Beamline Research Articles

Beam dynamics for RAON linac and beam lines

Beam dynamics for RAON linac and beam lines

Dosimetry in MRgPT: Impact of magnetic fields on TLD dose response during proton irradiation.

Proton beam therapy, when integrated with MRI guidance, presents complex dosimetric challenges due to interactions with magnetic fields. Prior research has emphasized the nuanced impact of magnetic fields on dosimetry. For thermoluminescent dosimeters (TLDs) the electron-return effect, alongside small air cavities surrounding the pellets, can lead to nonuniform dose distributions. Future MR-guided proton therapy will require reliable methods for end-to-end tests and dosimetric audits, which so far are often performed using TLDs equipped with phantoms. This implicates the necessity of accounting for theseinteractions. This study investigates the influence of magnetic fields on TLDs at two proton energies, using magnetic field strengths of 0, 0.25, and , aiming to clarify their impact on dose measurementaccuracy. The study was conducted at a synchrotron-based ion beam therapy beam line, enhanced by a resistive dipole magnet for creating magnetic fields up to to simulate MR-guided proton therapy. Individual correction factors were applied for TLD measurements. The impact of air gaps on the TLD signal was evaluated using three dedicated TLD holders with air gaps of 0.1, 0.25, and 0.5 mm surrounding the TLD pellets using the highest available proton energy of . Additionally, the influence of the magnetic field strength on the TLD response was evaluated for two proton energies of and . The study found no statistically significant variation in TLD dose response attributable to changes in the air gap or the presence of magnetic fields. A power analysis indicated an upper limit on a potential change in dose-response as small as 1.5%. The findings suggested that the impact of air gap variations and magnetic field strengths on the TLD response was below the detection threshold of TLD sensitivity. This emphasizes the suitability of TLDs for dose measurement in MR-guided proton therapy, indicating that additional correction factors may not be necessary despite the influence of magneticfields.

Accurate measurements of delayed neutron data for reactor applications: methodology and application to 235U(nth,f)

Large inconsistencies still exist in nuclear data libraries regarding the kinetic parameters of delayed neutron (DN) precursors. As an example, there is a 17% gap between ENDF-B/VIII.0 and JEFF-3.3 on the average lifetime T1/2 of DN precursors from thermal fission of 235U. This parameter is of major importance for reactivity predictions of nuclear reactors in nominal or accidental configurations. In this context, CEA is actively participating to the ALDEN project (Average number and Lifetime of DElayed Neutrons) which aims at providing the nuclear data community with new data sets of DN from thermal and fast neutron induced fission of various actinides. A dedicated experimental setup was designed and optimized for that purpose and is presented in this paper. It consists of a “long counter” detector containing 16 proportional counters filled with 3He, embedded in a high density polyethylene matrix. The detector surrounds a fissile target prepared in the form of a miniature fission chamber, containing a few hundreds of micro-grams of fissile material. This set-up is connected to fast and efficient neutron shutters that can produce step-irradiations of variable durations. The equations driving the DN counting following step-irradiations of the fissile target are established and discussed in the perspective of DN yield or group parameter measurement. A comprehensive analysis of the different steps of data reduction is detailed: dead time characterization, Region of Interest (ROI) determination, absolute and relative efficiency calibration, fission rate estimation, irradiation time and background determination, DN decay curve production and physical parameter fitting. Following a prototype experiment performed in 2018 at the PF1b cold neutron beam line of Institute Laue Langevin (ILL, Grenoble, France), we discuss here the analysis of two campaigns occurring in 2019 and 2021 in which significant improvements were achieved in terms of background minimization, counting statistics and fission rate determination. The achievements of this work are the measurement of the delayed neutron emission per fission for the thermal neutron induced fission of 235U, estimated at (1.625 ± 0.010) % and the group parameters leading to an estimated lifetime of T1/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{1/2}$$\\end{document} = (8.87 ± 0.10) s. Those results are consistent with the values recommended by the IAEA/CRP work and they come with reduced uncertainties compared with previously published results.

