John Power (Argonne National Laboratory)
SUP009
Advanced growth and characterization of alkali antimonide photocathodes for bright beam applications
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The properties of the photoemitting electron sources are the most determining factors contributing to the performance of the most advanced electron accelerator applications such as particle colliders, X-ray free electron lasers, ultra-fast electron diffraction and microscopy experiments. Therefore, low mean transverse energy (MTE), high quantum efficiency (QE) along with long operational lifetime and robustness under high electric fields and laser fluences must be demonstrated by the photocathode for these bright beam applications. Recent investigations have revealed that the epitaxial growth of single crystal cesium antimonides can be achieved by photocathode growth on lattice matched substrates. In this letter, the experimental setup for highly promising alkali antimonide photocathode growth by molecular beam epitaxy on lattice matched substrates and in-situ characterization with reflection high-energy electron diffraction (RHEED) has been presented. To adapt the L-band RF gun of Argonne Cathode Test-stand (ACT) for extensive testing of alkali antimonides in real accelerator conditions, compatible cathode plug design and smooth transportation process have been developed and also described in this paper.
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-THP004
About: Received: 09 Aug 2025 — Revised: 15 Aug 2025 — Accepted: 15 Aug 2025 — Issue date: 28 Jan 2026
SUP011
Effects of beam conditions on achieving compact longitudinal de-chirping using transverse deflecting cavities
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It has been shown that a transverse deflecting cavity (TDC)-based de-chirper can be made by altering the drift sections in a TDC-based chirper to form negative drifts. While five appropriately configured quadrupole magnets can implement such negative drifts, this approach is limited by spatial and experimental constraints. In this study, we investigate an alternative configuration that uses three quadrupole magnets to form a negative identity transport section between the TDCs instead of a negative drift. To assess the robustness of this proposed design, a computational study has been conducted on initial beam conditions to determine the operational limitations. This includes the effects of space charge and initial transverse beam conditions, such as beam size and divergence, on the resulting transverse emittance.
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WECN02
About: Received: 11 Aug 2025 — Revised: 13 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
SUP019
A W-band corrugated waveguide for high-efficiency high-gradient wakefield acceleration
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Compact RF structures in the sub-terahertz regime are promising for structure wakefield acceleration due to their ability in achieving high gradients in a reduced footprint. We report on the design, fabrication, and testing of a metallic corrugated waveguide operating at 110 GHz, tailored to the 42 MeV electron beam parameters at the Argonne Wakefield Accelerator (AWA). The experiment utilized the emittance exchange (EEX) beamline at AWA for longitudinal bunch shaping in two configurations: (1) a single short drive bunch to study high decelerating gradients, and (2) a two-bunch scheme featuring a triangularly shaped drive bunch followed by a long witness bunch to probe the wakefield and achieve a high transformer ratio. We will present the experimental design and results, which show good agreement with simulation predictions.
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP008
About: Received: 07 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 13 Aug 2025 — Issue date: 28 Jan 2026
SUP025
Investigation of wakefields in dielectric structures with different cross sections
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Dielectric-lined waveguides are a promising platform for high-gradient beam-driven dielectric wakefield acceleration (DWFA). We present experimental results from a recent study at the Argonne Wakefield Accelerator (AWA), focusing on the performance of three copper-coated dielectric structures with distinct cross-sections: circular, rectangular, and square. These geometries enable a comparative evaluation of the accelerating gradients and wakefield characteristics supported by each configuration. A key feature of this experiment is the use of a "loading bunch" to suppress the wakefield, demonstrating active control of energy transfer along the beam path. To directly measure wakefield suppression, a circular structure with an angled downstream cut was used to redirect coherent Cherenkov radiation into an autocorrelator for temporal diagnostics. Accelerating gradients were measured using a single-shot longitudinal phase space diagnostic, providing insight into geometry-dependent wakefield behavior. These results support future structure optimization efforts and advance experimental techniques for wakefield control in dielectric-based acceleration.
