Beamline Elements Research Articles

Graph learning for particle accelerator operations.

Particle accelerators play a crucial role in scientific research, enabling the study of fundamental physics and materials science, as well as having important medical applications. This study proposes a novel graph learning approach to classify operational beamline configurations as good or bad. By considering the relationships among beamline elements, we transform data from components into a heterogeneous graph. We propose to learn from historical, unlabeled data via our self-supervised training strategy along with fine-tuning on a smaller, labeled dataset. Additionally, we extract a low-dimensional representation from each configuration that can be visualized in two dimensions. Leveraging our ability for classification, we map out regions of the low-dimensional latent space characterized by good and bad configurations, which in turn can provide valuable feedback to operators. This research demonstrates a paradigm shift in how complex, many-dimensional data from beamlines can be analyzed and leveraged for accelerator operations.

Range shifter contribution to neutron exposure of patients undergoing proton pencil beam scanning.

Superficial targets require the use of the lowest energies within the available energy range in proton pencil-beam scanning (PBS) technique. However, the lower efficiency of the energy selection system at these energies and the requirement of a greater number of layers may represent disadvantages for this approach. The alternative is to use a range shifter (RS) at nozzle exit. However, one of the concerns of using this beamline element is that it becomes an additional source of neutrons that could irradiate organs situated far from the target. The purpose of this study is to assess the increase in neutron dose due to the RS in proton PBS technique. Additionally, an analytical model for the neutron production is tested. Two clinical plans, designed to achieve identical target coverage, were created for an anthropomorphic phantom. These plans consisted of a lateral field delivering an absorbed dose of 60Gy (RBE) to the target. One of the plans employed the RS. The MCNP code was used to simulate the plans, evaluating the distribution of neutron dose equivalent (Hn) and the equivalent dose in organ. In the plan with the RS plan, neutron production from both the patient and the RS were assessed separately. Hn values were also fitted versus the distance to field edge using a Gaussian function. Hn per prescription dose, in the plan using the RS, ranged between 1.4 and 3.7 mSv/Gy at the field edge, whereas doses at 40cm from the edge ranged from 9.9 to 32 μSv/Gy. These values are 1.2 to 10 times higher compared to those obtained without the RS. Both this factor and the contribution of neutrons originating from the RS increases with the distance from field edge. A triple-Gaussian function was able to reproduce the equivalent dose in organs within a factor of 2, although underestimating the values. The dose deposited in the patient by the neutrons originating from the RS predominantly affects areas away from the target (beyond approximately 25cm from field edge), resulting in a neutron dose equivalent of the order of mSv. This indicates an overall low neutron contribution from the use of RS in PBS.

Compact design of the 166.6 MHz superconducting cavity and its beamline elements for HEPS

The High Energy Photon Source (HEPS) is a 6 GeV diffraction-limited synchrotron light source under construction in Beijing. It will use five 166.6 MHz superconducting radio frequency (rf) cavities to accelerate the 200 mA electron beam in the storage ring. In the current lattice design, each straight section is 6 meters long to accommodate two 166.6 MHz cavities. The cavity adopts β=1 quarter-wave geometry, and the damping of the higher order modes is realized by using an enlarged cavity beam pipe to 505 mm and a ferrite absorber installed on the beam pipe. The low rf frequency, as well as the large beam aperture, added great challenges to the design of the 166.6 MHz cavity module to fit into a strictly limited longitudinal space. In addition, heat load optimization for the transition from room temperature to the cryogenic temperature, smooth tapering from the 505 mm beam aperture to the small diameter of the gate valves for impedance control, proper collimation of the synchrotron light to prevent thermal damage of delicate components, are also demanding requirements for a compact design. Accessibilities are also preserved for tuners and vacuum components to enable online maintenance. Finally, rf field leakage in the vacuum seal groove of the cavity is carefully examined to prevent overheating on the superconducting flange, which, in the worst scenario, may cause a thermal runaway, thus limiting the achievable accelerating gradient of the cavity. This paper presents the first compact design of the 166.6 MHz srf section for HEPS.

