A quadrupole wiggler consisting of a row of alternating-polarity permanent magnet-excited quadrupoles is used in a collinear wakefield accelerator under development at Argonne National Laboratory. Fine translational and angular adjustment mechanisms are implemented in all quadrupoles to obtain a better than $1\text{−}\mathrm{\mu }\mathrm{m}$ precision in the alignment of quadrupole wiggler assemblies. The quadrupole’s magnetic and mechanical designs are described. Two wiggler prototypes were fabricated, aligned, and characterized performing pulsed wire magnetic measurements. The sensitivity of the quadrupole wiggler alignment to the ambient temperature was measured.

The electron-ion collider crab Cavities will present a significant transverse impedance to the beam. The low-level radio frequency system will have to reduce the crab cavity impedance to prevent transverse instabilities, while regulating the crabbing voltage and minimizing the radio frequency noise levels injected into the beam. This work presents an estimate of the crab cavity impedance in the presence of feedback and the resulting stability margins using simplified stability criteria. Generalized stability criteria are also presented in this work and are used to more accurately estimate stability margins.

Hybrid multibend achromat (MBA) lattice with a pair of dispersion bumps separated by $-I$ transformation is used in some diffraction-limited storage ring (DLSR) designs, which can obtain relatively large dynamic apertures. However, the $-I$ transformation also largely restricts the horizontal tune of the lattice cell. In this paper, an MBA lattice with four dispersion bumps is proposed, which has relatively good flexibility in adjusting the number of bends in the lattice cell and the lattice cell tunes, while also achieving the effective sextupole cancellation within the lattice arc section. The new lattice can have a larger horizontal cell tune than the hybrid MBA lattice with the same number of bends, which is beneficial for reducing the emittance. In the new lattice, $-I$ transformation is not necessary for the sextupole cancellation between paired bumps, and a general relation of sextupole cancellation is used. Following this lattice concept, a 7BA lattice is preliminarily designed for a 1.5 GeV DLSR. This lattice concept can also be extended to the case of MBA lattice with more bumps.

In this contribution, we present the design of a resonant slow extraction based on the radio-frequency knockout (rf-KO) scheme, where we make use of the transverse resonance islands bucket (TRIB) optics. The generation of the TRIB optics is presented in two example lattices, which are considered for the potential upgrade of the current booster at DESY. The slow extraction studies are motivated to potentially supply high energy electron beams to the high energy physics beamline users. Simulations show an extraction efficiency in excess of 90% with a septum blade thickness of $100\mathrm{\mu }\mathrm{m}$.

GaAs-based photocathodes are the only viable source capable of providing spin-polarized electrons for accelerator applications. This type of photocathode requires a thin surface layer, in order to achieve negative electron affinity (NEA) for efficient photoemission. However, this layer is vulnerable to environmental and operational effects, leading to a decay of the quantum efficiency $\eta$ characterized by a decay constant or lifetime $\tau$. In order to increase $\tau$, additional agents can be introduced during the activation procedure to improve the chemical robustness of the surface layer. This paper presents the results of recent research on Li as an enhancement agent for photocathode activation using Cs and ${\mathrm{O}}_2$, forming Cs-${\mathrm{O}}_2$-Li as an enhanced NEA layer. Measurements yielded an increase in lifetime by a factor of up to $19\pm 2$ and an increase in extracted charge by a factor of up to $16.5\pm 2.4$, without significant reduction of $\eta$. This performance is equal to or better than that reported for other enhanced NEA layers so far.

Proton therapy presents an interesting and important challenge to accelerator physics. Practical restrictions such as room size, gantry weight, and cost have led to a demand for more compact and affordable devices. Success would benefit a significant number of patients every year. Dielectric wall accelerators could provide this breakthrough, but there is limited work available regarding their feasibility or possible integration into medical devices, and no solutions exist for longitudinal beam control. In this work, we discuss the development of a linear beam dynamics model for dielectric wall accelerators. The model is implemented as part of the open-source code transoptr. It is tested against the rf LINAC subroutine in transoptr and is used to study bunch injection and transport. Building on recent work, the effect of time-varying fields on beam dynamics is also investigated. Conditions for limiting transverse beam size and maintaining longitudinal stability are discussed, and considerations are given to accelerator and beamline design.

We investigate properties of optical elements in the optical cavity of an x-ray laser oscillator with emphasis on the power loss of a monochromatic Gaussian radiation beam upon passing through them using analytical and numerical approaches. Here we assume the optical cavity comprises of refractive lenses and Bragg crystals exploiting symmetric Bragg scattering. For the lens, we include focusing and curvature effects while we include angular filtering due to finite Darwin width of the Bragg crystal. Our results indicate the feasibility of x-ray power out-coupling in the range of 0.5%–28% with intracavity reflectivity of 67%–95% at 10.321 keV for nominal ($\ge 65\%$ reflectivity) cases. We also show the possibility of achieving high out-coupling of 35%–80% while restricting the intracavity reflectivity in the 19%–62% by adopting lossy cavities with $10–20\mathrm{\mu }\mathrm{m}$ thin crystals.

