FFAG Research Articles

Conceptual design of a nonscaling fixed field alternating gradient accelerator for protons and carbon ions for charged particle therapy

The conceptual design for a nonscaling fixed field alternating gradient accelerator suitable for charged particle therapy (the use of protons and other light ions to treat some forms of cancer) is described.49 MoreReceived 23 November 2012DOI:https://doi.org/10.1103/PhysRevSTAB.16.030101This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical Society

EMMA

EMMA stands for Electron Model for Many Applications and is expected to demonstrate the novel concept of a non-scaling Fixed Field Alternating Gradient (FFAG) accelerator. A non-scaling FFAG accelerator was originally invented to accelerate muons up to a few tens of GeV energy range although it is now hoped to have a wider variety of applications such as a proton driver for Accelerator Driven Sub-critical Reactor (ADSR). We will report the recent developments of the EMMA experiment, with more emphasis on acceleration of a muon beam.

EXPERIMENTAL ANALYSES OF SPALLATION NEUTRONS GENERATED BY 100 MEV PROTONS AT THE KYOTO UNIVERSITY CRITICAL ASSEMBLY

Neutron spectrum analyses of spallation neutrons are conducted in the accelerator-driven system (ADS) facility at the Kyoto University Critical Assembly (KUCA). High-energy protons (100 MeV) obtained from the fixed field alternating gradient accelerator are injected onto a tungsten target, whereby the spallation neutrons are generated. For neutronic characteristics of spallation neutrons, the reaction rates and the continuous energy distribution of spallation neutrons are measured by the foil activation method and by an organic liquid scintillator, respectively. Numerical calculations are executed by MCNPX with JENDL/HE-2007 and ENDF/B-VI libraries to evaluate the reaction rates of activation foils (bismuth and indium) set at the target and the continuous energy distribution of spallation neutrons set in front of the target. For the reaction rates by the foil activation method, the C/E values between the experiments and the calculations are found around a relative difference of 10%, except for some reactions. For continuous energy distribution by the organic liquid scintillator, the spallation neutrons are observed up to 45 MeV. From these results, the neutron spectrum information on the spallation neutrons generated at the target are attained successfully in injecting 100 MeV protons onto the tungsten target.

Particle orbit in a radial-sector scaling FFAG

The particle orbit in the bending magnet of a radial-sector FFAG accelerator is derived analytically in the approximation valid for a small bending angle. The orbit is described in terms of the distance from the machine center, r, and its variation is derived as a function of the bending angle. Also, the variation of the distance from the bending center, ρ, is derived as a function of the bending angle. The result shows how the ratio, r/ρ, can be made independent of the particle momentum, which is one of the conditions of the scaling property.

Conceptual design of multi-targets for accelerator-driven system experiments with 100-MeV protons

The Kyoto University Research Reactor Institute is engaged in research on an accelerator-driven system (ADS) using the fixed field alternating gradient accelerator at the Kyoto University Critical Assembly. With the aim of achieving the high-energy neutrons anticipated in the actual ADS experiments, we propose the use of a new target concept (the multi-target) in this study. The conceptual design of the multi-target is numerically carried out, and the high-energy neutrons generated by the injection of high-energy protons at the multi-target are successfully measured using a liquid organic scintillator in the experiments. The conceptual design and effectiveness of the multi-target is confirmed by the obtained neutron spectrum and neutron yield in both the experimental and calculated results.

Experimental study of resonance crossing with a Paul trap

The effect of resonance crossing on beam stability is studied systematically by employing a novel tabletop experimental tool and a multiparticle simulation code. A large number of ions are confined in a compact linear Paul trap to reproduce the collective beam behavior. We can prove that the ion plasma in the trap is physically equivalent to a charged-particle beam propagating through a strong focusing channel. The plasma confinement force is quickly ramped such that the trap operating point traverses linear and nonlinear resonance stop bands. Assuming a nonscaling fixed field alternating gradient accelerator composed of many identical FODO cells, we measure how much ion losses occur under diverse conditions. It is experimentally and numerically demonstrated that too slow resonance crossing leads to significant ion losses as expected. Particular attention must be paid to the linear coherent resonance excited at a quarter-integer tune. When the beam intensity is high, this type of linear stop band can seriously affect the beam quality even for rather fast resonance crossing. A scaling law is given of the emittance growth caused by the quarter-integer resonance crossing.

