Superconducting Ring Cyclotron Research Articles

A new multi-reflection time-of-flight mass spectrograph for the SLOWRI facility

A new multi-reflection time-of-flight mass spectrograph for nuclear mass measurements with high precision has been constructed at the SLOWRI facility at RIKEN-RIBF. We aim to couple this new device to a cryogenic gas cell operated at the BigRIPS facility of RIBF. It is part of the SLOWRI project for slowing down and stopping intense radioactive ion beams provided downstream of RIKEN’s superconducting ring cyclotron accelerator. In particular, this device is dedicated to be located at the end of the BigRIPS beam line to access ions that are presently guided to beam dumps during in-beam experiments. In this article the apparatus is described in detail.

New ion-optical operating modes of the BigRIPS and ZeroDegree spectrometer for the production and separation of high-quality rare isotopes beams and high-resolution spectrometer experiments

BigRIPS is a powerful two-stage in-flight separator for the research with exotic nuclei studied in frontier experiments since more than a decade. The ion-optical system is very versatile due to the multi-stage structure of BigRIPS combined with the ZeroDegree spectrometer or the Superconducting Ring Cyclotron (SRC). Various optical modes can be flexibly realized according to the purpose of experiments. Two categories of developments are presented here. One is a new operating mode of BigRIPS aiming at higher ion-optical resolving power. BigRIPS itself has a two-stage structure. Spatial isotope separation is made at both the first and second stages. In the standard operating mode of BigRIPS, at the second stage the two spatial separations with energy degraders are subtractive in their resolving powers. Here, we present the additive mode. With the resulting increased spatial separation power, the isotopic background can be substantially reduced. Higher ion-optical resolving powers of the first and second BigRIPS degrader stages are also investigated with the goals to reduce further the background and to yield access to new isotopes of heavier elements. The other development is a dispersion-matched system with BigRIPS for high-resolution spectrometer experiments. The BigRIPS and ZeroDegree spectrometer are presently two independent, coupled achromatic systems. A new dispersion-matched mode of BigRIPS and ZeroDegree will enable novel experiments. For high-resolution spectroscopy experiments with high-intensity light projectiles, SRC and BigRIPS can be operated as a dispersion-matched system. The described different ion-optical developments are a base for a new category of experiments exploring exotic nuclei and mesic atoms. Characteristic future experiments with these new ion-optical developments are exemplified in this report.

Operational Experience of the Superconducting Ring Cyclotron at RI Beam Factory (RIBF) and Upgrade Plans for RIBF Accelerators

The RIKEN Radioactive Isotope Beam Factory (RIBF) has successfully operated since the first beam was produced at the end of 2006 (more than six years). The aim of this project is to access the unexplored regions on the nuclear chart, those far from β-stability. Continuous effort over the past six years has improved the performance of the RIBF accelerator complex. The world's first superconducting ring cyclotron (SRC) is the final booster in the RIBF accelerator complex; it is able to accelerate heavy ions of any element to a speed of approximately 70% of the speed of light. The ring cyclotron consists of six major superconducting sector magnets, each with a maximum field of 3.8 T. The total stored energy is 240 MJ. The overall size of the cyclotron is 19 m in diameter and 8 m in height with a weight of 8300 tons. Reliable standby power supply systems and accurate control systems are necessary for long-term, stable operation of the cryogenic cooling system. For these purposes, a 6.5-MW co-generation system was installed, and the control system for the cryogenic cooling system was improved on the basis of operational experience. Despite our efforts to achieve long-term, stable operation, we have had some problems such as failure of the He compressors and refrigerators and coil discharge. We learned that any small component could easily disrupt the entire cooling system. The two biggest problems were liquid He leakage thorough a crack in a feedthrough into the thermal insulation vacuum on November 8th, 2005 and oil contamination in the He refrigerator found in February of 2008. Overcoming such big problems has resulted in the present, stable operation of the cryogenic cooling system of the SRC. One option for upgrading the RIBF accelerator includes the construction of another SRC (SRC2) to skip the charge strippers (which decrease the beam intensity by approximately one fifth). Our study shows that the design of the sector magnets of the SRC2 is not much more difficult than that of the first SRC.

Support Structure of Cold-Mass for Superconducting Ring Cyclotron and Electromagnetic Force Measurements With Strain Gauges

The superconducting ring cyclotron (SRC), which is the last-stage accelerator of the RIKEN RI-beam factory, was commissioned in December 2006, and it has since been operated for approximately five months each year. The SRC comprises six superconducting sector magnets, and the maximum magnetic field strength in the beam orbit region and the stored energy are 3.8 T and 240 MJ, respectively. The total weight is 8300 t. The cold-mass in each sector magnet consists of upper and lower main coils connected to each other at liquid helium temperature, and it weighs 24 t. The cold-mass is supported by eight titanium-alloy rods each in the vertical and azimuth directions, and with a stainless steel multifolded pipe in the radial direction to resist large electromagnetic forces. In order to measure the stress and movement in the cold-mass, a total of 208 strain gauges were attached on the main coil vessel, supports, etc., during construction. The strains generated during the excitation of the magnets were almost the same as the calculated values. Furthermore, there were negligible changes in the strains at all positions during the excitation measured in 2006 and 2013. These results verify the design effectiveness of the cold-mass support structure.

