Circular Accelerators Research Articles

Exploring the potential of resonance islands and bent crystals for a slow extraction from circular hadron accelerators

New developments in accelerator physics have broadened the set of available techniques for manipulating charged-particle beams. Adiabatic trapping and transport of a beam in resonance islands has been studied and successfully implemented at the CERN Proton Synchrotron to perform multiturn extraction. Bent crystals have been successfully installed in the CERN Large Hadron Collider, improving the cleaning performance of the collimation system, and at the CERN Super Proton Synchrotron for reducing losses at the extraction septum in the case of slow extraction. In this Letter, we discuss the potential of the combined use of resonance islands and bent crystals to devise a technique to perform slow extraction in circular hadron accelerators. The proposed approach is promising, particularly for applications with high-intensity beams, as it could dramatically reduce the losses on the extraction devices. Published by the American Physical Society 2024

Efficient algorithms for dynamic aperture and momentum acceptance calculation in synchrotron light sources

New algorithms useful for the calculation of dynamic aperture and momentum acceptance in circular accelerators, particularly synchrotron light sources, are developed and presented. The flood-fill tool from raster graphics inspired us to efficiently compute dynamic apertures by minimizing required trackings on stable initial coordinates, leading to several factors of speedup with respect to standard algorithms. A novel technique for momentum acceptance calculations, Fast Touschek Tracking, is developed. Thorough benchmarking using modern accelerator codes shows that the new technique can provide one or two orders of magnitude faster computation of local momentum acceptances with only limited loss of accuracy. Published by the American Physical Society 2024

Harmonic analysis of nonstationary signals with application to LHC beam measurements

Harmonic analysis has provided powerful tools to accurately determine the tune from turn-by-turn data originating from numerical simulations or beam measurements in circular accelerators and storage rings. Methods that have been developed since the 1990s are suitable for stationary signals, i.e., time series whose properties do not vary with time and are represented by stationary signals. However, it is common experience that accelerator physics is a rich source of time series in which the signal amplitude varies over time. Furthermore, the properties of the amplitude variation of the signal often contain essential information about the phenomena under consideration. In this paper, a novel approach is presented, suitable for determining the tune of a nonstationary signal, which is based on the use of the Hilbert transform. The accuracy of the proposed methods is assessed in detail, and an application to the analysis of beam data collected at the CERN Large Hadron Collider is presented and discussed in detail. Published by the American Physical Society 2024

Incoherent tune measurement of an ion storage ring using single ions

The measurement of betatron tunes is important in the studies of beam dynamics in circular accelerators. Here, we report a new method to extract the fractional tune values using revolution times of single ions stored for a few hundred turns in a heavy-ion storage ring utilizing a single time-of-flight detector. The experiment was done at the experimental Cooler Storage Ring (CSRe) in Lanzhou. The unbunched cocktail secondary beam was injected into the ring and allowed to coast without further excitation. Since the average number of simultaneously stored ions inside the 128.8 m-circumference ring was merely ∼20, the obtained tune values are considered to be incoherent. Given that the revolution time of an individual ion is related to its momentum, the chromaticity of the ring could be addressed. Moreover, the data indicate a possible beam mismatch in vertical direction y^ at the injection into CSRe. The new method is developed for ultralow beam intensities and is thus a sensitive approach to tune measurements. Thanks to its simplicity, the method can straightforwardly be employed at other circular accelerators by applying the same detection approach. Published by the American Physical Society 2024

Excitation signal optimization for minimizing fluctuations in knock out slow extraction

The synchrotron is a circular particle accelerator used for high energy physics experiments, material and life science, as well as hadron cancer therapy. After acceleration to the desired energies, particle beams are commonly extracted from the synchrotron using the method of resonant slow extraction. The goal is to deliver a steady particle flux—referred to as spill—to experiments and treatment facilities over the course of seconds while slowly emptying the storage ring. Any uncontrolled intensity fluctuations in the spill are detrimental to the efficiency of beam usage, as they lead to detector pileups or detector interlocks, hindering experiments and cancer treatment. Among the most widely used extraction scheme in medical facilities is the Radio Frequency Knock Out (RF-KO) driven resonant slow extraction, where the stored beam is transversely excited with a radio frequency (RF) field and the spill intensity is controlled by the excitation signal strength. This article presents particle dynamics simulations of the RF-KO system with the focus on finding effective mechanism for minimizing the intensity fluctuations while maintaining a good extraction efficiency and other advantages of KO extraction. An improved beam excitation signal which optimizes these main objectives is found, and is rigorously compared experimentally with other commonly applied techniques.

