Diamond Light Source has been operating in top-up mode for users since late 2008. To date, Diamond’s electron gun has operated in single-bunch mode for multiple-shot top-up of user beam, and multibunch mode for storage ring fill. The uneven bunch-to-bunch charge of the multibunch train is visible in the storage ring and so the fast multibunch fill must be followed by a slower single bunch correction before beam can be given to users. A new pulser has been developed that will generate a flat, fast-rising 500 MHz train of electron bunches from the gun that will enable a uniform fill of the storage ring without single bunch correction. Arbitrary bunch-by-bunch shaping of the train can be used for multibunch fill and top-up of any required fill pattern, thus exploiting the greater charge available in multibunch mode to reduce the number of top-up shots and consequent disturbance to users. Pulser development and results are presented, together with a report of progress towards multibunch top-up.

GaAs cathode is a unique device generating a spin-polarized electron beam by photo-electron effect with a circularly polarized laser illumination. Negative Electron Affinity (NEA) surface which is artificially made has an essential role in spin polarization, but the NEA surface has limited vitality. In this study, we activated GaAs as NEA cathode by evaporating Cs, K, and Sb metal on its cleaned surface. The experimental results including the quantum efficiency spectrum and the lifetime will be presented.

High brightness beams are desired for application to Inverse Compton Scattering (ICS) systems for generation of high-quality x- and γ-rays. It opens new opportunities for nuclear physics research in fields such as nuclear photonics, nuclear astrophysics, photo-fission, production of exotic nuclei, applications in medicine, industry and space science. In ICS mechanism high energy electron is interacting with photon. It results in scattered photon with high energy. Results from computer simulations are presented. Different configurations of S-band injector were analysed. Photocathode RF electron source with diverse arrangement of magnetic devices for beam confinement, and standing wave cavity for initial particle acceleration were implemented. Electron beam parameters have been investigated with use of computer program for tracking particle beam through defined external electric and magnetic fields. Because cross-section of collision between electron and photon beam is very low, high brightness electron beam is crucial specification for gamma beam systems. Electron beam parameters of interest are emittance, beam spot size, average energy, energy spread, electron bunch length, Twiss parameters. Beam density, number of particles in bunch must find good compromise between optimum necessary for creation of high-performance gamma rays and limit in available technology.

The performance requirements for next generation electron accelerators put ever increasing demand on the photocathode performance, where it fundamentally limits the achievable beam quality. Metal photocathodes are limited by their high work function and relatively low quantum efficiency, necessitating the use of high powered deep UV lasers. Metal oxide thin film interfaces have been shown to reduce the work function of the underlying metal photocathode, whilst maintaining the ease of use, high durability and fast response time. This leads to an improvement in quantum efficiency and spectral response to desirable incident laser sources. We present the characterisation of a thin film yttria (Y2O3) enhanced Au photocathode at various film thicknesses. Quantum efficiencies were measured at 265 nm along with surface compositions via X-ray photoelectron spectroscopy.

With the high accelerating gradient, radiofrequency (rf) gun has a significant feature of suppressing the growth of transverse emittance caused by space charge. Field emission cathodes were first used in vacuum electronic devices, which do not require the high electron beam intensity, but the cathode size and integrality. A new X-band (11.424 GHz) rf electron gun has been proposed with the highlight of four-feed coupler, which can eliminate the quadrupole field component observed and analyzed from the imagine experiment, which have affected the resolution of the imaging system to some content.

For the first time, photoemission of spin-polarized electron beams from gallium nitride (GaN) photocathodes are observed and characterized. The spin polarizations of the emitted electrons from epitaxially grown hexagonal and cubic GaN photocathodes activated to Negative Electron Affinity (NEA) via cesium deposition are measured in a retarding-field Mott polarimeter.

We study ultrafast laser surface nanopatterning as an alternative to improve the photo-emissive properties of metallic photocathodes. By tailoring the physical dimensions of these surface nanostructures, one can localize the optical field intensity and exploit plasmonic effects occurring in such nanostructures. As a result, this surface nanopatterning technique can become a great tool for improving metallic photocathodes photoemission behavior enabling their use for next generation high brightness electron sources. Our goal is to investigate such surface-plasmon assisted photoemission processes with a view on simplifying the photocathode production at CERN while extending the lifetime of existing photoinjectors. The performance of two different femtosecond laser nanopatterned plasmonic photocathodes was analyzed by measuring the quantum yield with a 65kV DC electron gun utilizing 266nm laser excitation generated by a nanosecond laser with 5ns pulse duration and 10Hz repetition rate. By comparing the electron emission of the copper surface nanostructured areas with that of a flat area, our results suggest quantum yield enhancements of up to 5 times.

INFN LASA photocathode lab develops and produces films that are used in high brightness photoinjectors. Besides the long-time and still on-going experience on Cs2Te, recently we have restarted an activity on alkali-antimonide films, sensitive to visible light, exploring the possibility of their stable operation in CW machine. We report in this paper the recent results obtained both on the advancements on cesium telluride and on the characterization of alkali antimonide.

The new C-Band RF gun, developed in the context of the European I.FAST project has been realized. It is a 2.5 cell standing wave cavity with a four port mode launcher, designed to operate with short rf pulses (300 ns) and cathode peak field larger than 160 MV/m. In the paper we present the realization procedure and the results of the vacuum and low power RF test. The gun is now ready for the high power test that will be performed at PSI, Switzerland.

