FFAG Research Articles

Design and beam dynamics validation of a spiral FFAG accelerator for CSNS-II

The fixed-field alternating gradient (FFAG) accelerator, with its compact structure and the combined advantages of high energy from synchrotrons and high beam intensity from cyclotrons, offers unparalleled benefits in accelerating protons, heavy ions, and short-lived particles such as muons and unstable nuclei. The China Spallation Neutron Source plans to establish an FFAG accelerator with a diameter of 20 meters at the end of the negative hydrogen linac for various purposes, including experiments in nuclear physics and medical applications. For this design, a scaling scheme using spiral magnets as the basic focusing structure is investigated to provide the proton beam with kinetic energy ranging from 300 MeV to 600 MeV. We present the design results for the scaling FFAG accelerator and discuss the optimization of the cell tune. A detailed beam dynamics verification and discussion of the proposed FFAG accelerator lattice are presented using the ray-tracing code Zgoubi, including off-axis optical characteristics, large amplitude transverse motion, and full-cycle longitudinal acceleration. The FFAG accelerator is demonstrated to provide a large transverse and longitudinal acceptance for the tracking beam in the designed lattice. A new simulation code based on Python for the study of FFAG accelerator beam dynamics has been developed, and the corresponding verification results are also presented.

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.

Neutron-production double-differential cross sections of natPb and 209Bi in proton-induced reactions near 100 MeV

The lack of double-differential cross-section (DDX) data for neutron production below the incident proton energy of 200 MeV hinders the validation of spallation models in technical applications, such as research and development of accelerator-driven systems (ADSs). The present study aims to obtain experimental DDX data for ADS spallation target materials in this energy region and identify issues related to the spallation models by comparing them with the analytical predictions. The DDXs for the (p,xn) reactions of natPb and 209Bi in the 100-MeV region were measured over an angular range of 30° to 150° using the time-of-flight method. The measurements were conducted at Kyoto University utilizing the FFAG accelerator. The DDXs obtained were compared with calculation results from Monte Carlo-based spallation models (INCL4.6/GEM, Bertini/GEM, JQMD/GEM, ISOBAR/GEM, CEM03.03, INCL4/ABLA, Bertini/ABLA, ISABEL/ABLA, INCL++/ABLA07, INCL++/GEMINI++, and INCL++/SMM) and the evaluated nuclear data library, JENDL-5. Comparison between the measured DDX and analytical values based on the spallation models and evaluated nuclear data library indicated that, in general, the CEM03.03 model demonstrated the closest match to the experimental values. Additionally, the comparison highlighted several issues that need to be addressed in order to improve the reproducibility of the proton-induced neutron-production DDX in the 100 MeV region by these spallation models and evaluated nuclear data library. To enhance the reproducibility of underperforming spallation models and evaluated nuclear data library, it is recommended to address each of the issues identified in this study.

Ionoacoustic application of an optical hydrophone to detect proton beam range in water.

