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Ice cores preserve past climatic changes and, in some cases, astronomical signals. Here we present a newly developed automated ice-core sampler that employs laser melting. A hole in an ice core approximately 3 mm in diameter is melted and heated well below the boiling point by laser irradiation, and the meltwater is simultaneously siphoned by a 2 mm diameter movable evacuation nozzle that also holds the laser fiber. The advantage of sampling by laser melting is that molecular ion concentrations and stable water isotope compositions in ice cores can be measured at high depth resolution, which is advantageous for ice cores with low accumulation rates. This device takes highly discrete samples from ice cores, attaining depth resolution as small as ~3 mm with negligible cross contamination; the resolution can also be set at longer lengths suitable for validating longer-term profiles of various ionic and water isotopic constituents in ice cores. This technique allows the detailed reconstruction of past climatic changes at annual resolution and the investigation of transient ionic and isotopic signals within single annual layers in low-accumulation cores, potentially by annual layer counting.

The 11th Symposium on Polar Science/Ordinary sessions: [OM] Polar Meteorology and Glaciology, Poster presentations, Mon. 16 Nov. - Fri. 18 Dec.

To achieve high-resolution selection and separation of mono-isotopic beams through projectile fragmentation or in-flight fission and to efficiently transport the secondary beams to the Rare-RI Ring (R3) for mass determination, the BigRIPS separator combined with the High-resolution Achromatic (HA) beam-line of SHARAQ is served as a two-stage separator. The first stage from F0 to F2 is used for separation of the nuclei of interest through a Bρ-ΔE-Bρ method and the second stage from F3 to S0 is employed for identification of the beam with a Bρ-ΔE-TOF method. With this scheme, all the secondary ions can be well separated on an event by event basis and be utilized for mass measurements by two complementary methods: the conventional magnetic-rigidity-time-of-flight (Bρ-TOF) method employing the BigRIPS-HA beam-line to measure exotic nuclides within 1 μ s and the newly established isochronous mass spectrometry (IMS) approach via the R3 with a measurement duration less than 1 ms. This report presents the technique advances of the BigRIPS-HA-SHARAQ-R3 as a separator/spectrometer and give a brief description of its application to the complementary TOF methods for mass measurements at RIBF.

A differential pumping system with a Plasma Window (PW) has been developed for an application to a window-less He gas charge stripper. A PW with Southern Methodist University design was newly fabricated and tested off-line for evaluation of differential pumping efficiency. Switching gases for plasma seed from Ar to He was tested. It was found that the PW reduced the pressure at the first differential pumping section to 1/13 for Ar and to 1/17 for He, comparing with differential pumping without PW. At the second pumping section, the pressures were drastically reduced to 1/160 and to 1/4,520 for Ar and He, respectively. These pressure reduction factors indicate that one differentially pumped stage could be removed from a conventional differential pumping system.

Recent developments in a charge-stripping system employing high-flow rate He gas circulation (~200 L/min) for 238U35+ beams injected at 10.8 MeV/u are reported. He gas is confined in a target section and is separated from a vacuum duct using five-stage differentially-pumped sections. To minimize the gas leakage rate via beam apertures, a high-performance differential pumping was required. To avoid huge gas consumption, a clean gas recycling with high-flow rate was simultaneously required. To realize these, we developed multi-stage mechanical booster pump array. The recycling rate of He gas was achieved as more than 99 %. The system performance has been checked with the present maximum beam current up to 13 eμA (~1 kW beam power).

See paper for full list of authors; The Korea Rare Isotope Accelerator, currently referred to as KoRIA, is briefly presented. The KoRIA facility is aimed to enable cutting-edge sciences in a wide range of fields. It consists of a 70 kW isotope separator on-line (ISOL) facility driven by a 70 MeV, 1 mA proton cyclotron and a 400 kW in-flight fragmentation (IFF) facility. The ISOL facility uses a superconducting (SC) linac for post-acceleration of rare isotopes up to about 18 MeV/u, while the SC linac of IFF facility is capable of accelerating uranium beams up to 200 MeV/u, 8 pμA and proton beams up to 600 MeV, 660 μA. Overall features of the KoRIA facility are presented with a focus on the accelerator design.

