The Round to Flat Beam Transformation (RFBT) is one of the emittance exchange techniques that can improve the Luminosity for the future accelerator project International Linear collider (ILC). RFBT experiment can be conducted in the KEK-STF, and the expected performance is 334 in emittance ratio. In December 2023, we performed a pilot experiment at STF to optimize the injector conditions. To improve the RF Gun of STF, we applied dry ice cleaning to reduce the field emission. The field enhancement factor was improved from 233 to 100.

The Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab operates hundreds of superconducting radio frequency (SRF) cavities in its two linear accelerators (linacs). Field emission (FE) is an ongoing operational challenge in higher gradient SRF cavities. FE generates high levels of neutron and gamma radiation leading to damaged accelerator hardware and a radiation hazard environment. During machine development periods, we performed gradient scans to record data capturing the relationship between cavity gradients and radiation levels measured throughout the linacs. However, the field emission environment at CEBAF varies considerably over time as the configuration of the radio frequency (RF) gradients changes and due to the changing behavior of field emitters. An artificial intelligence/machine learning (AI/ML) approach with transfer learning could be a valuable tool to mitigate FE and lower the radiation levels. In this work, we mainly focus on leveraging the RF trip data gathered during CEBAF operations. We develop a transfer learning-based surrogate model for radiation detector readings given RF cavity gradients to track CEBAF’s changing configuration and environment. Then, we could use the developed model in an optimization process for redistributing the RF gradients within a linac to minimize radiation levels.

Stationary CT is a novel CT technology to significantly improve scanning speed, by using distributed multiple ray sources instead of conventional helical rotation with single source. This work presents an S-band multi-beam accelerator as a multiple MV-level X-ray source for industrial stationary CT application. This accelerator consists of 7 parallel-distributed acceleration cavity and 6 coupling cavity, operating in pi/2 standing-wave mode with a centre frequency of 2998MHz. This structure can generate 0.7 MeV electrons with 100 mA peak current at each beamline according to the imaging requirement. The novel multiple high-energy X-ray source will fill in the blank of source requirements in industrial stationary CT application.

The space-charge neutralization of an ion beam by created electrons when the beam ionizes the gas is investigated using a three-dimensional electrostatic particle-in-cell code. Different kinds of injected gases are considered, and their space-charge compensation transient times are compared. The created secondary electrons by the beam collision with neutral gas along the beam trajectories are loaded in the simulation by a Monte Carlo generator, and their space charge contribution is added to the primary beam space charge densities. The injection and accumulation of secondaries are time-dependent and this process is continued until total space charge densities reach a steady state. In this study, a 2.4-meter LEBT line with two solenoid magnets is considered. Usually, the proton beam energy is 25 keV and the current level is around 10-15 mA. Additionally, beam extraction studies are conducted, and the extracted beam is used in both IBSIMU and Tracewin codes for LEBT lines to validate the results.

An electron beam degrader is under development with the objective of measuring the transverse and longitudinal acceptance of the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. This project is in support of the CE+BAF positron capability. Computational simulations of beam-target interactions and particle tracking were performed integrating the GEANT4 and Elegant toolkits. A solenoid was added to the setup to control the beam's divergence. Parameter optimization of the solenoid field and magnetic quadrupoles gradient was also performed to further reduce particle loss through the rest of the injector beamline.

The Variable Energy Gamma (VEGA) System is under implementation in Bucharest-Magurele Romania as one of the major components in the project of Extreme Light Infrastructure Nuclear Physics (ELI-NP). The VEGA System is designed as an advanced Laser Compton Scattering gamma-ray source with unique parameters in terms of high spectral density, monochromaticity, high polarizability, and energy tunability. It brings new opportunities and is dedicated for photonuclear research in both applied and fundamental physics, and will be open for worldwide users. Optimization of spectral density and guaranty of monochromaticity of the gamma-rays impose the necessity to control both, transverse emittance and energy spread, putting strong requirements on electron beam dynamics. The paper presents results from computer simulations carried out for the injector of the LCS gamma-ray source based on a normal-conducting RF LINAC, and investigation of a lattice configuration to optimize the electron beam parameters at the transfer line and storage ring entrance.