As accelerators and electron microscopes become more advancement, high-performance photocathodes are required. In particular, CsK2Sb photocathode is of interest because of its low emittance, excitability in visible light, and high quantum efficiency (QE). On the other hand, it has drawbacks such as weak structure, limited operating vacuum pressure, and short lifetime with time or charge. To resolve these issues, it is necessary to understand the molecular structure of the cathode and its degradation mechanism. In this study, we transported CsK2Sb photocathode to a beamline of synchrotron radiation facility using a vacuum transport system for surface analysis. Specifically, the cathode was deposited at the evaporation system at Nagoya University. We transported it to Aichi Synchrotron Radiation Center (Aichi SR) away from 15 km, and analyzed it in the depth direction by X-ray photoelectron spectroscopy (XPS) at BL7U. Based on the results, we quantitatively evaluated the composition ratios and stoichiometry of the cathode element (Sb, K, Cs). A Cs excess state was observed at the surface, and it is consistent with previous studies. It was observed that K was first desorbed among the three elements of cathode with sputtering. The cause is considered that weakest binding energy of K.

The high-energy upgrade of the Linac Coherent Light Source II (LCLS-II-HE) will extend the X-ray energy range up to 20 keV. The goal is to produce low emittance (0.1 mm∙mrad) electron bunches (100 pC/bunch) and accelerate 30 μA beams through the superconducting linac to 8 GeV. A low-frequency superconducting radio-frequency photo-injector (SRF-PI) will be a key aspect of the upgrade. An SRF-PI cryomodule with a 185.7 MHz Quarter-Wave Resonator (QWR) for operation at a cath-ode field of 30 MV/m and a cathode system compatible with high quantum efficiency photo-cathodes operating at 55-80 K or 300 K are currently being developed. We report on the design and fabrication status of the SRF-PI cryomodule and cathode system for LCLS-II-HE.

Fourth generation light sources require high brightness electron beams. To achieve this a cathode with a high quantum efficiency and low intrinsic emittance is required while also being robust with a long lifetime and low dark current. Alkali-metal photocathodes have the potential to fulfil these requirements and, as such, are an important area of research for the accelerator physics community. A Cs-Te photocathode grown at STFC Daresbury Laboratory is presented. Important photoemissive properties such as quantum efficiency (QE), mean transverse energy (MTE) and lifetime have been investigated using the Transverse Energy Spread Spectrometer (TESS). Elevated MTE beyond the Cs$_2$Te photoemission threshold is reported as well the QE decrease and MTE increase when a Cs-Te photocathode is subject to progressive oxygen degradation.

During the last run, the CLARA accelerator* ran with a 2.5 cell 10 Hz S-band RF gun which had a modified back plate to allow the use of INFN-style photocathode pucks. Previously this gun had used a solid wall back plate that also acted as the photocathode**. This presentation describes the different photocathodes that were used during the run and the various methods employed to prepare them for use. An initial cathode which was based on a solid Mo puck with the thin film of Cu grown using magnetron sputtering was seen to give high initial QE but a very fast degradation rate. Subsequent cathodes were hybrids with a Mo body and a solid copper tip for the active area. Several cathodes prepared using alternative techniques were employed, giving varied initial QE and lifetime. The final cathode used had satisfactory QE and a long enough lifetime to deliver a six month period of beam exploitation for external facility users. * D. Angal-Kalinin, et al, ‘Design, specifications, and first beam measurements of the compact linear accelerator for research and applications front end’ Physical Review Accelerators and Beams 23 (2020) 044801 ** T.C.Q. Noakes, et al, ‘Photocathode preparation and characteristics of the electron source for the VELA/CLARA facility’ Proceedings of the International Particle Accelerator Conference 2018 (IPAC-18), THPMK063, 2018, Vancouver, Canada

The C-band electron gun is an attractive option for lower emittance with compactness. In this paper, a new C-band photocathode gun has been developed. The electron gun experienced a high-power test and had preliminary reached the designed gradient on the cathode. The high-power test results are the basis of the beam dynamics design and beam testing.

High brightness photoinjectors demand low thermal emittance and high electric field to deliver brighter electron beams for modern accelerator-based scientific instruments. High quantum efficiency, low thermal emittance photocathodes, mainly semiconductors, easily degrade in poor vacuum conditions and could not operate with an extended lifetime. Therefore, an ultrahigh vacuum electron gun is necessary to accommodate advanced photocathodes for high performance and reliable operation. In this paper, we report on the development of an ultrahigh vacuum, high gradient S-band gun at Tsinghua University. The gun geometry is redesigned to reach more than one order of magnitude improvement of the vacuum level at the photocathode. Preliminary commissioning results of the new gun will be presented. The new gun and beamline will partially serve as a test facility for advanced semiconductor photocathodes. We will also report on the design and commissioning results of an alkali antimonide photocathode deposition system.

X-ray free electron lasers (XFEL) and other x-ray producing light sources are large, costly to maintain, and inaccessible due to minimal supply and high demand. In addition, concepts for future electron colliders benefit from cost reduction size is reduced through normal conducting RF cavities are operated at very high gradients. It is advantageous then to consider miniaturizing electron linacs through a variety of means. We intend to increase beam brightness from the photoinjector via high gradient operation (>120 MV/m) and cryogenic temperature operation at the cathode (<77K). To this end, we have fabricated a new 0.5 cell CrYogenic Brightness-Optimized Radiofrequency Gun (CYBGORG). CYBORG serves three functions: a stepping stone to a higher gradient cryogenic photoinjector for an ultra-compact XFEL (UCXFEL); a prototype for infrastructure development useful for concepts such as the Cool Copper Collider (C^3); and a test bed for cathode studies in a heretofore unexplored regime of cryogenic and very high gradient regime relevant for the National Science Foundation Center for Bright Beams. We present here commissioning status of CYBORG and the associated beamline focusing in particular on C-band RF power development and thermal balancing of the gun in the cryogenic environment.