A proposal for a fast infrared bursts detector

The gravitational wave GW170817 from a binary neutron star merger and the simultaneous electromagnetic detection of the GRB170717A by Fermi Gamma-Ray Space Telescope, opened a new era in the multi-messenger astronomy. Furthermore, the GRBs (Gamma-Ray Bursts) and the mysterious FRBs (Fast Radio Bursts) have sparked interest in the development of new detectors and telescopes dedicated to the time-domain astronomy across the electromagnetic spectrum. Time-domain astronomy aims to acquire fast astronomical bursts in temporal range between a few seconds down to 1 ns. Fast InfraRed Bursts (FIRB's) have been relatively understudied, often due to the lack of appropriate tools for observation and analysis. In this scientific scenario, the present contribution proposes a new detection system for ground-based reflecting telescopes working in the mid-infrared (mid-IR) range to search for astronomical FIRB's. Experience developed in the diagnostics for lepton circular accelerators can be used to design temporal devices for astronomy. Longitudinal diagnostic instruments acquire bunch-by-bunch particle shifts in the direction of flight, that is equivalent to temporal. Transverse device integrates the beam signal in the horizontal and vertical coordinates, as standard telescopes. The proposed instrument aims to work in temporal mode. Feasibility study tests have been carried out at SINBAD, the infrared beam line of DAFNE, the e+e- collider of INFN. SINBAD releases pulsed infrared synchrotron light with 2.7 ns separation. The front-end detector system has been evaluated to detect temporal fast infrared signals with 2–12 μm wavelengths and 1 ns rise times. The present contribute aims to be a step toward a feasibility study report.

Optimizing dynamic aperture studies with active learning

Dynamic aperture is an important concept for the study of non-linear beam dynamics in circular accelerators. It describes the extent of the phase-space region where a particle's motion remains bounded over a given number of turns. Understanding the features of dynamic aperture is crucial for the design and operation of such accelerators, as it provides insights into nonlinear effects and the possibility of optimising beam lifetime. The standard approach to calculate the dynamic aperture requires numerical simulations of several initial conditions densely distributed in phase space for a sufficient number of turns to probe the time scale corresponding to machine operations. This process is very computationally intensive and practically outside the range of today's computers. In our study, we introduced a novel method to estimate dynamic aperture rapidly and accurately by utilising a Deep Neural Network model. This model was trained with simulated tracking data from the CERN Large Hadron Collider and takes into account variations in accelerator parameters such as betatron tune, chromaticity, and the strength of the Landau octupoles. To enhance its performance, we integrate the model into an innovative Active Learning framework. This framework not only enables retraining and updating of the computed model, but also facilitates efficient data generation through smart sampling. Since chaotic motion cannot be predicted, traditional tracking simulations are incorporated into the Active Learning framework to deal with the chaotic nature of some initial conditions. The results demonstrate that the use of the Active Learning framework allows faster scanning of the configuration parameters without compromising the accuracy of the dynamic aperture estimates.

Heavy Ion Injection of Fixed-Field Alternating Gradient Accelerator

Abstract Much research in recent years has focused on circular accelerators that accelerate and store secondary particles with a large momentum spread, such as muons, unstable nuclei, and heavy ions with different charge states. A fixed-field alternating gradient (FFAG) accelerator with large transverse and momentum acceptance has obvious advantages for such requirements. A versatile beam injection method is required to accelerate secondary particles with a large momentum spread and different charge states with an FFAG accelerator. In the present study, a method for charge exchange injection of positive heavy ions using the large momentum acceptance of an FFAG accelerator is proposed. A charge injection system, which converts a He1+ beam to a He2+ beam, is developed for a 150 MeV FFAG accelerator at the Center for Accelerator and Beam Applied Science (CABAS) of Kyushu University. As the first step to verify the injection method, an orbit shift from one charge state to the other is demonstrated. This is the first demonstration of heavy ion injection using an FFAG accelerator.

