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The BigRIPS in-flight fragment separator in the RIKEN Radioactive Isotope Beam Factory project has been operated for nine years. Intense beams of heavy ions up to uranium with the beam power of 1-13 kW and the energy of 230-45 MeV/nucleon were used to produce the radioactive isotope beams by the BigRIPS fragment separator. The first superconducting triplet quadrupoles (STQ1) is in close proximity of the production target in the BigRIPS fragment separator and has been exposed to high radiation. The STQ1 consists of three air-core NbTi coils, wound by the wet-winding method, assembled in the liquid-helium bath cryostat. Based on the operation records of the superconducting magnet and its cryogenic system, the accumulated dose to the coils is evaluated to be order of 1 MGy. The observed impurities in the helium gas, such as tritium and hydrocarbons in the STQ1 cryostat, are presented as a possible radiation effect. Based on the excitation data of training ramps, we discuss the movement of the coils and a possible degradation of coils. No distinct degradation in the coil performance can be observed after nine years of operation.

The BigRIPS in-flight fragment separator in the RIKEN Radioactive Isotope Beam Factory (RIBF) project was commissioned in 2007 and has been operated for six years. The RIBF accelerator complex has provided a wide range of heavy ion beams from deuteron to uranium with the energy of 250-345 MeV/nucleon. More than 70 experiments of unstable nuclei have been performed using the RI beams produced by the BigRIPS fragment separator. The production target of the RI beams is in close proximity to the first superconducting triplet quadrupoles (STQs) in the BigRIPS fragment separator, so that the STQ is exposed to the high radiation, which causes “beam heat loads” to the cryogenic system. The STQ consists of three air-core NbTi coils with the maximum field gradients of 24 T/m, assembled in the liquid-helium bath cryostat with the warm bore radius of 90 mm. This paper presents measurements of the radiation heat loads to the STQ cryostat for a number of experienced heavy ion beams from oxygen to uranium with the beam power of 1-7 kW. Corresponding radiation transport calculations are presented, and radiation doses and damages to the STQ system are also discussed.

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.

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.

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.

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.

Two superferric quadrupoles with a pole-tip radius of 170 mm and a maximum pole-tip field of 2.4 T are designed for the BigRIPS projectile fragment separator at RIKEN. Taking the feasibility of coil winding into account, the shape of quadrupole coil has been optimized.

We report long-term operation of the superconducting triplet quadrupoles (STQs) with small cryocoolers for the BigRIPS in-flight separator and RI-beam delivery line. Each STQ is cooled by liquid helium bath cooling method with a small stand-alone cryogenic system in which a Gifford-McMahon (GM)/Joule-Thomson cryocooler and a GM cryocooler are mounted on the cryostat. While the GM/Joule-Thomson cryocooler recondenses evaporating helium gas in the helium vessel, the GM cryocooler cools the 70 K shield and current leads by conduction. We operate 21 STQ systems forming beam lines for more than five years. We report on how we maintain cryocoolers without warming up the magnets. Operational experiences including troubles in the long-term operation are also reported.