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP049
About: Received: 15 Aug 2025 — Revised: 18 Aug 2025 — Accepted: 19 Aug 2025 — Issue date: 28 Jan 2026
SUP031
RF breakdown and dark current studies in short-pulse acceleration
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Recent experimental studies at the Argonne Wakefield Accelerator (AWA) have shown that operating RF cavities with short pulses, only a few nanoseconds in duration, can raise the accelerating gradient to nearly 400 MV/m in a series of X-band structure tests. These results motivate further investigation into the breakdown physics underlying the short-pulse acceleration regime. In this work, we present analytical models and numerical simulations of dark current dynamics in X-band cavities driven by short RF pulses. These studies explore key phenomena associated with RF breakdown across various time scales, including field emission, secondary electron emission, and plasma formation, with particular focus on their dependence on RF pulse length. Building on these insights, we describe the design and experimental plan for a single-cell X-band RF cavity operating at 11.7 GHz, optimized for high-gradient operation with 6~ns long RF pulses and integrated with RF breakdown diagnostics. This work aims to deepen the understanding of RF breakdown physics in the short-pulse regime and support the development of compact linear accelerators for future applications.
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP079
About: Received: 08 Aug 2025 — Revised: 10 Aug 2025 — Accepted: 12 Aug 2025 — Issue date: 28 Jan 2026
THz detection and investigation of vacuum-compatible optical components
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Detecting terahertz (THz) radiation in ultra-high vacuum (UHV) environments presents notable challenges due to the limited availability of commercially compatible components. In preparation for upcoming THz measurements at the Argonne Wakefield Accelerator (AWA) facility, we investigated two critical aspects: (1) the THz transmission characteristics of fused silica windows, and (2) the suitability of commercial off-axis parabolic mirrors (OAPs) for use in UHV conditions. While fused silica is widely used in optical systems, its performance in the THz regime is rarely documented. We present transmission measurements and assess its viability for THz diagnostics. Additionally, we address the incompatibility of anodized, off-the-shelf OAPs with UHV by developing and testing both mechanical and chemical de-anodization techniques. These methods aim to maintain surface integrity and optical quality. This work provides practical guidelines and compatibility benchmarks for implementing THz diagnostics in UHV environments and serves as a reference for future experiments at AWA and other accelerator facilities.
Bayesian calibration of the AWA photocathode gun using YAG screen diagnostics and OPAL simulations
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We present a data-driven characterisation of the photocathode gun at the Argonne Wakefield Accelerator (AWA) using Bayesian inference, combined with OPAL beam dynamics simulations. Our methodology employs readily available YAG screen diagnostics to perform calibration across a range of experimental conditions, including varying cathode voltages, laser profiles, and beam currents. By integrating these diagnostics with forward beam dynamics simulations from OPAL, we estimate key gun parameters, such as the gun voltage and phase from beam current and solenoid currents. Ongoing work will further refine the calibration process and explore the integration of other diagnostics to enhance the inference process. This allows for more efficient and flexible calibration of complex accelerator systems, particularly with limited readily available measurements
Bright bunch generation in a short pulse high gradient RF gun operating in the transient regime
Normal-conducting accelerating structures capable of supporting GV/m-scale electric fields offer a promising pathway to compact accelerators. Similarly, achieving such high fields in photocathode guns is critical for the generation of bright electron bunches. Our group has demonstrated the generation of ~0.4 GV/m electric fields on a photocathode surface in an X-band (11.7 GHz) photoemission gun (Xgun) powered by short RF pulses (~9 ns). In this work, we investigate the RF characteristics and beam dynamics evolution in the transient field regime. Accurately accounting for the transient nature of the RF field is essential for optimizing the beam dynamics and ensuring the production of high-quality electron bunches.
Bayesian calibration of the AWA photocathode gun using YAG screen diagnostics and OPAL simulations
We present a data-driven characterisation of the photocathode gun at the Argonne Wakefield Accelerator (AWA) using Bayesian inference, combined with OPAL beam dynamics simulations. Our methodology employs readily available YAG screen diagnostics to perform calibration across a range of experimental conditions, including varying cathode voltages, laser profiles, and beam currents. By integrating these diagnostics with forward beam dynamics simulations from OPAL, we estimate key gun parameters, such as the gun voltage and phase from beam current and solenoid currents. Ongoing work will further refine the calibration process and explore the integration of other diagnostics to enhance the inference process. This allows for more efficient and flexible calibration of complex accelerator systems, particularly with limited readily available measurements
Development of diamond-based halo monitor diagnostics for an electron accelerator
High-resolution diagnostic instruments for measuring particle beam profile and charge are essential for characterizing the improved performance of charged particle accelerators. Beam diagnostics based on synthetic single crystal diamond (SCD) exhibit superior radiation-hardness, chemical stability, fast saturated drift speed, and unparalleled thermal conductivity. At Los Alamos National Laboratory (LANL), the SCD sensor and the high-speed signal acquisition system have been developed for measuring intensity of individual bunches. At the Argonne Wakefield Accelerator, a 63 MeV electron beam with diameter of 5 mm and charge below 10 pC used to measure the beam halo at a radial distance of 12 mm from the beam center. This presentation will report on the detailed SCD design and electronics, halo monitoring at various charges, bunches, and distances, and plans for future testing at LANL.