The BigRIPS fragment separator in the RIKEN RIBF project is characterized by fourteen superconducting triplet quadrupoles (STQ's) with large apertures and high-field gradients. While the five STQ's on the first stage of the BigRIPS are cooled by a liquid helium cryogenic plant, the nine STQ's on the second stage are cooled by small cryocoolers on their cryostat. This first stage serves to produce and separate RI beams, so that the first two STQs are exposed to the high radiation from the production target and beam dumps, which causes radiation heat loads as well as radiation damages. Measurements of the radiation heat loads to the cryostats of the first two STQs during commissioning operations of the RIBF facility are reported.

Carbon foils (C-foils) are extensively used as charge strippers for heavy-ion beams at the RIKEN RI beam factory. Multi-layer polymer coated C-foils (PCC-foils) of 300 μg/cm2 carbon thickness were irradiated by a 11 MeV/nucleon 238U35+ beam and their lifetimes were measured. Using an atomic force microscope (AFM) and an electron probe microanalyzer (EPMA), it was observed that the surface property and cross-sectional image of the PCC-foils had changed after the irradiation. A rotating-cylinder stripper device, which was developed to further increase the lifetime of C-foils, was also tested.

We are preparing for a high resolution spectroscopy of the 1s and 2s pionic states of 121Sn in the 122Sn(d,3He) reaction at the incident deuteron energy of ~500 MeV. The measurement will provide accurate information on the strong interaction between the pion and the nucleus, which leads to quantitative determination of the magnitude of the quark condensate at the normal nuclear density.

The BigRIPS fragment separator in the RIKEN RI beam factory has an air-core type superconducting quadrupole triplet as the first focusing element. The quadrupole triplet consists of three air-core superconducting coils having effective lengths of 500 mm, 800 mm, and 500 mm, and the maximum field gradients of 24 T/m, 20 T/m, and 20 T/m. All three quadrupoles are assembled into a single cryostat and cooled by liquid-helium bath cooling using a cryogenic plant. The coils have a flat racetrack shape and their warm bore radii are 90 mm, 120 mm, and 120 mm. Its cryostat characterized by gas-cooled current leads with multiple electrodes is also discussed.

In the RI beam factory project, heavy ion beams are transported from the K 2500 MeV superconducting ring cyclotron (SRC) to the superconducting fragment separator, called BigRIPS. Magnets for the beam transport line from the SRC to the BigRIPS are reported. All the magnets are resistive type and the beam line consists of two kinds of dipoles and three kinds of quadrupoles. One of the dipole, having the maximum field strength of 2.0 T, a gap height of 60 mm, and a core length of 3.51 m is discussed in detail.

Measurements of the magnetic field distributions of the superconducting triplet quadrupoles (STQs) and the room-temperature dipoles for the BigRIPS separator are performed in order to use ion optics calculations of the BigRIPS. This report describes the results of magnetic field-map measurement of the superferric-typed STQ and dipole magnet including the field mapping device we employed for the measurements.

Since 1997, RIKEN Nishina Center has been constructing the Radioactive Isotope Beam Factory (RIBF) and succeeded in beam commissioning of its accelerator complex at the end of 2006. The world's first superconducting ring cyclotron (SRC) is the final booster in the RIBF accelerator complex which is able to accelerate all-element heavy ions to a speed of about 70% of the velocity of light. Assembling of the superconducting sector magnets was completed in August 2005. The superconducting coils were successfully cooled down and excited for tests on many operational aspects: magnetic force, coil protection and quality of magnetic field, showing that they work as designed. After a series of tests the other components were installed and tested under stray fields from the sector magnets. Local magnetic shields were put to the components which could not work under the stray fields. After setups of beam vacuum and radio frequency, beam commissioning started. The first beam was extracted at the end of 2006 and the first uranium beam was extracted in March 2007.

The problem of handling the fragile carbon foils (mounting on the frame, placing in the stripper changer) that easily break when self-supporting has been solved by coating carbon foils with poly-monochloro-para-xylylene. It was found that the polymer-coating method could also be used to produce carbon foils thicker than 100 μg/cm2 by alternated deposition of carbon and poly-monochloro-para-xylylene layers. Carbon foil of 500 μg/cm2 thick and 10 cm in diameter was produced by this method and mounted to a foil holder. Results of lifetime measurement for singly coated foils are also presented.

Biological samples are irradiated with heavy-ion beams at a heavy-ion beam irradiation facility in RIKEN to perform mutation breeding. The energies of the heavy-ion beams are sufficiently high to irradiate biological samples of macroscopic thickness in air. A uniform dose distribution is a key to a systematic study of the effect of the heavy-ion beams, and thus to the improvement of mutation efficiency. We selected a sufficiently high beam energy to avoid the Bragg peak to realize a uniform dose distribution along the beam path. The outline of the beam line is presented. The linear energy transfers (LETs) of the heavy-ion beams are selected using a range shifter and an energy adjuster to investigate the LET dependence of the irradiation effect. More than five hundred samples are automatically sent to the beam position using an automatic sample changer, which put the heavy-ion beam induced mutation breeding to practical use. The structure and function of the automatic irradiation system are also presented.