The polarized pre-injector for the Electron-Ion Collider is intended to produce four bunches every second, each containing 7 nC, with 85% polarization along the longitudinal axis, for injection into the Rapid Cycling Synchrotron. The pre-injector consists of a polarized electron source, bunching section, longitudinal phase space manipulation, and SLC-Type LINAC. To reduce energy spread and increase bunch length, a compact zig-zag chicane and dechirp cavity rotate the bunch in longitudinal phase space. In this paper, we will discuss the progress of recent pre-injection design and RF frequency selection. Additionally, we will examine the effects of wakefield, as well as coherent and incoherent synchrotron radiation on beam quality.

The utilization of machine learning techniques in accelerator research has yielded remarkable advancements in optimization strategies. This paper presents a pioneering study employing a machine learning algorithm, GPTune, to optimize beam intensity by adjusting parameters within the EBIS injection and extraction beam lines. Demonstrating significant enhancements, our research showcases a remarkable 22% and 70% improvements in beam intensity at two different measurement locations.

The RPI LINAC refurbishment control system engineering plan outlines Cosylab's and RPI's approach to initiating and managing the control system architecture for an accelerator refurbishment project at RPI. One of the goals was to achieve a low total cost of ownership, which encompasses the direct price, the cost of maintenance, the upgrade potential, and the quality and cost of support services. To create the technical part RPI provided valuable knowledge and experience from running the RPI LINAC and Cosylab used prior experience and industry best practices to deliver high-level project documentation, which includes the control system architecture, strategies for device integration, and clearly defined scope descriptions. The documentation also covers specific content, such as detailed subsystem descriptions, device interface descriptions, subsystem operation descriptions and recommended implementation methods for specific device types. Several technical solutions, lead time comparisons, and the quality of support services were thoroughly evaluated. In terms of project management, a concrete upgrade plan was developed. A standard project management process was proposed. The work was divided into independent work packages, and included a recommended sequence within the project. The outcome of the study is a comprehensive document, which provides all the necessary information required to initiate the control software portion of the project.

The status of commissioning of the electron injector intended for the next phase of the proton driven wakefield experiment (AWAKE) is presented, showing first experimental results from operating the brazing-free electron gun. To provide a high-quality electron beam, the UV laser was centered on the copper cathode, and a novel simplex and beam-based alignment of the focusing solenoid was performed. Measurements of the beam parameters and working points are addressed. The electron gun is shown to provide a high quality, stable and reproducible beam.

This paper presents the final physics design of the Proton Improvement Plan-II (PIP-II) at Fermilab, focusing on the linear accelerator (Linac) and its beam transfer line. We address the challenges in longitudinal and transverse lattice design, specifically targeting collective effects, parametric resonances, and space charge nonlinearities that impact beam stability and emittance control. The strategies implemented effectively mitigate space charge complexities, resulting in significant improvements in beam quality—evidenced by reduced emittance growth, lower beam halo, decreased loss, and better energy spread management. This comprehensive study is pivotal for the PIP-II project's success, providing valuable insights and approaches for future accelerator designs, especially in managing nonlinearities and enhancing beam dynamics.

Accelerator-driven high brilliance neutron sources are an attractive alternative to the classical neutron sources of fission reactors and spallation sources to provide scientists with neutrons. A new class of such neutron facilities has been established referred to as High-Current Accelerator-driven Neutron Sources (HiCANS). The basic features of HiCANS are a medium-energy proton accelerator with of tens of MeV and up to 100 mA beam current, a compact neutron production and moderator unit and an optimized neutron transport system to provide a full suite of high performance, fast, epithermal, thermal and cold neutron instruments. The Jülich Centre for Neutron Science (JCNS) has established a project to develop, design and demonstrate such a novel accelerator-driven facility termed High Brilliance neutron Source (HBS). The aim of the project is to build a versatile neutron source as a user facility. Embedded in an international collaboration, the HBS project offers the best flexible solutions for scientific and industrial users. The overall conceptual and technical design of the HBS as a blueprint for the HiCANS facility has been published in a series of recent reports. The status and next steps of the project will be presented, focusing on the high-current linear accelerator and the proton beamline, including a novel multiplexer to distribute the proton beam to three different neutron target stations while adapting a flexible pulse structure.