Tracking system performance for the proposed SHADOWS experiment at CERN

The proposed SHADOWS experiment, Search for Hidden And Dark Objects With the SPS, is a proton beam-dump experiment at the CERN SPS. Positioned off-axis to suppress background, SHADOWS can profit from the high intensity ECN3 proton beam line, to explore the existence of a wide range of feebly-interacting particles (FIPs). The detector, with dimensions of 2.5 × 2.5 m2 and a length of 34 m, is designed for optimal tracking and timing performance, facilitating the identification and reconstruction of various visible final states of FIP decays. Despite the excellent outcome of the CERN SPS Committee review, the CERN Research Board decided to stop the project in March 2024. In this article we present the tracking system performance study based on simulation as presented in the Proposal. We show that using straw drift-tubes of 1 cm diameter, we can achieve a few mm vertex resolution and 1% mass resolution.

Measurement of the background in the CMS muon detector in pp\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${p}{p}$$\\end{document}-collisions at s=13\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sqrt{s} = 13$$\\end{document} TeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\,\ ext {Te}\\hspace{-.08em}\ ext {V}$$\\end{document}

The CMS detector, including its muon system, has been operating at the CERN LHC in increasingly challenging conditions for about 15 years. The muon detector was designed to provide excellent triggering and track reconstruction for muons produced in proton–proton collisons at an instantaneous luminosity (L\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {L}$$\\end{document}) of 1×1034\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1 \ imes 10^{34}$$\\end{document} cm-2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-2}$$\\end{document}s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document}. During the Run 2 data-taking period (2015–2018), the LHC achieved an instantaneous luminosity of twice its design value, resulting in larger background rates and making the efficient detection of muons more difficult. While some backgrounds result from natural radioactivity, cosmic rays, and interactions of the circulating protons with residual gas in the beam pipe, the dominant source of background hits in the muon system arises from proton–proton interactions themselves. Charged hadrons leaving the calorimeters produce energy deposits in the muon chambers. In addition, high-energy particles interacting in the hadron calorimeter and forward shielding elements generate thermal neutrons, which leak out of the calorimeter and shielding structures, filling the CMS cavern. We describe the method used to measure the background rates in the various muon subsystems. These rates, in conjunction with simulations, can be used to estimate the expected backgrounds in the High-Luminosity LHC. This machine will run for at least 10 years starting in 2029 reaching an instantaneous luminosity of L=5×1034cm-2s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {L} = 5 \ imes \ ext {10}^\ ext {34}\\,\ ext {cm}^\ ext {-2}\\,\ ext {s}^\ ext {-1}$$\\end{document} and increasing ultimately to L=7.5×1034cm-2s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {L} = 7.5 \ imes \ ext {10}^\ ext {34}\\,\ ext {cm}^\ ext {-2}\\,\ ext {s}^\ ext {-1}$$\\end{document}. These background estimates have been a key ingredient for the planning and design of the muon detector upgrade.

Irradiation system for biological experiments on BL14B1 at SPring-8

We present an irradiation system for biological experiments on BL14B1 beam line of SPring-8, where enables to use white and monochromatic X-rays (from 5 to 90 keV). An effective energy of white X-rays is assessed as 120 keV and their average dose rate is determined as approximately 170 Gy/s using a l-alanine dosimeter. Also, we speak about dosimetry of monochromatic X-rays using an optical stimulated luminescence detector. Average dose rates of monochromatic X-rays with 33.0, 33.2, 33.4 and 34.0 keV are estimated as 0.099 ± 0.006 Gy/s. The irradiation dose of white and monochromatic X-rays, of course, can be monitored using ionization chamber. When we use monochromatic X-rays with 33.2 keV, where is the K-shell absorption edge of iodine, Auger electrons are emitted, leading significant improvement of biological effectiveness. Thus, we have estimated the absorbed dose low-energy secondaries, such as Auger electrons and characteristic X-rays, emitted from iodine as 1.3 × 10−2 Gy/mM/min at BL14B1, depending on iodine concentration.

