Persistent current joints are crucial components of superconducting magnets—enabling the production of the high and ultra-stable magnetic fields required, for instance, for magnetic resonance measurements. At this critical juncture when persistent mode magnets containing commercial high temperature superconductors may soon become a reality, it is of value to take stock and evaluate current challenges faced in the field of jointing. This paper provides a review of progress made to date on the production and characterization of joints between the five major technological superconductors—NbTi, Nb3Sn, MgB2, BiSCCO and REBCO, including the materials that are used to make these joints.

https://iopscience.iop.org/article/10.1088/0953-2048/28/9/093001/pdf

Persistent current joints between technological superconductors

As promising magnet types, discrete-cosine-theta and canted-cosine-theta (DCT&CCT) superconducting magnets are designed for the High Energy Fragment Separator (HFRS), a fragment separator of the High Intensity Heavy Ion Accelerator Facility (HIAF). Quench protection is one of the key issues for DCT&CCT superconducting magnets due to low thermal conductivity between each turns and slow transverse quench propagation. Thermal quench-back induced by the center cooper wire as a heater automatically is a feasible quench protection option for the magnet wound with 6+1 type superconducting cables (six superconducting wires and one center cooper wire). In the present paper, an electro-thermal coupling model is developed and validated to deal with the dynamic coupling behaviors of electrical and temperature fields inside the superconducting magnets during quench protection process. The transient evolutions of current and voltage-to-ground are numerically obtained by finite element method, which shows obvious quench-back behaviors and agree well with the experimental measurements of the prototype magnet L800 in first round test. The hot-spot temperature can be reduced significantly considering quench-back effect. Furthermore, the quench protection baselines of temperature and quench integral are analyzed and predicted for L800, indicating that the magnet can be protected properly by the protection method with a quench-back at ultimate current 466A.

Electro-Thermal Coupling Model of Quench Protection With a Quench-Back for DCT&CCT Superconducting Magnets

General Assembly Layout The beam dynamics of superconducting (SC) heavy-ion linacs operating in the velocity range below 0.4c require a compact accelerating-focusing lattice. The use of SC solenoids together with SC RF resonators within a common cryostat can solve the real-estate problem. The solenoids must have low fringe fields to avoid magnetic- flux capture in the SC RF resonators. Also, incorporating dipole steering coils together with the SC solenoids in one magnet assembly can increase the compactness of the linac lattice. R&D work has been carried out to determine the feasibility of combining the three elements of high solenoid field, low fringe field, and integral dipole field, into one compact package. A 9-Tesla magnet has been initially designed and will be prototyped, with the goal of eventually developing 14-Tesla solenoids of similar design. The most important design issues are: 1) to minimize stray field in the RF cavity region using SC bucking coils and 2) to achieve adequate mechanical stability of the transverse dipole windings in the presence of forces produced by the solenoid/bucking coil assembly. The assembly, including terminals, switches, and protection circuit, are designed to fit inside a 25-cm diameter helium reservoir. The results of the preliminary design of the solenoid, including numerical simulations of the beam dynamics, are reported. The most important issues to be addressed in the

New Generation of Superconducting Solenoids for Heavy-Ion Linac Application

HIAF (High Intensity heavy ion Accelerator Facility) is the new generation heavy ion accelerator under construction in China. The HFRS (FRagment Separator of HIAF) is a fragment separator and also a transfer-line between the Booster Ring and the Spectrometer ring, which has magnetic rigidity up to 25 Tm. HFRS magnet system is composed of 11 superconducting dipoles and 13 sets of triplets. Several multipole magnets (an octupole coil, a quadrupole coil, and a sextupole coil) are nested together to compact the length of the HFRS-line. All of them feature high field gradients (13 T/m, 25 T/m2, 105 T/m3) and large bores (320 mm). To reduce the cold mass and ensure the field quality, the whole multipole magnets are all designed with coil-dominated magnets of CCT (Canted Cosine Theta) and DCT (Discrete Cosine Theta). This paper will introduce the general design process of an HFRS multipole module. The development process and test results of the prototype will be presented.

