Isochronous Field Research Articles

Optimization of the magnetic field in the SK1000 central region model magnet

This study presents a design scheme for a central region model magnet, based on a high-intensity compact cyclotron. The objective is to ensure the long-term stable production of therapeutic radionuclides such as 211At and 225Ac, while maintaining reasonable construction and operational costs. In-depth research into the design principles and core parameters of the CRM (Central Region Model) cyclotron magnet system, guided by the concept of isochronous magnetic field design, enabled the optimization of the magnet's dimensions and magnetic field distribution. The optimization results show that the magnet system meets the acceleration and focusing requirements of the particle beam, effectively prevents particles from entering dangerous resonance regions, and aligns with the theoretical requirements of isochronous magnetic fields. This method keeps the error between the calculated magnetic field and the theoretical design field within 5 Gauss, meeting the expected physical design standards.

Performance of a precise isochronous magnetic field over a wide momentum range in the Rare-RI Ring

The Rare-RI Ring is the isochronous storage ring constructed at the RIKEN radioactive isotope beam factory for high-precision mass measurements of extremely short-lived and rarely produced exotic nuclei via time-of-flight mass spectrometry. This is the only cyclotron-like heavy-ion storage ring that can satisfy the isochronous condition over a wide momentum range. The magnetic field is created with the assistance of 10 trim coils. A particle-tracking simulation was developed for tuning the magnetic field to reach high-precision isochronism. We successfully performed a commissioning experiment for the precise mass measurement of rarely produced nuclei, established by newly developed techniques: self-triggered injection together with in-flight particle identification, and high-precision isochronous adjustment. Experimental isochronism was obtained to be 4.7×10−6 for the standard deviation within ±0.3% of momentum range. The results showed that the high-precision isochronous magnetic field over a wide momentum range enabled precise mass determination.

Configuration of Zeros of Isochronous Vector Fields of Degree 5

In this paper, we give the algebraic conditions that a configuration of 5 points in the plane must satisfy in order to be the configuration of zeros of a polynomial isochronous vector field. We use the obtained results to analyze configurations having some of its zeros satisfying some particular geometric conditions.

Stress Study for Conduction Cooling Superconducting Magnet for Medical Cyclotron SC240

A high stress superconducting magnet for the 200MeV superconducting isochronous cyclotron has been constructed and operated to supply 3.6 T extraction magnetic field for proton therapy by CIM Inc. Based those experiences, A 240MeV superconducting isochronous cyclotron (so call SC240) for proton therapy is under development by CIM (F. Jiang et al., 2019). A superconducting magnet including 2 symmetry up/down split coils would be used to supply the 3.0 T isochronous extraction magnetic fields. The NbTi/Cu WIC conductor is selected to fabricate the superconducting coil. In this paper, the radial stress, hoop stress and displacement of the coil are investigated under different winding tension, cool down and Lorentz forces. Hoop stress is the most key point, the results are shown not more than 60 MPa, which meets the 80 MPa allowable requirement. Optimizing the coil stress design of SC240 can supply sufficient safety margin about lower 50% for hoop stress compared with SC200, which will minimize the risk of training times or avoid premature quench.

Numerical Evaluation on Electromagnetic and Thermal Stresses in Non-Circular REBCO Pancake Coils of Multi-Coil System For Skeleton Cyclotron

We proposed the air-core cyclotron using high-temperature superconducting (HTS) technology, named Skeleton Cyclotron, as high intensity compact, variable-energy and multi-particle cyclotron for RI production. Skeleton Cyclotron consists of HTS split circular main coils generating the isochronous field and HTS non-circular sector coils generating the azimuthally varying field (AVF). Now, we are currently developing the small-scale cryocooler-cooled HTS coil system of Skeleton Cyclotron, which accelerates the proton up to energy of 5 MeV at an extraction radius of 20 cm. Skeleton cyclotron is multi-coil system consists of HTS split circular main NI (no-insulation) coils and HTS non-circular sector NI coils. Therefore, the electromagnetic, thermal, and mechanical behaviors are expected to be very complicated. In this study, the structure analysis based on finite element method using COMSOL Multiphysics is performed for a non-circular sector coil. The coils in Ultra-Baby Cyclotron are reinforced with YOROI-coil structure. Therefore, the effect of YOROI-coil structure was numerically investigated during cool-down process and excitation process. YOROI-coil structure is effective for non-circular sector coil against the electromagnetic force.