Field mapping and alignment procedure for new photoinjector solenoid magnets at the Argonne Wakefield Accelerator
The Argonne Wakefield Accelerator test facility will be upgrading the RF photoinjector with a new symmetrized RF photogun (named G4) in order to increase beam brightness and stability. In conjunction with G4, three new solenoid coils have been commissioned to replace the previous solenoids, with new considerations to preserve field symmetry and combat higher order modes within the coil that could reduce beam quality. We report here on the recent field mapping efforts on the solenoid, as well as discuss how these measurements can be used to aid alignment of the coils during the installation of the new G4 RF photogun.
MOP048
Implementation of a 1550-nm laser system for beam characterization at the Argonne Wakefield Accelerator
153
Accurately recording an electron bunch’s longitudinal profile is an important diagnostic for wakefield accelerators employing shaped bunches to increase transformer ratios. Electro-optic sampling of terahertz radiation from the bunch is an attractive approach due to its non-destructive nature. In preparation for future characterization experiments, the Argonne Wakefield Accelerator test facility has recently installed a 1550 nm laser system, including the necessary support systems to synchronize with the photoinjector laser system at 81.25 MHz. We report here on the initial installation and synchronization demonstrations.
Paper: MOP048
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-MOP048
About: Received: 08 Aug 2025 — Revised: 13 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
MOP055
Low-charge, high-resolution beamline preparation for the nanopatterned microbunching experiment at Argonne Wakefield Accelerator
173
The emittance exchange (EEX) beamline at the Argonne Wakefield Accelerator (AWA) is designed to transfer properties of an electron beam phase space between the transverse and longitudinal planes. Recently, it has been proposed this beamline could be used to convert a microscale transverse modulation created by a TEM grid into a microbunch train in the longitudinal plane. Such a technique would be useful for obtaining nano-scale microbunching that does not rely on the sensitive process of FEL gain. This new approach has been proposed to enable development of a compact free-electron laser at Arizona State, greatly reducing size and cost compared with existing short wavelength FELs. To perform an exploratory demonstration of this concept at AWA, this experiment requires low normalized emittance (~50 nm·rad), low charge (~1pC) electron bunches, and transverse diagnostics with high-resolution (1-3 microns) and high-light-collection to resolve the modulation on the electron beam. This report will give a progress update on preparing the necessary beams and diagnostics at AWA for an emittance exchange experiment that would produce 100s of nm scale microbunches.
Paper: MOP055
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-MOP055
About: Received: 08 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
Progress report on the upcoming drive beam photoinjector upgrades at the Argonne Wakefield Accelerator
The Argonne Wakefield Accelerator test facility is dedicated to research on advanced acceleration, beam manipulation, and beam production. With a focus primarily in the development and testing of high-gradient wakefield-accelerator structures, the drive beamline RF photoinjector is capable of delivering high charge (100s of nC) 65 MeV electron bunch trains. We present the planned upgrades to the drive photoinjector aimed at increasing both beam brightness and stability, and report on the current progress for the first phase of the upgrade and upcoming RF gun installation.
Rotor-based multileaf collimator for beam shaping
Multileaf collimators (MLC) are versatile tools for beam shaping, both transversely or, when used in conjunction with an emittance exchange (EEX) beamline, longitudinally. The requirement for ultra-high vacuum compatibility introduces significant constraints on the design of a MLC. Here, we present a novel design for a MLC based on stacks of rotors with angularly dependent radii. The use of tabs and slots allow dozens of these rotors to be positioned using a single vacuum feedthrough, dramatically reducing complexity over independently positioned leaves. We discuss other design elements and also the considerations arising from having a volumetric rather than planar beam mask.