Design study of a non-scaling fixed-field alternating gradient accelerator

We present a design for a non-scaling fixed-field alternating gradient accelerator (FFAG) for proton beams of 250 MeV. For this design, a radial sector type FFAG that has a triplet structure of focusing-defocusing-focusing magnets is investigated as a machine to provide the proton beam. We show the design results for the non-scaling FFAG and discuss the optimization of the lattice parameters in the accelerator. The FFAG accelerator is shown to provide a large transverse acceptance from the tracking beam in the designed lattice. The proton beams in the designed FFAG accelerator may be utilized for various purposes such as experiments in nuclear physics and medical applications.

Magnetic Field Design of Coil-Dominated Magnets Wound With Coated Conductors

Coil-dominated magnets wound with coated conductors were designed for an FFAG accelerator for carbon therapy, which was designed by applying linear approximation. When designing the coil-end of the magnets, we applied differential geometry. To apply the differential geometry to three-dimensional windings with coated conductors, we introduced the concept of generalized flat-wise bending. Thereby, the combination of flat-wise bending and torsion was considered as bending of developable surface. Generated magnetic field was calculated, and the positions of conductors were optimized to minimize the field error. Three dimensional shapes of magnets were successfully designed with constraints on generalized flat-wise bending and edge-wise bending of coated conductors.

Use of transfer maps for modeling beam dynamics in a nonscaling fixed-field alternating-gradient accelerator

Transfer maps for magnetic components are fundamental to studies of beam dynamics in accelerators. In the work presented here, transfer maps are computed in Taylor form for a particle moving through any specified magnetostatic field by applying an explicit symplectic integrator in a differential algebra code. The techniques developed are illustrated by their application to study the beam dynamics in the electron model for many applications (EMMA), the first nonscaling fixed-field alternating-gradient accelerator ever built. The EMMA lattice has 4 degrees of freedom (strength and transverse position of each of the two quadrupoles in each periodic cell). Transfer maps may be used to predict efficiently the dynamics in any lattice configuration. The transfer map is represented by a mixed variable generating function, obtained by interpolation between the maps for a set of reference configurations: use of mixed variable generating functions ensures the symplecticity of the map. An optimization routine uses the interpolation technique to look for a lattice defined by four constraints on the time of flight at different beam energies. This provides a way to determine the lattice configuration required to produce the desired dynamical characteristics. These tools are benchmarked against data from the recent EMMA commissioning.

The Advantages and Challenges of Helical Coils for Small Accelerators—A Case Study

Most of today's particle accelerators are used in industry or for medical applications, for example, in radioisotope production and cancer therapy. One important factor for these applications is the size of the accelerator, which ideally should be as small as possible. In this respect, fixed-field alternating-gradient accelerators (FFAGs) can be an attractive alternative, which combine the best features of conventional synchrotrons and cyclotrons: FFAGs deliver better performance than synchrotrons while retaining flexibility. Of particular interest are accelerators for protons of moderate energy (0.25-1 GeV) and light ions such as carbon (up to 400 MeV per nucleon), for example, for proton/carbon-ion charged particle therapy or potential future applications such as accelerator-driven subcritical reactors. Due to high magnetic rigidity, a compact machine can be only achieved by using high field superconducting magnets. A disadvantage of FFAGs is that the magnetic elements can be very challenging. Quite often, complicated multipole fields are required, in combination with stringent geometric constraints. In this paper, we demonstrate the advantages of helical coil technology by means of an accelerator for proton therapy.