Accelerating Dynamic Aperture Evaluation Using Deep Neural Networks

The Dynamic Aperture is an important concept for the study of non-linear beam dynamics in a circular accelerator. The DA is defined as the extent of the phase-space region in which the particle’s motion remains bounded over a finite number of turns. Such a region is shaped by the imperfections in the magnetic fields, beam-beam effects, electron lens, electron clouds, and other non-linear effects. The study of the DA provides insight into the mechanisms driving the time evolution of beam losses, which is essential for the operation of existing circular accelerators, such as the CERN Large Hadron Collider, as well as for the design of future ones. The standard approach to numerical evaluation of the DA relies on the ability to accurately track initial conditions, distributed in phase space, on a realistic time scale, and this is computationally demanding. To accelerate the angular DA calculation, we propose the use of a Machine Learning technique for the angular DA regression based on simulated HL-LHC data. We demonstrate the implementation of a Deep Neural Network model by measuring the time and assessing the performance of the angular DA regressor, as well as carrying out studies with various hardware architectures including CPU, GPU, and TPU.

Coherent dispersion effects in 2D and 3D high-intensity beams

Both space charge and dispersion have an effect on high-intensity beams in circular accelerators or transport sections with bending magnets and may lead to emittance growth and beam loss. In this paper, we present an investigation of the combined effect of dispersion and space charge on two-dimensional beams deepening the understanding of the 120° dispersion-induced instability. We also investigate the 90° envelope instability, which in the absence of the dispersion, mixes the confluent and parametric resonances. We show here that the presence of dispersion and high intensity breaks the overlapping and separates the two resonances. Furthermore, we study the beam dynamics of three-dimensional bunched beams and find the surprising result that the synchrotron motion can split the dispersion mode into two equally separated “sideband” modes according to the beam intensity and synchrotron frequency.

High-precision and high-efficiency measurement method of accelerator tunnel control network based on total station angle observation

Given the importance of accelerator devices, major developed and emerging countries around the world have invested substantial human and material resources into the development, construction, and operation of more advanced large-scale accelerator devices. High-precision and high-efficiency alignment of the control network is crucial for the stable operation of accelerators. This study proposes a method for measuring tunnel control networks using total station angle observation. By taking advantage of the high precision of angle observation with a total station, we use the measured results of the designed and deployed control points measured by the laser tracker to simulate the total station angle observations, combined with some length scale values in the control network measured by the laser range finder. With the angle observations and several known distances, the point coordinates can be calculated by angle intersection methods. Only angle observations are used from total stations, while different length scale reference conditions are added to constrain the control network. This is done by calculating the point accuracy of the China Spallation Neutron Source circular accelerator. The overall plane point accuracy can reach 66 μm. By using this method, personnel will spend less time on the site and are at lower risk of radiation exposure, for example by automating measurements at night. This method can be used at nighttime for measurements, avoiding the need for daytime work and shielding employees from severe radiation exposure. By employing this method, efficiency can be increased twice. For on-site measurement, it enables monitoring and automated measurement during operation, as well as providing reference for the installation and measurement of tunnel control networks for large scale accelerators such as the Circular Electron Positron Collider.

Conceptual Design of a 20 T Hybrid Cos-Theta Dipole Superconducting Magnet for Future High-Energy Particle Accelerators

High energy physics research will need more and more powerful circular accelerators in the next decades. It is therefore desirable to have dipole magnets able to produce the largest possible magnetic field, in order to keep the machine diameter within a reasonable size. A 20 T dipole is considered a desired achievement since it would allow the construction of an 80 km machine, able to circulate 100 TeV proton beams. In order to reach 20 T, a hybrid Low-Temperature Superconductor (LTS) - High-Temperature Superconductor (HTS) magnet is needed, since LTS technology is presently limited to ∼16 T for accelerator magnet applications. In this paper, we present the design of a 6 layers 20 T hybrid dipole magnet using Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn (LTS) and Bi2212 (HTS). We show that it is possible to achieve this magnetic field with accelerator field quality, with sufficient margin on a realistic conductor, keeping the stresses within safe limit, avoiding conductor degradation.