Compression Tests at High Strain Rate on 3D-Printed CuCrZr Alloy Specimens - Material Model Calibration

CuCrZr alloy is used to produce actively cooled components for high heat flux elements of beamlines and for heat sink of plasma facing components in nuclear fusion devices such as ITER and DEMO. It has an excellent thermal conductivity and specific mechanical strength, together with a high electrical conductivity that is giving high push to its use. Recently, CuCrZr alloy was also considered as an attractive material for Additive Manufacturing, leading to extend its application in the field of strain rate studies. As a matter of fact, its strain rate dependency is playing an important role for vertical target plasma-facing units components uses as heat sink in the ITER divertor or as structural material for actively cooled plasma facing components. This paper describes the results obtained by quasi-static and dynamic compression tests carried out on CuCrZr specimens produced by laser Powder Bed Fusion (PBF), with Selective Laser Melting (SLM) technology. Quasi-static tests have been conducted by means a servo-hydraulic tensile machine, while a direct tension-compression split Hopkinson bar has been used to perform the tests at high strain rate. Since dedicated heat treatments are required to obtain optimal combination of strength, ductility, and conductivity, some of the specimens have been heated up to 560 – 580 °C for 4 – 5 h and then cooled in air. Eventually, the calibration of the most appropriate constitutive models for 3D-printed CuCrZr alloy deformed at high strain rate has been carried out by means an inverse analytical procedure.

Optical Fibers as Dosimeter Detectors for Mixed Proton/Neutron Fields—A Biological Dosimeter

In recent years, proton therapy has gained importance as a cancer treatment modality due to its conformality with the tumor and the sparing of healthy tissue. However, in the interaction of the protons with the beam line elements and patient tissues, potentially harmful secondary neutrons are always generated. To ensure that this neutron dose is as low as possible, treatment plans could be created to also account for and minimize the neutron dose. To monitor such a treatment plan, a compact, easy to use, and inexpensive dosimeter must be developed that not only measures the physical dose, but which can also distinguish between proton and neutron contributions. To that end, plastic optical fibers with scintillation materials (Gd2O2S:Tb, Gd2O2S:Eu, and YVO4:Eu) were irradiated with protons and neutrons. It was confirmed that sensors with different scintillation materials have different sensitivities to protons and neutrons. A combination of these three scintillators can be used to build a detector array to create a biological dosimeter.

Concrete shielding activation for proton therapy systems using BDSIM and FISPACT-II

Proton therapy systems are used worldwide for patient treatment and fundamental research. The generation of secondary particles when the beam interacts with the beamline elements is a well known issue. In particular, the energy degrader is the dominant source of secondary radiation. This poses new challenges for the concrete shielding of compact systems and beamline elements activation computation. We use a novel methodology to seamlessly simulate all the processes relevant to the activation evaluation. A realistic model of the system is developed using Beam Delivery Simulation (BDSIM), a Geant4-based particle tracking code that allows a single model to simulate primary and secondary particle tracking and all particle-matter interactions. The secondary particle fluxes extracted from the simulations are provided as input to FISPACT-II to compute the activation by solving the rate equations. This approach is applied to the Ion Beam Applications (IBA) Proteus®ONE (P1) system and the shielding of the proton therapy research centre of Charleroi, Belgium. Proton loss distributions are used to model the production of secondary neutrals inside the accelerator structure. Two models for the distribution of proton losses are compared for the computation of the clearance index at specific locations of the design. Results show that the variation in the accelerator loss models can be characterised as a systematic error.

Position sensitive detectors in proton therapy: online monitoring of the beam position

