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We report the high-gradient tests results of a novel traveling wave accelerating structure for $\beta =0.3$ based on a novel approach of operating at the first negative spatial harmonic. Accelerating gradients of 50 MV/m and peak electric fields of 160 MV/m were achieved in a single structure consisting of 15 coupled cells during tests at the advanced photon source. This work was performed by RadiaBeam, in collaboration with the Argonne National Laboratory, as a part of a Research and Development Program for the development of an ultrahigh-gradient linear accelerator, the Advanced Compact Carbon Ion Linac, for hadron therapy.

In this article, we propose the conceptual design, with supporting beam dynamics results, of a normal conducting, separated-sector cyclotron with a strong-focusing field gradient designed to accelerate light ions with a charge-to-mass ratio of 1/2 up to 15–20 MeV/u. The design can support a host of applications for therapy, radiobiology, material science, and instrumentation development. The light-ion species, which can include a mixed ion beam, can be dynamically chosen to provide a range of characteristic signals appropriate for specific material identification such as special nuclear materials. A conservative baseline concept is presented which has been optimized for radioisotope production of alpha emitters and theranostic radiopharmaceuticals. The modular design is also demonstrated to be scalable in gross physical parameters by a factor of 2–3, thereby reducing the size, weight, and power requirements (SWaP) and enabling near-term security applications.

The capability to produce high current, low loss, and extracted external ion beams presents an enabling technology for nuclear security, isotope production, and medical applications. We report on a novel, continuous-wave cyclotron for accelerating light ions with a charge-to-mass ratio of 1/2, which is designed for 1 mA maximum and 15 MeV/u energy. This article details the conceptual electromagnetic (EM) and engineering design including the 1.1 T sector magnets and 45 MHz, 200 kV radio frequency (RF) cavities. We discuss the cyclotron beam parameters with respect to potential commercial and industrial applications. The general concept and the accelerator’s layout are followed by a detailed EM design of magnets and RF cavities. Finally, practical engineering design considerations will be provided.

The development of novel high-gradient accelerating structures operating at THz frequencies is critical for future free-electron lasers and TeV scale linear colliders. To reach high energies with reasonable length requires high accelerating gradients of ~100 MV/m. The main limitation to reaching these high-energy gradients is the vacuum RF breakdown phenomenon, which disrupts normal accelerator operations. For stable operations and to understand the breakdown microscopic dynamics, a new device capable of detecting the breakdown occurrences is required. In this paper, we provide the design of a pulse length monitor based on an analog to digital converter for fast signal digitization without the need to use high-speed digitizers to be used in a commercial mm-wave heterodyne spectrometer.

Quantum computers (QC), if realized, could disrupt many computationally intense fields of science. The building block element of a QC is a quantum bit (qubit). Qubits enable the use of quantum superposition and multi-state entanglement in QC calculations, allowing a QC to simultaneously perform millions of computations at once. However, quantum states stored in a qubit degrade with decreased quality factors and interactions with the environment. One technical solution to improve qubit lifetimes and network interactions is a circuit comprised of a Josephson junction-based qubit located inside of a high Q-factor superconducting 3D cavity.It is known that niobium resonators can reach $Q_{0}>10^{11}$Q0>1011. However, existing cavity geometries are optimized for particle acceleration rather than hosting qubits. RadiaBeam Technologies, in collaboration with Argonne National Laboratory and The University of Chicago, has developed a niobium superconducting radio frequency quarter-wave resonant cavity (QWR) for quantum computation. A 6 GHz QWR was optimized to include tapering of the inner and outer conductors, a toroidal shape for the resonator shorting plane, and an inner conductor tip to reduce parasitic capacitance. In this paper, we present the results of the resonator design optimization, fabrication, processing, and testing.

Although linear accelerators are used in many security, industrial and medical applications, the existing technologies are too large and expensive for several critical applications such as radioactive source replacement, field radiography and mobile cargo scanners. One of the main requirements for these sources is to be highly portable to allow field operation. In response to this problem, RadiaBeam has designed a hand-portable 1 MeV X-ray source, scalable to higher energies, based on Ku-band split electron linac, that can be used for Ir-192 radioisotope replacement. In this paper, we present its multiphysics and engineering design studies, as well as an accelerating structure prototype along with RF measurements.