Adiabatic bunch compression in storage rings from self wakes generated in Cherenkov waveguides

Equilibrium bunch lengths typical to modern day light sources of tens of picoseconds limit the spectral reach of superradiant approaches for exploring materials and biological samples. In particular, generation of terahertz radiation seems appealing for pump-probe experiments.Taking advantage of self-wakes generated by carefully chosen structure one can control the bunch length and shape the bunch profile to increase significantly the high-frequency spectral components. Numerical analysis indicates the presence of self-consistent steady states that can be obtained with passive corrugated or dielectric structures. This approach has potential applications for generating superradiant terahertz radiation and pulse shaping in circular accelerators.

Experimental HTSC-MAGLEV System and Efficiency Evaluation of a Noncontact Acceleration of IFE Target Placed in a Levitating Carrier

Over the last two decades, superconducting materials have undergone an evolution that has broadened its application space. This work focuses on the issue of noncontact acceleration of fusion targets for fueling of a commercial Inertial Fusion Energy (IFE) power plant. This approach attracts a significant interest due to its potential for almost frictionless motion. The operational principle is the magnetic acceleration of the levitating target carrier (or HTSC-sabot) made from high-temperature superconducting tapes of the second generation (2G-HTSC). From physics, the possibility of their practical applications is directly related to the flux pinning of quantized magnetic flux lines in the superconductors (so called, high-pinning, Type-II HTSCs). The article describes the important achievements made in this area: 1) measurements of the magnetic moment of 2G-HTSC tapes (Tc = 92 K) in the wide temperature range of 10–95 K; 2) building a circular PMG system (outer radius is R = 50 mm, В = 0.13−0.25 T) to study magneto-thermo-mechanical interactions between HTSC-sabot and permanent magnets under external variable load with a rate of 2‒5 Hz; 3) studying a static and dynamic stability of the guidance force for a set of different top-down suspended HTSC-sabots; 4) calculation of the HTSC-sabot velocity at which it leaves a circular trajectory at temperatures of ~ 80 K to evaluate its behavior at T ~17 K. The obtained results are in a good agreement that will allow one to estimate the parameters of a circular accelerator of R = 1 m based on HTSC magnetic levitation (HTSC-MAGLEV) transport; the operating temperature is T ~17 K which is characteristic of the target delivery to IFE power plant. The results of this work provide theoretical and experimental support for the practical design and application of such ac-celerator for reaching the target injection velocities in the range of 200−400 m/s.

Fourth generation switching power supply for circular induction accelerators.

A switching power supply (SPS) was applied as the high-frequency bipolar high-voltage pulse source required to accelerate charged particles in the induction synchrotron, which was a novel synchrotron proposed at the High Energy Accelerator Research Organization (KEK) in 2006, and it was also used in other circular induction accelerators proposed thereafter, including the induction sector cyclotron and the induction microtron. As the heart of the circular induction accelerator, the SPS has recently been developed up to a fourth generation system that uses newly developed 3.3kV high-speed SiC metal-oxide-semiconductor field-effect transistors(MOSFETs). The updates involved in this new SPS include the use of two parallel MOSFETs in each arm to shunt heat dissipation at high frequencies, optimization of the bus pattern, with low parasitic capacitance among the arms to improve the drain-source voltage (VDS) balance, and addition of current sampling circuits to provide an economical method to monitor the operating status in large-scale application scenarios. The heat power and temperature characteristics of the MOSFETs were studied specifically in both individual tests and SPS tests. To date, the new SPS has achieved 2.5 kV-17.4A bipolar output at 350kHz in continuous mode operation. The highest junction temperature of the MOSFETs was estimated to be 98 °C.

Bayesian optimization of the beam injection process into a storage ring

We have evaluated the data-efficient Bayesian optimization method for the specific task of injection tuning in a circular accelerator. In this paper, we describe the implementation of this method at the Karlsruhe Research Accelerator with up to nine tuning parameters, including the determination of the associated hyperparameters. We show that the Bayesian optimization method outperforms manual tuning and the commonly used Nelder-Mead optimization algorithm both in simulation and experiment. The algorithm was also successfully used to ease the commissioning phase after the installation of new injection magnets and is regularly used during accelerator operations. We demonstrate that the introduction of context variables that include intra-bunch scattering effects, such as the Touschek effect, further improves the control and robustness of the injection process.