The RIKEN RI Beam Factory (RIBF) has started its operation after ten years of construction [1]. It is designed to provide beams of various kinds of unstable nuclei with the world's highest intensities. The institute RIKEN was founded in 1917, and covers a variety of research fields such as physics, chemistry, medical science, biology, and engineering. RIKEN has a long history of constructing accelerators. The first cyclotron in Japan was built in 1937 by Yoshio Nishina in the former RIKEN campus, and the RIKEN's 4th cyclotron completed in 1966 was the first heavy-ion cyclotron in Japan, which accelerated light nuclei to the energy around 7 MeV/nucleon.

In order to greatly upgrade the capability of its existing heavy-ion accelerator facility, RIKEN is constructing a new radioactive isotope (RI) beam facility, called “RI Beam Factory”. This facility is of an in-flight RI beam separation scheme. Three new ring cyclotrons with K-values of 570 MeV, 980 MeV and 2500 MeV, respectively, boost energies of the output beams from the existing K540-MeV ring cyclotron up to 440 MeV/nucleon for light ions and 350 MeV/nucleon for very heavy ions. The K2500-MeV ring cyclotron, SRC is the world’s first superconducting ring cyclotron. These energetic heavy-ion beams are converted into intense RI beams via projectile fragmentation of stable isotopes or in-flight fission of uranium isotopes by a superconducting fragment separator, BigRIPS. The combination of the SRC and the BigRIPS will greatly expand our knowledge of nuclear world into presently inaccessible region on the nuclear chart. The new ring cyclotrons and the Big RIPS will be commissioned in late 2006. Construction of a part of major experimental installations planned is expected to start in 2007.

The ionization efficiency of an electron cyclotron resonance ion source (ECRIS) is generally high and all elements can be fundamentally ionized by the high-temperature plasma. We focused our attention on the high potentiality of ECRIS as an ion source for mass spectrometers and attempted to customize a mass spectrometer equipped with an ECRIS. Precise measurements were performed by using an ECRIS that was specialized and customized for elemental analysis. By using the charge-state distribution and the isotope ratio, the problem of overlap, such as that observed in the spectra of isobars, could be solved without any significant improvement in the mass resolution. When the isotope anomaly (or serious mass discrimination effect) was not observed in ECR plasma, the system was found to be very effective for isotope analysis. In this paper, based on the spectrum (ion current as a function of an analyzing magnet current) results of low charged state distributions (2+, 3+, 4+, …) of noble gases, we discuss the feasibility of an elemental analysis system employing an ECRIS, particularly for isotopic analysis. The high-performance isotopic analysis obtained from an ECRIS mass spectrometer in this study suggests that it can be widely applied to several fields of scientific study that require elemental or isotopic analyses with high sensitivity.

The feasibility of using a Compton camera for multitracer imaging has been demonstrated with the results of two biological sample imaging experiments. The distribution of the multitracer administered to a soybean sample and a tumor-bearing mouse has been visualized for each nuclide simultaneously. Three-dimensional images of the multitracer have been obtained even though the samples were measured from a fixed direction.

Superconducting triplet quadrupoles (STQs) with large apertures and high field-gradients are employed for the in-flight radioactive-isotope (RI) beam separator BigRIPS at RIKEN. It consists of fourteen STQs and six room-temperature dipoles. The use of the STQs makes it possible to achieve important features of the BigRIPS separator: large acceptances and a large magnetic rigidity, allowing efficient production of RI beams. The BigRIPS separator is presently under construction and assembly as a major installation in the RIKEN RI-beam factory project, and the commissioning is scheduled in early 2007. In this paper we present the status and overview of the BigRIPS separator, emphasizing the STQs and their liquid-helium cryogenic systems.

RIKEN Nishina Center for accelerator-based science in RIKEN is constructing the radioactive isotope beam factory (RIBF), which is capable of providing the world's most intense RI beams over the whole range of atomic masses. The world's first superconducting ring cyclotron (SRC) is the final booster in the RIBF accelerator complex which is able to accelerate all-element heavy ions to a speed of about 70% of the velocity of light. Assembling of six superconducting sector magnets in the SRC vault was completed in August 2005. This paper describes results of their cool-down and excitation tests, which were performed to check the magnet system from the various points of views: magnetic force, coil protection, magnetic field and operation of their cryogenic cooling system.