TUBN01
Flat beam PWFA theory and experiment at AWA
314
A wakefield experiment at the Argonne Wakefield Accelerator (AWA) facility utilizes flat electron beams with highly asymmetric transverse emittances to drive plasma wakefields in the underdense regime. These beams create elliptical blowout structures, producing asymmetric transverse focusing forces. The experiment utilizes a compact 4-cm-long capillary discharge plasma source developed at UCLA. Analytic models of blowout ellipticity and matching conditions, supported by particle-in-cell simulations, guide the experiment's design. Engineering preparations including the use of windows for vacuum-gas separation, beam transport and diagnostics are discussed along with the first beam runs which involve flat beam generation and transport. The theory of flat beam plasma wakefield interaction will also be discussed
Paper: TUBN01
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-TUBN01
About: Received: 09 Aug 2025 — Revised: 13 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
TUP021
BeamNetUS pilot year report: Enabling access to beam test facilities
394
BeamNetUS is a network of facilities united in a common mission to advance accelerator research and applications of accelerator technology through improving awareness and access to these unique facilities. For its pilot campaign, the network includes facilities at Argonne National Laboratory, Brookhaven National Laboratory, Fermi National Accelerator Laboratory, Lawrence Berkeley National Laboratory, SLAC National Accelerator Laboratory, and Thomas Jefferson National Accelerator Facility. These facilities provide complementary capabilities enabling research in plasma physics, beam physics, material science, radiofrequency sources and structures, nuclear physics and electron beam irradiation. In 2025, BeamNetUS awarded time at the facilities through a competitive review process with a remit towards creating new, productive engagements. User awards were given to universities, industry and other laboratories. At NAPAC25 in a satellite meeting, we reflect on the BeamNetUS experience in its pilot year and plans for the future.
Paper: TUP021
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-TUP021
About: Received: 08 Aug 2025 — Revised: 13 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
TUP048
Generation of low-emittance bunches with selective collimation at the Argonne Wakefield Accelerator
461
The Argonne Wakefield Accelerator (AWA) facility’s drive-beam linear accelerator can generate electron bunches at a wide range of charge - from 100 pC to 100 nC. This gives us a unique opportunity to study selective transverse collimation as a method to increase beam brightness using various initial bunch charges. This paper presents numerical modeling of the scheme. Simulations were performed to explore the impact of a collimating aperture on emittance, scraping the outermost electrons and retaining only the inner core of the beam with the goal of maximizing the beam brightness for a 100-pC electron beam. An optimization of various beamline parameters, including the initial bunch charge, was done to produce possible operating points that generate the lowest emittance. These simulations inform an experimental campaign that is also discussed in this work.
Paper: TUP048
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-TUP048
About: Received: 13 Aug 2025 — Revised: 13 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
TUP067
Mitigation of coherent synchrotron radiation by bunch profile optimization and shielding
518
The mitigation of the effects of coherent synchrotron radiation (CSR) is a key challenge in generating high brightness beams. Shielding by parallel plates installed in the dipole magnet vacuum chambers shows promise, both in simulation and experiment at small shielding gap separations. In this work, we consider a beam traversing a chicane with larger cm-scale separations on each dipole, necessitating the combined use of longitudinal profile shaping and shielding to reduce emittance growth. We model the radiated CSR using a 3D integrated Green's function technique that accounts for the complete 6D phase space of the bunch along with image charges to model shielding. This method is used in conjunction with a genetic algorithm to optimize the longitudinal current profile. Our results indicate current profiles that differ to results derived without shielding and allow for effective mitigation of emittance growth at cm-scale gaps. We will present details of the simulation and optimization method along with future plans, including ongoing experiments at the Argonne Wakefield Accelerator as part of a collaboration that seeks to investigate the effects of CSR on beams.
