Search citation statements
Paper Sections
Citation Types
Year Published
Publication Types
Relationship
Authors
Journals
Use of high-temperature superconductors (HTSs) for current leads to deliver power to devices at liquid helium temperature, now near commercial realization, has the potential to reduce refrigeration requirements and helium boil-off to values significantly lower than the theoretically best values achievable with conventional leads. Considerable advantage is achieved by operating these leads with an intermediate-temperature heat sink. The HTS part of the lead can be made from pressed and sintered powder. Powder-in-tube fabrication is also possible, but the normal metal part of the lead acts as a thermal short and cannot provide much stabilization without increasing the refrigeration requirement. For lead stability, designs with low current density are favored. Such leads can be manufactured with today's technology, and refrigeration requirements are lower for the same allowable burnout time. Higher current densities result in lower boil-off for the same lead length, but burnout times can be very short. In comparing experiment to theory in open systems, the density of helium vapor must be accounted for in calculating the expected boil-off. For very-low-loss leads, two-dimensional heat transfer and the state of the dewar near the leads may play dominant roles in lead performance.
General design equations derived from one dimensional energy balance equations are solved to evaluate generalized characteristics of gas cooled current leads which are made of high temperature superconducting (HTSC) material. Design parameters of the conductor and the cooling channel are combined into a single general cooling parameter with the consideration of laminar flow. Generalized characteristics of HTSC current leads, namely the heat fiow from the cold end of the leads, the geometrical dimension of the conductor and the pressure drop of the cooling gas are represented in a design chart with the general cooling parameter. Thermal runaway of the conductor is analyzed for various geometrical dimensions in the case of stoppage of the cooling gas with the consideration of the quench propagation. The temperature rise time works as a criterion for determining the g e e metrical dimension. By determining the geometrical dimension according to the criterion, the heat flow from the cold end is estimated to be less than 0.lmWIA I. hTRODUCFIONSuperconducting magnets are operated by supplying the electric current through cufTent leads fiom the power supply at the room temperature. Usual cryogenic systems for superconducting magnets employ conventional copper current leads, which are made of copper material. Conventional current leads are cooled by cold helium gas and optimized to minimize the heat leak into the low temperature region with the consumption of cooling gas flow as small as possible. The usual design procedure requires iterative and complicated calculation to evaluate such operational characteristics as the heat le& as a function of the geometry of the conductor, the pressure drop of the cooling gas and the temperature rise time of the conductor during the thermal runaway[l],[2]. To simplify the design procedure, we developed a generalized design method. In this method, the characteristics of leads, such as the heat leak, the geometrical dimension of the conductor and the pressure drop of the cooling gas, were obtained in the generalized form and summarized in a design chart [3]. Sevea-al current leads were designed by the use of the design chart and exhibited good operational performance[4], [5]. Even in the case of an ideal heat exchange, optimum copper leads has a lower limit of the heat leak of -1 .O mW/A[ 11.Because of the generation of no Joule heating and very low thermal conductivity, high temperature superconducting (HTSC) material has a possibility of the application to current leads which reduce the lower limit of the heat leak of the Manuscript received October 17, 1994. This work was supported in part bv Inoue Foundation for Science. NOMENCLATURE C Specific heat of conductor (J w1 R I ) C Specific heat of helium gas (J k') d8 Hydraulic diameter i. e. d = 4sdf(m) f Cooling perimeter (m) F f m d z e d by current ( d A ) G m per unit area in cooling channel (kg m-2 8") Z Current (A) 1 Conductor length effective for heat exchange (m) m Mass flow rate of cooling gas @g i ' ) M m normalized by curren...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.