Bell inequality is violated in charmonium decays

The experimental data on the helicity amplitudes of charmonium decays allow us to measure entanglement in final state spin correlations and test possible violations of the Bell inequality. We find that the Bell inequality is violated with a significance of 5σ or more in the decays ηc,χc0,J/ψ→Λ+Λ¯, J/ψ→Ξ−+Ξ¯+,Ξ0+Ξ¯0,Σ−+Σ¯+,Σ0+Σ¯0, ψ(3686)→Ξ−+Ξ¯+,Σ−+Σ¯+,Σ0+Σ¯0, χc0,χc1→ϕ+ϕ. The decays ψ(3686)→Λ+Λ¯ and Ξ0+Ξ¯0 show the same violation but with less significance. The decay ψ(3686)→Ω−+Ω¯+ displays entanglement. These results firmly establish the presence of entanglement and quantum nonseparability at high energies, in a setting with particles of different spins and interacting through electroweak and strong interactions. In addition, the relatively long lifetime of some of the strange baryons produced in the decays provides a natural probe to test whether quantum spin correlations remain after the particles have interacted with the beam pipe and the first few layers of the detector. Published by the American Physical Society 2024

Advancements in experimental techniques for measuring dipole moments of short-lived particles at the LHC

ALADDIN is a proposed fixed-target experiment at the LHC for the direct measurement of charm baryon dipole moments. The detector features a spectrometer and a Cherenkov detector, while the experimental technique is based on the phenomena of particle channelling and spin precession in bent crystals. TWOCRYST, a proof-of-principle test at the LHC for the proposed experiment, is planned during the LHC Run 3. Recent channelling efficiency measurements performed at the CERN SPS of bent crystals developed at INFN are presented, marking significant progress towards its realisation. The silicon pixel detector for TWOCRYST is under construction. It will work in the secondary vacuum of a Roman Pot positioned inside the LHC beam pipe. The design, construction and integration of the pixel detector inside the Roman Pot will be discussed, along with the design and perspectives for the proposed ALADDIN experiment.

The impact of stray magnetic fields on the KSTAR NBI performance

The stray magnetic fields generated by a plasma discharge impact the performance of neutral beam injection (NBI), leading to a decline in the plasma performance of the Korea Superconducting Tokamak Advanced Research (KSTAR). To evaluate the impact of the stray magnetic field on the NBI performance, a Monte Carlo simulation tool was developed. The simulation tool integrates the stray magnetic fields, NBI beam line components, and charge exchange processes comprehensively, allowing for quantitative analysis of the NBI performance reduction due to the stray magnetic fields. The high pressure of the beam chamber, along with the stray magnetic fields, causes a significant reduction of the beam power, emphasizing the need to maintain low vacuum pressure. However, the stray magnetic field does not significantly affect the injection angle of the beam particles reaching the tokamak. Predictive integrated simulations show that the decrease in beam performance due to stray magnetic fields can affect a degradation in plasma performance during long pulse discharge in KSTAR.

Simulation and experiment of CRAFT NNBI cryopump

The cryogenic vacuum system is an important subsystem of Comprehensive Research Facility for Fusion Technology Negative Neutral Beam Injector, which provides vacuum environment support for various experiments related to the beam generation and transport process. In the paper, a simulation and experimental study of the Comprehensive Research Facility for Fusion Reactor Negative Neutral Beam Injector (CRAFT NNBI) cryopump performance has been carried out. The Beam Line Vessel (BLV) and its components are modeled by Solidworks, the pressure distribution, gas molecular velocity distribution and adsorption uniformity of the crysorption pump in the BLV are analyzed by simulation using the Molflow software, at the same time, the performance of the south cryopump is tested experimentally using in-situ measurement method. The simulation results show that the average pressure near the Neutralizer is 8.5*10-3 Pa, the average pressure near the Electrical Residual Ion Dump (ERID) is 8*10-3 Pa, and the average pressure near the Calorimeter is 9*10-3 Pa. The adsorption percentage fluctuates around 12%, which indicates that single structure plays the function of adsorption efficiently, the theoretical pumping speed of the south cryopump on H2 was calculated to be 7.34*105 L/s, total theoretical pumping speed of two cryopumps can reach 3.67*106 L/s. The experimental results showed that when the south cryopump was operation, the pressures near the Neutralizer were 2.8*10-2 Pa, the pressures near the ERID were 2.7*10-2 Pa, and the pressures near the Calorimeter were 7*10-3 Pa, the actual pumping speed of the south cryopump on H2 was 6.37*105 L/s, total actual pumping speed of two cryopumps can reach 3.1*106 L/s.