Proton range uncertainty has been the main factor limiting the ability of proton therapy to concentrate doses to tumors to their full potential. Ionoacoustic (IA) range verification is an approach to reducing this uncertainty by detecting thermoacoustic waves emitted from an irradiated volume immediately following a pulsed proton beam delivery; however, the signal weakness has been an obstacle to its clinical application. To increase the signal-to-noise ratio (SNR) with the conventional piezoelectric hydrophone (PH), the detector-sensitive volume needs to be large, but it could narrow the range of available beam angles and disturb real-time images obtained during beam delivery. To prevent this issue, we investigated a millimeter-sized optical hydrophone (OH) that exploits the laser interferometric principle. For two types of IA waves [γ-wave emitted from the Bragg peak (BP) and a spherical IA wave with resonant frequency (SPIRE) emitted from the gold fiducial marker (GM)], comparisons were made with PH in terms of waveforms, SNR, range detection accuracy, and signal intensity robustness against the small detector misalignment, particularly for SPIRE. A 100-MeV proton beam with a 27 ns pulse width and 4 mm beam size was produced using a fixed-field alternating gradient accelerator and was irradiated to the water phantom. The GM was set on the beam's central axis. Acrylic plates of various thicknesses, up to 12mm, were set in front of the phantoms to shift the proton range. OH was set distal and lateral to the beam, and the range was estimated using the time-of-flight method for γ-wave and by comparing with the calibration data (SPIRE intensity versus the distance between the GM and BP) derived from an IA wave transport simulation for SPIRE. The BP dose per pulse was 0.5-0.6Gy. To measure the variation in SPIRE amplitude against the hydrophone misalignment, the hydrophone was shifted by±2mm at a maximum in lateral directions. Despite its small size, OH could detect γ-wave with a higher SNR than the conventional PH (diameter, 29mm), and a single measurement was sufficient to detect the beam range with a submillimeter accuracy in water. In the SPIRE measurement, OH was far more robust against the detector misalignment than the focused PH (FPH) used in our previous study [5%/mm (OH) versus 80%/mm (FPH)], and the correlation between the measured SPIRE intensity and the distance between the GM and BP agreed well with the simulation results. However, the OH sensitivity was lower than the FPH sensitivity, and about 5.6-Gy dose was required to decrease the intensity variation among measurements to less than 10%. The miniature OH was found to detect weak IA signals produced by proton beams with a BP dose used in hypofractionated regimens. The OH sensitivity improvement at the MHz regime is worth exploring as the next step.

Measurement of double-differential neutron yields for iron, lead, and bismuth induced by 107-MeV protons for research and development of accelerator-driven systems

For the research and development of accelerator-driven systems (ADSs) and fundamental ADS reactor physics research using the Kyoto University Critical Assembly combined with the fixed-field alternating gradient (FFAG) accelerator, we are conducting a series of experiments on double-differential neutron yields using the FFAG accelerator at Kyoto University. This paper presents an overview of the experiments together with preliminary results.

Measurement of 107-MeV proton-induced double-differential thick target neutron yields for Fe, Pb, and Bi using a fixed-field alternating gradient accelerator at Kyoto University

ABSTRACT Double-differential thick target neutron yields (TTNYs) for Fe, Pb, and Bi targets induced by 107-MeV protons were measured using the fixed-field alternating gradient accelerator at Kyoto University for the research and development of accelerator-driven systems (ADSs) and fundamental ADS reactor physics research at the Kyoto University Critical Assembly (KUCA). Note that TTNYs were obtained with the time-of-flight method using a neutron detector system comprising eight neutron detectors; each detector has a small EJ-301 liquid organic scintillator and photomultiplier tube. The TTNYs obtained were compared with calculation results using Monte Carlo-based spallation models (i.e. INCL4.6/GEM, Bertini/GEM, JQMD/GEM, and JQMD/SMM/GEM) and the evaluated high-energy nuclear data library, i.e. JENDL-4.0/HE, implemented in the particle and heavy ion transport code system (PHITS). All models, including JENDL-4.0/HE, failed to predict high-energy peaks at a detector angle of . Comparing the energy- and angle-integrated spallation neutron yields at energies of ≤20 MeV estimated using the measured TTNYs and the PHITS indicated that INCL4.6/GEM would be suitable for the Monte Carlo transport simulation of ADS reactor physics experiments at the KUCA.

Fabrication and Test of a 1:4 Scaled HTS Coil for the Defocusing Magnet of 2 GeV FFAG Accelerator

The basic design of a 2 GeV fixed field alternating gradient (FFAG) accelerator was proposed by China Institute of Atomic Energy (CIAE) in 2019. A preliminary study of high temperature superconducting (HTS) magnet for the 2 GeV FFAG accelerator lattice scheme was carried out, considering the beam loss of high energy proton beams and energy efficiency of the main machine. In order to demonstrate the feasibility of manufacturing a spiral-shaped HTS magnet with concave edges based on ReBCO tapes, a 1:4 scaled HTS model magnet is being developed in CIAE. First, the design and fabrication of the 1:4 scaled prototype HTS magnet with concave edges will be described in detail. Then, each double pancake (DP) was tested by liquid nitrogen (LN) immersion. The terminal voltage and magnetic field variation were measured and simulated. Finally, the whole assembled HTS magnet was cooled down to 23 K using helium gas pipeline contact cooling and operated on 300 A for over 24 hours. The central magnetic field reached 719.5 mT, without iron. More detailed electromagnetic characteristics of the magnet during the excitation will be illustrated, which is much helpful for the fabrication of the final full-size HTS magnets.