Field quality and surface resistance studies of a superconducting REBa2Cu3O7−x —Cu hybrid coating for the FCC beam screen

To ensure beam stability in the future circular collider study of the European Organization for Nuclear Research, RE(=Y, Gd, Eu)Ba2Cu3O 7−x high-temperature superconductor was proposed as a low-surface impedance coating for its beam screen. Unfortunately, persistent currents in the superconductor will degrade the magnetic field homogeneity inside the beam chamber, endangering the stability of the beam trajectory. To counteract this effect, we have explored the possibility of using a highly conductive hybrid coating made of Cu and REBa2Cu3O 7−x . This decreases the surface impedance when compared to that of pure copper, while maintaining high magnetic field quality inside the beam screen chamber. This work formulates guidelines for hybrid coating geometries to comply with the field quality criterion of a circular accelerator during operation with dipole magnets by means of finite elements numerical analysis. We produced hybrid coating samples with compliant geometries via photolithography. Scanning Hall microscopy and radio-frequency characterization have given the first experimental confirmation that these hybrid coatings offer high field quality and present a surface resistance lower than that of copper for the beam screen of the future circular hadron collider. The excellent agreement shown between experimental results and simulations validates that the numerical analysis performed throughout this work can be used as a prediction tool for future proposed geometries.

Measurement of transverse beam emittance of split beams for the CERN Proton Synchrotron Multi-Turn Extraction

Crossing a horizontal nonlinear resonance is the approach that can be used to split a beam in several beamlets with the goal to perform multi-turn extraction from a circular particle accelerator. Such an approach has been successfully implemented in the CERN Proton Synchrotron and is used routinely for the production of high-intensity proton beams for fixed-target physics at the Super Proton Synchrotron. Recently, thanks to the deployment of diamond detectors, originally installed to monitor the beam losses at extraction, it has been possible to measure the horizontal beam emittance of the split beam just prior to extraction. This is the first time that an emittance measurement is attempted for split beams, i.e. in a regime of highly nonlinear beam dynamics. In this paper, the technique is presented and its application to the analysis of the experimental data is presented and discussed in detail. This result is essential for the performance assessment of the splitting process and for the design of further performance improvements.

Probing the diffusive behaviour of beam-halo dynamics in circular accelerators

Circular particle accelerators at the energy frontier are based on superconducting magnets that are extremely sensitive to beam losses as these might induce quenches, i.e. transitions to the normal-conducting state. Furthermore, the energy stored in the circulating beam is so large that hardware integrity is put in serious danger, and machine protection becomes essential for reaching the nominal accelerator performance. In this challenging context, the beam halo becomes a potential source of performance limitations and its dynamics needs to be understood in detail to assess whether it could be an issue for the accelerator. In this paper, we discuss in detail a recent framework, based on a diffusive approach, to model beam-halo dynamics. The functional form of the optimal estimate of the perturbative series, as given by Nekhoroshev’s theorem, is used to provide the functional form of the action diffusion coefficient. The goal is to propose an effective model for the beam-halo dynamics and to devise an efficient experimental procedure to obtain an accurate measurement of the diffusion coefficient.

Towards 20 T Hybrid Accelerator Dipole Magnets

The most effective way to achieve very high collision energies in a circular particle accelerator is to maximize the field strength of the main bending dipoles. In dipole magnets using Nb-Ti superconductor the practical field limit is considered to be 8-9 T. When Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconductor material is utilized, a field level of 15-16 T can be achieved. To further push the magnetic field beyond the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn limits, High Temperature Superconductors (HTS) need to be considered in the magnet design. The most promising HTS materials for particle accelerator magnets are Bi2212 and REBCO. However, their outstanding performance comes with a significantly higher cost. Therefore, an economically viable option towards 20 T dipole magnets could consist in an “hybrid” solution, where both HTS and Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn materials are used. We discuss in this paper preliminary conceptual designs of various 20 T hybrid magnet concepts. After the definition of the overall design criteria, the coil dimensions and parameters are investigated with finite element models based on simple sector coils. Preliminary 2D cross-section computation results are then presented and three main layouts compared: cos-theta, block, and common-coil. Both traditional designs and more advanced stress-management options are considered.