The Round to Flat Beam Transformation (RFBT) is one of the emittance exchange techniques that can improve the Luminosity for the future accelerator project International Linear collider (ILC). RFBT experiment can be conducted in the KEK-STF, and the expected performance is 334 in emittance ratio. In December 2023, we performed a pilot experiment at STF to optimize the injector conditions. To improve the RF Gun of STF, we applied dry ice cleaning to reduce the field emission. The field enhancement factor was improved from 233 to 100.

Single-spoke resonators (SSRs) have been developed and tested for the RAON SCL2 project. The design pa-rameters for the SSRs are provided, and the performance of the superconducting cavities is assessed. The single-spoke resonator cavities, cryogenic systems, cryostats, and human machine interface (HMI) are depicted for a vertical test. Calibration and cavity preparations are demonstrated to evaluate the performance of the super-conducting cavities. Testing of the single-spoke resonator type 1 (SSR1) performance is conducted via a vertical test. Q slopes are presented as a function of accelerating field, and Lorentz force detuning (LFD) as well as pres-sure sensitivity are conducted for the superconducting cavities.

The bunching system of injector Linac in High Energy Photon Source (HEPS) includes two sub-harmonic bunchers, a pre-buncher and a traveling wave S band buncher. The buncher is a 6-cell constant impedance traveling wave structure operating in 2π/3 mode at 2998.8 MHz. In this paper, the design and test of the traveling wave buncher are presented. First, the characteristic parameters are optimized in CST. Then the buncher is precisely tuned and cold tested with a vector network analyzer after fabrication. Finally, the high power test was finished before installation in Linac. The buncher can operate stably with input power of 10 MW after a week of conditioning. So far the buncher has been applied successfully in Linac of HEPS.

As a part of the High Energy upgrade to the Linac Coherent Light Source II at SLAC, LBNL is responsible for the update of the undulators of the Soft X-Ray (SXR) line. In order to span the required photon energy range, the SXR undulators require longer magnetic period. This increased magnetic period leads to higher magnetic force, requiring updates to certain elements of the design. In contrast, many elements can safely remain unchanged. This presentation details the updates and analyses performed to support the adaptation to HE-SXR, as well as pre-production undulator results.

The front end of the 800-MeV proton linac at the Los Alamos Neutron Science Center (LANSCE) is still based on Cockcroft-Walton voltage generators that bring proton and H- beams of various flavors to 750 keV. We have developed 3D CST models of the LANSCE front-end elements including low-frequency and main bunchers. The fields in these elements are calculated with MicroWave and ElectroMagnetic Studio. Beam dynamics is modeled with Particle Studio for beams with realistic charge distributions using the CST calculated fields. The modeling results provide insight into linac operations and a guidance for designing a modern, RFQ-based front end for the LANSCE linac.

The Los Alamos Neutron Science Center (LASNCE) is over 50 years old. Currently, Cockroft-Waltons are being used to accelerate H+ and H- beams to 750 keV. The LANSCE Modernization Project (LAMP) is proposing to replace the font-end of LANSCE with a Radio-Frequency Quadrupole (RFQ). A RFQ Test Stand is being commissioned at LANL for technical demonstration of simultaneous dual-beam species acceleration through a RFQ under the timing constraints required by the LANSCE users facilities. We will describe the status and present initial results of the 35keV H+ line on the RFQ Test Stand.

