No abstract

The nonuniform superconducting current distribution in a REBCO coated conductor, including a varying-field-induced screening current, is responsible for a significant magnetization effect that not only degrades the field quality of REBCO magnets, but introduces risks of overstressing the conductor. This paper presents our experimental and simulation studies on the screening current effect on an 800 MHz (18.8 T) REBCO insert (H800) that together with a 500 MHz LTS nuclear magnetic resonance (NMR) magnet (L500) constitutes the MIT 1.3 GHz LTS/HTS NMR magnet (1.3 G). To develop our simulation model, which was subsequently validated by a good agreement between simulation and experiment, we chose H800, Coil 1 of the 3-coil assembly operated alone and the entire H800, for the sources of experimental data, specifically their remnant fields after current discharge and diminished axial fields during operation. Armed with this valid model, we examined in detail the negative effects of screening current on H800, an important 1.3 G component. Our simulation indicates that the screening current, nonuniformly distributed in the REBCO conductor, not only deteriorates H800 field, both strength and homogeneity, thus that of 1.3 G, but may overstress the REBCO conductor.

Mitochondrial Ca uptake is gated by the mitochondrial calcium uniplex, which is comprised of mitochondrial calcium uniporter (MCU), the Ca pore-forming subunit of the complex, and its regulators. Ca influx through MCU affects both mitochondrial function and movement in neurons, but its direct role in mitochondrial movement has not been explored. In this report, we show a link between MCU and Miro1, a membrane protein known to regulate mitochondrial movement. We find that MCU interacts with Miro1 through MCU's N-terminal domain, previously thought to be the mitochondrial targeting sequence. Our results show that the N-terminus of MCU has a transmembrane domain that traverses the outer mitochondrial membrane, which is dispensable for MCU localization into mitochondria. However, this domain is required for Miro1 interaction and is critical for Miro1 directed movement. Together, our findings reveal Miro1 as a new component of the MCU complex, and that MCU is an important regulator of mitochondrial transport. Mitochondrial calcium level is critical for mitochondrial metabolic activity and mitochondrial transport in neurons. While it has been established that calcium influx into mitochondria is modulated by mitochondrial calcium uniporter (MCU) complex, how MCU regulates mitochondrial movement still remains unclear. Here, we discover that the N-terminus of MCU plays a different role than previously thought; it is not required for mitochondrial targeting but is essential for interaction with Miro1, an outer mitochondrial membrane protein important for mitochondrial movement. Furthermore, we show that MCU-Miro1 interaction is required to maintain mitochondrial transport. Our data identify that Miro1 is a novel component of the mitochondrial calcium uniplex and demonstrate that coupling between MCU and Miro1 as a novel mechanism modulating both mitochondrial Ca uptake and mitochondrial transport.

No abstract

We present a No-Insulation (NI) Multi-Width (MW) winding technique for an HTS (high temperature superconductor) magnet consisting of double-pancake (DP) coils. The NI enables an HTS magnet self-protecting and the MW minimizes the detrimental anisotropy in current-carrying capacity of HTS tape by assigning tapes of multiple widths to DP coils within a stack, widest tape to the top and bottom sections and the narrowest in the midplane section. 1,2 In the event of a quench, we confirmed that the magnet current in an NI winding automatically bypassed the quench spot through turn-to-turn contacts from its original spiral path and that the magnet remained stable even though its operating current was pushed to twice the magnet critical current.1 Due to this self-protecting feature, an NI magnet requires a minimum amount of stabilizer, just enough for ease of splicing and handling.3-8 The absence of both turn-to-turn insulation and the extra stabilizer needed in its insulated (INS) counterpart makes the NI magnet highly compact and enhances its overall current density. 9-18Commercial 2G conductor comes as tape with width/ thickness ratio in a range of 5-40. 19,20 Unlike a conventional assembly of DP coils, in which the DP coils are wound with the same-width 2G tape, [21][22][23] in our MW technique, we place DP coils of the narrowest tape width in the magnet midplane section, placing DP coils of gradually wider tapes away from the midplane, with the widest-tape DP coils at the top and bottom sections, where the normal field that limits 2G tape performance is at its peak. This MW technique significantly enhances the overall current density of such a DP coil assembly at a given operating current.On one hand, the NI technique enables an HTS magnet to be self-protecting and thus to operate at a high current density (>150 kA/cm 2 ), 2 both features are not possible with the conventional HTS magnet. On the other hand, the MW technique is the most suitable and effective approach to "conductor-grade" 24 DP coils wound with highly anisotropic 2G HTS tape. A combination of NI and MW techniques (NI-MW) thus not only satisfies key operation requirements in protection and stability but also enables HTS magnets to be highly compact, which will lead to significant reduction in magnet price, one of the decisive factors in the marketplace.To demonstrate the NI-MW concept, we have designed and constructed a test NI-MW magnet as seen in Fig. 1(a). It consists of a stack of seven DP coils wound with "bare (no copper stabilizer)" 2G conductor, manufactured by AMSC without any turn-to-turn insulation (NI technique). The original conductor was 46-mm wide and then was mechanically slit to have a target width. The conductor width is 2.5 mm for the center DP coil (DP4 in Fig. 1) and increases up to 4.0 mm for the top and bottom DP coils (DP1 and DP7). As a result, this MW magnet generates 22% greater field than its single-width (SW) counterpart with the same overall dimensions (inner diameter, outer diameter, and height) as those of the SW mag...

A no-insulation (NI) technique has been applied to wind and test a NI HTS (YBCO) double-pancake coil at 4.2 K. Having little detrimental effect on field-current relationship, the absence of turn-to-turn insulation enabled the test coil to survive a quench at a coil current density of 1.58. The NI HTS coil is compact and self-protecting, two features suitable for large highfield magnets. To investigate beneficial impacts of the NI technique on 1 GHz LTS/HTS NMR magnets, we have designed six new NI HTS inserts for our ongoing 1.3 GHz LTS/HTS NMR magnet, which require less costly LTS background magnets than the original insulated HTS insert. A net result will be a significant reduction in the overall cost of an LTS/HTS NMR magnet, at 1.3 GHz and above.

No abstract

In this paper we present details of a 600 MHz HTS insert (H600) double pancake (DP) windings. It will first be operated in the bore of a 500 MHz LTS magnet, achieving a frequency of 1.1 GHz. Upon completion of H600, we will embark on the final phase (Phase 3B) of a 3-Phase program began in 2000: completion of a high resolution 1.3 GHz LTS/HTS magnet. In Phase 3B, the H600 will be coupled to a 700 MHz LTS magnet to achieve the ultimate frequency of 1.3 GHz. The HTS insert is composed of two concentric stacks of double pancakes, one wound with high strength BSCCO-2223 tape, the other with YBCO coated conductor. Details include conductor and coil parameters, winding procedure, DPs mechanical support and integration to the background 500 MHz LTS magnet. Test results of individual DPs in LN2 are also presented.