Beam dynamics simulations in traveling wave (TW) accelerating structures with significant beam loading is a challenging problem. Some codes are capable of calculating the TW electromagnetic fields , and some can track particles through such fields, but most cannot treat both self-consistently. A few commercial codes can model the physics correctly at the expense of many processor-hour computations to obtain converged self-consistent solutions. However, simple, accurate equations of motion for intensive beam dynamics in TW accelerating structure analysis have been previously obtained by Masunov and subsequently implemented in the Hellweg code, which was developed at the Moscow Engineering-Physics Institute. Hellweg is based on equations that allow fast simulations of beam dynamics while taking into account such effects as beam loading, space charge, and external magnetic fields . In this paper, we describe in detail some recent improvements to the Hellweg physics kernel. We have generalized the Masunov results into a 3D set of equations of motion, which include all spatial components of the radiofrequency (RF) and external magnetic fields. We have also improved the Lapostolle space charge model to the general 3D ellipsoid form for any dimensions’ ratio, consideration for the particles outside the beam core, and the fields from the neighboring bunches that can exist in the real machine. These modifications allow approaching the Hellweg accuracy to the self-consistent commercial codes while keeping the simulation time short, which is essential during the linac design and optimization stage. The implementation of these new capabilities in Hellweg is carefully benchmarked against other codes and analytical calculations. The code is freely available with an open source license.

The Argonne Tandem Linac Accelerator System (ATLAS) is planning an upgrade to a multi-user facility to simultaneously accelerate both stable beams from an ECR ion source and radioactive beams from an Electron Beam Ion Source charge breeder. The ATLAS Multi-User Upgrade will need to provide high transmission of ion beams with a mass-to-charge ratio up to 7 as it enables more options to alternate radioactive and stable beams. Currently, the bunching is provided with a lumped circuit multi-harmonic buncher, which cannot effectively operate at the required amplitude of the saw-tooth voltage for ions with mass-to-charge ratio of 7 due to thermal issues. RadiaBeam Systems in collaboration with Argonne National Laboratory has designed a four-harmonic coaxial resonator buncher with the ATLAS fundamental frequency of 12.125 MHz, and a compact, less than 2-m-long, footprint, capable of providing the required voltage of 6.2 kV. This device allows fast and reliable pre-bunching of DC ion beams with the capability of fast switching of heavy-ion radioactive and stable beams for delivery to multiple users. In this paper, we will discuss the RF and engineering design considerations of this buncher.

Measurements of longitudinal beam profile in non-relativistic hadron accelerators are usually performed with Bunch Shape Monitors that utilize secondary electron emission to reproduce the shape of a primary ion beam . The existing devices, however, have poor electron collection efficiency from the wire and are limited to one dimensional measurements of the phase coordinate. In this paper we present the performance improvements for a bunch shape monitor for proton beams used in the Spallation Neutron Source accelerator. These improvements were achieved by adding focusing optics between the wire and the entrance slit, which will also allow measurements over a much higher dynamic range. Here we present the design, simulation and experimental test results of the developed new electron beam guidance system for the existing SNS bunch shape monitor that allowed significant improvement in the collection efficiency.

RadiaBeam has developed a novel, flexible linac for electrons and X-rays (FLEX) capable of energy variation from 2 to 9 MeV within a single RF pulse. This accelerator employs a robust traveling wave accelerating structure with a large energy and power acceptance that allows the unique features of deep energy and current variation required for novel adaptive cargo inspection techniques and Computed Tomography. Robust RF and water-cooling systems allow average beam powers up to 15 kW, upgradable to 57 kW, at 6 MeV, potentially making this accelerator useful for electron beam irradiation applications. The high peak currents of the electron beam produced by FLEX enable novel FLASH radiotherapy methods with fast dose delivery. In this paper, we present the linac design and its components, as well the results of the experimental demonstration of beam acceleration with energy variation.