D-Pace has a self-heated hot-cathode Penning ion source test stand at their Ion Source Test Facility (ISTF). High-charge state production of boron, arsenic, and phosphorous is interesting to the ion implantation industry, as it allows for higher energy implants of these dopants using the same accelerating gradient in a given accelerator system. We use Neon and Krypton as proxy gases to investigate whether the Penning ion source could be used for high-charge state production in ion implanters. We were able to produce charge states up to Ne$^{3+}$ ($>$ 200 $e \mu$A) and Kr$^{6+}$ ($>$ 7 $e \mu$A). The obstacles in using the current Penning ion source test stand are discussed, with comments on how to potentially increase the current output, stability, and lifetime of this ion source.

The high-intensity, polarized electron source is a critical component for the electron-ion collider which requires a polarized electron gun with higher voltage and higher bunch charge compared to any existing polarized electron source. At Brookhaven National Laboratory, we have built and successfully conditioned the inverted HVDC photoemission gun up to 350 kV. We report on the performance of GaAs photocathode to generate 70 µA average current and up to 16 nC bunch charge with a long lifetime using a circularly polarized laser at 780 nm wavelength. We discuss the Distributed Bragg Reflector GaAs/GaAsP Super Lattice photocathode performance in the DC gun and the anode bias and voltage impact on the lifetime. The gun also integrated a cathode cooling system for potential application on high-current electron sources. The various novel features are implemented and demonstrated in this polarized HVDC.

The high Quantum Efficiency (QE) and low Mean Transverse Energy (MTE) of alkali antimonide photocathodes enable the production of bright electron beams for a variety of accelerator applications. Growing alkali antimonide photocathodes requires an elaborate growth chamber and an operator with considerable expertise. Moreover, their sensitivity to chemical poisoning requires storage in an ultra-high vacuum environment, which poses a significant challenge to their commercialization. As a step towards commercialization, we developed a “cathode-in-a-can" system to provide photoinjector facilities with high performance, air sensitive photocathodes. This system allows for a cathode to be grown at one facility, shipped in a compact vacuum-sealed canister to another facility, then removed from the canister and transferred to the photoinjector to preserve the cathode’s excellent photo-emitter qualities.

The generation of high--brightness electron beams is a crucial area of particle accelerator research and development. Photocathodes which offer high levels of quantum efficiency when illuminated at visible wavelengths are attractive as the drive laser technology is greatly simplified. The higher laser power levels available at longer wavelengths create headroom allowing use of manipulation techniques to optimise the longitudinal* and transverse** beam profiles, and so minimise electron beam emittance. An example of this are bi-alkali photocathodes which offer quantum efficiency ~ 10% under illumination at 532 nm. Another solution is the use of modified photoemissive surfaces. Caesium has a low workfunction and readily photoemits when illuminated at green wavelengths (~532nm). Caesium oxide has an even lower workfunction and emits at red wavelengths (~635nm). We present data on our work to create a hybrid copper photocathode surface modified by implantation of caesium ions, measuring the surface roughness and probing its structure using MEIS. We measure the energy spread of photoemitted electrons, the QE as a function of illumination wavelength, and the practicality of this surface as a photocathode by assessing its lifetime on exposure to oxygen.

In this paper, a cooling scheme was designed for the THU VHF gun, and simulations of thermal and structural analyses were conducted. A total of 19 independent cooling channels were designed and distributed on the gun to remove the heat generated. The maximum temperature was 67.8 ℃ with a total flow rate of 3.28 L/s and dissipation power of 92.5 kW. The accelerating gap distance decreased by 124 um when heat and vacuum loads were applied. The tuning efficiency was 2.075 kHz/kN, and the maximum stress was 65.2 MPa. It is safe to conclude that the cooling scheme of the THU VHF gun meets the thermal and structural requirements and shows good properties in the temperature, deformation, and stress distributions. Future publications will thoroughly discuss the recent progress of the THU VHF gun.

Strong laser-field electron emission enhanced by nanostructures is a growing topic of study, owing to its ability to generate high brightness beams. Experiments have shown that the nanoblade structure, a wedge shape, notably outperforms nanotips in the peak fields achieved. These higher fields result in a brighter emission. In this paper we study the thermodynamics of the electron system restricted to a nanostructure. Thermal diffusion of deposited energy near the apex of the structure is dominated by the electronic distribution on the electron-phonon timescale. We show analytically through use of the temperature-squared heat equation that the nanoblade, owing to its larger opening angle and higher dimensionality, thermomechanically outperforms the nanotip.

Electron beams serve many important roles from free electron lasers to medical imaging. Every time beam brightness is improved, a wide variety of fields take another step forward. Nanopatterned field emission cathodes serve as an excellent opportunity to continue to push the envelope on extreme high brightness beams. Their fabrication is thus of crucial importance to this objective. In the past KOH wet etching was performed to create two atomically sharp ridges. This is done by leveraging the selectivity of KOH to etch along a single plane in the silicon crystal. This process is generally used in micro-machining to create a whole array of atomically sharp ridges and cannot be used to produce less than 2. By adopting a different nanofabrication process, a single ridge can be isolated. Additionally, more flexible nanofabrication techniques can be employed to create novel arrangements of blades, such as concentric rings of ridges.