Compact liquid hydrogen, deuterium, and helium targets were constructed for radioisotope beam experiments at RIKEN. Hydrogen, deuterium, or helium gas is liquefied by a Gifford–McMahon cycle refrigerator instead of being supplied as a cryogenic liquid. The liquefied gas is accumulated in a target cell placed at the center of a γ -ray detector array. The targets were operated stably in several experiments.

We propose a new colliding system of electrons and radioactive (unstable nucleus) ions, in which a high-energy electron beam collides with its self-confining radioactive ions in a target region locally formed in an electron storage ring. These ions are transversely confined in the electron stream by repetitious transverse focusing kicks given by electron bunches, and are drifting back and forth between electrostatic mirrors. In the present paper, a practical application of this system is described to a specific electron-scattering experiment on a double-magic unstable 132 Sn nucleus to measure its unknown charge distribution. We discuss performance of the target and estimate the achievable luminosity.

Irradiation tests have been carried out in view of selecting the cryogenic temperature sensors for use in the RIKEN Superconducting Ring Cyclotron (SRC). About 300 temperature sensors will be installed, and most of them will be exposed to high radiation doses during the operation of accelerator. Those cryogenic temperature sensors, Cernox/spl trade/, CGR and PtCo, at room temperature were bombarded by the intense 210 MeV proton beam at the RIKEN Accelerator Research Facility (RARF) of RIKEN.

Three superferric quadrupoles with a pole-tip radius of 170 mm and a design field gradient of 14.1 T/m have been constructed and mapped for use as spectrometer elements. All three quadrupoles are assembled into a single cryostat and cooled by liquid-He bath cooling method. A small Gifford-McMahon/Joule-Thomson (GM/JT) cooler, mounted on the cryostat, requiries He gas that evaporates in the He vessel. The high-T/sub c/ superconducting current leads and radiation shield surrounding the He-vessel, cooled by a small GM cooler, reduce the heat load of the He vessel. Both cryocoolers operate using separate water-cooled compressors and allow us a stand-alone operation of the quadrupole magnets without big cryoplant. Results of quench protection tests, measured heat loads and mapped results are presented.

K2500 - superconducting ring cyclotron with 6-sectors is being constructed at RIKEN as one of the energy booster of the existing K540 ring cyclotron. The bending magnet for beam injection should be superconducting. Required fields are 3.8 T and radius of the coils is 1.2 m. After the fabrication, it was cooled down and excited. The magnet reached the designed field with one quench and training effect were clearly observed, which shows that it will works well to inject the beam into the superconducting cyclotron.

The sector magnets of the K2500-MeV superconducting ring cyclotron (SRC), which is under construction for the RIKEN RI beam factory, are described. The SRC consists of six sector magnets, four rf resonators, etc. each sector magnet is 7.2 m in length and 6 m in height and 800 t (metric ton) in weight; the sector angle is 25 deg. The required maximum magnetic field is 3.8 T. the superconductor for the main and trim coil has a rectangular shape (8 mm by 15 mm) consisting of a Rutherford-type NbTi cable located at the center of an Al-alloy stabilizer housing. The main coil is bath-cooled and the trim coil is directly cooled. Each component of the sector magnet as well as the cryogenic cooling system was completed in the spring of 2003.

We have constructed four high performance electron cyclotron resonance (ECR) ion sources in RIKEN and produced a variety of intense beams of heavy ions (e.g., 2 emA of Ar8+, 0.6 emA of Kr13+, 0.3 emA of Xe20+). During the improvement of their performance, we found that several key parameters play essential role on increasing the beam intensity. The parameters are plasma electrode position, magnetic field configuration, property of the chamber wall material and position of a biased disk. To investigate how the parameters influence on the beam intensity, we made a systematic study using the laser ablation method. In these experiments, we observed that Bmin influences the electron density and confinement time of ECR plasma.

We successfully extracted a 1.9 mA Ar 8+ ion beam and a 1 mA Ar 9+ ion beam from the RIKEN 18 GHz ECR ion source at the extraction voltage of 17 kV and the microwave power of 700–800 W . To obtain these intensities, we optimized the magnetic field configuration and the plasma electrode position.