Reciprocity is a fundamental physical principle that roots in the time‐reversal symmetry of physical laws. It allows making predictions on any arbitrary complex system's response and operation and hence simplifies the analysis. However, there are many practical situations in which it is advantageous to break reciprocity, e.g., isolators preventing wave scattering back to lasers and generators, full‐duplex systems for multiplexing transmission and receiving in the same channel, nonreciprocal cavity excitation, and protection of fragile states of superconductor quantum computers from thermal noise. The most widespread approach to time‐reversal symmetry breaking and nonreciprocity based on magnetic field biasing suffers from bulkiness, cost ineffectiveness, and loss, motivating researchers and engineers to search for more practical approaches. Herein, the up‐and‐coming advances in optical nonreciprocity, including new materials (Weyl semimetals, topological insulators, metasurfaces), active structures, time‐modulation, parity‐time (PT)‐symmetry breaking, nonlinearity combined with a structural asymmetry, quantum nonlinearity, unidirectional gain and loss, chiral quantum states and valley polarization are overviewed. A general description of nonreciprocal systems is provided and the pros and cons of the mentioned approaches to nonreciprocity are discussed.

A tubular disk-and-ring, tapered accelerating structure for small electron linacs and MicroLinacs is considered. It consists of metal and dielectric elements inserted into a metallic tube to eliminate multi-cell, multi-step brazing. The structure enables a wide range of phase velocities (including non-relativistic), a wide bandwidth allowing large number of cells (for standing wave mode) or short filling time (for traveling wave mode), combination of compensated and purely π-mode cells, alternative periodic focusing built-in to the RF structure (the disks), and combining of RF and vacuum windows. RF and accelerating performance of such a long structure having up to four dozens cells is analyzed. Some of beam dynamics, thermal, and vacuum aspects of the structure and MicroLinac performance are considered as well.

The development of high-gradient accelerating structures for low-$\ensuremath{\beta}$ particles is the key for compact hadron linear accelerators. A particular example of such a machine is a hadron therapy linac, which is a promising alternative to cyclic machines, traditionally used for cancer treatment. Currently, the practical utilization of linear accelerators in radiation therapy is limited by the requirement to be under 50 m in length. A usable device for cancer therapy should produce 200--250 MeV protons and/or $400--450\text{ }\text{ }\mathrm{MeV}/\mathrm{u}$ carbon ions, which sets the requirement of having $35\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ average ``real-estate gradient'' or gradient per unit of actual accelerator length, including different accelerating sections, focusing elements and beam transport lines, and at least $50\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ accelerating gradients in the high-energy section of the linac. Such high accelerating gradients for ion linacs have recently become feasible for operations at S-band frequencies. However, the reasonable application of traditional S-band structures is practically limited to $\ensuremath{\beta}=\mathrm{v}/\mathrm{c}g0.4$. However, the simulations show that for lower phase velocities, these structures have either high surface fields ($g200\text{ }\text{ }\mathrm{MV}/\mathrm{m}$) or low shunt impedances ($l35\text{ }\text{ }\mathrm{M}\mathrm{\ensuremath{\Omega}}/\mathrm{m}$). At the same time, a significant ($\ensuremath{\sim}10%$) reduction in the linac length can be achieved by using the $50\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ structures starting from $\ensuremath{\beta}\ensuremath{\sim}0.3$. To address this issue, we have designed a novel radio frequency structure where the beam is synchronous with the higher spatial harmonic of the electromagnetic field. In this paper, we discuss the principles of this approach, the related beam dynamics and especially the electromagnetic and thermomechanical designs of this novel structure. Besides the application to ion therapy, the technology described in this paper can be applied to future high gradient normal conducting ion linacs and high energy physics machines, such as a compact hadron collider. This approach preserves linac compactness in settings with limited space availability.