This paper introduces a novel bead-falling measurement method for the precise and efficient mapping of electromagnetic fields within radio-frequency (rf) cavities, which are crucial components in the design of accelerators. The traditional bead-pull method, while effective, involves mechanical complexities and is prone to errors from wire perturbations. The innovative method reported here leverages the simplicity and accuracy of free-falling beads to mitigate these issues. This technique eliminates the need for a wire-pulley system, thereby simplifying the experimental setup and reducing potential mechanical errors. We detail the development and operational principles of this new method, including the design of a compact, portable measurement device that integrates a bead/droplet release system and a bead detection system linked to a vector network analyzer. The device has been tested with a three-gap buncher cavity and a scaled Alvarez-type cavity, demonstrating its ability to perform rapid, reliable field measurements under various challenging conditions, including low signal-to-noise ratios and environmental vibrations. The results confirm the method’s superiority in precision and operational efficiency, potentially setting a new standard for rf cavity diagnostics and tuning.

The generation of electron bunches on the attosecond timescale is important for a multitude of accelerator-based applications. Here, we report on a tomographic measurement of the (pre)linearized longitudinal phase space of a low charge 3 MeV electron bunch generated with the 1.6 cell Pegasus photoinjector for the generation of attosecond bunches. The nonlinear correlations in the longitudinal phase space induced by space charge at the photocathode, radiofrequency field curvature of the gun, and vacuum dispersion are compensated using a compact X-band linearizer. Then, the initial and compensated phase of the picosecond electron bunch is precisely reconstructed by neural network assisted tomographic reconstruction from momentum spectra at varying buncher linac phase. Finally, we combine the measured phase space shape with particle tracking simulations to show that electron bunches as short as 941 as develop downstream the beamline.

In the main ring (MR) of the Japan Proton Accelerator Research Complex, one of the primary sources of beam loss is the betatron resonance. A factor determining the strength of betatron resonances is the symmetry of optics, which relies on the quadrupole field errors in the ring. In the beam tuning of the MR, correcting quadrupole field errors plays a significant role in reducing beam loss. This paper introduces and examines a precise method to evaluate time-varying quadrupole field errors at individual quadrupole magnets around the ring through closed-orbit measurements in the MR. By applying this method, we experimentally determined substantial quadrupole field errors due to eddy currents on the vacuum ducts during acceleration. The methods developed in this paper are employed in the beam tuning for the user operations of the MR.

The beam response to an external periodic excitation delivers relevant information about the optics, tune distribution, and stability of a circulating beam in a storage ring. In this contribution, the horizontal beam response to the excitation (transfer function) under conditions typical for slow extraction is presented for a coasting beam. The resulting spectrum exhibits a splitting behavior. The single particle dynamics is discussed and an interpretation based on the simulation results is presented.

In this paper, we use one-dimensional measurements to infer the four-dimensional phase space density of an accumulated proton beam in the Spallation Neutron Source (SNS) accelerator. The reconstruction was performed by maximizing the distribution’s entropy subject to the measurement constraints and thus represents the most conservative inference from the data. The reconstructed distribution reproduces the measured profiles down to the noise level, and simulations indicate that the problem is reasonably well constrained. Similar measurements could serve as benchmarks for beam dynamics simulations in the SNS or hadron accelerators.

Plasma cleaning is extensively employed in superconducting radio-frequency (SRF) accelerators to mitigate field emissions induced by hydrocarbon contaminants. This study explores the plasma physical characteristics and modulation techniques in a commonly utilized 1.3 GHz 9-cell tesla-shaped SRF cavity through the integration of optical emission spectroscopy and a plasma fluid model. Investigations of argon and neon plasma demonstrate that argon generates a higher electron density due to its lower ionization energy, while neon plasma exhibits higher electron temperature and potential that promotes the decomposition of oxygen and the rate of surface chemical reactions. Furthermore, the research reveals that the electron density, temperature, and electric potential of the neon plasma within the cavity exhibit a centrally symmetric distribution, with maximum values of $1\times {10}^{15}{\mathrm{m}}^{-3}$, 0.53 eV, and 24.5 V, respectively. Subsequently, the effects of power, gas pressure, and frequency on the physical properties of the plasma are systematically analyzed. Among these, the 640 nm spectral line was selected as a qualitative indicator of glow intensity and plasma state changes within the cavity due to its strongest peak intensity. Findings indicate that increasing power and gas pressure enhance electron density and 640 nm spectral line intensity while reducing electron temperature. Additionally, comparative analysis of plasma properties in cells 1-9 reveals that most cells exhibit higher electron temperature and electron density at frequency II. (Frequency I serves as the transfer mode for plasma transfer, while frequency II acts as the stable mode for plasma stabilization.) Consequently, plasma cleaning of the 1.3 GHz 9-cell cavity using neon gas at this frequency is anticipated to yield superior cleaning outcomes. These findings enhance our understanding and control of plasma behavior within the SRF cavity and provide valuable insights for optimizing plasma cleaning processes.