A radio frequency quadrupole LINAC has been designed for the VECC-RIB project for an input beam energy of 1.0 keV/u and q/A≥1/16. The output energy will be about 90 keV/u for a 3.4 m long, 35 MHz structure. A half-scale cold model of the RFQ has been fabricated and tested for rf structure design study. The beam dynamics and rf-structure design along with the results of the cold model tests will be presented.

We measured the beam intensity of highly charged heavy ions (O, Ar and Kr ions) as a function of the minimum strength of mirror magnetic field (Bmin) of the RIKEN liquid-He-free super conducting electron–cyclotron resonance ion source. In this experiment, we found that the optimum value of Bmin exists to maximize the beam intensity of highly charged heavy ions and the value was almost the same ( ∼0.49 T ) for various charge state heavy ions.

A high energy resolution Compton camera consisting of position-sensitive germanium detectors is proposed for multitracer imaging. The distributions of the number of gamma-ray interaction points in both detectors are calculated by the Monte Carlo simulations. The effects of multiple scattering on the performance of the Compton camera are discussed. A gamma-ray tracking algorithm is used to determine the first interaction point in the second detector. The efficiency and spatial resolution of a Compton camera for gamma rays of different energies, emitted from different positions are also simulated.

A K2500 superconducting ring cyclotron with 6-sectors is being constructed at RIKEN as one of the energy boosters of the existing K540 ring cyclotron. The bending magnet for beam injection should be superconducting. Required fields are about 4 T and the radius of curvature of the coils is about 1.2 m. Its design was finalized for real production based on successful results of the R&D coils. In this paper the final design will be described with the status of the fabrication.

Special designs have been adopted for the magnetic channels of the injection and extraction systems of the RIKEN Superconducting Ring Cyclotron (SRC). These magnetic channels are installed in the chambers between upper and lower coils of the sector magnets of the SRC, and superimpose additional magnetic fields on the base field of the sector magnets to inject or extract various beams. Maximum magnetic rigidity of the beam is considerably higher than that of conventional cyclotron, and the spaces to install the magnetic channels are limited by the size of the chambers and turn separation of the beams. Therefore powerful and compact magnetic channels are required. And besides, all magnetic channels were specified as normal-conducting magnets to reduce fabrication cost and to assure reliability. However, it is difficult to generate high magnetic fields by conventional normal-conducting magnetic channels with conductors only. Therefore, novel designs for powerful and compact normal-conducting magnetic channels were devised by use of iron as efficiently as possible. Detail designs are in progress.

For the design of the protection system of the superconducting main coils of the RIKEN superconducting ring cyclotron, the quench characteristics is calculated in terms of current decay, temperature rise, voltage development etc., using the computer program "QUENCH-M." The AC losses and pressure rise pertaining the quench are also estimated.

A high-energy resolution Compton camera consisting of two segmented Ge detectors is proposed for multitracer research. The basic parameters affecting its spatial resolution are described. Monte Carlo simulations were performed to optimize the detector system. Its suitability for multitracer technology was demonstrated by a test experiment.

The buildup of a plasma produced by short-pulse (0.05–1.2 μs), high-power (60–100 kW) microwaves is studied in a pressure range of 10 mTorr–10 Torr, by measurements of the temporal variation of the current and the optical intensity. The plasma is produced in a cylindrical tube and confined by a minimum-B field. The buildup of the electron current and the optical intensity are found to continue beyond the end of the pulse, for a few to tens of μs depending upon the pressure, and a minimum in their peak values and buildup times occur around 1 Torr. Increase in microwave pulse duration increases the buildup rate and peak current, whereas the pulse repetition frequency (10–500 Hz) has only a weak influence. The results are discussed from the growth of electron temperature during the pulse, and the following plasma evolution after the end of pulse. Collisional wave absorption, electron cyclotron heating, and diffusion are found to play important roles in plasma production and maintenance over the pressure range.

A K2500 superconducting ring cyclotron with 6-sectors is being constructed at RIKEN as an energy booster of the existing K540 ring cyclotron. The bending magnet for beam injection should be superconducting. Required fields are about 4 T and curvature of the coils is about 1.2 m. We developed test cells for the bending magnet. The results are very promising for the real bending magnet. In the paper the results of the test cells and the design of the real bending magnets are described.

