J." Yamamoto

K. Ishibashi

K. Maehata

M. Takeo

T. "Nishioka

T. Mito

National Institute for Fusion Science (NIFS-Repository)

§28. Design Chart of High Temperature Super-conducting Current Leads Cooled with Laminar Flow Gas Nishioka, T., Maehata, K., Ishibashi, K., Takeo, M. (Kyushu Univ.) Mito, T., Yamamoto, J. General design equationsO derived from one di-mensional energy balance equations of current leads made of high temperature superconducting (HTSC) material for the cooling by the laminar flow gas were solved to evaluate generalized char-acteristics such as the heat flow from the cold ends Oc [mW/A], the geometrical dimension of the con-ductor D [ A/m] and the pressure drop of the cool-ing gas ~P/C1[PaAsm2fkg]. A general cooling pa-rameter Ytam was introduced to evaluate generalized characteristics for the laminar flow cooling. The parameter Ylam indicates the relationship between the geometrical dimension of the conductor and cooling channel of the leads. Gas-cooled HTSC leads are assumed to be operated in the temperature range from 4.2K to 77K under the condition of the self-sustained cooling. The use of larger geometri-cal dimension allows further reduction of the heat flow from the cold ends, while such geometrical dimension accelerates the temperature rise of the conductor in the case of an accidental thermal run-away. Therefore, the generalized temperature rise time T in the case of stoppage of the cooling gas was obtained by solving the time dependent heat balance equation with the consideration of the quench propagation. In this work, the maximum permissible temperature of the conductor is as-sumed to be 300K to prevent leads from any dam-age. Generalized characteristics of HTSC leads · cooled with laminar flow gas were arranged in Figure 1 by means of the generalized temperature rise time T. The effect of the gas cooling appears explicitly in the range of Ytam > l.Ox1Q-7 m2JA2. Symbols plotted in Figure 1 shows generalized characteris-tics of conduction-cooled HTSC leads. As an ex-ample, values of Q: and I is taken to be 2.lx1Q-4 WI A and 0.20m, respectively for both HTSC leads. Figure 1 indicates values of Ylam and T are l.OxlQ-8 m2fA2, 2.0x1Q4 sfm2 for gas-cooled HTSC leads, whereas value of T for conduction cooled leads is 4.0xl02 sfm2. Temperature rise time of gas-cooled and conduction-cooled HTSC leads is estimated to be 800 s and 16 s, respec-tively. Values of T indicate the difference of the safety sense between gas-cooled HTSC leads and conduction-cooled HTSC leads. Various high performance gas-cooled HTSC leads can be designed simply by the use of the de-sign chart in consideration of the thermal runaway. Nomenclature ';;? ........ ~ '<t b .---.......... cl d Hydraulic diameter [m] I Current [A] l Conductor length [ m] m Mass flow rate of helium gas [kgs-1] ll.P Pressure drop of cooling gas [Pa] Qc Heat flow from cold end normalized by the current [W/A] r Ratio of length along channel to l s Cross-sectional area of conductor [ m2] s g Cross-sectional area of cooling channel [ m2] ts temperature rise time [ s] Ytam=S Sgkf2, S=s/1, Sg=sgll, D=l/S G=mls g' Ct=r S G !d2, T=tslz2 --- T=5.0X103 s/m2 o T=1.0X102 s/m2 -- - T=1 .0X 104 s/m2 • T=4.0X102 s/m2 - - - T=2.0X 104 s/m2 6 T=2.0X103 s/m2 ----- T=4.0X104 s/m2 .& T=5.0X103 s/m2 104 c; 103 ~ ,_....,'-.. E N 102 ........ ~ <( <( D ------------------------('() ro 101 0 e:. .---u .... 0 10° ........ a.. <1 Fig.l. Design chart of HTSC leads with laminar flow gas Reference 1) Nishioka, T. et al. Advances in Superconductivity VII (Proceedings of the ISS'94) vol. 2, p. 1231. 33 

Design Chart of High Temperature Superconducting Current Leads Cooled with Laminar Flow Gas

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