Possible solution for the integer resonance crossing problem of GeV-class isochronous Fixed-Field Alternating Gradient accelerators

Fixed-Field Alternating Gradient accelerators (FFAG, also known as FFA) are promising candidates for next-generation GeV-class proton driver with average beam power of several megawatts. In isochronous accelerators, radial tunes are approximately increasing with beam energy in a linear way, and thus the integer resonance crossing problem becomes the major bottleneck of GeV-class isochronous FFAG design. In 2019, China Institute of Atomic Energy (CIAE) proposed an isochronous FFAG conceptual design with capability of producing 2GeV/6MW continuous wave (CW) proton beam. However, this conceptual design shows that the beam size is blown up at high energy region due to the third harmonic magnetic field caused by imperfections. The reason is that the integer resonance vr=3 causes a large coherent oscillation, and this large amplitude is not compatible with the following third order intrinsic resonance 3vr=10. In order to correct the large coherent motion before reaching the 3vr=10 resonance, we propose an idea of integer resonance suppressor (IRS) which intentionally introduces the third harmonic magnetic field. Our calculation shows that third harmonic field of 10Gs is acceptable with proper IRS settings, meaning that the requirements of magnet manufacture and installation can be relaxed. The increased imperfection tolerances will make magnet manufacture and installation much easier.

Technical Note: Range verification of pulsed proton beams from fixed-field alternating gradient accelerator by means of time-of-flight measurement of ionoacoustic waves.

Ionoacoustics is one of the promising approaches to verify the beam range in proton therapy. However, the weakness of the wave signal remains a main hindrance to its application in clinics. Here we studied the potential use of a fixed-field alternating gradient accelerator (FFA), one of the accelerator candidates for future proton therapy. For such end, magnitude of the pressure wave and range accuracy achieved by the short-pulsed beam of FFA were assessed, using both simulation and experimental procedure. A 100MeV proton beam from the FFA was applied on a water phantom, through the acrylic wall. The beam range measured by the Bragg peak (BP)-ionization chamber (BPC) was 77.6mm, while the maximum dose at BP was estimated to be 0.35Gy/pulse. A hydrophone was placed 20mm downstream of the BP, and signals were amplified and stored by a digital oscilloscope, averaged, and low-pass filtered. Time-of-flight (TOF) and two relative TOF values were analyzed in order to determine the beam range. Furthermore, an acoustic wave transport simulation was conducted to estimate the amplitude of the pressure waves. The range calculated when using two relative TOF was 78.16±0.01 and 78.14±0.01mm, respectively, both values being coherent with the range measured by the BPC (the difference was 0.5-0.6mm). In contrast, utilizing the direct TOF resulted in a range error of 1.8mm. Fivefold and 50-fold averaging were required to suppress the range variation to below 1mm for TOF and relative TOF measures, respectively. The simulation suggested the magnitude of pressure wave at the detector exceeded 7 Pascal. A submillimeter range accuracy was attained with a pulsed beam of about 21ns from an FFA, at a clinical energy using relative TOF. To precisely quantify the range with a single TOF measurement, subsequent improvement in the measuring system is required.

Optics design of vertical excursion fixed-field alternating gradient accelerators

Vertical excursion fixed-field alternating gradient accelerators can be designed with tunes that are invariant with respect to momentum and trajectories that are scaled images of each other displaced only in the vertical direction. This is possible using guiding fields that have a vertical exponential increase, with a skew quadrupole component in the magnet body and a solenoid component at the magnet ends. Because of the coupling this introduces, orbit and optics calculations and optimisation of parameters need to be performed numerically. In this paper, idealised magnetic fields are calculated from first principles, taking into account end fields. The parameter dependence of the optics and the dynamic aperture of the ring are calculated for the example of a ring with an approximately 25 m circumference that accelerates proton beams from 3 MeV to 12 MeV. The paper reports for the first time the design of such an accelerator lattice using tools specifically devised to analyse transverse coupled optics without the need for approximations.