Spot-scanning is a highly dynamic treatment method in proton therapy, tailored to each tumor shape individually. By superimposing many single spots in all three spatial axes, a prescribed dose is applied to the tumor volume. To minimize dose inhomogeneity across this volume, tight constraints on the beam position accuracy apply: for a dose inhomogeneity below 1%, a longitudinal beam position accuracy of the order of 1 mm is necessary, whereas in the lateral plane, the accuracy needs to be roughly one order of magnitude better. Longitudinal position control is achieved through selecting the beam energy; laterally, this is achieved by two sweeper magnets, allowing position changes within milliseconds. Such dynamics and accuracy constraints require an online measurement of the beam position to enable and maintain high treatment quality assurance. Gantry 2 at the Center for Proton Therapy at PSI operates a plane parallel strip ionization chamber for this purpose as the final beamline element before the patient. The foil-based detector design is optimized for an in-situ placement in the beam axis and keeps beam disturbance at a minimum. A strip pitch of 2 mm allows to reconstruct the Gaussian shape beam profile with the desired accuracy. These beam profiles are analyzed (and verified) during a treatment on a spot-by-spot basis, before the next spot is applied, introducing a dead time after every spot. Applying 50, 000 spots in a treatment introduces the challenge to data acquisition and — processing in terms of keeping treatment times reasonable. Data pileup and long dead times are mitigated by optimized front-end electronics and early-stage data processing, without compromising data quality and the accuracy of the measured beam position.

Determining Out-of-Field Doses and Second Cancer Risk From Proton Therapy in Young Patients-An Overview.

Proton therapy has the potential to provide survival and tumor control outcomes comparable and frequently superior to photon therapy. This has led to a significant concern in the medical physics community on the risk for the induction of second cancers in all patients and especially in younger patients, as they are considered more radiosensitive than adults and have an even longer expected lifetime after treatment. Thus, our purpose is to present an overview of the research carried out on the evaluation of out-of-field doses linked to second cancer induction and the prediction of this risk. Most investigations consisted of Monte Carlo simulations in passive beam facilities for clinical scenarios. These works established that equivalent doses in organs could be up to 200 mSv or 900 mSv for a brain or a craniospinal treatment, respectively. The major contribution to this dose comes from the secondary neutrons produced in the beam line elements. Few works focused on scanned-beam facilities, but available data show that, for these facilities, equivalent doses could be between 2 and 50 times lower. Patient age is a relevant factor in the dose level, especially for younger patients (by means of the size of the body) and, in addition, in the predicted risk by models (due to the age dependence of the radiosensitivity). For risks, the sex of the patient also plays an important role, as female patients show higher sensitivity to radiation. Thus, predicted risks of craniospinal irradiation can range from 8% for a 15-year-old male patient to 58% for a 2-year-old female patient, using a risk model from a radiological protection field. These values must be taken with caution due to uncertainties in risk models, and then dosimetric evaluation of stray radiation becomes mandatory in order to complement epidemiological studies and be able to model appropriate dose–response functions for this dose range. In this sense, analytical models represent a useful tool and some models have been implemented to be used for young patients. Research carried out so far confirmed that proton beam therapy reduces the out-of-field doses and second cancer risk. However, further investigations may be required in scanned-beam delivery systems.

CoSyR: A novel beam dynamics code for the modeling of synchrotron radiation effects

The self-consistent nonlinear dynamics of a relativistic charged particle beam interacting with its complete self-fields is a fundamental problem underpinning many of the accelerator design issues in high brightness beam applications, as well as the development of advanced accelerators. Particularly, synchrotron radiation induced effects in a magnetic dispersive beamline element can lead to collective beam instabilities and emittance growth. A novel beam dynamics code is developed based on a Lagrangian method for the calculation of the particles’ radiation near-fields using wavefront/wavelet meshes via the Green’s function of the Maxwell equations. These fields are then interpolated onto a moving mesh for dynamic update of the beam. This method allows radiation co-propagation and self-consistent interaction with the beam in 2D/3D simulations at greatly reduced numerical errors. Multiple levels of parallelisms are inherent in this method and implemented in our code CoSyR to enable at-scale simulations of nonlinear beam dynamics on modern computing platforms using MPI, multi-threading, and GPUs. The current 2D implementation of CoSyR has been used to evaluate the transverse and longitudinal coherent radiation effects on the beam and to investigate beam optics designs proposed for mitigation of beam brightness degradation in a magnetic bunch compressor. In this paper, the design of CoSyR, as well as the benchmark with other coherent synchrotron radiation models, are described and discussed. Extension of the core algorithms to 3D is possible and planned.