Design and relative calibration of a beam profile measurement system for the SC200 superconducting cyclotron

The SC200 superconducting cyclotron promoted by the ASIPP (Hefei, China) and the Joint Institute for Nuclear Research (Dubna, Russia) has made significant progress. A new beam profile measurement system (BPMS) has been developed to operate inside the cyclotron to acquire information of the transverse beam profile. We present the structural layout of the BPMS in frame of the SC200 superconducting cyclotron operating scenario with many details, e.g. high magnetic field, compact structure, high radio frequency interference and strong irradiation, etc. The influences of the magnetic field, heat-dissipating method, and other factors on the BPMS were described in detail and solved. The energy loss, spectral matching, and the temperature dependency of the scintillation screen, as well as the directional characteristic of the imaging system were all taken into account for a relative calibration of the BPMS. The BPMS was adopted for beam diagnosis during the initial commissioning phase of the SC200, and the experimental results of light output and horizontal beam sizes were calibrated to provide quantitative information. Furthermore, the beam loss and vertical distribution of the beam were calculated, which provide important basis for beam tuning and optimization of the cyclotron. The successful application of the BPMS inside the compact cyclotron is of great significance for further shimming and optimization of the isochronous field.

Magnetic Field Measurement, Shimming and Processing for 230 MeV Superconducting Cyclotron Main Magnet

A 230 MeV compact superconducting cyclotron CYCIAE-230 is being constructed by the China Institute of Atomic Energy, which can be used for proton therapy and space radiation physics research. The technology of magnetic field measurement, shimming and processing is the primary task to realize the isochronous acceleration of cyclotron. The CYCIAE-230 has high magnetic field, high field gradient and dense rotation orbits. Therefore, the isochronous field and tune diagram need to be amended simultaneously. The first harmonic is also shimmed at the same process to ensure a good extraction efficiency by using precessional extraction. The precision of field measurement, shimming and processing is much higher and the algorithm is much more difficult than those in normal temperature cyclotron. In addition, the compact structure of the magnet has very narrow installation space, which makes the design of the mapper more difficult. The process of main magnet construction includes strict control of room temperature and electromagnetic compatibility (EMC), precise measurement of magnetic field, comprehensive research of beam dynamics and multi-dimensional numerical control (NC) processing under the control of complex algorithms. In this paper, the magnetic field measurement, shimming and processing of the main magnet will be illustrated in detail.

A Design Study on No-Insulation HTS Isochronous Cyclotron Magnet for Carbon Ion Therapy

Provided that a cyclotron system requires DC magnetic field, the no-insulation (NI) high temperature superconductor (HTS) magnet may be a good candidate as it may enable the cyclotron magnet to be more compact and reliable, yet operate under the liquid-helium-free environment. Here we report on a design study on an NI HTS isochronous cyclotron magnet for an acceleration of carbon ion up to an energy level of 385 MeV/u. To obtain a target beam stability, HTS coils were designed with the so-called “hill” and “valley” structure to generate a designated magnetic field profile. After the initial design on yokes and HTS coils was completed, a final design on the cyclotron magnet design was completed and its performance was analyzed using a 3D finite element method. This paper presents the magnet design and performance analyses in details that include: (1) electromagnetic design of the HTS coils and iron yokes for isochronous magnetic field; (2) mechanical stress with the use of stainless steel co-winding to limit the peak magnetic hoop stress; (3) charging and discharging scenarios with the non-linear NI characteristics considered; and (4) first-cut post-quench analysis with an estimated peak temperature and unbalanced force within the NI HTS coils.