Construction of SuperKEKB vacuum control system and its eight years operation experience

SuperKEKB has two main rings (MRs), namely low- and high-energy rings, with circumferences of 3 km; beam transport (BT) lines; and a positron damping ring (PDR). We upgraded the MRs and BT line vacuum control systems and designed a new PDR vacuum control system for upgrading KEKB to SuperKEKB.Here, we describe the basic configuration of the vacuum control system, which includes the interlock logic (gate valve open/closed control, non-evaporable getter pump activation, and beam abortion). We subsequently present the collimator driving system and the cooling water control system for the beam pipe of the final focusing superconducting quadrupole magnet as examples of special SuperKEKB vacuum control systems. Examples of problems in the SuperKEKB vacuum control system, including the discharge at the high-voltage connector of the ion pump, stoppage of the cooling water pump for the vacuum system, and failure of the collimator position measurement device are described.

40 MHz readout of CMS silicon modules in a high intensity beam

In order to maintain its outstanding performance under the challenging conditions brought by the high-luminosity LHC, the CMS collaboration is preparing the production of a new outer tracker detector. The upgraded detector modules will feature two silicon sensors and the ability of reading out correlated clusters, or stubs, compatible with high transverse momentum particles at the full 40 MHz collision rate. With the detector design being finalised and mass production planned to start during the second half of 2024, the scalability of the readout system and the study of the commissioning and characterisation of the detector in realistic conditions are ever-more pressing.In this context, a joint beam-test was organised in collaboration with the MUonE collaboration where twelve modules were placed in an asynchronous muon beam line reaching particle rates of about 50 MHz, with the full stub stream being recorded to disk triggerless. The experiment and read-out chain is outlined, the commissioning procedures and operational challenges discussed and resulting system performance are presented.

MoEDAL Search in the CMS Beam Pipe for Magnetic Monopoles Produced via the Schwinger Effect.

We report on a search for magnetic monopoles (MMs) produced in ultraperipheral Pb-Pb collisions during Run 1 of the LHC. The beam pipe surrounding the interaction region of the CMS experiment was exposed to 184.07 μb^{-1} of Pb-Pb collisions at 2.76TeV center-of-mass energy per collision in December 2011, before being removed in 2013. It was scanned by the MoEDAL experiment using a SQUID magnetometer to search for trapped MMs. No MM signal was observed. The two distinctive features of this search are the use of a trapping volume very close to the collision point and ultrahigh magnetic fields generated during the heavy-ion run that could produce MMs via the Schwinger effect. These two advantages allowed setting the first reliable, world-leading mass limits on MMs with high magnetic charge. In particular, the established limits are the strongest available in the range between 2 and 45 Dirac units, excluding MMs with masses of up to 80GeV at a 95% confidence level.

Simulation of charge-exchange induced NBI losses on EAST

The neutral beam injection is widely adopted in tokamaks as a key heating tool, playing a crucial role in generating burning plasmas. However, the loss of beam ions can damage the first wall and reduce the heating efficiency, resulting in failure to maintain steady-state conditions. In this work, the effect of neutral particles in the edge on fast ions generated by NBI in the Experimental Advanced Superconducting Tokamak (EAST) device is studied using the particle tracer code (PTC). The poloidal distribution of neutral particles is calculated by edge plasma simulation code SOLPS-ITER. In this simulation, four beam lines in EAST are considered: co-current tangential (co-tang), co-current perpendicular (co-perp), counter-current tangential (ctr-tang) and counter-current perpendicular (ctr-perp). It is shown that, in the absence of neutral particles, the loss fraction of ctr-injection is considerably higher than that of the co-injection. When considering the neutral particles, it is found that the ctr-perp injection demonstrates a significant variation in particles loss fraction (ranging from 18.56% to 25.42%) compared to the other three injection configurations. In terms of the loss fraction induced by neutral particles, ctr-injection exceeds co-injection, and perpendicular configuration exceeds tangential configuration. Furthermore, the difference of charge exchange ratios of three different energy (full energy, half energy, one third energy) of the four injections can be attributed to variations in the poloidal trajectories associated with each of these injections. Moreover, approximately half of fast ions which undergo neutralization directly lose to the first wall while the rest re-enter the bulk plasma and re-ionize. Except for the ctr-tang injection, the reionization ions from the other three injections exhibit effective confinement.

