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Because low-temperature superconducting (LTS) magnets can conduct large electric current and generate intense magnetic fields under cryogenic conditions, such magnets are used in many applications such as MRI, nuclear magnetic resonance spectrometers, and mass spectrometers. However, an abnormal termination called “quench” disturbs the normal operation and increases the magnet temperature. To protect the LTS magnet from excessive heat, the maximum temperature of a magnet under the quench process should be calculated. The design of a superconducting magnet protection system is performed according to the calculated maximum temperature. This is why accurate estimation of magnet temperature is important. The quench process of a superconducting magnet involves complex physical mechanisms, which requires a thermal–electrical simulation using computational analysis. We propose a highly efficient and reliable three-dimensional quench calculation method that can calculate the magnet temperature in the quench process. The LTS magnet is divided into many unit nodes; multiphysics analysis at each node is carried out with respect to the elapsed time. To verify the feasibility of the simulation, LTS magnet quench experimental results were compared with the simulation results. This study has the potential to develop a computational method for heat propagation analysis of a superconducting magnet. [ABSTRACT FROM PUBLISHER]

A 3-T 100-mm winding bore conduction-cooled REBCO magnet has been designed, constructed, and tested. It consists of a stack of double pancake coils wound with metallic cladding (MC) REBCO tapes, for which 1–2 \mu \textm stainless steel was clad in a hermetic way around the tapes. This approach, first proposed by the SuNAM Company Ltd. in 2015, is expected to substantially reduce the charging time delay of a no-insulation magnet, which in turn will be effective in the manipulation of screening currents in such a way as to improve the field homogeneity of magnets, particularly for nuclear magnetic resonance or MRI. This paper presents test results for our approach on the current sweep cycling, which is used to reduce the screening current-induced fields in a newly constructed 3-T 100-mm MC all-REBCO magnet [ABSTRACT FROM PUBLISHER]

Recently various high temperature superconducting (HTS) conductors have been commercialized in the power applications. While a BSCCO becomes tape or wire, others coated conductors (CC) are tapes. An HTS magnet utilized with these conductors can be fabricated as a form of pancake winding or layer winding. In the case of HTS magnet using a thin and rectangular tape, the pancake winding method is satisfied in the practical cases because of its suitable features. However, one of the disadvantages of this winding method is increasing brands and splices. From this point of view, we propose a layer winding method using an HTS tape and fabricated HTS layer coils. To verify the feasibility of the proposed winding method, critical current and over-current tests are investigated in liquid nitrogen and the results are compared with those of pancake coils. In addition, operating characteristics on the condition of various winding tensions are analyzed. [ABSTRACT FROM PUBLISHER]

A non-inductive coil is an essential element of a resistive superconducting fault current limiter (FCL). A bifilar pancake type non-inductive coil, which is most common type, has two drawbacks; difficulty of paralleling tapes and a high risk of electrical breakdown at the terminal part. Although the bifilar type is simple as an element, large-scale FCL needs quite a number of series and parallel connections between elements. To make a non-inductive coil using conventional inductive elementary coils, we propose a novel structure of the coil. It looks like a toroid but entire inductance is near zero. This coil can overcome the drawbacks of conventional bifilar coil. In this paper, we confirm the new concept by numerical analyses. A few kinds of new models are compared, and then we concluded the proposed toroidal shape one is most suitable. This new structure coil can help implement of a hybrid FCL which is to generate the magnetic field at only fault. [ABSTRACT FROM AUTHOR]

High-Tc superconducting (HTS) wires have showed good capabilities as an alternative conductor for superconducting magnet. The HTS wires have more current carrying capability within high external magnetic field and its stability against external disturbance is much higher than the low temperature superconducting (LTS) wires. But the HTS wire has slower normal zone propagation (NZP) velocity which makes HTS magnets hard to be protected from unexpected hot spot. This paper presents experimental test and numerical analysis about the relation between transport current and rate of temperature rise in a hot spot. A sample which contained a HTS wire, a heater, and temperature sensor was fabricated and an experimental test on measuring normal zone propagation and temperature of the HTS wire was conducted. A numerical model was also built to estimate transient temperature rise of a winding pack model which was representing practical winding of HTS magnets. The numerical model and its numerical estimation results are expected to be a guideline about designing proper protection technique and operating current for HTS magnets. [ABSTRACT FROM AUTHOR]

This paper presents the results of work, experimental and simulation, performed on an YBCO pancake coil to develop a detect-and-activate-the-heater (DAH) protection technique. In this DAH protection technique a "protection heater" (PH) is activated, upon the detection of a quench zone in a coil, to create an additional normal zone to absorb the stored magnetic energy sufficient to keep the initially quenched zone (hot spot) from overheating. It is computed that a protection heater for most coils needs to cover only a fraction of the winding to keep the quenched zone from overheating. The pancake coil used in the experiment, 100-mm i.d., 190-mm 04., and 4.3-mm height, is dry-wound with copper plated YBCO tape, 4.3-mm wide, 96.3-μm thick, 100-m long, and is turn-to-turn insulated with 38-μm thick Nomex spacer. The pancake stores a magnetic energy of 30 J at an operating current of 80 A at 65 K. Because the smaller the magnet size, the less applicable the assumption of adiabatic conditions is and also the more beneficial NZP becomes that would otherwise be negligible in "large" magnets, the hot spot temperature observed in the experiment with this "small" test coil was much less than that computed based on the assumptions of adiabatic conditions and no NZP. To validate the basic concept and consequences of DAH protection technique either a test coil has to be large or if the same coil is to be used, it should be tested at the temperature range close to 20-30 K so that the coil can carry a large current and thus store a large magnetic energy. [ABSTRACT FROM AUTHOR]

Abstract: With the successful commercialization of Bi-2223 powder-in-tube wire, various attempts in the R&D of the high-T c superconducting (HTS) magnets for high magnetic field applications are being implemented actively. Operating temperature of HTS magnet has to be maintained at the designed level but the magnetic energy and mechanical disturbance can cause unstable operational temperature of HTS magnet. Especially, the generated heat energy of inner HTS winding is apt to be accumulated, so the normal region appears in HTS winding. This paper deals with the quenching characteristics of three kinds of selected Bi-2223 wires: the high current density wire (HC-A) and the high strength wire (HS-A) made by AMSC and HTS wire (HW-I) made by Innost. The Innost wire has the highest minimum quench energy (MQE). The high current density wire has the highest normal zone propagation velocity (NZPV). [Copyright &y& Elsevier]