennis Gabor in the year 1947 and is therefore also known as Gabor-lenses. Previous studies have shown the strong linear focusing forces of a confined electron plasma. In this paper, the first confinement of a pure proton plasma in a Gabor-lens will be discussed. The confinement of a positive space charge column provides either a linear de-focusing force for positively charged ion beams or a linear focusing force for negatively charged heavy ion beams. Very first results of proton confinements and their diagnostics will be presented. A special focus lies on the diagnosis of the proton density distribution, as well as the comparison between the behavior of the proton and electron clouds.

The interactions of charged particles with carbon nanotubes (CNTs) may excite electromagnetic modes in the electron gas that makes up the nanotube surface. This novel effect has recently been proposed as an alternative method to achieve ultra-high gradients for particle acceleration. In this contribution, the excitations produced by a localized point-like charge propagating in a single wall nanotube are described by means of the linearized hydrodynamic model. In this model, the electron gas is treated as a plasma with specific solid-state properties. The governing set of differential equations consists of the continuity and momentum equations for the electron fluid, in conjunction with Poisson's equation. Through numerical simulations, we investigate the influence of key factors, including the driving velocity, CNT radius, surface density and the friction (between the electron fluid and the ionic lattice) parameter, on the excited wakefields, comparing the results with Particle-in-Cell (PIC) simulations. A comprehensive discussion is presented to analyze similarities, differences and limitations of both methods. This research provides a valuable perspective on the potential use of CNTs to enhance particle acceleration techniques, paving the way for further advancements in high-energy physics and related fields.

We discuss a compact, laser-plasma-based scheme for the generation of positron beams suitable to be implemented in an all-optical setup. A laser-plasma-accelerated electron beam hits a solid target producing electron-positron pairs via bremsstrahlung. The back of the target serves as a plasma mirror to in-couple a laser pulse into a plasma stage located right after the mirror where the laser drives a plasma wave (or wakefield). By properly choosing the delay between the laser and the electron beam the positrons produced in the target can be trapped in the wakefield, where they are focused and accelerated during the transport, resulting in a collimated beam. This approach minimizes the ballistic propagation time and enhances the trapping efficiency. The system can be used as an injector of positron beams and has potential applications in the development of a future, compact, plasma-based electron-positron linear collider. After injection, positrons can be accelerated to high energies in a plasma (e.g., using a plasma column) for applications to plasma-based colliders.

Dielectric-lined waveguides have been extensively studied for high-gradient acceleration in beam-driven dielectric wakefield acceleration (DWFA) and for beam manipulations, including the application of zero transverse force modes in the waveguides. In this paper, we investigate the zero transverse force modes excited by a relativistic electron bunch passing through a dielectric waveguide with a rectangular transverse cross section. Numerical simulations were performed to optimize the start-to-end beamline using Opal-t, ELEGANT, and WARPX. A Longitudinal Phase Space (LPS) measurement system is used to understand the interaction of the beam with the waveguide modes, and analysis of the resolution of the LPS system was conducted. We will discuss preliminary experimental data collected at the Argonne Wakefield Accelerator (AWA) benchmarked with the simulation results.

In collinear wakefield acceleration, two figures of merits, gradient and transformer ratio, play pivotal roles. A high-gradient acceleration requires a high-charge beam. However, shaping current profile of such high-charge beam is challenging, due to the degradation by CSR. Recently proposed method, utilizing transverse deflecting cavities (TDC) for shaping, has shown promising simulation results for accurate shaping of high-charge beams. This is attributed to its dispersion-less feature. We plan to experimentally demonstrate high-gradient (>100 MV/m) and high-transformer ratio (>5) collinear structure wakefield acceleration. The experiment is planned at Argonne Wakefield Accelerator Facility. We present results from start-to-end simulations for the experiment.

Previously we had developed a new method to fabricate corrugated waveguides (CW) operating in sub-THz frequency regime. As the next step, collaborative effort is underway to demonstrate GW-level high-power sub-THz pulse generation using a CW. We plan to fabricate a CW operating at around 400 GHz. This waveguide will be driven by a bunch train including 16 bunches with nanocoulomb-level charges per bunch. We present an overview of project’s current status.

In the field of structure wakefield acceleration there is considerable interest in radiofrequency (RF) structures capable of producing high gradients. Structures in the sub-terahertz (sub-THz) regime are of note due to their high gradient and high efficiency, allowing for a low physical footprint. In the pursuit of this goal we have designed a metallic corrugated W-band structure using the CST Studio Suite. After optimizing for the maximum achievable gradient from a nominal Argonne Wakefield Accelerator (AWA) electron bunch at 65 MeV with a Gaussian distribution we attempted to achieve a higher transformer ratio using a shaped bunch. Shaped bunches such as these are achievable at the AWA emittance exchange (EEX) beamline. Preliminary results from the structure testing at AWA using shaped electron bunches will be presented. Further tests are planned, involving a comprehensive optimization of the beamline at AWA.