LhARA: The Laser-hybrid Accelerator for Radiobiological Applications

The “Laser-hybrid Accelerator for Radiobiological Applications,” LhARA, is conceived as a novel, flexible facility dedicated to the study of radiobiology. The technologies demonstrated in LhARA, which have wide application, will be developed to allow particle-beam therapy to be delivered in a new regimen, combining a variety of ion species in a single treatment fraction and exploiting ultra-high dose rates. LhARA will be a hybrid accelerator system in which laser interactions drive the creation of a large flux of protons or light ions that are captured using a plasma (Gabor) lens and formed into a beam. The laser-driven source allows protons and ions to be captured at energies significantly above those that pertain in conventional facilities, thus evading the current space-charge limit on the instantaneous dose rate that can be delivered. The laser-hybrid approach, therefore, will allow the radiobiology that determines the response of tissue to ionizing radiation to be studied with protons and light ions using a wide variety of time structures, spectral distributions, and spatial configurations at instantaneous dose rates up to and significantly beyond the ultra-high dose-rate “FLASH” regime. It is proposed that LhARA be developed in two stages. In the first stage, a programme of in vitro radiobiology will be served with proton beams with energies between 10 and 15 MeV. In stage two, the beam will be accelerated using a fixed-field alternating-gradient accelerator (FFA). This will allow experiments to be carried out in vitro and in vivo with proton beam energies of up to 127 MeV. In addition, ion beams with energies up to 33.4 MeV per nucleon will be available for in vitro and in vivo experiments. This paper presents the conceptual design for LhARA and the R&D programme by which the LhARA consortium seeks to establish the facility.

Tune compensation in nearly scaling fixed field alternating gradient accelerators

In this paper, we investigate the stability of the particle trajectories in Fixed Field alternating gradient Accelerators (FFA) in the presence of field errors: The emphasis is on the scaling radial sector FFA type: a collaboration work is on-going in view of better understanding the properties of the 150 MeV scaling FFA at KURRI in Japan, and progress towards high intensity operation. Analysis of certain types of field imperfections revealed some interesting features about this machine that explain some of the experimental results and generalize the concept of a scaling FFA to a non-scaling one for which the tune variations obey a well defined law. A compensation scheme of tune variations in imperfect scaling FFAs is presented. This is the cornerstone of a novel concept of a non-linear non-scaling radial sector fixed tune FFA that we present and discuss in details in the last part of this paper.

Fabrication of a Model Magnet Using Coated Conductors for FFAG Accelerators

Fabrication of a Model Magnet Using Coated Conductors for FFAG Accelerators

Special issue on accelerator-driven system benchmarks at Kyoto University Critical Assembly

ABSTRACTThe accelerator-driven system (ADS) had been proposed for producing energy and transmuting minor actinide and long-lived fission products. ADS has attracted worldwide attention in recent years because of its superior safety characteristics and potential for burning plutonium and nuclear waste. At the Institute for Integrated Radiation and Nuclear Science, Kyoto University, a series of ADS experiments with 14 MeV neutrons was launched in fiscal year 2003 at the Kyoto University Critical Assembly (KUCA). Also, the high-energy neutrons generated by the interaction of 100 MeV protons with tungsten target was injected into the KUCA core on March 2009. The ADS experiments with 100 MeV protons obtained from the FFAG accelerator have been carried out to investigate the neutron characteristics of ADS. This special issue aims at concentrating on experimental analyses for the ADS benchmarks at KUCA on the basis of most recent advances in the development of computational methods, and contributing to academic progress for ADS research field in the future.

Remodeling of 150 Mev Ffag Main Ring At Kurns To Pion Production Ring

A possibility of remodeling main ring of 150 MeV FFAG accelerator at Kyoto University, Institute for Integrated Radiation and Nuclear Science (KURNS) to Pion Production Ring (PPR) for muon transmutation study has been discussed. Design was made on the assumption that 400 MeV proton beams circulate and hit a target in the ring to generate pions. Optimizations of lattice parameters and 3D magnet modeling are reported.