Neutron dosimetry at HK-1 beam line of LVR-15 reactor for biomedical sample irradiations

Neutron dosimetry at HK-1 beam line of LVR-15 reactor for biomedical sample irradiations

Phase space reconstruction technique for beam optimization in the Low Energy High Intensity Proton Accelerator (LEHIPA)

The Low Energy High Intensity Proton Accelerator (LEHIPA) has been commissioned to the design energy of 20 MeV at BARC, India. The low energy beam transport (LEBT) channel of LEHIPA consists of two solenoids and drift spaces for matching the 50 keV proton beam from the ECR ion source (ECR-IS) to the RFQ. The ion beam extracted from the ECR-IS also contains molecular species like H2 + and H3 +. Proton fraction in the beam is found to degrade slowly with time due to surface contamination of the plasma chamber and this reduction in proton beam current has implications for longitudinal and transverse beam dynamics. Hence, it becomes important to characterise the beam at different proton fraction levels to understand the end-to-end beam dynamics of LEHIPA. Computed Tomography (CT) technique has been used for the beam phase-space reconstruction in LEHIPA, using a Python program, incorporating the feature of filtering secondary species from the beam profiles measured using slit scanners in the LEBT. Simultaneous Algebraic Reconstruction Technique (SART) is used in the reconstruction since it is identified to be a better technique for a limited number of projections. The reconstruction program is benchmarked with the TraceWin beam dynamics code and implemented on the measured beam profiles to recreate the phase space distribution at the beginning of LEBT. Further, the tomographic reconstruction method is compared with the solenoid scan method and the rms emittance values are found to be in good agreement. The measured tomographic phase space distribution has then been used as TraceWin input for LEHIPA end-end beam dynamics simulations and the LEHIPA beam line parameters are re-optimized for minimum beam emittance growth. This paper presents the simulations of CT technique, benchmarking simulations with TraceWin, phase space reconstruction with measured beam profiles and beam dynamics studies of LEHIPA using the reconstructed beam distributions.

Design of a Facility for Simultaneous Irradiation with Two Ion Beams based on the HIPR Accelerator for Simulations Neutron Influence

Ion accelerator facility is a powerful tool to simulate neutron irradiation effects in reactor materials. Defects in the crystal lattice arise and the accumulation of transmutation products (helium and hydrogen) occurs in the structure of the material under the action of neutrons in the structural materials of nuclear installations. At Kurchatov Complex for Theoretical and Experimental Physics the heavy ion accelerator HIPr (heavy ion prototype) is used to simulate radiation damage in steels and alloys using a 5.6 MeV Fe2+ ion beam. The second beam line is designed at the HIPr facility to simultaneously implant helium (or hydrogen) into the region of defects. The second beam line provides a beam of helium ions with energy up to 300 keV. The report presents a description of second beam line design and a status of construction the second beam line.

Monte Carlo simulations of microdosimetry and radiolytic species production at long time post proton irradiation using GATE and Geant4-DNA.

Radiobiological effectiveness of radiation in cancer treatment can be studied at different scales (molecular till organ scale) and different time post irradiation. The production of free radicals and reactive oxygen species during water radiolysis is particularly relevant to understand the fundamental mechanisms playing a role in observed biological outcomes. The development and validation of Monte Carlo tools integrating the simulation of physical, physico-chemical and chemical stages after radiation is very important to maintain with experiments. Therefore, in this study, we propose to validate a new Geant4-DNA chemistry module through the simulation of water radiolysis and Fricke dosimetry experiments on a proton preclinical beam line. In this study, we used the GATE Monte Carlo simulation platform (version 9.3) to simulate a 67.5 MeV proton beam produced with the ARRONAX isochronous cyclotron (IBA Cyclone 70XP) at conventional dose rate (0.2Gy/s) to simulate the irradiation of ultra-pure liquid water samples and Fricke dosimeter. We compared the depth dose profile with measurements performed with a plane parallel Advanced PTW 34045 Markus ionization chamber. Then, a new Geant4-DNA chemistry application proposed from Geant4 version 11.2 has been used to assess the evolution of , , , , , , and reactive species along time until 1-h post-irradiation. In particular, the effect of oxygen and pH has been investigated through comparisons with experimental measurements of radiolytic yields for and Fe3+. GATE simulations reproduced, within 4%, the depth dose profile in liquid water. With Geant4-DNA, we were able to reproduce experimental radiolytic yields 1-h post-irradiation in aerated and deaerated conditions, showing the impact of small changes in oxygen concentrations on species evolution along time. For the Fricke dosimeter, simulated G(Fe3+) is 15.97±0.2 molecules/100eV which is 11% higher than the measured value (14.4±04 molecules/100 eV). These results aim to be consolidated by new comparisons involving other radiolytic species, such as or to further study the mechanisms underlying the FLASH effect observed at ultra-high dose rates (UHDR).