The Evolution of Lateral Dose Distributions of Helium Ion Beams in Air: From Measurement and Modeling to Their Impact on Treatment Planning

To start clinical trials with the first clinical treatment planning system supporting raster-scanned helium ion therapy, a comprehensive database of beam characteristics and parameters was required for treatment room-specific beam physics modeling at the Heidelberg Ion-Beam Therapy Center (HIT). At six different positions in the air gap along the beam axis, lateral beam profiles were systematically measured for 14 initial beam energies covering the full range of available energies at HIT. The 2D-array of liquid-filled ionization chambers OCTAVIUS from PTW was irradiated by a pencil beam focused at the central axis. With a full geometric representation of HIT’s monitoring chambers and beamline elements in FLUKA, our Monte Carlo beam model matches the measured lateral beam profiles. A second set of measurements with the detector placed in a water tank was used to validate the adjustments of the initial beam parameters assumed in the FLUKA simulation. With a deviation between simulated and measured profiles below ±0.8 mm for all investigated beam energies, the simulated profiles build part of the database for the first clinical treatment planning system for helium ions. The evolution of beamwidth was also compared to similar simulations of the clinically available proton and carbon beam. This allows a choice of treatment modality based on quantitative estimates of the physical beam properties. Finally, we investigated the influence of beamwidth variation on patient treatment plans in order to estimate the relevance and necessary precision limits for lateral beam width models.

Study of the radioactive contamination of the ion source complex in the Selective Production of Exotic Species (SPES) facility.

The Isotope Separation On-Line (ISOL) technique is today established as one of the primary methods to produce high-intensity and high-quality radioactive beams. This technique produces, for a given amount of the desired isotope, many orders of magnitude of other radioactive species. Due to the activation generated by interactions of the primary beam, intense neutron fields, and deposition of the produced radioactive ions inside beam line elements, an ISOL facility in operation becomes an intense radioactive source. Therefore, the biological hazard imposes severe radiological safety challenges to the design, operation, maintenance, and final decommissioning of such facilities. A challenging component is the ion source complex, where the ion extraction electrode provides the extraction of radioactive ions from the ion source and the first acceleration to the extracted beam. The radioactive contamination of this sub-component is studied, by means of the FLUKA code, in the case of the Selective Production of Exotic Species facility, which is in the advanced construction phase at Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, Padua, Italy. The developed model includes isotope production by the interactions of a 40MeV energy proton beam on a 238UCx target, selection of radioactive isotopes that are able to stick on the electrode tip, time evolution of the deposited isotopes during the operation and cooling periods before maintenance interventions, and evaluation of the ambient dose equivalent rate generated by the contamination of the electrode tip. Based on these results, the possibility of manual interventions for maintenance and emergency vs the use of remote handling systems is discussed.

Wakefield effects and mitigation techniques for nanobeam production at the KEK Accelerator Test Facility 2

The ATF2 beam line at KEK was built to validate the operating principle of a novel final-focus scheme devised to demagnify high-energy beams in future linear lepton colliders; to date vertical beam sizes as small as 41 nm have been demonstrated. However, this could only be achieved with an electron bunch intensity $\ensuremath{\sim}10%$ of nominal, and it has been found that wakefield effects limit the beam size for bunch charges approaching the design value of ${10}^{10}{e}^{\ensuremath{-}}$. We present studies of the impact of wakefields on the production of ``nanobeams'' at the ATF2. Wake potentials were evaluated for the ATF2 beam line elements and incorporated into a realistic transport simulation of the beam. The effects of both static (component misalignments and rolls, magnet strength errors and beam position monitor resolution) and dynamic (position and angle jitter) imperfections were included and their effects on the beam size evaluated. Mitigation techniques were developed and applied, including orbit correction, dispersion-free steering, wakefield-free steering, and interaction point tuning knobs. Explicit correction knobs to compensate for wakefield effects were studied and applied, and found to significantly decrease the intensity dependence of the beam size.