Paper: TUP067
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-TUP067
About: Received: 08 Aug 2025 — Revised: 13 Aug 2025 — Accepted: 13 Aug 2025 — Issue date: 28 Jan 2026
Preliminary experimental analysis of CSR shielding effects in a chicane compressor
We present preliminary analysis results from a recent experiment investigating CSR shielding effects on a beam propagating through a chicane compressor. The experiment was conducted at the Argonne Wakefield Accelerator (AWA) facility. Two identical doglegs with reversing quadrupoles—flip the beam—allow the beamline to function as a chicane. Shielding gaps of 1, 2 , and 3 cm were tested using manually adjustable plates inside the dipole magnet chambers. The longitudinal phase space was measured both upstream and downstream of the chicane. To compare CSR-dominated propagation with ignorable CSR case, a wide slit was also applied to cut the beam charge.
WECN02
Effects of beam conditions on achieving compact longitudinal de-chirping using transverse deflecting cavities
683
It has been shown that a transverse deflecting cavity (TDC)-based de-chirper can be made by altering the drift sections in a TDC-based chirper to form negative drifts. While five appropriately configured quadrupole magnets can implement such negative drifts, this approach is limited by spatial and experimental constraints. In this study, we investigate an alternative configuration that uses three quadrupole magnets to form a negative identity transport section between the TDCs instead of a negative drift. To assess the robustness of this proposed design, a computational study has been conducted on initial beam conditions to determine the operational limitations. This includes the effects of space charge and initial transverse beam conditions, such as beam size and divergence, on the resulting transverse emittance.
Paper: WECN02
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WECN02
About: Received: 11 Aug 2025 — Revised: 13 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
WEP008
A W-band corrugated waveguide for high-efficiency high-gradient wakefield acceleration
701
Compact RF structures in the sub-terahertz regime are promising for structure wakefield acceleration due to their ability in achieving high gradients in a reduced footprint. We report on the design, fabrication, and testing of a metallic corrugated waveguide operating at 110 GHz, tailored to the 42 MeV electron beam parameters at the Argonne Wakefield Accelerator (AWA). The experiment utilized the emittance exchange (EEX) beamline at AWA for longitudinal bunch shaping in two configurations: (1) a single short drive bunch to study high decelerating gradients, and (2) a two-bunch scheme featuring a triangularly shaped drive bunch followed by a long witness bunch to probe the wakefield and achieve a high transformer ratio. We will present the experimental design and results, which show good agreement with simulation predictions.
Paper: WEP008
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP008
About: Received: 07 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 13 Aug 2025 — Issue date: 28 Jan 2026
Developing a hybrid accelerating structure based on short-pulse Structure Wakefield Acceleration
Structure Wakefield Acceleration (SWFA) powered by -short RF pulses (~10 ns) generated by Two-Beam Acceleration (TBA) at the Argonne Wakefield Accelerator (AWA) has demonstrated effective suppression of RF breakdowns and achieved gradients exceeding 400 MV/m at X-band (11.7 GHz) frequencies. To fully exploit the benefits of this short RF pulse operation, an accelerating structure must simultaneously achieve two goals: high group velocity (Vg) to ensure rapid RF filling (need for high efficiency), and simultaneously maintain high shunt impedance (R) (need for high accelerating gradient). Conventional accelerating structures involve inherent tradeoffs between these parameters, limiting their effectiveness in the short-pulse regime. To this end, we developed a hybrid structure composed of two co-optimized sub-structures fed by one coupler at the middle: one backward wave (BW) filling and one forward wave (FW) filling sub-sections.This design not only preserves the short-pulse advantage, it also simplifies the setup (one input coupler for two structures) and enhances the beam’s energy gain by doubling the acceleration length without requiring extended RF pulse duration. In this work, we present the detailed RF design with preliminary beam dynamics simulations demonstrating efficient energy gain within a compact acceleration length.
WEP049
Progress report on two-bunch excitation of wakefield in dielectric structures
777
Wakefield accelerators have the potential to achieve accelerating fields in the GV/m range, offering a promising path to more compact and cost-effective acceleration compared to conventional methods. Structure-based wakefield accelerator (SWFA) technology provides a viable approach to implementing beam-driven wakefield acceleration. An experiment at the Argonne Wakefield Accelerator (AWA) will utilize dielectric-lined structures to explore multi-beam excitation of wakefields for wakefield-pulse shortening and mapping of the transverse wakefield topology. These structures were commercially sourced and require a thin metallic film deposited on their outer surface. The first part of this paper summarizes the preparation of these structures. In parallel, a two-bunch beam configuration is required to support the experimental investigation, where one bunch excites the wakefield and the second serves as a loading or probe bunch. The experimental generation and testing of this two-bunch scheme at AWA are presented in this work.
