Performance of MgB2 Superconductor Developed for High-Efficiency Klystron Applications
Summary (2 min read)
I. INTRODUCTION
- Magnetic resonance imaging (MRI) using MgB 2 wires 1.6 km in length made by the ex situ method has already been implemented as the first practical use of MgB 2 [2] .
- To achieve high efficiency magnets for klystrons (klystron magnets), the authors developed an MgB 2 wire and a magnet that can be operated at high temperatures and have low power consumption.
- These data can contribute to further research and practical applications of MgB 2 wires and magnets.
A. 8-km Long MgB 2 Wire
- The MgB 2 wire for the klystron magnet, with a unit length of 8 km, was made by the in situ method as follows.
- The sintering condition of this wire was 600°C for 6 h.
B. Measurement of I c and Its Deviation in Short Sample Wires
- The I c values were measured by the typical four-probe method.
- The length of all short sample wires was 35 mm; the temperature of the wires was controlled using helium gas cooling and a heater.
- The criterion of the electric field was 1 μV/cm, and the distance between voltage taps was 5 mm.
- I c values obtained from these three samples show the long-range homogeneity.
- The number of samples was twenty-one, and they were sampled from near the D-end.
C. Homogeneity Evaluation of the MgB 2 Wire in a Magnet
- Unlike in high-temperature coated conductors, the I c values of the MgB 2 wire cannot be measured along the wire's longitudinal direction with liquid nitrogen bath cooling.
- Instead, the authors can evaluate the homogeneity of the wire by making a magnet and measuring the current sharing temperature T cs of the magnet.
- Here, the coil winding was conductioncooled by a cold head and the temperature distribution in the coil winding was estimated to be smaller than 1 K.
- If the measured values agree with the estimated ones, it means that almost all the wires wound as a magnet have the same I c -B-T properties.
- Main specifications of the magnet are as follows.
C. I c Homogeneity of the MgB 2 Wire Evaluated in a Magnet
- According to the design of the klystron magnet using Wire-C and Wire-D, the rated operational current is 57.1 A, and the maximum magnetic field of the coil winding is 1.06 T [11] .
- Fig. 4 shows a comparison between the coil load line of the magnet and the I c -B-T property obtained from a short sample wire at the C-end.
- The authors can also estimate the T cs values at other operating currents using the same method.
- This estimation was confirmed by additional measurements as follows.
- As shown in Fig. 6 , 36.0 K is the threshold temperature for a measurable non-zero resistivity, and this value agrees well with the expected value from the fitting function shown in Fig. 5 .
D. Next Steps
- The I c variation of the MgB 2 wire was small enough, and the magnet performance represented by T cs was nearly equal to the estimated value.
- The ideal process for making MgB 2 magnets is said to be the React&Wind method, so the authors should develop MgB 2 wires which can be used for the React&Wind method without I c degradation.
- The C-doped 1.5 mm wire was made by the in situ method and reported in their past study [4] .
- The wire for klystron magnets has higher J e compared to other typical wires in 6.5 T or lower magnetic field.
IV. SUMMARY
- The results of evaluation of the homogeneity is summarized as the following four points:.
- 3) The T cs values measured for the klystron magnet agreed well with the estimated values from I c -B-T properties of the short sample wires.
- 4) It can be said that the performance of the 8-km long wire was uniform enough to make MgB 2 coils and magnets.
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Citations
8 citations
Cites background from "Performance of MgB2 Superconductor ..."
...However, to save energy as mentioned above, decreasing the current is effective, so the MgB2 conductor for the magnet has been developed [5]....
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6 citations
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Cites background from "Performance of MgB2 Superconductor ..."
...4 shows superconductor performance of the MgB2 conductor [7]....
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References
31 citations
"Performance of MgB2 Superconductor ..." refers background in this paper
...1: 2 without a carbon dopant, because at high temperatures and in low magnetic fields a pure MgB2 wire has higher Jc than a carbon-doped MgB2 wire [12]....
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22 citations
"Performance of MgB2 Superconductor ..." refers background or methods in this paper
...A coil made with a 300-m long wire [4] and a coil with a 1....
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...[4] and it has the highest Je between 6 T to 7 T....
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...5 mm wire was made by the in situ method and reported in our past study [4]....
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13 citations
"Performance of MgB2 Superconductor ..." refers background or methods in this paper
...7-km long MgB2 wire was wound as a coil and the good homogeneity of this wire was shown [5]....
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...7-km long wire for MRI use [5] were successfully implemented....
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9 citations
Additional excerpts
...[6] K. Konstantopoulou, J. Hurte, P. W. Retz, and A. Ballarino, “Design optimization and evaluation of the 3 kA MgB2 cable at 4.3 K for the superconducting link project at CERN,” Supercond....
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...The use of MgB2 is not limited to magnets; MgB2 wires have been used as power cables in superconducting (SC) links at CERN [6] and in the Best Paths project [7]....
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...The use of MgB2 is not limited to magnets; MgB2 wires have been used as power cables in superconducting (SC) links at CERN [6] and in the Best Paths...
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...A. Yamamoto is with the High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan, and is also with European Organization for Nuclear Research (CERN), Geneva 1211, Switzerland....
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8 citations
"Performance of MgB2 Superconductor ..." refers background or methods in this paper
...Details of these specifications are also written in reference [11]....
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...coils) and to make the current leads of the magnet finer [11]....
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...According to the results of the quench tests, this temperature margin may be reduced [11]....
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...The method of measuring Tcs is written in the reference [11] and can be summarized as follows....
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