Engineering Study of the Sector Magnet for the Dae<formula formulatype="inline"><tex Notation="TeX">$\delta$</tex></formula> alus Experiment

The Daeδalus experiment seeks to evaluate neutrino scattering effects that go beyond the standard model. Modular accelerators are employed to produce 800 MeV proton beams at the megawatt power level directed toward a target, producing neutrinos. The Superconducting Ring Cyclotron consists of identical sectors (currently 6) of superconducting dipole magnets with iron return frames. The Daeδalus Collaboration has produced a conceptual design for the magnet, which, after several iterations, is the current best design that achieves the physics requirements of the experiment. The main purpose of the analytical effort, results of which are presented here, is to develop a viable engineering design satisfying requirements to the superconductor, as well as structural and cryogenic requirements. The work includes proposed conceptual approaches, solid modeling and analyses for the conductor and winding pack design, high-temperature superconductor and copper current leads for the magnet, structural design of the magnet cold mass, cryostat and warm-to-cold supports, cryogenic design of the magnet cooling system, and magnet power supply sizing. A description of the winding pack design, structural analysis, and cryogenic system is reported.

Progress of RIBF accelerators

In order to greatly expand scientific opportunities with radioactive isotope (RI) beams, RIKEN has constructed a new heavy-ion accelerator facility, called “RI Beam Factory (RIBF).” Three new ring cyclotrons with K-values of 570 MeV, 980 MeV, and 2600 MeV, respectively, boost the energies of the output beams from the existing K540-MeV ring cyclotron up to 440 MeV/u for light ions and 345 MeV/u for very heavy ions. These energetic heavy-ion beams are converted into intense radioactive isotope (RI) beams via projectile fragmentation of stable isotopes or in-flight fission of uranium isotopes by a superconducting fragment separator, BigRIPS. The three ring cyclotrons were commissioned in 2006, and RI beams from uranium were first obtained in 2007. The beam intensities and available ion species are increasing at RIBF, owing to the continuous efforts that have been made since the first beam. So far, we have accelerated deuteron, helium, nitrogen, oxygen, aluminum, calcium, zinc, krypton, xenon, and uranium beams with the superconducting ring cyclotron (SRC). The extracted beam intensities reached 1000 pnA for the helium and oxygen beams, and the calcium beam intensity exceeded 400 pnA recently. The intensities of the xenon and uranium beams are also increasing they reached 24 and 3.6 pnA, respectively. This paper illustrates the construction, commissioning, and various improvements carried out for the RIBF accelerators, as well as the present accelerator performance.

Magnets for the Beam Transport Line in the RIKEN RI Beam Factory

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.

Commissioning of the Superconducting Ring Cyclotron for the RIKEN RI Beam Factory

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.

RI Beam Factory Project at RIKEN

The RI Beam Factory (RIBF) is presently the top world-class radioactive-isotope (RI) beam facility in the world. This facility is based on the in-flight method to produce fast RI beams. High-energy and intense primary beams accelerated by a superconducting ring cyclotron (SRC) are converted, via the projectile fragmentation or fission reaction channels, to RI beams at a new fragment separator called BigRIPS. Construction of SRC and BigRIPS has been completed in March, 2007. Construction of major experimental installations has been commenced in 2007. Physics opportunities with the RIBF are discussed herein.

超伝導リングサイクロトロン（ＳＲＣ）の概要

The RIKEN Nishina Center began construction of the Radioactive Isotope Beam Factory (RIBF) in 1997, and succeeded in commissioning the beam 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. It is capable of accelerating all-element heavy ions to a speed of about 70% of the speed of light. Assembly 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 supplied for the components that could not work under the stray fields. After setting the 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 Superconducting Ring Cyclotron in RIKEN

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.

The RIKEN RI Beam Factory Project: A status report

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 570MeV, 980MeV and 2500MeV, respectively, boost energies of the output beams from the existing K540-MeV ring cyclotron up to 440MeV/nucleon for light ions and 350MeV/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.

Superconducting Bending Magnet for the RIKEN Superconducting Ring Cyclotron

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.

Sector Magnets for the RIKEN Superconducting Ring 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.

Radiation Effects on Cryogenic Temperature Sensors of Cernox, CGR and PtCo

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.

Design of the magnetic channels for the RIKEN superconducting ring cyclotron

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.

Quench analysis of RIKEN superconducting ring cyclotron

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.

Design and fabrication of the superconducting bending magnet for the injection system of the RIKEN SRC

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.

Superconducting bending magnet for superconducting ring cyclotron

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.

Superconducting magnetic channel for the RIKEN superconducting ring cyclotron

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.