Simulation and experimental benchmarking of a proton pencil beam scanning nozzle model for development of MR-integrated proton therapy.

MR-integrated proton therapy is under development. It consists of the unique challenge of integrating a proton pencil beam scanning (PBS) beam line nozzle with an magnetic resonance imaging (MRI) scanner. The magnetic interaction between these two components is deemed high risk as the MR images can be degraded if there is cross-talk during beam delivery and imageacquisition. To create and benchmark a self-consistent proton PBS nozzle model for empowering the next stages of MR-integrated proton therapy development, namely exploring and de-risking complete integrated prototype system designs including magnetic shielding of the PBS nozzle. Magnetic field (COMSOL ) and radiation transport (Geant4) models of a proton PBS nozzle located at OncoRay (Dresden, Germany) were developed according to the manufacturers specifications. Geant4 simulations of the PBS process were performed by using magnetic field data generated by the COMSOL simulations. In total 315 spots were simulated which consisted of a scan pattern with 5cm spot spacings and for proton energies of 70, 100, 150, 200, and 220MeV. Analysis of the simulated deflection at the beam isocenter plane was performed to determine the self-consistency of the model. The magnetic fringe field from a sub selection of 24 of the 315 spot simulations were directly compared with high precision magnetometer measurements. These focused on the maximum scanning setting of 20cm beam deflection as generated from the second scanning magnet in the PBS for a proton beam energy of 220MeV. Locations along the beam line central axis (CAX) were measured at beam isocenter and downstream of 22, 47, 72, 97, and 122cm. Horizontal off-axis positions were measured at 22cm downstream of isocenter ( 50, 100, and 150cm from CAX). The proton PBS simulations had good spatial agreement to the theoretical values in all 315 spots examined at the beam line isocenter plane (0-2.9mm differences or within 1.5% of the local spot deflection amount). Careful analysis of the experimental measurements were able to isolate the changes in magnetic fields due solely to the scanning magnet contribution, and showed 1.9 1.2 -9.4 1.2 changes over the range of measurement locations. Direct comparison with the equivalent simulations matched within the measurement apparatus and setup uncertainty in all but one measurementpoint. For the first time a robust, accurate and self-consistent model of a proton PBS nozzle assembly has been created and successfully benchmarked for the purposes of advancing MR-integrated proton therapy research. The model will enable confidence in further simulation based work on fully integrated designs including MRI scanners and PBS nozzle magnetic shielding in order to de-risk and realize the full potential of MR-integrated proton therapy.

Development of a 166.6MHz β = 1 higher-order-mode-damped superconducting cavity.

The storage ring of the high energy photon source will be driven by five 166.6MHz β = 1 quarter-wave superconducting cavities operating at 4K. A higher-order-mode-damped superconducting cavity was designed with excellent rf and mechanical properties based on the successful development of the proof-of-principle cavity. The mechanical design of the dressed cavity was focused on addressing stress safety throughout the processes, tunability, frequency detuning due to pressure fluctuation, and Lorentz force, among other factors. A new liquid helium vessel was designed along with a comprehensive stiffening scheme to mitigate the surging peak stress on the cavity resulting from the significantly unequal beam pipe size. In the first batch, three cavities were manufactured, and surface preparations were carefully conducted to eliminate defects and etching traces while ensuring cleanliness. The cavity's Q0 at the design voltage of 1.5 MV reached 3.8 × 109 at 4K, comfortably surpassing the design goal. Field emission onset was not observed during the entire test up to a peak electric field of 60 MV/m, thanks to the optimized processing procedures. Subsequently, one cavity was welded with the newly designed helium vessel and vertically tested at 2K, achieving an rf performance comparable to the bare cavities, demonstrating the success of the jacketed cavity. This paper presents the design, fabrication, surface preparation, and cryogenic tests of the first higher-order-mode-damped 166.6MHz β = 1 superconducting cavity.