Paper: WEP049
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP049
About: Received: 15 Aug 2025 — Revised: 18 Aug 2025 — Accepted: 19 Aug 2025 — Issue date: 28 Jan 2026
WEP079
RF breakdown and dark current studies in short-pulse acceleration
847
Recent experimental studies at the Argonne Wakefield Accelerator (AWA) have shown that operating RF cavities with short pulses, only a few nanoseconds in duration, can raise the accelerating gradient to nearly 400 MV/m in a series of X-band structure tests. These results motivate further investigation into the breakdown physics underlying the short-pulse acceleration regime. In this work, we present analytical models and numerical simulations of dark current dynamics in X-band cavities driven by short RF pulses. These studies explore key phenomena associated with RF breakdown across various time scales, including field emission, secondary electron emission, and plasma formation, with particular focus on their dependence on RF pulse length. Building on these insights, we describe the design and experimental plan for a single-cell X-band RF cavity operating at 11.7 GHz, optimized for high-gradient operation with 6~ns long RF pulses and integrated with RF breakdown diagnostics. This work aims to deepen the understanding of RF breakdown physics in the short-pulse regime and support the development of compact linear accelerators for future applications.
Paper: WEP079
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP079
About: Received: 08 Aug 2025 — Revised: 10 Aug 2025 — Accepted: 12 Aug 2025 — Issue date: 28 Jan 2026
WEP083
Status of the experimental demonstration of GW power generation from THz-TBA
855
We present the current status of preparations for the experimental demonstration of GW power generation from THz-TBA. The presentation will cover the status of structure fabrication, RF power extraction and absolute power measurement, and THz drive beam preparation. Currently, 0.4 THz structures are being fabricated using two improved methods over previous fabrication techniques. RF power extraction will be achieved using an on-axis elliptical horn antenna and off-axis parabolic mirrors. The RF power will be detected with a bolometer and calibrated based on the total beam energy loss measured by a spectrometer. In recent machine studies, we successfully generated a high-charge bunch train (1 nC/bunch) compatible with 0.4 THz structure.
Paper: WEP083
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP083
About: Received: 08 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
THz detection and investigation of vacuum-compatible optical components
Detecting terahertz (THz) radiation in ultra-high vacuum (UHV) environments presents notable challenges due to the limited availability of commercially compatible components. In preparation for upcoming THz measurements at the Argonne Wakefield Accelerator (AWA) facility, we investigated two critical aspects: (1) the THz transmission characteristics of fused silica windows, and (2) the suitability of commercial off-axis parabolic mirrors (OAPs) for use in UHV conditions. While fused silica is widely used in optical systems, its performance in the THz regime is rarely documented. We present transmission measurements and assess its viability for THz diagnostics. Additionally, we address the incompatibility of anodized, off-the-shelf OAPs with UHV by developing and testing both mechanical and chemical de-anodization techniques. These methods aim to maintain surface integrity and optical quality. This work provides practical guidelines and compatibility benchmarks for implementing THz diagnostics in UHV environments and serves as a reference for future experiments at AWA and other accelerator facilities.
WEP091
Transverse deflecting cavity optimization for active control of electron beam energy chirp
873
The Transverse Deflecting Cavity Based Chirper (TCBC) is a novel concept of imposing and removing a significant energy chirp of an ultra-relativistic electron beam. The TCBC method requires much less footprint, compared to the conventional chirping and dechirping method involving operating a linear accelerator off-crest. When the compressed bunch is very short, the dechirping has to rely on the wakefields. We present our updated design of the L-band traverse deflecting cavity (TDC) for demonstrating the TCBC concept at the Argonne Wakefield Accelerator (AWA) facility. Our TDC design update is based on the original design provided by Tsinghua University. The TDC design update focused on ensuring improved performance under more intense electromagnetic fields, reducing the peak pulsed temperature rise. The tuners of the TDC were meanwhile reworked to allow greater adjustability of the resonant frequency and of the electromagnetic field balance among the cells. We also report the tolerance study of the TDC. Two copies of the TDC with the updated design are currently under fabrication with Dymenso, LLC.