DCT&CCT Superconducting Multiplets for HIAF-HFRS

As the special machines that can accelerate charged particle beams to high energy by using electromagnetic fields, particle accelerators have been widely applied in scientific research and various areas of society. The development of particle accelerators in China started in the early 1950s. After a brief review of the history of accelerators, this article describes in the following sections: particle colliders, heavy-ion accelerators, high-intensity proton accelerators, accelerator-based light sources, pulsed power accelerators, small scale accelerators, accelerators for applications, accelerator technology development and advanced accelerator concepts. The prospects of particle accelerators in China are also presented.

Particle Accelerators in China

The fragment separator of the HIAF (High Intensity Heavy Ion Accelerator Facility) project called HFRS requires quadrupoles with high gradients (11.4 T/m) and large bores (320 mm in diameter). The iron dominated magnets with superconducting coils have been widely used in the similar facilities such as A1900, BigRIPS, Super!FRS and RISP with the advantages of low request for coils installation precision, simple fabrication and low cost, but they have large cold mass and helium containment, which result in long time cooling down and high pressure rise during a quench. In addition, due to iron saturation, it is hard to guarantee on the field quality in the operated field range. A new coil dominated design based on the Canted!Cosine!Theta geometry is presented for HFRS, which is expected to overcome these problems. The design superimposes several layers of oppositely wound helical windings to generate high quality quadrupole. Sextupole, octupole and steering dipole can also be easily integrated to reduce the length of cryostat. This paper reports the detailed design of HFRS multiplets based on the CCT concept and the construction of a subscale prototype.

Multipole magnets for the HIAF fragment separator using the Canted-Cosine-Theta (CCT) geometry

In the project of Heavy Ion Medical Machine, there are eight dipole magnets in the synchrotron and ten dipole magnets in the high-energy beam line used for beam bending. Both types of dipole magnets have the same bending radius and bending angle, but the gaps are different. The maximum magnetic field of synchrotron dipole is 1.66 T, and the high beam line dipole is 1.6 T. The magnetic field calculation and the structure design are presented in this paper; the trim slot in the pole and the removable pole ends are used in order to reach the required field homogeneity. The magnetic field measurement results, which include field homogeneity and reproducibility, are also shown in details. The test results show that the dipole magnet design could satisfy the major specified physical requirements.

The Main Dipole Magnets Design and Test of HIMM Project

A compact solenoid for the China Accelerator Driven Subcritical System (China-ADS) injector II has been developed. It includes a focusing solenoid and two steering dipoles. The magnet is compact with an entire length of 160 mm, including the helium vessel and the side flanges. Nonlinear optimization method was used to meet the requirement of focusing strength and stray field with minimized solenoid volume. The steering dipoles are placed inside the solenoid to reduce the magnet size. The structural analysis, quench protection design, and fabrication and test results are presented in this paper.

A Compact Superconducting Solenoid for China-ADS Injector II

The High Intensity Heavy-ion Accelerator Facility (HIAF) is a new project under construction in China, which will provide beams of stable and unstable heavy ions with high energies, high intensities, and high quality. This paper discusses the superconducting magnet system for this accelerator complex. It will consist of a Nb3Sn magnet with the peak field of 12 Tesla for the ECR ion source operated at 45 GHz, 52 solenoids typically 676 mm long with an operating field of 7.5 Tesla for the superconducting Linac called iLinac, 11 superferric dipoles with 320 mm wide good field region, 13 coil-dominated multiplets with an aperture of 320 mm, gradient 13 T/m for the fragment separator HFRS. This paper reports the design and prototype development status of the main components.

Wenjie Yang

Papers

Multipole magnets for the HIAF fragment separator using the Canted-Cosine-Theta (CCT) geometry

DCT&CCT Superconducting Multiplets for HIAF-HFRS

The Main Dipole Magnets Design and Test of HIMM Project

A Compact Superconducting Solenoid for China-ADS Injector II

Superconducting Magnet Development for the HIAF Accelerator Complex