A. Iwamoto

A. Kimura

J. Yamamoto

N. Kimura

S.W. Kim

T. Mito

T. Shintomi

Y. Makida

National Institute for Fusion Science (NIFS-Repository)

§24. Experimental Studies on Stability and Current Distribution of Rutherford Cables Kin1,S.W., Shintomi,T., Kitnura,N., Makida,Y. (National Laboratory for High Energy Physics) Mito,T., Iwamoto,A.,Yatnan1oto,J. Kin1ura,A.(The Graduate University for Advanced Studies) Superconducting cables for patticle accelerator n1agnets are n1ulti-stranded to increase cmTent carrying capacity. However, the cunent canying capacity of such cables is less than the sum of the cunent capacities of the individual strands in the cable. It is not possible in practice to obtain the cunent capacity and stability expected fr01n calculations due to lack of uniformity of cunent distribution in the cable. Even if the currents are evenly distlibuted in the steady state, there can be cunent re-distribution or conu11utation in transient state, and this makes the cable unstable. This con1mutation can introduce a fast quench to the whole cable. 1l.2l. 3l To obtain the effect of current distribution, we have 1neasured the MQE (n1ini1nmn quench energy) and normal zone propagation behaviors of two types of Rutherford cables with and without CuMn batTier around the bundle of filatnents, in the presence of various transpo11 currents, n1agnetic fields and heating pulse widths. The only one difference between the two cables is that the cable with banier has bigger interstrand contact resistance. The cables were heated by spot heaters with various energy, and the MQE' s were obtained. Normal zone propagation and cmTent shming phenomena were detected by pairs of voltage taps soldered to alte1nate strands on both sides of the cables. 2).3) Fig. 1 shows the MQE vs. heating pulse width. In this figure, pre-heat data tnean the data taken after heating with energy slightly less than MQE, and reset means no pre-heat. Fig. 2 shows voltages n1easured at the taps on cable with higher contact resistance. 2).3) In this experin1ents, we could see that there is cmTent re-distlibution even in the cable with low contact resistance and that the pre-heating makes the MQE higher. Also we found that the cable with higher contact resistance is tnore stable though there is a large current re-distlibution in the heater strand as shown in Fig. 2. The cable with higher contact resistance was always n1ore stable if the transport current is low or the heating pulse is short. :~ ) These results suggest that the normal zone propagation is controlled by heat transfer between strands when the transport cun·ent is low. It is well known the normal zone propagation for high transpot1 cunent is electromagnetic phenomenon. To verify this suggestion, we need more expe1iments including measuren1ent of MQE and normal zone propagation in the region of high current and shot1er heating pulse. 16 ~-----------------------------14 12 ..., ..§.. 10 w 0 :E 0.1 --o-WitiJOut barrier(rcsct) -+--Without barrier(pre-heat) -0-With barrier( reset) ---With barrier(pre-heat) 10 Pulse width [mS] (Log scale) 100 Fig. I MQE's of two kinds of cables vs. heating pulse width 16 14 12 > 10 Heater pulse I -------, ..§.. 8 Q) C'l ~ 6 0 > 4 2 0 -2 ~~+-~+-+-~~~~+-~-~~~'~ 0 5 10 15 20 25 30 35 40 Time [mS] Fig. 2. Voltage measured by taps on strands References 1) A. Kimura, et al., Stabilities of the Rutherford Cables with Cu and CuMn Bartier, IEEE Trans. on Applied Superconductivity, 2( 1995)2. 2) S. W. Kim, et al., Studies on stabilities of superconducting Rutherford Cables, ICMC ( 1995). 3) S. W. Kitn, et. al, Expetimental studies on stabilities of Rutherford Cables for supercon-ducting accelerator n1agnets, MT-14(1995). 29 

Experimental Studies on Stability and Current Distribution of Rutherford Cables

Experimental Studies on Stability and Current Distribution of Rutherford Cables

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