History and recent progress of QMG™ and QMG bulk magnets

Morita, Mitsuru

doi:10.1088/1742-6596/1054/1/012046

Cited by 4 publications

(2 citation statements)

References 13 publications

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“…The reinforcement concept was, in fact, first proposed by Morita et al in 2017 for ring-shaped bulk magnets [16,17], where they demonstrated that the proposed structure significantly decreased the mechanical strains experienced by the superconductor and prevented crack formation. Furthermore, the resultant composite proposed here also benefits from improved thermal stability as a result of enhanced thermal capacitance and thermal conductivity, which helps to reduce the occurrence of flux jumps.…”

Section: Introductionmentioning

confidence: 99%

Composite stacks for reliable > 17 T trapped fields in bulk superconductor magnets

Huang

Shi

Srpcic

et al. 2019

Supercond. Sci. Technol.

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Trapped fields of over 20 T are, in principle, achievable in bulk, single-grain high temperature cuprate superconductors. The principle barriers to realizing such performance are, firstly, the large tensile stresses that develop during the magnetization of such trapped-field magnets as a result of the Lorentz force, which lead to brittle fracture of these ceramic-like materials at high fields and, secondly, catastrophic thermal instabilities as a result of flux movement during magnetization. Moreover, for a batch of samples nominally fabricated identically, the statistical nature of the failure mechanism means the best performance (i.e. trapped fields of over 17 T) cannot be attained reliably. The magnetization process, particularly to higher fields, also often damages the samples such that they cannot repeatedly trap high fields following subsequent magnetization. In this study, we report the sequential trapping of magnetic fields of ~ 17 T, achieving 16.8 T at 26 K initially and 17.6 T at 22.5 K subsequently, in a stack of two Ag-doped GdBa2Cu3O7-δ bulk superconductor composites of diameter 24 mm reinforced with (1) stainless-steel laminations, and (2) shrink-fit stainless steel rings. A trapped field of 17.6 T is, in fact, comparable with the highest trapped fields reported to date for bulk superconducting magnets of any mechanical and chemical composition, and this was achieved using the first composite stack to be fabricated by this technique. These post-meltprocessing treatments, which are relatively straightforward to implement, were used to improve both the mechanical properties and the thermal stability of the resultant composite structure, providing what we believe is a promising route to achieving reliably fields of over 20 T.

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Section: Introductionmentioning

confidence: 99%

Composite stacks for reliable > 17 T trapped fields in bulk superconductor magnets

Huang

Shi

Srpcic

et al. 2019

Supercond. Sci. Technol.

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“…A preferable approach is to construct the Bitter stack from discs of HTS bulk superconductor that allow current to be transferred directly across both top and bottom faces. Electromagnets comprising of spirally cut HTS bulk superconductors have previously been demonstrated [15][16][17], however there are no reports of using these materials in a Bitter-like bulk architecture.…”

Section: Introductionmentioning

confidence: 99%

A proof-of-concept Bitter-like HTS electromagnet fabricated from a silver-infiltrated (RE)BCO ceramic bulk

Taylor,

Weijers,

Ainslie

et al. 2024

Supercond. Sci. Technol.

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A novel concept for a compact high-field magnet coil is introduced. This is based on stacking slit annular discs cut from bulk (RE)BCO ceramic in a Bitter-like architecture. Finite-element modelling shows that a small 20-turn stack (with a total coil volume of <20 cm3) is capable of generating a central bore magnetic field of >2 T at 77 K and >20 T at 30 K. Unlike resistive Bitter magnets, the HTS Bitter stack exhibits significant non-linear field behaviour during current ramping, caused by current filling proceeding from the inner radius outwards in each HTS layer. Practical proof-of-concept for this architecture was then demonstrated through fabricating an uninsulated 4-turn prototype coil stack and operating this at 77 K. A maximum central field of 0.382 T was measured at 1.2 kA, with an accompanying 6.1 W of internal heat dissipation within the coil. Strong magnetic hysteresis behaviour was observed within the prototype coil, with ≈30% of the maximum central field still remaining trapped 45 min after the current had been removed. The coil was thermally stable during a 15 min hold at 1 kA, and survived thermal cycling to room temperature without noticeable deterioration in performance. A final test-to-destruction of the coil showed that the limiting weak point in the stack was growth-sector boundaries present in the original (RE)BCO bulk.

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Common Correlated Effects Estimation of Heterogeneous: Dynamic Panel Quantile Regression Models

2018

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This paper proposes a quantile regression estimator for a heterogeneous panel model with lagged dependent variables and interactive effects. The paper adopts the Common Correlated Effects (CCE) approach proposed by Pesaran (2006) and Chudik and Pesaran (2015) and demonstrates that the extension to the estimation of dynamic quantile regression models is feasible under similar conditions to the ones used in the literature. We establish consistency and derive the asymptotic distribution of the new quantile regression estimator. Monte Carlo studies are carried out to study the small sample behavior of the proposed approach. The evidence shows that the estimator can significantly improve on the performance of existing estimators as long as the time series dimension of the panel is large. We present an application to the evaluation of Time-of-Use pricing using a large randomized control trial. JEL-Codes: C210, C310, C330, D120, L940. The paper is organized as follows. The next section introduces the model and the proposed estimator. It also establishes the asymptotic properties of the estimator. Section 3 provides simulation experiments to investigate the small sample performance of the proposed estimator. Section 4 demonstrates how the estimator can be used in practice by exploring an application of electricity pricing and smart technology. Section 5 concludes. Mathematical proofs are provided in the Appendix and additional Monte Carlo results are offered in an online Supplement. Notations: Generic positive finite constants are denoted by K a , K b , . . ., and can take different values at different instances and are bounded in N and T (the panel dimensions). The largest and the smallest eigenvalues of the N × N real symmetric matrix A = (a ij ) are denoted by ζ max (A) and ζ min (A), respectively, and its spectral (or operator) norm by ∥A∥ = ζ 1/2 max (A ′ A). a.s. −→ denotes almost sure convergence, ℓ 1 −→ convergence in the ℓ 1 norm, p −→ convergence in probability, and d −→ convergence in distribution. We denote ∥x∥ 1 = ∑ n i=1 |x i | as the ℓ 1 norm of vector x. All asymptotics are carried out under N and T → ∞, jointly. Model and assumptionsWe consider a dynamic panel data model for i = 1, 2, . . . , N and t = 1, 2, . . . , T , where y it ∈ R is the response variable for cross-sectional unit i at time t and y it−1 denotes a lagged dependent variable. Consider the following conditional panel quantile function:The variable x it is a p x × 1 vector of regressors specific to cross-sectional unit i at time t,is a vector of latent factor loadings, and α i (τ ) is an individual effect potentially correlated with the regressor variables, x it . The term f ′ t γ i (τ ) can be interpreted as a quantile-specific function capturing unobserved heterogeneity that was not adequately controlled by the inclusion of x it .The model can be considered to be semi-parametric since the functional form of the conditionalis left unspecified and no parametric assumption is imposed on the relation between the regressors and the latent va...

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History and recent progress of QMG™ and QMG bulk magnets

Cited by 4 publications

References 13 publications

Composite stacks for reliable > 17 T trapped fields in bulk superconductor magnets

Composite stacks for reliable > 17 T trapped fields in bulk superconductor magnets

A proof-of-concept Bitter-like HTS electromagnet fabricated from a silver-infiltrated (RE)BCO ceramic bulk

Common Correlated Effects Estimation of Heterogeneous: Dynamic Panel Quantile Regression Models

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