Current Status of and Challenges for No-Insulation HTS Winding Technique

In this paper we summarize what we have learned so far and discuss key technical challenges that face the HTS “NI” magnet wound with the no-insulation (NI) technique, focusing one of its beneficial features, self-protecting. We first describe the basic features of the NI winding technique, including lumped circuit and distributed network models. Next, we present results of a stand-alone NI magnet composed of REBCO double-pancake coils, showing that the magnet is indeed self-protecting. In the last part of this paper, we discuss the technical issues, often called “NI behaviors”, objectionable demerits that still remain, particularly in nested-coil NI magnets. These include charging delay, non-linear magnet constant in time-varying operation, unbalanced forces that can overstrain the conductor. We conclude the paper with our conviction, and optimism, that the NI winding technique is viable for HTS magnets, high-field and large electric power devices

Observation of ferromagnetic semiconductor behavior in manganese-oxide doped graphene

We have doped manganese-oxide onto graphene by an electrochemical method. Graphene showed a clear ferromagnetic semiconductor behavior after doping of manganese-oxide. The manganese-oxide doped graphene has a coercive field (Hc) of 232 Oe at 10 K, and has the Curie temperature of 270 K from the temperature-dependent resistivity using transport measurement system. The ferromagnetism of manganese-oxide doped graphene attributes to the double-exchange from the coexistence of Mn3+ and Mn4+ on the surface of graphene. In addition, the semiconducting behavior is caused by the formation of manganese-oxide on graphene

Comparison Study on Harmonic Loss of MW-Class Wind Generators With HTS Field Winding

This paper investigates the effect of slot-pole combination on harmonic loss such as iron loss and eddy-current loss in wind generators with high-temperature superconductor field winding. In order to study the effect of stator configuration, three wind generators having the same rotor structure but different stators were purposely designed to produce 11 MW. In the analysis, 2-D time-stepped finite element analysis was used to estimate flux density waveforms, and then harmonic iron loss in the stator yoke and rotor eddy-current loss were obtained. From the simulation results, we showed that the harmonic effect on stator iron loss is not significant because magnetic loading by field winding dominates. Meanwhile, we found that the eddy-current loss in the rotor by harmonics of magneto motive force strongly depends on the slot-pole combination.close0

Design Study on a 100-kA/20-K HTS Cable for Fusion Magnets

Due to the >100 times higher thermal stability of HTS (high temperature superconductor) than that of LTS (low temperature superconductor) and the capability of HTS to be operated at a liquid-helium-free temperature, an HTS cable is being considered a possible alternative to LTS for fusion magnets such as Toroidal Field (TF) coils in Tokamaks, and Helical coils in Stellarators. This paper presents a first-cut design of a 100- kA/20-K HTS cable, which could be an option for fusion magnets. Thermal behaviors of the cable were analyzed and compared quantitatively with those of a 100-kA/4.2-K Nb3Sn cable using the CryoSoftTM code THEA. In the paper, we demonstrated that the conventional concepts of the ???current sharing temperature (Tcs)??? and the ???minimum quench energy (MQE)??? may not be suitable for design and analysis of the HTS cable. Instead, ???thermal runaway temperature (TR)??? and ???minimum runaway energy (MRE)??? were proved to be more effective. Also, the post-quench temperature rise of the HTS cable, simulated by the THEA, was compared with that by the conventional analytic Z-function approach. The results demonstrate that the Z-function approach, proven to be effective for an LTS cable, may significantly overestimate the post-quench temperature rise of an HTS cable.close0

In vivo 3D Reconstruction of the Human Pallidothalamic and Nigrothalamic Pathways With Super-Resolution 7T MR Track Density Imaging and Fiber Tractography

The output network of the basal ganglia plays an important role in motor, associative, and limbic processing and is generally characterized by the pallidothalamic and nigrothalamic pathways. However, these connections in the human brain remain difficult to elucidate because of the resolution limit of current neuroimaging techniques. The present study aimed to investigate the mesoscopic nature of these connections between the thalamus, substantia nigra pars reticulata, and globus pallidus internal segment using 7 Tesla (7T) magnetic resonance imaging (MRI). In this study, track-density imaging (TDI) of the whole human brain was employed to overcome the limitations of observing the pallidothalamic and nigrothalamic tracts. Owing to the super-resolution of the TD images, the substructures of the SN, as well as the associated tracts, were identified. This study demonstrates that 7T MRI and MR tractography can be used to visualize anatomical details, as well as 3D reconstruction, of the output projections of the basal ganglia