We have measured the contamination in an Al2O3 rod and the elemental composition in cinnabar (Tenjinyama ancient tomb) by using the electron cyclotron resonance ion source (ECRIS) and the RIKEN linear accelerator (RILAC) complex. Elements of mass smaller than 100, such as 50V, 55Mn and 75As, were mainly searched for using this system. The ionization chamber and the Si detector were used for atomic number assignment. The production of positive ions in the ECRIS is not influenced by ionization selectivity. In the measurement of elements, spectroscopic interference with molecules does not exist due to complete ionization in the resonance zone of high temperature by the ECR plasma. The development and establishment of these systems will play an important role in trace element analysis. We developed this system for practical use and also considered other possibilities for these devices.

A “two-ion-source” beam transport line between a surface ionization source and a 6.4 GHz on-line Electron Cyclotron Resonance Ion Source (ECRIS) for the production of multi-charged radioactive ions has been designed. The 1+ ions from the surface ionization source are decelerated and focused onto the ECRIS plasma so that they can be efficiently trapped there and further ionized to charge state q>1+. A scheme for stepwise and gradual deceleration of the 1+ ion beam consisting of a multi-electrode decelerator and a tuning electrode placed before the ECRIS has been optimized. The beam dynamics calculations show that the 1+ beam decelerated to energies of 20–50 eV could be focused to a spot size smaller than the radial dimensions of the ECR plasma zone.

A six-sector superconducting ring cyclotron (SRC) is being constructed as a primary post accelerator of the existing accelerator complex for the RIKEN RI beam factory. In the SRC some superconducting magnets with high performances will be used for beam injection and extraction. Design study and R&D of them are described along with brief description of the outline of the systems.

A six-sector superconducting ring cyclotron (SRC) is being constructed as a primary post accelerator of the existing accelerator complex for the RI beam factory. Mechanical design of the main coil vessel of the SRC is described.

A new type of variable-frequency radio-frequency quadrupole (RFQ) linac has been constructed as a new preinjector for the RIKEN heavy-ion linac (RILAC). The RFQ resonator, based on a folded-coaxial structure with a movable shorting plate, is compact even in a low frequency region below 20 MHz. It accelerates ions with mass-to-charge ratios of 5.3 to 26.4 in the energy range up to 450 keV per charge, by varying its resonant frequency from 17.4 to 39.0 MHz. Moreover, the power loss is small in the low frequency region; the rf power consumption in cw mode is 7 kW at 17.4 MHz, and it increases to 30 kW at 39.0 MHz at the maximum intervane voltage of 36.8 kV. We initiated this project in 1991, and installed the new preinjector consisting of an electron cyclotron resonance ion source of 18 GHz and this RFQ in 1996. Since the installation, the beam intensity has become larger by more than 1 order of magnitude than that formerly obtained with the Cockcroft–Walton preinjector. Recently, the maximum power of the beam extracted from the RILAC and that from the ring cyclotron has reached 560 W and 2 kW, respectively.

Design, especially about the structure and quench stability, of the superconducting sector magnets for the RIKEN superconducting ring cyclotron is described. Special features of the sector magnets are the triangular shape superconducting coil, cold pole arrangement for supporting of the huge magnetic forces and the cryogenic stable coils. A full-scale superconducting model is now under construction as a prototype sector magnet.

The trim coil system of a superconducting ring cyclotron currently under design at RIKEN is composed of five sets of superconducting and twenty sets of normal-conducting coils. A major correction for isochronization of the magnetic field is accomplished by the superconducting coils, and a fine correction by the normal-conducting coils. For an optimal design of the system, a numerical procedure was developed to generate isochronous fields for design nuclei and consequently current settings on the main and trim coils, employing an iteration of a least-squares fitting to minimize orbital frequency errors. The main and normal-conducting coils can also be used to correct unwanted harmonic fields with sector dependent and/or radially localized excitations. The correction schemes were conceived for presumed error fields, alignment tolerances being estimated based upon beam optics requirements. On the other hand, a new trim coil design was envisaged, which comprises only superconducting trim coils. The subcoils in the present five-set design can be independently excited to replace the normal-conducting coils. This option may be more economical, but complications on the superconducting coil system raise a reliability concern.

Superconducting sector magnets are to be the main components of the superconducting ring cyclotron for the RIKEN RI beam factory. A full-scale prototype sector magnet is being developed and constructed. One of the critical points of the design is how to support the huge magnetic force exerted on the superconducting main coil. A cold-pole arrangement is adopted as the solution to this problem. Unbalanced magnetic forces were measured using 1/6-scaled-Cu/Fe magnets. A cryogenic stabilizing method is applied to make the main and trim coils quench-free. The whole structure, magnetic force and its support structure, quench protection, eddy current loss in the cold-pole, and helium cooling system are described.