The minimum achievable particle beam emittance in an electron accelerator depends strongly on the intrinsic emittance of the photocathode electron source. Reducing the electron beam emittance in an accelerator which drives a FEL delivers a significant reduction in the saturation length for an X-ray FEL, thus reducing the machine’s construction footprint and operating costs whilst increasing X-ray beam brightness. The intrinsic emittance is correlated to the mean transverse energy (MTE), therefore measuring the MTE is a notable figure of merit for photocathodes used as electron sources. This work presents the Transverse Energy and Momentum Analyser (TEMA), a system which will measure the MTE of different cathodes, such as Cs_2Te currently used at FLASH and European XFEL.

The photoinjectors of FLASH at DESY (Hamburg, Germany) and the European XFEL are operated by laser driven RF-guns. In both facilities cesium telluride (Cs$_2$Te) photocathodes are successfully used since several years. We present recent data on the lifetime and quantum efficiency (QE) of the current photocathode at FLASH \#105.2, operated before and after a long shutdown. In addition, data for the cathodes that recently have been exchanged at the European XFEL will be presented.

An electron beam test stand was designed and constructed at CERN, under the umbrella of the Hi-Lumi project, to tests components for the Hollow Electron Lens (HEL), and in collaboration with the ARIES project for testing the Space Charge Compensation gun. The test facility features normal conductive magnets providing solenoid fields of the order of fractions of Tesla, beam diagnostics including screens (YAG, Cromox and OTR) for the full electron beam characterisation, a Faraday Cup collector to measure the total electron current, and a high voltage power supply up to 40 kV (with the possibility of biasing both gun and collector). It offers the possibility of testing high current and high perveance guns, different beam instrumentation (Beam Position Monitors and Beam Gas Curtain monitors are some examples), electron collectors, and beam pulse modulators. In this paper the facility is described and the first results validating the design of the HEL gun are presented.

Our laboratory has been studying about polymer electrolyte membrane (PEM) for polymer electrolyte fuel cell (PEFC) by irradiation graft polymerization using electron beam accelerator. Irradiation graft polymerization can reduce the production cost of the PEM compared with the current product, perfluoro-sulfonic acid (PFSA) ionomer such as Nafion®︎ by DuPont. We have two methods to fabricate high-performance PEMs using the accelerator. One is to give the micro-structure of hydrophilic and hydrophobic region to the PEM. The other is to generate the concentration gradient of hydrophilic region inside of the PEM. Both methods were able to generate high power density as much as Nafion®︎. In previous study, we used ion beam to give these characteristics. Ion beam has highly straightness and easy to create micro-structure and the concentration gradient of hydrophilic region inside of the PEM. But, its production equipment costs too much. Therefore, in this study, we use electron beam that production equipment costs less than ion beam and fabricate the PEM which has above both methods for advanced application of the electron beam accelerator.

SOLARIS injector LINAC is designed to efficiently fill the electron storage ring. The injection currently takes place at 540 MeV, two times per day. After the accumulation of electron current, the energy is ramped up inside the ring to 1.5 GeV via two active RF cavities. Top-up injection would be of extreme benefits for user operation, therefore here we present a simulation study for the design of a new injector that would make this possible in the future. The major constraint for the simulation campaigns has been the space available in the existing LINAC tunnel. The idea is to replace the current machine (or modifying it) without infrastructural interventions in terms of tunnel expansion. Performed studies demonstrate that the best solution is provided by a Hybrid S-band/C-band LINAC. Simulations have been performed using different codes and results are shown here. Finally, a new machine working at 1.5 GeV would also pave the way to further diagnostic and/or experimental beamlines for particles and radiation solely based on the LINAC. In particular, one of the main goals is to achieve bunch compression below the picosecond level and low-emittance beams for a future short-pulse facility or a Free Electron Laser.

In order to promote the studies of low emittance RF photo cathode and high gradient accelerating structures, a C-band test platform has been initialized since late 2021. In this paper, an overview of the present status and future plans of this platform is given, including a 3.6-cell C-band RF photo cathode and a C-band RF traveling-wave accelerating structure. In addition, other on-going studies on this platform, such as the test of a cryo-copper accelerating structure and the development of short pulse high gradient parallel-coupled structures, are briefly introduced.

Ultrafast electron diffraction (UED) is a powerful tool for the direct visualization of structural dynamic process-es in matter on atomic length and time scales. Observa-tions on a femtosecond time scale with atomic resolution spatially have long been a goal in science and are current-ly achieved with large photo injectors developed for FEL frontends. Here we demonstrate a compact 180 keV photocathode S-band electron gun, which employs field-enhancement at a pin-shaped cathode to produce an extraction field strength of 102 MV/m driven by a rack-mountable solid state 10 kW peak power supply. Simula-tions predict that high-brightness electron bunches with RMS duration of 10 fs, a radius of 135 μm, and spatial emittance of 0.1 mm-mrad are possible for a bunch charge of 10 fC. The impact of laser spot size and dura-tion, as well as their spatial distribution, on the temporal bunch length of electrons on the specimen was investigat-ed. Following the successful completion of the condition-ing phase of the RF gun and multipacting suppression, photo-triggered electrons using a UV laser on the photo-cathode were observed.