Subcritical Multiplication Parameters of the Accelerator-Driven System with 100 MeV Protons at the Kyoto University Critical Assembly

Basic experiments on the accelerator-driven system (ADS) at the Kyoto University Critical Assembly are carried out by combining a solid-moderated and -reflected core with the fixed-field alternating gradient accelerator. The reaction rates are measured by the foil activation method to obtain the subcritical multiplication parameters. The numerical calculations are conducted with the use of MCNPX and JENDL/HE-2007 to evaluate the reaction rates of activation foils set in the core region and at the location of the target. Here, a comparison between the measured and calculated eigenvalues reveals a relative difference of around 10% in C/E values. A special mention is made of the fact that the reaction rate analyses in the subcritical systems demonstrate apparently the actual effect of moving the tungsten target into the core on neutron multiplication. A series of further ADS experiments with 100 MeV protons needs to be carried out to evaluate the accuracy of subcritical multiplication parameters.

D132 沸騰熱伝達におよぼす紫外線及び放射線照射の影響(OS-15: 沸騰・凝縮伝熱および混相流の最近の進展(3))

Effect of surface wettability on boiling heat transfer was studied by applying radiation induced surface activation. Oxidized metal surfaces were irradiated by ultraviolet light, gamma ray, and proton beam, to investigate the radiation effect on the surface wettability. Proton irradiation experiments were performed at the FFAG accelerator complex of Kyoto University with 100MeV proton energy. Wettability enhancement on the oxidized metal surface was observed in each radiation method, where the radiation conditions were 20 minutes exposure with 5mW/cm^2 for ultraviolet, 97kGy for gamma ray, and 50 hours irradiation with 4.7nA for 100MeV proton beam, respectively. In addition, boiling heat transfer experiment was also performed with and without gamma ray irradiation. Experimental results show that the critical heat flux increases with the gamma-ray irradiated copper surface, however the heat transfer enhancement was not obvious at present experimental conditions.

Compact superferric FFAG accelerators for medium energy hadron applications

Medium energy hadron beams are desirable in various applications such as accelerator-driven subcritical systems (ADSR), high intensity neutron sources and carbon therapy. Compactness and easy operation characters are important for this energy region, especially in the case of medical use purposes. This paper introduces a novel superferric scheme with scaling fixed-field alternating gradient (FFAG) accelerators, which can provide 400MeV/u carbon ions for cancer therapy. By employing a maximum field of 5T with a high field index, 8.5m diameter with 85cm radius excursion is achieved in a single FFAG ring. The lattice configuration and design of superferric magnet sectors with high permeability materials were described in detail. This scheme can also be extended to other hadron applications.

HIGH-ORDER OUT-OF-PLANE EXPANSION FOR 3D FIELDS

The precise determination of the dynamics in accelerators with complicated field arrangements such as Fixed Field Alternating Gradient accelerators (FFAG) depends critically on the ability to describe the appearing magnetic fields in full 3D. However, frequently measurements or models of FFAG fields postulate their behavior in the midplane only, and rely on the fact that this midplane field and its derivatives determine the field in all of space. The detailed knowledge of the resulting out-of-plane fields is critical for a careful assessment of the vertical dynamics. We describe a method based on the differential algebraic (DA) approach to obtain the resulting out-of-plane expansions to any order in an order-independent, straightforward fashion. In particular, the resulting fields satisfy Maxwell's equations to the order of the expansion up to machine precision errors, and without any inaccuracies that can arise from conventional divided difference or finite element schemes for the computation of out-of-plane fields. The method relies on re-writing the underlying PDE as a fixed point problem involving DA operations, and in particular the differential algebraic integration operator. We illustrate the performance of the method for a variety of practical examples, and obtain estimates for the orders necessary to describe the fields to a prescribed accuracy.