A disk-loaded waveguide (DLW) is the most common structure for compact linear accelerators working in a traveling wave (TW) regime. Among its advantages are high shunt impedance and manufacturing simplicity. The other popular structure is an on-axis coupled bi-periodical accelerating structure (BAS) that works in standing wave (SW) regime. Both the standing and the traveling wave regimes have their own advantages and disadvantages. The design of the hybrid accelerator with SW buncher and TW accelerating section presented in this paper unites the advantages of both regimes. For example, the buncher in the hybrid accelerator is shorter than in a pure TW accelerator, and it requires no solenoid; this structure is more technologically convenient as it does not require a circulator. The other way to combine the advantages of DLW and BAS is to design a magnetic coupled disk-loaded waveguide (DLW-M). This paper also presents the results of a survey study that analyzed the electrodynamical parameters of such a structure and compared them with those of DLW. The experimental data is also presented. Higher order modes, multipacting discharge and thermal simulations show that DLW-M structure is more preferable to classical DLW.

X-ray inspection systems for cargo containers, capable of performing Z analysis, are an actively evolving type of equipment for cargo inspections [1–3]. A linear electron accelerator with fast energy tuning, operating in the mode of interlacing low- and high-energy electron pulses, has been developed for use in such a system. The output electron energy in this accelerator can vary in the range of 3–15 MeV under software control. An X-ray radiographic image of a container is obtained in a monoenergetic mode with a beam energy of 9 MeV. Pulses with energies of 4 and 9 MeV are used to recognize materials inside a container (i.e., perform Z analysis). The standing-wave linear electron accelerator operates at a frequency of 2856 MHz, its pulse repetition frequency with different energies is 240 Hz, the pulse duration is 10 μs, and the beam energy in each pulse is >10 J.

In this paper Hellweg 2D code is introduced. It is a special tool for electron dynamics simulation in waveguide travelling wave accelerating structure. The underlying theory of this software is based on the differential equations of motion. The effects considered in this code include beam loading, space charge forces and external magnetic field. Hellweg 2D is capable of dealing with multisectional accelerators. Along with the analysis of electron linacs, this program is able to synthesize accelerating structures. This paper provides the comparison of the PARMELA, Hellweg 2D and experimental data of the existing facilities. The results of beam dynamics simulation in a hybrid accelerator with a standing wave (SW) buncher and travelling wave (TW) regular section are presented.

A new computer code for 3D simulation of multipacting phenomenon in axisymmetric and non-axisymmetric radio frequency (RF) structures is presented. The goal of the simulation is to determine resonant electron trajectories and electron multiplication in RF structure. Both SW and TW structures of normal and superconductivity have been studied. Simulation results are compared with theoretical calculations and experimental measurements.

We have developed a new design for a 176 MHz cw radio-frequency quadrupole (RFQ) for the SARAF upgrade project. At this frequency, the proposed design is a conventional four-vane structure. The main design goals are to provide the highest possible shunt impedance while limiting the required rf power to about 120 kW for reliable cw operation, and the length to about 4 meters. If built as designed, the proposed RFQ will be the first four-vane cw RFQ built as a single cavity (no resonant coupling required) that does not require π -mode stabilizing loops or dipole rods. For this, we rely on very detailed 3D simulations of all aspects of the structure and the level of machining precision achieved on the recently developed ATLAS upgrade RFQ. A full 3D model of the structure including vane modulation was developed. The design was optimized using electromagnetic and multiphysics simulations. Following the choice of the vane type and geometry, the vane undercuts were optimized to produce a flat field along the structure. The final design has good mode separation and should not need dipole rods if built as designed, but their effect was studied in the case of manufacturing errors. The tuners were also designed and optimized to tune the main mode without affecting the field flatness. Following the electromagnetic (EM) design optimization, a multiphysics engineering analysis of the structure was performed. The multiphysics analysis is a coupled electromagnetic, thermal and mechanical analysis. The cooling channels, including their paths and sizes, were optimized based on the limiting temperature and deformation requirements. The frequency sensitivity to the RFQ body and vane cooling water temperatures was carefully studied in order to use it for frequency fine-tuning. Finally, an inductive rf power coupler design based on the ATLAS RFQ coupler was developed and simulated. The EM design optimization was performed using cst Microwave Studio and the results were verified using both hfss and ansys . The engineering analysis was performed using hfss and ansys and most of the results were verified using the newly developed cst Multiphysics package.