A cryogen-free Nb-Ti superconducting magnet has been designed by ASG for IBA’s new synchro-cyclotron accelerator for cancer proton therapy. This solution allows a significantly more compact layout, as well as a global reduction of costs and an easier operation. One of the most challenging tasks was the achievement of a temperature distribution on the coils compatible with the operation of Nb-Ti in high magnetic field with enough temperature margin, and without cryogenic fluids. A 3-D thermal model has been run to optimize design choices. Then a fully functional prototype has been assembled and successfully tested. Series production has then been launched. Up to now, a magnet is already operational, while other three have been delivered to IBA for final acceptance and other six are in production. A description of the system and thermal calculation results are presented and compared with the measurements of the tests. The experience confirmed that simulation model reproduces satisfactorily the actual system, and that the cooling system has been properly sized to fulfill cool down and operational duties.

The heavy ion synchrotron SIS100 is the main accelerator of the Facility for Antiproton and Ion Research (FAIR) project, located in Darmstadt, Germany. Within the four families of superconducting Quadrupole Doublet Modules (QDM), the development of the injection and extraction modules is the highest in difficulty due to the complex configuration, and the stringent position-stability requirements to be fulfilled. These modules are formed by two different beam branches, which have various components installed (e.g. focusing and defocusing main quadrupole magnets, low current quadrupole magnets, etc.). The positioning of the inner magnets is critical due to the maximum allowed displacements relative to the ion optical lattice positions to be 125 µm for the main QP magnets, 175 µm for the corrector magnets, and 50 µm for the cryostat. The LHe cooling systems for the magnets and the ultra-high vacuum components are formed by split circuit schemes for different beam branches in each module. All LHe pipes are conducted from the modules to adjacent cryogenic bypass lines. The thermomechanical design results in an unique challenge in terms of development and mechanical integration of these QDMs.

CLIQ (Coupling-Loss-Induced Quench) is an innovative method for the protection of high-field superconducting magnets. With respect to the conventional technology based on quench heaters, it offers significant advantages in terms of electrical robustness and energy-deposition velocity. Its effective intra-wire heating mechanism features a fast and homogeneous transition to the normal state of the winding pack, hence assuring a quick magnet discharge and avoiding overheating of the coil’s hot-spot. Furthermore, it is possible to implement CLIQ as a time- and cost-effective repair solution for the protection of existing magnets with broken quench heaters.
After being successfully tested on model magnets of different geometries and made of different types of superconductor, CLIQ is now applied for the first time for the protection of a full-scale quadrupole magnet. A 3.4 meter long, 140 mH, LHC matching quadrupole magnet is equipped with dedicated terminals to allow the connection of a 500 V CLIQ system. Experimental results convincingly show that CLIQ can protect this coil over the entire range of operating conditions. The complex electro-thermal transient during and after a CLIQ discharge are successfully reproduced by means of a 2D model. Once validated, the model can be used to assess CLIQ behaviour over a wider range of operating conditions and further optimize its performance.
The successful test is part of the R&D program of CLIQ quench protection systems, which has convincingly demonstrated the maturity of this technology and its effectiveness even for large-scale magnet systems. The proposed CLIQ-based solution for the quench protection system of the LHC matching quadrupole magnet is now ready to be implemented in the LHC machine.

The REBCO superconducting coil is essential to construct next generation high field superconducting magnets. For example, a 25T cryogen-free superconducting magnet consists of REBCO inner and low temperature superconducting (LTS) outer coils and is under construction at Tohoku Univ. To achieve further high fields in the future, the quench protection of the REBCO coils is still a challenging issue due to the slow normal zone propagation in the REBCO tapes. The most severe condition for the REBCO coils is a large current induced by accidental quenches of the LTS outsert coils, which may cause to burn out the REBCO coils. In spite of the great importance to clarify the hotspot characteristics, it has not been studied experimentally because of a risk to damage the REBCO coil.
In this work, we fabricated a REBCO single pancake coil and exposed it to quenches of an LTS magnet to investigate hotspot characteristics of the REBCO coil. Electromagnetic responses of the REBCO coil during the quenches of the LTS magnet were measured at various temperatures with various dump resistances. The resistive voltage in the REBCO coil increases more rapidly at the lower initial temperature. Thermo-electromagnetic numerical simulation was also performed considering the physical properties of the REBCO tapes. The hotspot volume and the temperature rise will be discussed based on the experimental and numerical results.

Part of this work was supported by a Grand-in-Aid for Scientific Research (No. 25246032) and by Grant-in-Aid for Research Activity Start-up (No. 26889005) from the Japan Society for the Promotion of Science (JSPS).

The maximum RF surface magnetic field (BS) achieved with Superconducting RadioFrequency (SRF) bulk Nb cavities is often limited by anomalous Joule losses due to heating of normal-resistive defects embedded onto the RF surface. At high BS (e.g BS>50 mT), the defect temperature increases strongly with BS, leading to a thermal runaway of the cavity or quench. We started recently a R&D program for developing new diagnostic tools devoted to detection and locating of thermal quenches in SRF Cavities via 2nd sound events in superfluid helium (HeII). Two types of Quench Detectors (QD) were investigated: 1) Capacitive sensors namely Oscillating Superleak Transducer (COST), 2) Low REsponse Time ResIstive THermometers (LRETRITH). A test stand operating at He II bath Temperature T0 from 1.6 K up to Tl was used for the calibration and characterization of the QD: it allows precise and controlled experimental simulation of SRF cavity quench using Joule heated sources. The heaters of different sizes and geometries, were subjected to pulsed heat flux qP (pulse duration tP= 10µs-10ms, peak qP < 2MW/m2). Experimental runs were performed to study the dynamic response of QD as function of several parameters (heat source size and geometry, T0, tP and peak qP) and experimental data are presented. Further, a Second Sound Resonator (SSR), with a pair of COSTs at its two extremities as Second Sound Generator (SSG) and Detector (SSD) respectively and housing also a low thermal capacity heater (SSG) and a LRETRITH (SSD) assembly was developed. The first results, with SSR operated in either a resonating mode (AC excitation) or in a shock wave mode (pulsed excitation), are reported. Finally COST detectors were successfully used for locating and characterizing quench sources in various bulk niobium SRF cavities resonating at two different frequencies f0 (f0 =88 MHz and f0 =352 MHz). We studied also the quench dynamics and critical size of hot spot normal resistive area leading to cavity quench.