A Proton Beam Delivery System Variant for the Oncological Ophthalmological Center for Proton Radiation Therapy at the NRC “Kurchatov Institute”—PNPI

A variant of the proton beam delivery system with an energy of 60 MeV for the future oncological ophthalmological center for proton radiation therapy at the isochronous cyclotron C-80 at PNPI was designed. The requirements to the beam characteristics were defined. On the basis of a series of calculations, the optimal parameters and composition of the beam line elements were determined. It is shown that such a beam line allows one to alternately and efficiently switch from the isotope production mode on the cyclotron to the mode of operation of the center for proton radiation therapy without fundamental overhaul of the accelerator systems.

Multi-objective optimization of the matching beamline for external injection into a laser-driven plasma accelerator

Accelerators based on laser plasma wakefield acceleration are of great interest for a new generation of compact machines. External injection of an electron beam from an RF injector into a plasma accelerating stage has the advantage that a well-controlled and fully characterized beam can be used. The matching of the electron bunches into an accelerating plasma wakefield places high demands on the electron beam quality. The electron beam size must be extremely small to match the field structure inside the plasma wake. The short period of the accelerating field in the plasma requires a bunch length in the (sub-)fs range. These electron beam properties result in a high electron density and strongly space charge dominated bunches. The beamline upstream of the plasma must be able to control the significant effect of space charge on the bunch and to transversely match the beam to the focusing fields of the plasma. Further constraints to the beamline design are given by the in-coupling of the high-power drive laser and the implementation of diagnostic tools. Choosing suitable settings for the beamline elements in order to match the beam thus poses a great challenge. Using multi-objective optimization, suitable settings for the beamline elements can be extracted from Pareto optimum solutions. The development of a universal multi-objective optimization algorithm for beamline matching as well as first optimization results are presented.

Challenges and tolerances for a compact and hybrid ultrafast X-ray pulse source based on RF and THz technologies

We present an in-depth tolerance study and investigation of the main challenges towards the realization of a hybrid compact ultrafast (fs to sub-fs) X-ray pulse source based on the combination of a conventional S-band gun as electron source and a THz-driven dielectric-loaded waveguide as post-acceleration and compression structure. This study allows us determining which bunch properties are the most affected, and in which proportion, for variations of the parameters of all the beamline elements compared to their nominal values. This leads to a definition of tolerances for the misalignments of the elements and the jitter of their parameters, which are compared to the state-of-the-art in terms of alignment precision and stability of operation parameters. The most challenging aspects towards the realization of the proposed source, including THz generation and manufacturing of the dielectric-loaded waveguide, are finally summarized and discussed.

A new approach to the mechanics of DNA: Atoms-to-beam homogenization

It is useful to describe the deformation characteristics of long biological macromolecules, such as deoxyribonucleic acid (DNA), by means of terms such as “bending”, “stretching”, or “twisting”. These terms are borrowed from classical beam theory, a traditional and widely known subfield of continuum mechanics, whereas the standard numerical modeling procedure for macromolecules, which is molecular dynamics, does not allow for explicit introduction of the aforementioned deformation modes. This somehow puts some limit to the mechanical understanding of biological macromolecules. As a remedy, we here propose an upscaling (or homogenization) approach, spanning a new conceptual bridge from molecular dynamics to beam theory. Firstly, we apply the principle of virtual power (PVP) to classical continuum beams subjected to stretching and twisting, as well as to atomic compounds represented as discrete systems of mass points in the framework of molecular dynamics. Equating virtual power densities associated with continuum and discrete representations provides homogenization rules from the atomic compounds to the continuum beam line elements. Secondly, the forces acting on the aforementioned mass points are derived from energy potentials associated with bond stretching, valence and torsion angle variations, as well as electrostatic and van der Waals interactions. Application of this strategy to a specific DNA sequence consisting of 20 base pairs reveals deformation-dependent conformational changes, as well as paradox phenomena such as “stretching due to overwinding”, in line with known experimental observations.