We present a beam-focusing architecture using electro- and permanent magnets for a novel compact electron beam buncher under development for space-borne electron accelerators. Developing compact and efficient accelerator components has become desirable with renewed interest in using space-borne electron beams for ionospheric aurora research and very low frequency wave generation for particle removal from the magnetosphere. An electron gun injects a direct current electron beam, and the buncher modulates the DC beam into periodic bunches at a frequency of 5.7 GHz. A 5.7 GHz linear accelerator in the downstream will capture the bunched beam with minimal acceptance mismatch. The beam modulation is done by three radiofrequency pillbox cavities. The buncher uses the electrostatic potential depression (EPD) method to shorten the structure length remarkably. The electron gun and a tunable solenoid provide the initial focusing of the beam. We then use a series of permanent magnets surrounding the buncher cavities clamped together by ferromagnetic steel plates to focus the beam through the buncher. Permanent magnets do not consume any power and weigh less than solenoid magnets, which provide equivalent focusing, making them ideal for use on a satellite or sounding rocket. We use the three-dimensional (3D) particle tracking solver from CST Studio Suite to simulate the beam-focusing.

A single wide-momentum-acceptance FFA beam line allows for recirculating a beam several times through a linac. Such a scheme provides an efficient path towards high-energy, high-power continuous beams. This paper describes the development of a conceptual design of an FFA RLA focusing on but not limited to a high-power hadron beam case. We present a complete optics design including arc, linac, and matching sections. The matching sections are implemented following the adiabatic approach whereby matching of all beam passes occurs simultaneously within a single beam line. Harmonic correction is applied for precise orbit and optics control of the individual passes. We discuss approaches to optimization of the linac timing and control of the longitudinal beam dynamics.

The Continuous Electron Beam Accelerator Facility (CEBAF) operates hundreds of superconducting radio frequency (SRF) cavities in its two linear accelerators (linacs). Field emission (FE) is an ongoing operational challenge in higher gradient SRF cavities. FE generates high levels of neutron and gamma radiation leading to damaged accelerator hardware and a radiation hazard environment. During machine development periods, we performed invasive gradient scans to record data capturing the relationship between cavity gradients and radiation levels measured throughout the linacs. However, the field emission environment at CEBAF varies considerably over time as the configuration of the radio-frequency (RF) gradients changes or due to the strengthening of existing field emitters or the abrupt appearance of new field emitters. To mitigate FE and lower the radiation levels, an artificial intelligence/machine learning (AI/ML) approach with transfer learning is needed. In this work, we mainly focus on leveraging the RF trip data gathered during CEBAF normal operation. We develop a transfer learning based surrogate model for radiation detector readings given RF cavity gradients to track the CEBAF’s changing configuration and environment. Then, we could use the developed model as an optimization process for redistributing the RF gradients within a linac to mitigate field emission.

The international e-e FCC study group aims to design an accelerator complex capable of injecting tunable and high charge electron-positron bunches into a collider with center-of-mass energy between 90 and 365 GeV. The injector complex will boost the initial energy of the electron-positron bunches using multiple linacs accelerating only electrons, only positrons, and both species up to the booster injection energy of 20 GeV. The requirements on the charge poses several challenges for the injector chain due to the important role played by the wakefield both in the longitudinal and in the transverse planes. We optimized the bunch length, the RF aperture of the accelerating cavities and the linacs’ layout to match the target parameters at the booster injection. In the longitudinal space we studied the impact of the wakefield on the final beam energy spread. In the transverse plane we minimized the emittance growth due to static errors along the different sections using several orbit steering algorithms, and we verified the impact of dynamic errors for the most promising designs. Furthermore, we designed an energy compressor to add flexibility to our design, and to widely scan the beam charge without strongly modifying the final bunch parameters. In this work we present a summary of these studies, which led to the linac design satisfying all the present requests for the injection to the booster. This current design is the basis for the injector complex cost estimation.

Shanghai HIgh repetitioN rate XFEL and Extreme light facility (SHINE) is an x-ray FEL facility, consisting of an 8 GeV CW superconducting linac and 3 FEL undulator lines, covering the spectral ranges 0.4-25 keV. Photoinjector using VHF gun is one of the key part of the facility. The installation of the electron gun section of the SHINE injector has been completed in August 2023. RF conditioning and commissioning were carried out from September to December. In this paper, we will introduce the installation progress of the injector and show some commissioning results of the electron gun section.

