Optimization of a Mechanical Bridge Joint Structure in a Stacked HTS Conductor

Kawai, Kenji; Seino, Y.; Yanagi, N.; Tamura, H.; Sagara, A.; Hashizume, Hidetoshi

doi:10.1109/tasc.2013.2239335

Cited by 25 publications

(12 citation statements)

References 8 publications

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“…5 (a), a mechanical joint technique developed at Tohoku University can be applied instead of the formerly considered soldering method [32]. For a mechanical lap joint, the joint resistivity is estimated to be ∼10 pΩm 2 [33,34], giving an overall joint resistance of ∼1 nΩ for a 100-kA conductor (consisting of 2 connections per joint with 40 HTS tapes, each having a 50-mm joint length). The entire helical coil system has 7,800 joints (390 turns, 10 segments, 2 coils), and requires a ∼5 MW increase in the electrical power to the cryoplant for a coil operation temperature of 20 K. This is acceptable given the power requirements of ∼30 MW for a LTS system operated at 4 K. To further reduce the refrigeration power, we propose the "finger-type" joint shown in Fig.…”

Section: Segmented Fabrication Of Large Complex Coils Using Hts Condumentioning

confidence: 99%

“…In 2012, a 30-kA-class conductor sample was fabricated using the latest GdBCO tape produced by Fujikura Ltd. Twenty tapes were simply stacked in 10 layers and 2 rows [19]. In the sample, a bridge-type mechanical lap joint developed at Tohoku University [33,34,38] was used so that the racetrack shaped sample formed a short circuit. A sample current was induced by changing the bias magnetic field, and a critical current of 45 kA was measured at 20 K and 6 T [39].…”

Section: Development Of 100-ka-class Hts Conductor and Joint For Ffhr-d1mentioning

confidence: 99%

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Feasibility of HTS Magnet Option for Fusion Reactors

Yanagi

Terazaki

Natsume

et al. 2014

Plasma and Fusion Research

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Conceptual design studies are being carried out on the application of high-temperature superconducting (HTS) conductors and coils to the magnet systems of fusion reactors. A 100-kA-class HTS conductor is required to be applied at high magnetic fields of > 12 T. A simple stack of YBCO tapes embedded in copper and stainless-steel jackets is found to be a practical approach to producing large-scale conductors that exhibit high cryogenic stability and mechanical rigidity. The feasibility of the segmented fabrication method for large complex HTS coils, such as the helical coils in the LHD-type helical fusion reactor FFHR-d1, is being investigated by developing mechanical bridge-type lap joint technology of HTS conductors.

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Section: Segmented Fabrication Of Large Complex Coils Using Hts Condumentioning

confidence: 99%

Section: Development Of 100-ka-class Hts Conductor and Joint For Ffhr-d1mentioning

confidence: 99%

Feasibility of HTS Magnet Option for Fusion Reactors

Yanagi

Terazaki

Natsume

et al. 2014

Plasma and Fusion Research

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“…HTS conductors for the coil consist of untwisted stacked layers of REBCO tape inside a rectangular or a concentric copper and stainless steel jackets. The joint sections are arranged in a step-wise geometry and the tape layers are joined either by soldering [6], [7] or by mechanical bridge joints (bridge-type lap joints) [8], [9]. The jackets are then fixed by welding or bolting to ensure the required tensile strength.…”

Section: Introductionmentioning

confidence: 99%

“…The jackets are then fixed by welding or bolting to ensure the required tensile strength. Because the joint resistivity of the mechanical joint is nearly equal to that of the soldered joint [9], using a mechanical joint is attractive, because doing so simplifies fabrication.…”

Section: Introductionmentioning

confidence: 99%

Performance of a Mechanical Bridge Joint for 30-kA-Class High-Temperature Superconducting Conductors

Kawai

Seino

Ohinata

et al. 2014

IEEE Trans. Appl. Supercond.

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In this report, we propose segment-fabricated hightemperature superconducting (HTS) magnets as candidates for the FFHR-d1 heliotron-type fusion reactor. The FFHR-d1 requires 100-kA-class superconducting conductors used at 12 T for a pair of helical coils. We fabricated and tested two 30-kA-class GdBCO conductors with bridge-type mechanical lap joints (mechanical bridge joints). This report details the design of the joint section and the experimental results of those samples, especially, those of their joints. We improved the geometry of the joint region in a second sample, based on our results from the first. The second sample has sufficiently low joint resistance (less than 5 nΩ), and we could apply 70 kA to it without causing quenching at the joint. Its joint resistance was also acceptable for providing the electric power required to run the cryoplant for the segmented HTS helical coils.

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“…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][4][5][6][7][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][10][11][12][13][14][15][16][17][18] Commercial 2G conductor comes as tape with width/ thickness ratio in a range of 5-40.…”

mentioning

confidence: 99%

No-insulation multi-width winding technique for high temperature superconducting magnet

Hahn

Kim

Park

et al. 2013

Applied Physics Letters

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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...

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Optimization of a Mechanical Bridge Joint Structure in a Stacked HTS Conductor

Cited by 25 publications

References 8 publications

Feasibility of HTS Magnet Option for Fusion Reactors

Feasibility of HTS Magnet Option for Fusion Reactors

Performance of a Mechanical Bridge Joint for 30-kA-Class High-Temperature Superconducting Conductors

No-insulation multi-width winding technique for high temperature superconducting magnet

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