The ARES linac at DESY (Deutsches Elektronen-Synchrotron) is a dedicated accelerator research and development facility for advanced accelerator technologies and applications, including high gradient accelerating schemes, high-resolution diagnostics and medical applications. It provides ultra-short, high quality electron beams with charges between a few femtocoulombs and a few hundred picocoulombs, with energies up to 155 MeV, characterized by high reproducibility and stability. The electron bunches are generated in a photoinjector comprising a UV laser and a normal conducting S-band gun with an exchangeable cathode material, enabling the required wide charge range and temporal bunch profile. A set of movable mirrors allows to change the position of the laser spot on the cathode, which in combination with bunch charge diagnostics downstream of the gun can be used for measuring the extracted charge as a function of the laser position. With this method the emission homogeneity and changes of the cathode can be studied and different cathode materials can be compared. We present the first results using this technique at ARES, including charge map and quantum efficiency (QE) measurements.

A research project was initiated at HZB to develop a new E-Gun control system for the Linac Gun to realize the advanced demands from the BESSY II injection scheme. The Flexi-Gun system will allow significantly higher flexibility in both pulse load and pulse timing structure. The purpose built gun test stand is equipped with a diagnostic beamline. Developed and manufactured in-house, the potential for knowledge transfer has led to a collaboration with ALBA for start-to-end particle tracking simulations. This article presents the motivation and potential of the Flexi-Gun, the development of the driver board and control, and the first measurements of the beam parameters. With the "Flexi-Gun" project, the upgraded Linac E-Gun becomes the optimal injector for BESSY II.

Plasma accelerators are emerging as formidable and innovative technology for the creation of table-top devices thanks to the possibility to sustain several GV/m accelerating gradients at normal conducting temperature. Among others, the particle-driven configuration has been successfully tested at the SPARC_LAB test facility also demonstrating the emission of plasma-based FEL radiation in SASE and seeding operation. Recently we have performed further experimentals devoted to heightening the accelerating gradient in the plasma. The so-called comb beam has been set up with a 500pC driver followed by a 50pC trailing bunch. The maximum measured energy gain in the plasma has been of almost 30 MeV turning in an accelerating gradient of the order of 1.2 GV/m. The result represents a fundamental achievement also looking at the forthcoming EuPRAXIA@SPARC_LAB plasma-based user facility. Further experimental runs are planned for the next year on the measurements of transverse quality of the electron beam and its eventual preservation. The paper reports on the obtained experimental results and on the numerical studies for the next future experiment at the SPARC_LAB test-facility.

This talk will report on the status C-band high gradient research program at Los Alamos National Laboratory (LANL). The program is being built around two test facilities: C-band Engineering Research Facility in New Mexico (CERF-NM), and Cathodes And Radio-frequency Interactions in Extremes (CARIE). Modern applications require accelerators with optimized cost of construction and operation, naturally calling for high-gradient acceleration. At LANL we commissioned a high gradient test stand powered by a 50 MW, 5.712 GHz Canon klystron. The test stand is capable of conditioning accelerating cavities for operation at surface electric fields higher than 300 MV/m. CERF-NM is the first high gradient C-band test facility in the US. CERF-NM was fully commissioned in 2021. In the last several years, multiple C-band high gradient cavities and components were tested at CERF-NM. Currently we work to implement several updates to the test stand including the ability to autonomously operate at high gradient for the round-the-clock high gradient conditioning. Adding capability to operate at cryogenic temperatures is considered. The construction of CARIE began in October of 2022. CARIE will house a cryo-cooled copper RF photoinjector with a high quantum-efficiency cathode and produce an ultra-bright 250 pC electron beam accelerated to the energy of 10 MeV. The status of the facility, the designs of the photoinjector and the beamline, and plans for photocathode testing will be presented.

We present our 1.6-cell radiofrequency cavity design for a photoinjector under development for producing intense electron bunches with 250-pC beam charge and normalized emittance below 100 nm rad for cryogenic temperature operation. The cavity cell profile was designed by SLAC and UCLA, optimized for maximal shunt impedance and minimal peak magnitude of the electric and magnetic field. The pi-mode accelerating fields are established in the cells with power coupled into each cell individually through the slot on the sidewall, and the peak electric field magnitude has been tuned to be equal in the two cells. The coupling waveguide network was designed to achieve critical coupling into the port of the input power waveguide and to achieve the desired power distribution. The cavity design has been completed for initial high-gradient test at room temperature.

In high-gradient accelerator structures, field emission produces dark current that behaves much differently than the main photobeam current. This dark current can damage accelerator components and increase the radiation dose in the surrounding area. Thus it is important to analyze its behavior when designing a new accelerator or subsystem, such as the superconducting low-emittance injector (LEI) currently under development for the LCLS-II high-energy upgrade (LCLS-II-HE). In principle, the emission of dark current is governed by the Fowler-Nordheim (FN) equation*. In practice, variations in surface quality result in localized emission sites at locations that are not predictable a priori. Since the superconducting gun for the LEI does not exist yet, particles must be tracked from a dense array of initial positions and times on all likely emission surfaces and assigned weights according to the FN equation in the early design phases to inform the placement of collimators. We present the results of tracking studies using BMAD** and Python to analyze dark current in the LEI.