Metamaterial accelerators driven by nanosecond-long RF pulses show promise to mitigate RF breakdown. Recent high-power tests at the Argonne Wakefield Accelerator (AWA) with an X-band metamaterial structure have demonstrated to achieve a gradient of 190 MV/m, while we also observed a new acceleration regime, the breakdown-insensitive acceleration regime (BIAR), where the RF breakdown may not interrupt acceleration of a main beam. Statistical analysis between different breakdown types reveals that the characteristics of the BIAR breakdown are beneficial to high-gradient acceleration at short pulse lengths.

Ultrafast Electron Diffraction (UED) is a pioneering method for real-time observation of atomic-level structures. Recent advancements leverage relativistic electrons from radiofrequency (RF) guns to overcome space charge limitations, enhancing resolution. While perspectives may differ, an ongoing debate surrounds the optimal energy for a UED instrument. Our study contributes to this discussion by employing an 8.2 MeV electron beam and a compact post-sample magnetic optical system with small-gap Halbach permanent magnet quadrupoles. This system allows tunable magnification and improved reciprocal space resolution in a compact footprint, as demonstrated in simulations and experiments with a single crystal Au sample.

We have fabricated corrugated structures for sub-THz regime by stacking disks. By sending electron beams into the structure, the wakefield of 200 GHz was successfully measured. The frequency and power levels of wakefield were very similar to our design. For the our next target of gigawatts power, we have newly designed a structure of 400 GHz. More precise fabrication is required compared to the 200 GHz structure. The die stamping method was changed to the LIGA process for the production of each disk. And we improved the assembly method as well. In the previous fabrication, the maximum error was around 10 micrometers. The errors may be reduced to one-tenth of the previous one. In this paper, we will introduce the new design.

C-band accelerators have been of particular interest in recent years due to their ability to provide high gradients and transport high charge beams for applications such as colliders and medical technologies. New Advancements in high gradient technologies that can suppress the breakdown rate in a particular structure by using distributed coupling, cryogenic cooling, and copper alloys. Previous work has shown each of these separately to significantly improve the maximum gradient. In this work, for the first time, we will combine all three methods in an ultra-high gradient structure and benchmark the difference between Cu and CuAg. The exact same structures were previously tested at room temperature and showed gradients in excess of 200 MeV/m and a 20% improvement in the CuAg version over its pure Cu counterpart [1]. These structures are now tested at 77K simultaneously. They were found to perform similarly due to the presence of significant beam loading. Taking beam loading into account, a maximum achievable gradient of 200 MeV/m achieved for a 1 µs pulse at an input power of 5 MW into each cavity with a breakdown rate of 1e-1 breakdown/pulse/m.

The newly commissioned CYBORG (CrYogenic Brightness Optimized Radiofrequency Gun) beamline at UCLA operates in a high gradient, low temperature regime inaccessible to most other existing photoguns and cathode testing infrastructure. The beamline is designed to study electron emission in regime. The final intended configuration of the beamline will be used for studies of novel photocathodes including low mean transverse energy (MTE), high quantum efficiency (QE) semiconductor cathodes dependent on future laser improvement. In the near term, the unique environment allows us to study temperature dependent effects on dark current. Notable reduction in dark current at cryogenic temperatures was observed, a behavior not predicted by Fowler-Nordheim type field emission. Initial results are presented.

High field radio frequency (RF) accelerating structures are an essential component of modern linear accelerators (linacs) with applications in photon production and ultrafast electron diffraction. Most advanced designs favor compact, high shunt impedance structures in order to minimize the size and cost of the machines as well as the power consumption. However, breakdown phenomena constitute an intrinsic limitation to high field operation which ultimately affects the performance of a given structure requiring dedicated tests. The introduction of a recent design based on cryogenic distributed coupling structures working at C-band (~6 GHz) allows to increase the shunt impedance by use of alternative distribution schemes for the RF power while mitigating the breakdowns thanks to the low temperature. In this paper we introduce the plan for high field and breakdown tests envisioned for a simple two-cell version of the aforementioned structure. Moreover, we discuss the joining procedure utilized to unify the two fabricated halves of such a structure and relying on the diffusion bonding technique which constitutes an attractive alternative to the brazing approach.

A Dielectric Disk Accelerator (DDA) is a metallic accelerating structure loaded with dielectric disks to increase its shunt impedance. These structures use short RF pulses of 9 ns to achieve accelerating gradients of more than 100 MV/m. Single cell and multicell clamped structures have been designed and high power tested at the Argonne Wakefield Accelerator. During testing, the single cell clamped DDA structure achieved an accelerating gradient of 102 MV/m with no visible damage in the RF volume region. The minimal damage that was seen outside the RF volume was likely due to RF leakage from uneven clamping during assembly. Based on the success of that experiment, a clamped multicell DDA structure has been designed and tested at high power. Simulation results for this new structure show a 108 MV/m accelerating gradient with 400 MW of input power with high shunt impedance and group velocity. Engineering designs were improved from the single cell structure for a more consistent clamping over the entire structure. Up to this point in the high power experiments, the results show a peak input power of 222 MW correlating to an accelerating gradient of 80 MV/m. Testing of this structure will continue January 2024.