Paper: WEP091
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP091
About: Received: 08 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 15 Aug 2025 — Issue date: 28 Jan 2026
Monte-Carlo modeling and experimental investigation of photoemission from CsTe semiconductor photocathode under high fields
Beam brightness can be enhanced with high gradient operation in photocathode guns. Such high gradient guns, such as the L-band gun at the Argonne Wakefield Accelerator (AWA) facility and the C-band high gradient gun being commissioned in the CARIE project at Los Alamos National Laboratory, are also typically equipped with semiconductor photocathodes due to their high quantum efficiency. To investigate the photoemission process in semiconductor thin-film photocathode under such conditions, we developed Monte-Carlo transport and photoemission models employing electronic, phonon, dielectric and optical properties directly from Density Functional Theory (DFT) calculation, as well as the photo excitation model based on the light interference effect in thin films. This photoemission model is further employed in photocathode gun simulation and used to investigate a recent high-gradient experiment conducted at the AWA photo injector. We will discuss the effects of the high field gradient on photoemission through a comparison of the measurement and the simulated beam dynamics.
WEP100
Upgraded photoinjector laser pulse train generator at the Argonne Wakefield Accelerator
888
The Argonne Wakefield Accelerator (AWA) facility operates a high-charge (100s of nC) electron beam in a bunch train, with eight electron bunches at a 769 ps spacing matching the linac operating frequency of 1.3 GHz. AWA’s electron beam is optimized for producing large wakefields in resonant structures to study structure wakefield acceleration. This is achieved by maximizing total beam charge, and by correct bunch train timing to enhance the wakefield via inter-bunch coherence. The properties of the bunch train are determined by a “multisplitter” in the photoinjector laser system, in which a series of beamsplitters splits one laser source into eight - ideally equal - pulses. However, AWA’s previous system did not split pulses evenly, with up to a 2:1 ratio between pulse energies within a train. Damaging electrical breakdown events within the electron gun, driven by high single bunch charge, occurred at lower total charge in this non-uniform set-up, limiting maximum charge. Thus, a new multisplitter using polarizing beamsplitters and half-wave plates (HWPs) was implemented. Unlike the previous fixed-ratio beam-splitter design, the new system enables tuning the splitting ratio for each beamsplitter, resulting in a more uniform pulse train. Large 2” optics and uncoated HWPs are also used to increase the laser intensity damage threshold (LIDT). This paper presents the design, characterization and lessons learned in early commissioning of AWA's upgraded laser pulse train generator.
Paper: WEP100
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP100
About: Received: 08 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
THP004
Advanced growth and characterization of alkali antimonide photocathodes for bright beam applications
939
The properties of the photoemitting electron sources are the most determining factors contributing to the performance of the most advanced electron accelerator applications such as particle colliders, X-ray free electron lasers, ultra-fast electron diffraction and microscopy experiments. Therefore, low mean transverse energy (MTE), high quantum efficiency (QE) along with long operational lifetime and robustness under high electric fields and laser fluences must be demonstrated by the photocathode for these bright beam applications. Recent investigations have revealed that the epitaxial growth of single crystal cesium antimonides can be achieved by photocathode growth on lattice matched substrates. In this letter, the experimental setup for highly promising alkali antimonide photocathode growth by molecular beam epitaxy on lattice matched substrates and in-situ characterization with reflection high-energy electron diffraction (RHEED) has been presented. To adapt the L-band RF gun of Argonne Cathode Test-stand (ACT) for extensive testing of alkali antimonides in real accelerator conditions, compatible cathode plug design and smooth transportation process have been developed and also described in this paper.
Paper: THP004
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-THP004
About: Received: 09 Aug 2025 — Revised: 15 Aug 2025 — Accepted: 15 Aug 2025 — Issue date: 28 Jan 2026
The Reconfiggler: A uniquely versatile wiggler
Wigglers are periodic arrays of magnets with myriad applications in accelerator physics. Generally though, they are only tunable by adjusting the gap between jaws. Here, we present a wiggler based on diametrically magnetized cylindrical magnets with independently adjustable angle. This allows the realization of arbitrary (bandwidth constrained) magnetic configurations. We illustrate its application to the recently proposed "transverse wiggler" concept for transverse phase space control.