A typical commercially available thermionic triode e-gun operates in 10-15 kV range. Certain linac accelerating structures may benefit from higher voltage injection. Based on commercially available low voltage e-guns Varex Imaging High Energy Sources Group has developed an e-gun that could be operated in extended range of voltages of 10-40 kV, provides high adjustability of injecting beam parameters. The new e-gun can be utilized with both triode and diode options

In this paper, we present the benchmark results of Bmad space charge tracking on the Electron-Ion Collider cooler injector lattice. Bmad, GPT, and Impact-T are compared in terms of accuracy and performance. We highlight the importance of space charge algorithm and demonstrate that the adaptive step size control improves the performance of Bmad space charge tracking.

Nanostructured electron sources exhibiting simultaneous spatio-temporal confinement to nanometer and femtosecond level along with a low emittance can be used for developing future ordered electron sources to generate unprecedented electron beam brightness and can revolutionize stroboscopic ultrafast electron scattering and steady-state electron microscopy applications. In addition, high current density electron beams generated from nanostructured electron sources can be used for applications that include nanoelectronics and dielectric laser accelerators. In this work, we report our efforts to develop and characterize two kinds of nanostructured electron sources: (i) nitrogen incorporated ultrananocrystalline diamond [(N)UNCD] tips and (ii) plasmonic Archimedean spiral focusing lens. We demonstrate the ability to fabricate these cathodes and characterize them using a photoemission electron microscope under femtosecond laser illumination thereby demonstrating the ability of these structures to be used for next generation electron sources.

Integrating the advances made in photonics with efficient electron emitters can result in the development of next generation photocathodes for various accelerator applications. In such photonics-integrated photocathodes, light can be directed using waveguides and other photonic components on the substrate underneath a thin (<100 nm) photoemissive film to generate electron emission from specific locations at sub-micron scales and at specific times at 100 femtosecond scales along with triggering novel photoemission mechanisms resulting in brighter electron beams and enabling unprecedented spatio-temporal shaping of the emitted electrons. In this work we have demonstrated photoemission confined in the transverse direction using a nanofabricated Si3N4 waveguide under a ∼20 nm thick cesium antimonide (Cs3Sb) photoemissive film. This work demonstrates a proof of principle feasibility of such photonics-integrated photocathodes and paves the way to integrate the advances in the field of photonics and nanofabrication with photocathodes to develop next-generation high-brightness electron sources for various accelerator applications.

For the Linac travelling wave S-band injector at ELSA a new electron gun is being designed, to enhance the beam parameters of the old gun. Furthermore, a new single bunch injection mode is to be realized alongside the standard long pulse (multi bunch) mode, allowing to use the gun for normal operation for the experimental program as well as enabling single bunch operations for accelerator research and development. For that matter a dual-use design is pursued utilizing a dispenser cathode both as photo- as well as thermionic cathode. First steps including the design of the gun assembly and studies about its usability as a photoemitter are conducted. A preliminary design of the gun assembly and simulation results are presented.

A prototype electron lens for space charge compensation in the synchrotron SIS18 that could pave the way for pushing the space charge limit of hadron synchrotrons is currently under development at GSI. Accompanied by beam transport simulations, a 3D construction model is being worked out as well as the integration into the existing accelerator facility. The electron gun and collector conceptual design studies are completed and their technical design is ongoing. In a continuing collaboration with GSI, an electron lens test stand was designed and constructed at Goethe-University Frankfurt in order to commission major parts of the electron lens e.g. electron gun, collector and diagnostics. The demonstration of beam extraction from a tungsten cathode heated by an arc discharge, technically realized in the IRME-gun that was developed within the ARIES collaboration*, is under preparation and first results of this new heating concept look very promising. In this contribution, the conceptual layout of the electron lens and its major components will be outlined as well as its preliminary technical layout. Furthermore, first measurements of the electron beam extracted from the IRME-Gun will be presented.

Extraction of beam from the Fermilab Delivery Ring for the Mu2e Experiment is hindered by large radiative losses initiated within the electrostatic septum (ESS) components of the resonant extraction system (RES). Of particular concern are beam losses causing potential damages to the support components of the RES, diminished intensity for experimental statistics, and high radiation levels in the area of the RES. Here we present the detailed study of beam energy deposition and radiation levels of components and surrounding regions of the ESS in the RES at Fermilab using the MARS Monte Carlo code system.

In a linear collider, the colliding beam has to be flat in the transverse plane to suppress energy spread by Beamstrahlung and to maximize the luminosity, simultaneously. In the current design of ILC, the flat beam is realized by the asymmetric emittance generated by the radiation-damping effect. We propose to generate the equivalent beam directly in the injector linac employing the emittance repartitioning. As an experimental demonstration, a beam experiment was carried out at KEK-STF. We present the experimental results.

A simple acceleration of a high charge, needle-shaped electron bunch from a cathode is affected by strong correlated emittance growth due to current-dependent transverse space-charge forces. It was shown that such emittance growth could be reversed by focusing the bunch soon after it emerges from the cathode, and that one can expect to retrieve the emittance the beam was born with – the intrinsic emittance. We present a space charge emittance compensation study for a 250 pC radiofrequency photoinjector based on a 100 pC design developed by the UCLA team. We expect that a bright electron beam with an order of magnitude improvement over currently operating photoinjectors can be achieved with 250 pC electron bunches that maintain their emittance below 100 nm-rad.