ORGANIZING COMMITTEE

International Journal of Modern Physics AVol. 26, No. 10n11, pp. ix (2011) SPECIAL ISSUE: Fixed Field Alternating Gradient Accelerators: Proceedings of the International Conference (FFAG'09) Dedicated to Alessandro G. Ruggiero for His Many Contributions to the Rebirth of the FFAG Fermilab, USA, 21–25 September 2009; Editors: C. Johnstone, M. Berz and P. SnopokNo AccessORGANIZING COMMITTEEhttps://doi.org/10.1142/S0217751X11053092Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail You currently do not have access to the full text article. Recommend the journal to your library today! FiguresReferencesRelatedDetails Recommended Vol. 26, No. 10n11 Metrics History PDF download

UPGRADING EMMA TO USE LOW-FREQUENCY RF CAVITIES

EMMA is an experiment to study beam dynamics in fixed field alternating gradient accelerators (FFAGs). It accelerates the beam in about 10 turns using 1.3 GHz cavities in a mode like that used for muon accelerators. Many applications of FFAGs prefer to have slower acceleration, typically thousands of turns. To do so in EMMA would require the RF system to be replaced with a low-frequency, high-gradient system. This paper describes the motivation for studying slow acceleration in EMMA and the required parameters for an RF system to do that. It then describes the technology needed for the RF system.

ON SOME ERRORS AND BIAS IN PROTON COMPUTED TOMOGRAPHY

Novel accelerator technology, including Fixed Field Alternating Gradient Accelerators (FFAG) coupled with medical imaging devices, hold significant promise for enhanced proton therapy. The accuracy and efficiency of proton therapy treatments will see improvements with the implementation of proton computed tomography (pCT), currently under development. Here, we analyze the robustness of the image reconstruction method in pCT with respect to three different error sources and conclude that pCT is inherently resilient with respect to errors in mean ionization potential, discrete sampling of proton trajectories and bias in the limit of large radiation doses.

ADVANCES IN NONLINEAR NON-SCALING FFAGs

Accelerators are playing increasingly important roles in basic science, technology, and medicine. Ultra high-intensity and high-energy (GeV) proton drivers are a critical technology for accelerator-driven sub-critical reactors (ADS) and many HEP programs (Muon Collider) but remain particularly challenging, encountering duty cycle and space-charge limits in the synchrotron and machine size concerns in the weaker-focusing cyclotrons; a 10–20 MW proton driver is not presently considered technically achievable with conventional re-circulating accelerators. One, as-yet, unexplored re-circulating accelerator, the Fixed-field Alternating Gradient or FFAG, is an attractive alternative to the other approaches to a high-power beam source. Its strong focusing optics can mitigate space charge effects and achieve higher bunch charges than are possible in a cyclotron, and a recent innovation in design has coupled stable tunes with isochronous orbits, making the FFAG capable of fixed-frequency, CW acceleration, as in the classical cyclotron but beyond their energy reach, well into the relativistic regime. This new concept has been advanced in non-scaling nonlinear FFAGs using powerful new methodologies developed for FFAG accelerator design and simulation. The machine described here has the high average current advantage and duty cycle of the cyclotron (without using broadband RF frequencies) in combination with the strong focusing, smaller losses, and energy variability that are more typical of the synchrotron. The current industrial and medical standard is a cyclotron, but a competing CW FFAG could promote a shift in this baseline. This paper reports on these new advances in FFAG accelerator technology and presents advanced modeling tools for fixed-field accelerators unique to the code COSY INFINITY.1

S-CODE FOR FIXED FIELD ALTERNATING GRADIENT ACCELERATOR DESIGN AND PARTICLE TRACKING

The constant field nature of a fixed field alternating gradient (FFAG) accelerator requires a modeling which separates the layout of accelerator elements from the geometry of beam orbits. A new code, named s -code, is made to design an FFAG accelerator and to track a beam in it. We will describe the model of accelerator elements and the way to integrate the equation of motion of a particle.

ADVANCEMENT OF THE SCALING FFAG ACCELERATOR FOR ADSR, PULSED-SNS AND MUON ACCELERATION

Progress in the study of beam optics and acceleration of the scaling FFAG accelerator has been presented in this paper.