Development of proton beam irradiation system for small animals using FFAG accelerator

To evaluate the biological effect of boron compounds on normal tissues in boron neutron capture therapy, it is necessary to compare the radiation effects of neutron irradiation and gamma ray irradiation on small animals in nonclinical studies. Neutron beams and gamma rays are difficult to collimate; thus, it is impossible to administer a dose on each part of the normal tissues of small animals. Therefore, we have developed a method to compare biological effects by irradiating neutrons and gamma rays after irradiating a proton beam to the point just before the threshold dose at which the biological effects occur. We aim to develop an irradiation field that irradiates proton beams locally using a fixed-field alternating-gradient (FFAG) accelerator and a small ridge filter.An aluminum scatterer, transmission dose monitor, ridge filter, range shifter, collimator, and a proton beam from the FFAG accelerator were used to form an irradiation field with a spread out Bragg peak (SOBP) with a length of 10 mm and a size of 10 mm2.Dose measurement was performed using a Gafchromic film and an ionization chamber. The irradiation system was simulated using the PHITS Monte Carlo simulation code, and simulation results were compared with experimental results.We succeeded in forming an irradiation field with a dose rate of 14.3 ± 0.24 Gy/min, an SOBP length of 10 mm, and a size of 10 mm2.

Evaluation of asymmetric quadrupoles for a non-scaling fixed field alternating gradient accelerator

A non-scaling fixed field alternating gradient (NS-FFAG) accelerator was constructed, which employs conventional quadrupoles. The possible demerit is the beam instability caused by the variable focusing strength when the orbit radius of the beam changes. To overcome this instability, it was suggested that the asymmetric quadrupole has different current flows in each coil. The magnetic field of the asymmetric quadrupole was found to be more similar to the magnetic field required for the FFAG accelerator than the constructed NS-FFAG accelerator. In this study, a simulation of the beam dynamics was carried out to evaluate the improvement to the beam stability for the NS-FFAG accelerator using the SIMION program. The beam dynamics simulation was conducted with the ‘hard edge’ model; it ignored the fringe field at the end of the magnet. The magnetic field map of the suggested magnet was created using the SIMION program. The lattices for the simulation combined the suggested magnets. The magnets were evaluated for beam stability in the lattices through the SIMION program.

Medical therapy and imaging fixed-field alternating-gradient accelerator with realistic magnets

NORMA is a design for a normal-conducting race track fixed-field alternating-gradient accelerator (FFAG) for protons from 50 to 350 MeV. In this article we show the development from an idealised lattice to a design implemented with field maps from rigorous two-dimensional (2D) and three-dimensional (3D) FEM magnet modelling. We show that whilst the fields from a 2D model may reproduce the idealised field to a close approximation, adjustments must be made to the lattice to account for differences brought about by the 3D model and fringe fields and full 3D models. Implementing these lattice corrections we recover the required properties of small tune shift with energy and a sufficiently-large dynamic aperture. The main result is an iterative design method to produce the first realistic design for a proton therapy accelerator that can rapidly deliver protons for both treatment and for imaging at up to 350 MeV. The first iteration is performed explicitly and described in detail in the text.

Corrections to “Design and Magnetic Field Analyses of Spiral Sector Magnet in an FFAG Accelerator for Carbon Cancer Therapy” [Jun 16 Art. no. 4402206

Corrections are made to the original article listed above.

Scaling Fixed-Field Alternating-Gradient Accelerators with Reverse Bend and Spiral Edge Angle.

A novel scaling type of fixed-field alternating-gradient (FFAG) accelerator is proposed that solves the major problems of conventional scaling FFAGs. This scaling FFAG accelerator combines reverse bending magnets of the radial sector type and a spiral edge angle of the spiral sector type to ensure sufficient vertical focusing without relying on extreme values of either parameter. This new concept makes it possible to design a scaling FFAG for high energy (above GeV range) applications such as a proton driver for a spallation neutron source and an accelerator driven subcritical reactor.