The upgrade of the European XFEL to support a future high duty cycle (HDC) operation mode requires new design concepts for the photoinjector. In particular, the electron gun is crucial for achieving high quality beams at high peak currents. Among other variants, a 1.6-cell TESLA-type RF-gun is the preferable solution for the HDC EuXFEL. The SRF gun design, however, requires the application of unconventional emittance compensation schemes. One alternative is embedded RF focusing by means of a retracted cathode. Such a scheme has been previously successfully tested, e.g., at the ELBE accelerator of the HZDR. However, the beam dynamics characterization and parameter optimization for this design remains a challenge. This is primarily due to the 3D geometry of the cathode region, which cannot be easily handled by available tracking codes. In this work, we present a simulation and optimization study of the EuXFEL injector line including the geometrical and space charge effects related to a retracted-cathode SRF gun design.

In the injector section of electron linacs, both internal space charge forces and wakefield effects influence the beam dynamics. To account for both effects, full electromagnetic PIC simulations are usually required. Unfortunately, PIC solvers require large computational resources. On the other hand, particle-tracking codes in the bunch reference frame describe the beam dynamics under space-charge fields. These codes, however, often fail to include the effect of geometric wakefields especially for low energy beams. As an alternative modeling approach, we propose to decouple the wakefield scattered by the geometry from the space-charge field. Then, we use for each of the contributions the simulation approach that is more appropriate for the respective interaction. We decompose the total electromagnetic field into an incident and a scattered part. The incident field is computed by a space-charge solver in the rest frame of the bunch assuming that particles are in free space. Since this field does not fulfill the boundary conditions at the chamber walls, it acts as an excitation for the scattered part. The latter can be efficiently computed using a particle-free wakefield code. In the full paper, we will present beam dynamics simulations for the injector section of the European XFEL. The aim of these simulations is the quantification of the uncorrelated energy spread induced by geometric wakefields at low energies, which so far is not considered in existing wakefield models.

The performance of superconducting cavities depends extremely on the material and surface properties. In the last decades processes have been developed for the successful series production of accelerating cavities needed for large scale facilities like the European XFEL. A main feature of these cavities are relatively large beam ports on both sides which can be used for the surface treatment processes. In contrast, superconducting gun cavities have only one beam port and a half-cell with a back-wall acting as mirror plate with some small space for the cathode in the center. Being apparently only a small feature, this fact tuns out requiring special attention for the surface treatment. This is in particular the case, if the target are similar high gradients like in the accelerating cavities. In our contribution we present the experience made within the last years and how we finally achieved high gradients.

The electrodeposition of copper onto niobium using commercial acidic and alkaline electrolytes was tested. The continuous dense polycrystalline copper films were successfully obtained in aqueous alkaline-type bath containing copper sulphate, sodium hydroxide and sodium gluconate. The effect of benzotriazole and sodi-um lauryl sulphate additives on the morphology and crystal structure of the deposited copper was investigat-ed by optical and scanning electron microscopy, and X-ray diffraction. No copper oxides were found in the grown films. Copper films had moderate adhesion properties that would be insufficient for cryocooler application. We are currently exploring different com-positions of electrolyte baths for obtaining the coatings on niobium with improved adhesion.

The European Spallation Source (ESS) will accelerate a beam of protons with a beam pulse width 2.86ms long and pulse repetition frequency 14Hz. The acceleration will be provided by 155 cavities, out of which 97% of the cavities are superconducting. The first section of the ESS superconducting linac is the Spoke linac. The spoke linac increases the beam energy from 90MeV to 216MeV using the 26 superconducting Spoke cavities, resonant at 352MHz, situated in 13 cryomodules. The spoke cavities are powered by Spoke RF Power Stations (RFPS). The maximum power requirement for the spoke RFPS is 400kWp@352MHz. Outputs of two tetrode TH595A based amplifiers are combined to achieve 400kW output. The RFPS are delivered by Elettra as a part of Italian in-kind contribution towards the construction of ESS. The detailed design of RFPS is done by ESS and Elettra. At present, 27 RFPS are delivered to ESS. Out of these, 20 RFPSs are installed and commissioned at ESS gallery. Out of these, four RFPSs are under soak testing at 400kWp and four RFPSs are under soak testing at 300kWp. The present paper discusses test results, issues faced during soak testing and their possible mitigations.

The cost of a klystron for the SNS is estimated to be in the $200K range. A magnetron with the same power level is about one-fourth the cost. With ancillary equip-ment to functionally duplicate the performance of the klystron and allowing for the reduced lifetime of the magnetron compared to the klystron, about half the cost. Additional operational cost savings are related to the 805 MHz magnetron 90% efficiency, which for some applica-tions is twice that of a corresponding klystron.

NEG-coated chambers have been adopted as the beam ducts for large particle accelerators and synchrotron light sources for the sake of the lower yields of the photon stimulated desorption (PSD) and the photoelectrons (PE) from the NEG films in addition to their pumping performance. Measurement of the photoelectron yield (PEY) was performed at the BL19B (PSD) beamline of the 1.5 GeV Taiwan Light Source (TLS) which simultaneously measures the PSD-yield. An aluminium cathode was inserted in the tubes and a positive bias of voltage for extraction of the photoelectrons applied. The PEY was obtained by dividing the photoelectron current by the photon flux of the synchrotron radiation. Measurements of the PEY include various types of NEG-coated stainless steel tubes and the bare tubes of titanium and aluminium alloys for the comparison. The experimental system and the results will be described in this presentation.

The 288m long SLS 2.0 Storage Ring consists of several vacuum chambers with unique geometries. Complicated features, with many changes in the cross sections, are essential to provide the best impedance matching and to allow synchrotron light extraction under the tight geometrical constraints. In order to speed up the commissioning time, it was decided to NEG coat most of the vacuum chambers. A new magnetron sputtering setup has been developed in Paul Scherrer Institute, where the plasma length, defined by thin solenoids, is relatively small. The solenoids are then travelling over the entire vacuum chambers more than ten times per coating process to assure best possible thickness uniformity. Flexibility provided by this solution allows to coat various vacuum vessels in one assembly. This paper will describe this NEG coating setup and show results on SLS 2.0 vacuum chambers.