Evaluation of shimmed DECY-13 MeV Cyclotron Magnet Using H- Beam Tracking Simulation

Abstract –Using OPERA3DTM, the magnet poles’ shimming that provide an isochronous magnetic field in DECY-13 cyclotron was designed and calculated. The shimmed magnet poles as designed were placed in the magnet and the distribution of the magnetic field in the magnet axis direction (Bz) was measured in radial ( x and y) directions using 2 probes covering x=0 to 480 mm for one probe and 481 to 960 mm for the other, and y=0 to 960 mm, all were done at z=0 in 9 hours of scanning at 5 mm steps. This paper describes the interpolation and extrapolation to obtain data for magnetic field components (Bx, By,Bz) at 1 mm resolution and at z≠0 as required for beam tracking simulations. The tracking results are used to evaluate the distribution of the shimmed magnetic fields of DECY-13. The program for the interpolation and extrapolation was written and run using a free software Scilab 5.4.1, and tested against OPERA3DTM design data. The beam can reach final energy of 13 MeV when both data was applying in the beam tracking simulation.. However when the measured data was used, the final energy of the beam reached only 3 MeV, meaning that at the place where that energy was reached the magnetic field is no longer is of isochronous and the shimming of the magnetic poles’ must be improved or redesigned to reach the final beam energy of 13 MeV.Key words: isochronous, DECY-13 cyclotron, Scilab 5.4.1, interpolation and extrapolation, beam tracking simulation

Design and Research of Magnetic Field Mapping System for SC200

The SC200 cyclotron is the critical component of the proton therapy system, which is being jointly developed by the Institute of Plasma Physics Chinese Academy of Sciences (ASIPP), Hefei, China, and the Joint Institute for Nuclear Research (JINR), Dubna, Russia. It is an isochronous cyclotron to accelerate H+ ions and extract proton beam energies of 75–200 MeV with the maximum beam intensity of $1~\mu \text{A}$ . The maximum magnetic field intensity of the SC200 cyclotron is 4.6 T, and the accuracy of measurements for the average isochronous field is required to be better than $10^{-4}$ . The magnetic gap decreases from 37 mm at cyclotron center to 9 mm at the pole edge. Hence, the difficulty of designing a magnetic field measurement system is increased because of the required magnetic field accuracy and the narrow gap between the poles. A measurement system has been developed to measure the magnetic field distribution in the median plane of the cyclotron by the SENIS Hall probe. After the Hall probe is calibrated by NMR, the measurement accuracy can reach $\pm 4\times 10^{-4}$ under the magnetic field intensity of 5 T. The position of the Hall probe will be monitored by grating and optical encoder, respectively, so as to ensure its correct positions. To verify the performance of the mapping system, it has been tested in the SC200 cyclotron with the designed vacuum degree. The test results showed that the mapping system can run smoothly and meet the measurement requirements of the SC200 cyclotron.

Calculation of the ideal isochronous field for the SC200 cyclotron using the Nelder-Mead simplex algorithm

ABSTRACT In this paper, we propose a numerical method for ideal isochronous field calculation for the SC200 isochronous cyclotron based on the Nelder-Mead simplex algorithm. In this method, the radial field distribution is represented by an nth-order polynomial, an objective function is defined to describe the relative error of the orbital frequency, and the ideal isochronous field is calculated by optimizing the coefficients of the polynomial to minimize the objective function using the Nelder-Mead simplex algorithm. A comparative analysis of the proposed method and conventional methods indicates that the proposed method provides a more accurate ideal isochronous field, especially in the vicinity of the extraction region where the field flutter is large.

Research on the effect of magnet parameters on the isochronous field of a superconducting cyclotron

It is a complicated task to obtain an isochronous field of a cyclotron magnet. Due to non-linear property of iron, iterated simulation of magnet design takes a long time to get an isochronous field. As an example, for a magnet design of a 240 MeV (SC240) superconducting cyclotron, the effect of main parameters of a magnet system on the magnetic field was studied, among them the azimuthal sector width, the spiral sector angle, the gap between sectors, the depth of valley region, the position of the coil, the shape of the coil and the excited current of the superconducting coil. It was found that the azimuthal average magnetic field can be increased by any of the following methods, including enlarging azimuthal width, increasing excited current of the superconducting coil, narrowing of the gap between sectors, reducing the depth of the valley region or decreasing the distance between the coil and the mid-plane. In addition, axial oscillation frequency can be improved by increasing the spiral angle, the depth of the valley region, or decreasing the gap between sectors.