A compact react and wind solenoid magnet was previously tested for critical current performance from 4.2 to 30K and 0 to 5T. Tests showed the magnet critical current correlated to within 10% of the short length conductor critical current. It is composed of a 243 m single length of 36 filament, 0.55 mm diameter conductor with 50 µm thick s-glass insulation, manufactured by Hyper Tech, continuously wound onto a 100 mm inside diameter, 100mm long, 770 turn, 5 layer solenoid coil. The quench propagation tests presented in this paper are carried out on the same coil, in a background field which allows to an extent a decoupling of the peak field in the windings from the conductor field performance. Layer by layer non-inductive instrumentation of the coil, together with coil dc, and short length test data enables voltage characteristics to be spatially determined. Using a quench heater located centrally in the winding, the propagation characteristics in the radial and tangential directions and the minimum quench energy as a function of temperature and field are measured. The results are compared to data on the temperature and field dependent minimum quench energy characteristics of adiabatic short length MgB2 conductor.

We present a prototype design and performance of a continuous rotating bearing system using a superconducting magnetic bearing (SMB) that operates at a temperature of 4 K. This system is designed in order to test a compatibility of the SMB as a bearing of a polarization modulator for a next generation CMB polarization satellite mission, LiteBIRD.

Measurements of a cosmic microwave background (CMB) polarization provide a tool to probe the physics of early universe, i.e. cosmic inflation. LiteBIRD is a dedicated satellite mission to measure the CMB polarization with an unprecedented accuracy. One of the key instruments to achieve such science objective is a polarization modulator. The modulator consists of an optical element, half-wave plate, in a telescope and it needs to rotate continuously at a rotational frequency of 1 Hz and a temperature of 4 K during the observations. The past balloon-borne CMB experiment, EBEX, employs such this modulator using the SMB, and the successful demonstration triggers the interest to make the technology be compatible with a space mission.

For use in a space mission, there are three major challenges to overcome, 1) surviving the vibration at launch, 2) minimizing the heat dissipation due to the limited cooling power, and 3) degradation due to the cosmic rays.
We design and construct the prototype SMB system to address the first two challenges. The SMB consists of a ring shaped NdFeB magnet and an array of YBCO high temperature superconductor (HTS) tiles. The inner diameter of the magnet ring is 65 mm. Three cryogenic actuators support the rotor magnet ring until the HTS tiles are cooled below its critical temperature. This support mechanism also serves as a launch-lock to survive during a launch. Both an optical chopper and a Hall sensor encode the rotational frequency of a rotor.
In this presentation, we report the design and its performance of the prototype system. We measure the dynamical properties, such as the coefficient of friction and the vibration. We relate the dynamical properties, the magnetic non-uniformity of the rotor magnet to the heat dissipation measurements. We finally discuss the scalability to a larger diameter SMB system. We discuss the requirement and the optimizations of the system parameters in order to design the flight compatible system.

Superconducting applications are now closely related to the heat losses produced by current leads located between room temperature and low temperature for connection with power supply. Various types of flux pump are being researched where the necessary DC current is supplied by the AC power source to reduce the heat losses. The flux pump is placed in the cryostat and controlled by the power supply at room temperature. And, the DC current is induced by an electromotive force pulse causing time varying magnetic field of an HTS wire in the flux pump. It can be categorized into the rotating type and static type. The rotating type flux pump is energized by the time varying magnetic field of the permanent magnets in rotating part. The static type flux pump uses superconducting switches or rectifiers acting as the permanent magnets of the rotating type flux pump. This type doesn’t need rotating motion device and has safer performance than the rotating type.
In this paper, we have built a flux pump based on full-wave rectifier and analysed performance of the flux pump for superconducting applications. The flux pump has been designed by using a 3D finite elements method program. It consists of the full-wave rectifier which converts the whole of the input waveform to one of constant polarity at its output, an iron-core, and the HTS wire. The rectifier and the iron-core are located under room temperature. The iron-core helps that magnetic flux by output of the rectifier penetrates the HTS wire perpendicularly. The induced DC current in the HTS wire directly flows to the HTS coil at low temperature. For an experimental study we have developed the main components of the flux pump such as the rectifier, iron-core and HTS coil. The induced DC current has been measured depending on the air-gap between the iron-core and the HTS wire, and the cycle of the full-wave output. To increase the pumping current, we have suggested a new connection method of the HTS wire and the coil. These results of the flux pump have been discussed in detail, and will be effectively utilized for static superconducting applications.

This work was supported by the Power Generation & Electricity Delivery Core Technology Program of the Korea Institute of Energy  Technology Evaluation and Planning (KETEP), granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea.
 (No. 20142020103560)