The Superconducting RF photo-injector with the prototype 1.4 lambda/2-cell Niobium cavity of the bERLinPro Energy Recovery Linac (ERL), recently renamed to SEALab*, was tested and characterized in a dedicated beam test facility called Gunlab to analyze its performance for the ERL**. After dismantling and refurbishing of the cavity, a small surface defect was found close to the cathode opening and by simulated reconstruction of the set-up it was demonstrated to be the main source of the dark current measured at Gunlab. Later, a method was found to remove that defect***, but still the question remains, what amount of dark current is acceptable for an ERL injector, especially for the SRF systems? In this contribution, we show a fully 3D simulation based emulation of the dark current measurements in Gunlab and extrapolate the impact on the complete injector at bERLinPro (SEALab). Here, it can be shown, that besides a small meshed beam loss diagnostics, methods need to be found to determine the amount of field emitted current dumped into the SRF systems.

Ultrashort electron beams with high brightness are of vital significance in probing nanoscopic dynamics on the pico-to-femtosecond temporal scales. Electron sources are the most critical element in such apparatuses, whose advancements are expected to further improve the resolving capabilities. In this contribution, we report on the development of a DC photocathode electron gun aiming at delivering optimal-quality electron beams for ultrafast electron scattering and photocathode studies. The 200 kV gun features simplicity and adjustability in fabrication and assembling, and is compatible with INFN/DESY/LBNL-type photocathode plugs. The design, fabrication and conditioning processes of the gun are discussed in detail, along with preliminary beam measurement results where nm-scale emittance is demonstrated.

We built a test stand for evaluating the performance of the thermionic electron sources for the electron lens project at the Integrable Optics Test Accelerator (IOTA) in Fermilab. The lens will be used to study nonlinear dynamics and electron cooling of 2.5 MeV protons with strong space charge. The test stand will validate the characteristics of the thermionic sources and the main parameters of the generated beams. In this paper we present the results of the commissioning of the UChicago test stand and validation of the hollow beam source.

The brightness of the beam in any linear accelerator can be no greater than at its source. Thus characterization of source initial conditions, including spatial and momentum distributions, is then critical to understand brightness evolution in a linac. Often measurement of the initial momentum distribution is hampered by imperfect knowledge of either the spatial source distribution or the downstream particle optics. Here we describe a method of recovering the transverse momentum space of a beam at the particle source without prior knowledge of the electron optics used to obtain the phase space or any source parameters; only linearity of the transport is assumed. We then demonstrate this method experimentally by measuring a 4D phase space using an aperture scan and subsequently recover the transverse phase space of a beam emitted by an alkali antimonide photocathode.

The Laser Powder Bed Fusion (LPBF) is an AM technology suitable to produce almost free-form metallic components. At Legnaro National Laboratories of the Italian National Institute for Nuclear Physics, the LPBF process was recently used to produce parts of the Forced Electron Beam Induced Arc Discharge (FEBIAD) ion source for the SPES Isotope Separation On-Line (ISOL) facility. Such device is a critical component for the ISOL process, as its correct functioning is fundamental to ensure the availability of the radioactive ion beam to the experimental users. One of the main parts of the ion source is the tantalum cathode, a component that is electrically heated up to 2200°C and is subjected to thermal stresses. Currently, the cathode is produced by subtractive manufacturing processes and TIG welding, which are not trivial in the case of Tantalum. Therefore, the cathode lacks dimensional/geometrical precision, affecting the performance repeatability and reliability of the ion source. The LPBF technology allows to perform a morphological/topological optimization of the cathode aiming to overcome the intrinsic assembly limits of the present design and making more repeatable and reliable the ion source performance. In this work, the production of the prototypical cathodes via AM, the results of dimensional–geometrical measurements, and the endurance high-temperature test are presented.

Anodic bonding technology is a method which mainly by the aid of the electric field and temperature for connecting two materials such as glass-glass or glass-silicon wafer substrate by forming covalent bonding. The bent monochromator used in the synchrotron radiation which was made by high quality silicon wafer bonded onto concave cylindrical shape Pyrex glass base. In the past, it is made by gluing. The anodic bonding method for fabricating the bent monochromator which has more advantages than bonding by glue, such as tight bonging, non-intermediate, and simple process. This paper describes the detailed manufacturing processes and testing results.

Additive Machining (AM) technology is already used in many manufacturing domains and provides many benefits such as design freedom, cooling, and performance improvements as well as significant manufacturing time reduction. AM is also being considered for the manufacture of a Radio Frequency Quadrupole, where an important unknown is the voltage holding capability of AM surfaces. To address this question a series of high electrical field tests was performed on additively manufactured (AM) pure copper electrodes using the CERN pulsed dc high-voltage system. The tests were carried out with different test surface conditions such as “rough”, as built by AM, post-processed and machined. During each test, an ultra-high vacuum was maintained, and the breakdown rate monitored by changing the electric field level and pulse structure. The initial results provide the first reference values for AM built pure copper electrodes performance under vacuum arc breakdown test. According to test results, AM process and material powder characterisation as well as post-processing will be improved in preparation for RF power and beam tests on a full RFQ prototype.