Field Mapping System Design for the Superconducting Cyclotron CYCIAE-230

A superconducting cyclotron named CYCIAE-230 is designed and under construction at the China Institute of Atomic Energy, Beijing, China, to provide a 230-MeV proton beam for cancer therapy. The cryogenic system has been completed and the machining of the magnet will be finished soon. The shimming procedure will be performed to obtain the final isochronous field, which requires the field measurement precision to be 5 × 10–5. A search-coil sensor based mapping system was developed to satisfy the measurement accuracy requirements, including a nuclear magnetic resonance probe to precisely measure the field at the cyclotron center and a moving search coil to obtain the field differences. Moreover, a Hall probe is integrated in the system to verify the field data. The system allows the probe motion and data acquisition to be performed automatically. In this paper, the field mapping requirements are listed, the design and calibration of the coil is described, and the field mapping system, including mechanical structure and control system, is presented in detail.

Time‐of‐flight mass spectrographs—From ions to neutral atoms

AbstractAfter their introduction to space physics in the mid 1980s time‐of‐flight (TOF) spectrographs have become a main staple in spaceborne mass spectrometry. They have largely replaced magnetic spectrometers, except when extremely high mass resolution is required to identify complex molecules, for example, in the vicinity of comets or in planetary atmospheres. In combination with electrostatic analyzers and often solid state detectors, TOF spectrographs have become key instruments to diagnose space plasma velocity distributions, mass, and ionic charge composition. With a variety of implementation schemes that also include isochronous electric field configurations, TOF spectrographs can respond to diverse science requirements. This includes a wide range in mass resolution to allow the separation of medium heavy isotopes or to simply provide distributions of the major species, such as H, He, and O, to obtain information on source tracers or mass fluxes. With a top‐hat analyzer at the front end, or in combination with deflectors for three‐axis stabilized spacecraft, the distribution function of ions can be obtained with good time resolution. Most recently, the reach of TOF ion mass spectrographs has been extended to include energetic neutral atoms. After selecting the arrival direction with mechanical collimation, followed by conversion to ions, adapted TOF sensors form a new branch of the spectrograph family tree. We review the requirements, challenges, and implementation schemes for ion and neutral atom spectrographs, including potential directions for the future, while largely avoiding overlap with complementary contributions in this special issue.

OPTIMATION OF DECY-13 CYCLOTRON MAGNET MAPPING SYSTEM

OPTIMATION OF DECY-13 CYCLOTRON MAGNET MAPPING SYSTEM. A cyclotron magnet serves to deflect the particle beam so that the beam trajectory is circular and also serves to focus the beam. The magnetic flux density of a cyclotron magnet must satisfy the isochronous field. The magnetic field distribution need to be measured in order to know that the magnetic flux density have fulfilled the isochronous field, therefore a mapping system is needed to obtain the magnetic field distribution data. The design and construction of mechanical system of magnetic field mapping has been carried out in 2013 using fly mode algorithm, but the test results is not accurate yet. Therefore it is necessary to optimize of the magnetic field mapping system. The aim of this optimation i s to improve the accuracy of step position and the precission of magnetic field measurement of the mapping system of DECY-13 cyclotron magnet. The research was done by changing the mapping methods that previously based on the fly mode with the step mode. In the step mode, the magnetic field data will be taken when the probe has been completely stopped at the specified position. The magnet mapping system has been optimized with 99.89% of the average step position accuracion. The mapping system has to start at minimum of 2 hours after the MPS is turned on, in order to get 3.53 gauss of the precision of magnetic field measurement. Although the magnetic field measurement of 1st sensor and 2nd sensor have 6.3 gauss of measurement maximum different but the two sensors have the same pattern of magnetic field average. The mapping result from one of 2 sensors can be used to calculate magnetic field parameter if the magnetic field is symmetric.