For the development of X-band deflecting structure at Shanghai Synchrotron Radiation Facility (SSRF), two units of X-band deflecting structures totally including six RF structures have been used on SXFEL successfully for ultra-fast beam diagnostics. The construction of another new FEL facility has started from 2018, which is named Shanghai high repetition rate XFEL and extreme light facility (SHINE). Four units of X-band deflectors will be installed on SHINE. The design and measurement of the first prototype has been finished, and the high power test will be carried out soon, in this paper, the design and measurement results will be presented.

The injector section of the SHINE device is currently in the debugging phase. The electron beam energy in the injector section is low and is significantly affected by the geomagnetic field, with an intensity of approximately 250 milligauss. Through theoretical optimization, adjustments to the positions and intensity parameters of helical coils and corrector magnets are being made to significantly reduce the growth of beam emittance under the influence of the geomagnetic field. The aim is to optimize the beam quality of the injector section of the SHINE device based on this model.

The initial design of the capture cavities for a continuous wave (CW) polarized positron beam for the Continuous Electron Beam Accelerator Facility (CEBAF) upgrade at Jefferson Lab is presented. A chain of standing wave multi-cell copper cavities inside a solenoid tunnel are selected to bunch/capture positrons in CW mode. The capture efficiency is studied with varying cavity gradients and phases. The heating load from the incoming particle radiation shower and RF field will limit the achievable gradients, especially the first cavity. The cooling method and results are shown. The beam loading cancellation from positrons and electrons are investigated.

The addition of spin-polarized, continuous-wave (c.w.) positron beams to the 12 GeV Continuous Electron Beam Accelerator Facility (CEBAF) would provide a significant capability to the experimental nuclear physics program at Jefferson Lab. Based on bremsstrahlung and pair-production in a high-Z target, the positron source requires a 120 MeV spin-polarized c.w. electron beam of several milliamperes. While the beam dynamics of the high-current electron beam are tenable, sustaining this current for weeks of user operations requires an unprecedented charge lifetime from a high-polarization GaAs-based photocathode. A promising approach to exceed the kilocoulomb charge lifetime barrier is reducing the ion back-bombardment fluence at the photocathode. By increasing the laser size and managing the emittance growth with an adequate cathode/anode design, significantly enhanced charge lifetime may be achieved. Based upon a new simulation model that qualitatively explains the lifetime data previously measured at different spot sizes, we describe the practical implications on the parameter space available for a kilocoulomb-lifetime polarized photogun design.

We report on the status of a degrader device to generate large phase space beams for machine acceptance studies in the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. The degrader device consists of thin, low-Z targets to degrade the electron beam phase space through multiple scattering, two apertures to define the maximum transverse emittance, and a solenoid to aid in matching to the rest of the injector beamline. The engineering design of the degrader device and projected degraded beam phase space parameters obtained from simulation are presented.

We present an initial capture concept for the continuous wave (CW) polarized positron beam at the Continuous Electron Beam Accelerator Facility (CEBAF) upgrade at Jefferson Lab. This two-step concept is based on (1) the generation of bremsstrahlung radiation by a longitudinally polarized electron beam (1 mA, 120 MeV, >90% polarization), passing through a tungsten target, and (2) the production of e+e- pairs by these bremsstrahlung photons in the same target. To provide highly-polarized positron beams (>60% polarization) or high-current positron beams (>1 μA) with low polarization for nuclear physics experiments, the positron source requires a flexible capture system with an adjustable energy selection band. The results of beam dynamics simulations and calculations of the power deposited in the positron capture section are presented.

The program to upgrade CEBAF cryomodules has been implemented to enhance the energy gain of refurbished cryomodules up to 75 MeV. This strategy involves reusing the waveguide end-groups from original CEBAF cavities produced in the 1990s, and existing five elliptical cell cavities are replaced with a new optimized cell shape cavity constructed from large-grain, ingot Nb material. Following fabrication, each cavity undergoes centrifugal barrel polishing and electropolishing and then is tested at 2.07 K. Eight cavities are then assembled into "cavity pairs" and tested at 2.07 K before integration into the cryomodule. This paper presents the outcomes of the cavity qualification for the third C75 module, providing a detailed account of the assessment in both a vertical cryostat and the commissioning results of the cryomodule. Furthermore, efforts have been made to address performance limitations arising from field emission and multipacting.