Shielding calculations for the design of new beamlines at ALBA synchrotron

ALBA is a Spanish synchrotron facility generating intense beams of synchrotron radiation from a 3 GeV electron accelerator. At ALBA Synchrotron, electrons are first accelerated in a 110 MeV linear accelerator and then injected in Booster ring which increases the energy up to 3 GeV. Finally, the electron beam is stored in a synchrotron Storage Ring with a current up to 400 mA emitting intense beam of synchrotron radiation. Both the Booster and the Storage Ring are located inside the same concrete building, the Tunnel, while the LINAC is located in a separated concrete building, the Bunker. Outside the Tunnel, and tangentially to the Storage Ring, are located the experimental research laboratories, the Beamlines, where scientists receive synchrotron light for a wide variety of experiments. At present ALBA has 8 Beamlines installed, 3 Beamline under construction, and 1 Beamlines in the design stage.This paper details the design of the shielding elements of the new Beamlines under construction called LOREA, NOTOS and XAIRA. The first one is a soft X-ray and the other two are hard X-ray Beamlines. Shielding calculations are performed using FLUKA Monte Carlo code and aim at quantifying the total dose rate produced by the different sources of radiation at the Beamlines in operation. In particular, it details the dose generated by the gas bremsstrahlung radiation resulting from the interaction of the 3 GeV electron beam with the residual gas of the storage ring vacuum chamber and compares it to the dose rate generated by the insertion device radiation flux. The objective of the FLUKA simulations performed in this work is to establish the requirements for all the Beamline shielding elements to ensure a public dose (dose rate lower than 0.5 μSv/h) outside the shielding during Beamline operation. Results from the simulations set the general requirements for all the Beamline shielding elements, from a radiation protection point of view.

Dynamical simulations of the Muon Campus at Fermilab

The Muon Campus at Fermilab is a system through which muons are delivered to the storage ring of the Muon [Formula: see text] Experiment (E989). It consists of a set of 1 km beamlines that transport and prepare a highly polarized muon beam out of secondaries produced downstream a target station. Realistic simulations of this beam delivery system (BDS) using COSY INFINITY, and presented here, contribute to the understanding and characterization of the muon beam production in relation to the statistical and systematic uncertainties of the E989 measurement, intended to be smaller than 0.14 parts per million to achieve the goals of the experiment. The impact of nonlinearities from fringe fields and high-order contributions on the BDS performance are presented, as well as detailed studies of the interactions between secondaries and the beamline elements apertures, particle decay channels, spin dynamics and beamline misalignments.

Grating metrology for X-ray and V-UV synchrotron beamlines at SOLEIL.

Diffraction gratings are key elements of soft X-ray synchrotron beamlines. Besides wavelength dispersion, specific parameters can be tailored to adjust the energy dependent efficiency and focusing, and to correct wavefront aberrations. As key elements of a beamline, any departure from the design values can severely reduce the overall performance. On the other hand, known non-conformities can often be corrected by slight adjustment of the alignment parameters. A careful and accurate metrology is therefore required before installation on the beamline. After presenting what variable line spacing gratings, variable groove depth gratings, and alternate multilayer gratings are, the use of the SOLEIL long trace profiler for the measurement of groove density variation along the surface and of the atomic force microscope for the groove geometry and roughness characterizations will be discussed. A few examples of grating metrology will be presented and analyzed with the help of optical simulations.

Attosecond Pulse Shaping by Multilayer Mirrors

The emerging research field of attosecond science allows for the temporal investigation of one of the fastest dynamics in nature: electron dynamics in matter. These dynamics are responsible for chemical and biological processes, and the ability to understand and control them opens a new door of fundamental science, with the possibility to influence all lives if medical issues can thereby be addressed. Multilayer optics are key elements in attosecond experiments; they are used to tailor attosecond pulses with well-defined characteristics to facilitate detailed and accurate insight into processes, e.g., photoemission, Auger decay, or (core-) excitons. Based on the investigations and research efforts from the past several years, multilayer mirrors today are routinely used optical elements in attosecond beamlines. As a consequence, the generation of ultrashort pulses, combined with their dispersion control, has proceeded from the femtosecond range in the visible/infrared spectra to the attosecond range, covering the extreme ultraviolet and soft X-ray photon range up to the water window. This article reviews our work on multilayer optics over the past several years, as well as the impact from other research groups, to reflect on the scientific background of their nowadays routine use in attosecond physics.