Application and Development of a Method to Shim the Isochronous Field in Small Cyclotrons

Several small cyclotrons have been constructed at CIAE to extract 14-MeV proton beam from 100 to 400 μA for various medical applications, e.g., isotope production. The magnet mapping and shimming for the isochronous field is commonly an iterative process, which is critical for a commercial cyclotron to save the manufacturing time and reduce the cost. A numerical method is established to get the isochronous field by cutting the shimming bars at both sides of the sector pole. The method has been employed to shim the magnet for two small cyclotrons in CIAE. During the shimming process for the second cyclotron, this method has been developed to reduce the number of iterations and overall time for field mapping with the experience from the first cyclotron and accurate results of three-dimensional finite-element simulation. The shimming result shows that it satisfies the requirement of isochronism and focusing characteristics. In this paper, the development of the method is presented in detail, and the improvement for the shimming procedure is illustrated with the shimming data for the two small cyclotrons.

Design Study of a 250 MeV Isochronous Cyclotron for Proton Therapy

In this paper, the magnetic field design of a superconducting fixed-frequency isochronous cyclotron with four spiral sectors for proton therapy was performed. The basic parameters of the isochronous cyclotron magnet and its characteristics are described. Several magnet sectors were designed during the iteration process to achieve an isochronous magnetic field. The result of 3-D magnetic field simulation using OPERA-3D and the analysis of the designed magnetic field are presented. A special geometry was introduced into the sector gap to achieve the isochronous condition, and the spiral angle was adjusted to control the vertical focusing parameter. The equilibrium orbits were checked for the designed magnetic field, and a single particle tracking simulation was performed with CYCLONE code.

Development of a Cyclotron Magnet

We developed a cyclotron magnet at the Institute of Modern Physics, Chinese Academy of Sciences (IMP, CAS); the whole system include one main magnet, one solenoid, and two quadrupoles, and is used to accelerate the ${H}^{-}$ beam. This paper describes the magnetic field design of one cyclotron, and several shimming methods are used to meet the isochronous magnetic field of the ${H}^{-}$ beam, including the pole face shimming method and side shimming method. The final optimization results show that the error between simulation and theory value is small. For the purpose of comparison, a detail magnetic field measurement on the cyclotron are carried out, the results show that the isochronous deviations between the measurements and theory values are less than 5 G at most radii, which satisfy the design requirement.

Design study of the KIRAMS-430 superconducting cyclotron magnet

Design study of superconducting cyclotron magnet for the carbon therapy was performed at the Korea Institute of Radiological and Medical Science (KIRAMS). The name of this project is The Korea Heavy Ion Medical Accelerator (KHIMA) project and a fixed frequency cyclotron with four spiral sector magnet was one of the candidate for the accelerator type. Basic parameters of the cyclotron magnet and its characteristics were studied. The isochronous magnetic field which can guide the 12C6+ ions up to 430MeV/u was designed and used for the single particle tracking simulation. The isochronous condition of magnetic field was achieved by optimization of sector gap and width along the radius. Operating range of superconducting coil current was calculated and changing of the magnetic field caused by mechanical deformations of yokes was considered. From the result of magnetic field design, structure of the magnet yoke was planned.

Design, Construction, Installation, Mapping and Shimming for a 416 ton Compact Cyclotron Magnet

The construction of a 100-MeV high-intensity cyclotron, from which proton beam will be extracted through stripping to several proton beam lines for different users, has been completed at China Institute of Atomic Energy. Given that it is the H-ions that are to be accelerated in the machine, the peak field is only 1.35 T. To simplify the fabrication, the pole adopts straight sector instead of the spiral one. Meanwhile, vertical focusing should be sufficiently high to obtain high-current proton beam. All these demands make it particularly difficult for the design and fabrication of the main magnet, which is heavy in weight and challenging to meet precision requirement in fabrication. In the process, we have developed a high-performance parallel computation PIC code for beam dynamics of high-current cyclotrons and for FFAGs, which can be used for beam dynamic simulation at a very precise level. The result is then applied to guide the design, fabrication, installation, magnetic mapping, and shimming of the 416-ton main magnet with a precision requirement up to 0.05 mm. Another challenge is due to the deformations of the magnet without/with the vacuum. The whole map measured in the vacuum has to be completed in such a big machine for the first time in the world. The result shows that all requirements, including the isochronous field, vertical focusing, and imperfection fields, have been satisfied properly. The first beam and the stable beam for an 8-h commissioning test had been achieved on July 4 and July 25, 2014, respectively.