Distributed-coupling structures has been proposed as an advanced type of high-gradient accelerators, RF power flow independently into each cavity.This method has few advantages such as high shunt impedance, superior power efficiency, and low costs. And the most distributed-coupling structures typically set 0° or 180° as the phase advance which can simplify the design.In this study we introduces a new-designed distributed-coupling structures with phase advance greater than 180°. This choice of angle will significantly reduce costs without affecting the shunt impedance.

Stationary CT is a novel CT technology to significantly improve scanning speed, by using distributed multiple ray sources instead of conventional helical rotation with single source. This work presents an S-band multi-beam accelerator as a multiple MV-level X-ray source for industrial stationary CT application. This accelerator consists of 7 parallel-distributed acceleration cavity and 6 coupling cavity, operating in pi/2 standing-wave mode with a centre frequency of 2998MHz. This structure can generate 0.7 MeV electrons with 100 mA peak current at each beamline according to the imaging requirement. The novel multiple high-energy X-ray source will fill in the blank of source requirements in industrial stationary CT application.

A new X-band mode converter for the Very Compact Inverse Compton Scattering Gamma-ray Source (VIGAS) program in Tsinghua University has been fabricated and conducted low-power testing. S11 is under -30 dB with -0.05 dB of S21 at the operating frequency of 11.424GHz according to the low-power test using the vector network analyzer, which is consistent with simulation results.

A new X-band phase shifter for the Very Compact Inverse Compton Scattering Gamma-ray Source (VIGAS) program in Tsinghua University has been fabricated and conducted high-gradient testing. After 10 h of conditioning in the Tsinghua X-band high-power test stand (TPOT), the phase shifter reached a peak power of 72 MW at 230 ns pulse width, and peak power of 82 MW at 130 ns pulse width.

The space-charge neutralization of an ion beam by created electrons when the beam ionizes the gas is investigated using a three-dimensional electrostatic particle-in-cell code. Different kinds of injected gases are considered, and their space-charge compensation transient times are compared. The created secondary electrons by the beam collision with neutral gas along the beam trajectories are loaded in the simulation by a Monte Carlo generator, and their space charge contribution is added to the primary beam space charge densities. The injection and accumulation of secondaries are time-dependent and this process is continued until total space charge densities reach a steady state. In this study, a 2.4-meter LEBT line with two solenoid magnets is considered. Usually, the proton beam energy is 25 keV and the current level is around 10-15 mA. Additionally, beam extraction studies are conducted, and the extracted beam is used in both IBSIMU and Tracewin codes for LEBT lines to validate the results.

An electron beam degrader is under development with the objective of measuring the transverse and longitudinal acceptance of the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. This project is in support of the CE+BAF positron capability. Computational simulations of beam-target interactions and particle tracking were performed integrating the GEANT4 and Elegant toolkits. A solenoid was added to the setup to control the beam's divergence. Parameter optimization of the solenoid field and magnetic quadrupoles gradient was also performed to further reduce particle loss through the rest of the injector beamline.

At Varex Imaging Corporation, we have started a transition to our in-house supply of Accelerator Beam Centerlines (ABC), replacing Varian as a supplier. As part of this program we are considering changing design of our K-15, the only standard production unit capable of delivering Bremsstrahlung at 12000 R/min@1m by striking a copper target with high energy electron beam at 15 MeV. We plan on changing the RF source from frequency of 2856 MHz, used by Varian to 2998 MHz, establishing one common frequency for all our S-Band linear accelerator supply. We may be using a two-section design of the new 15 MeV ABC and yet various designs are being investigated, including, but not limited to two collinear standing wave (SW) sections and a patented combination of SW and Traveling Wave (TW) Sections with reverse feed. We have analyzed both concepts and present the preliminary analysis results. The platform can be used for running guides at various energy levels from 2 to 20 MeV, continuously changing energy or doing that selectively, various combinations of energy levels will be possible, also, upgrading the platform to higher average beam power levels. Indeed, operating at high average beam power above 1-2 kW level may require new advanced target development, and in case of e-beam applications, a scan horn will be required for extracting e-beam from vacuum to air.