For double-ring colliders, it is a vital task to make the two beams meeting each other properly at the interaction point. BEPCII is a double-ring collider that operates in the decay mode, as the beam currents decrease over time, the beam orbits need to be continuously adjusted to maintain the optimum collision conditions. Originally, this task was carried out manually, with operators adjusting three offset control knobs ($x,y,y^{\prime }$) according to the luminosity. There is a crucial necessity to implement advanced automated control approaches. However, the feedback methods are ineffective due to the constraints imposed by machine characteristics. Nevertheless, the optimization methods are also limited by the slow response speed of BEPCII and have intrinsic limitations. Reinforcement learning (RL), which learns from past experiences, provides a new approach for handling such problems. In this paper, we implemented two automated control methods: the dither method and the deep $Q$-network (DQN) RL method. The dither method is a numerical optimization method used to provide more online data for DQN training. With the help of the historical data from the dither method, we successfully trained a DQN agent to control the offset knobs to optimize the luminosity. The DQN method exhibited significantly better performance than the dither method, achieving faster optimization speeds and yielding higher integral luminosity. Furthermore, the DQN method has been integrated into the daily operations of BEPCII, achieving long-term stable deployment and effectively substituting manual labor.

Typical parameters of electron bunches available now in undulator x-ray FELs enable generation of induced radiation in crystal-based x-ray volume free electron laser (XVFEL). An important peculiarity of an undulator x-ray FEL is electron bunch spatial modulation matching the radiation wavelength. Therefore, x-ray FEL can be considered as a modulator of electron bunch density. As a result, a facility combining an undulator, which produces a modulated beam, and a crystal, on which the modulated beam is incident, can be considered to be similar to a klystron, which is a well-known source for microwaves emission. The use of a premodulated beam enables to generate and observe superradiation and induced radiation in a crystal-based XVFEL. The number of quanta radiated in a crystal-based XVFEL corresponds (or even exceeds) the number of quanta produced by the XFEL in the same frequency range.

Contaminations on the active surface of high-power microwave resonators, such as radio-frequency accelerator cavities, can greatly enlarge electron field emission and reduce their performance. In this work, we demonstrate the use of ozone to clean the surface of niobium superconducting radio-frequency cavities resulting in reduced field emission and enhanced accelerating gradient before onset of field emission. We report results from processing four cavities.

We have conducted 0D, 1D, 2D, and 3D simulations of an idealized coaxial impedance-matched Marx generator (IMG) [Phys. Rev. Accel. Beams 20, 040402 (2017)]. The 0D calculations were conducted with a four-element circuit model; the 1D, 2D, and 3D calculations were conducted with highly resolved, fully electromagnetic representations. The IMG consists of 30 stages distributed axially and connected electrically in series. Each stage is powered by two bricks separated by 180° and connected electrically in parallel. Each brick comprises two opposite-polarity capacitors in series with a single switch. The bricks drive an internal impedance-matched coaxial transmission line terminated by a resistive load. The simulations neglect effects due to the switch-triggering circuit, the capacitor-charging circuit, external conducting boundaries, and reactive components of the load. We find dimensionality does not significantly affect the electrical power delivered by the IMG to its load: peak load powers estimated by the 0D, 1D, 2D, and 3D simulations agree to within 1%. The 3D calculations demonstrate that electromagnetic power radiated by the bricks, and axial gaps between stages, reduces the peak load power by less than $\sim 1\%$. Each simulation assumes the load impedance is 34% above that at which the load power is maximized. Operating an IMG with such an overmatched load offers several advantages while decreasing the peak load power by only 2%. The 0D, 1D, 2D, and 3D models outlined herein could be adapted to assess computationally competing IMG designs, and conduct a variety of numerical IMG experiments, before an IMG is constructed.

ISAC-TRIUMF operates targets under proton irradiation in the high-power regime of 50 kW ($100\mathrm{\mu }\mathrm{A}$, 500 MeV) to produce radioactive isotope beams using the isotope separation on-line technique. The targets irradiated at ISAC have a total stopping power significantly lower than 500 MeV resulting in a residual high-power proton beam downstream of the target. The coupling of a supplementary target in a downstream position allows for additional scientific output. Irradiation conditions have been analyzed with the fluka code and relevant achievable research within operational limitations explored. Prominently, the study of material degradation under high radiation fields is of increasing interest due to the steady demand for high-performance materials for new-generation nuclear applications and beam-intercepting components at high-power particle accelerator facilities. Successive irradiations at ISAC yield relevant radiation damage of bulk material samples which can then be characterized using already existing facilities at TRIUMF and partner facilities. Additionally, a variety of isotopes produced by transmutation with research applicability can be harvested from these irradiations. With the purpose of unlocking this complementary research at ISAC-TRIUMF, a secondary target, attached to the primary ISAC target system, has been designed and commissioned.