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  1. 020 学位論文
  2. 高エネルギー加速器科学研究科
  3. 12 加速器科学専攻

Field Quality Change of Superconducting Accelerator Magnets due to Re-magnetization of Superconductor

https://ir.soken.ac.jp/records/625
https://ir.soken.ac.jp/records/625
6c249c70-a076-48f0-80a9-5afcac09d88e
名前 / ファイル ライセンス アクション
甲800_要旨.pdf 要旨・審査要旨 / Abstract, Screening Result (297.8 kB)
甲800_本文.pdf 本文 (35.5 MB)
Item type 学位論文 / Thesis or Dissertation(1)
公開日 2010-02-22
タイトル
タイトル Field Quality Change of Superconducting Accelerator Magnets due to Re-magnetization of Superconductor
タイトル
タイトル Field Quality Change of Superconducting Accelerator Magnets due to Re-magnetization of Superconductor
言語 en
言語
言語 eng
資源タイプ
資源タイプ識別子 http://purl.org/coar/resource_type/c_46ec
資源タイプ thesis
著者名 杉田, 圭

× 杉田, 圭

杉田, 圭

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フリガナ スギタ, ケイ

× スギタ, ケイ

スギタ, ケイ

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著者 SUGITA, Kei

× SUGITA, Kei

en SUGITA, Kei

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学位授与機関
学位授与機関名 総合研究大学院大学
学位名
学位名 博士(理学)
学位記番号
内容記述タイプ Other
内容記述 総研大甲第800号
研究科
値 数物科学研究科
専攻
値 12 加速器科学専攻
学位授与年月日
学位授与年月日 2004-09-30
学位授与年度
値 2004
要旨
内容記述タイプ Other
内容記述 Superconducting accelerator magnets are fundamental components of high-energy particle accelerators. Very high field quality and stability of the magnets are required in order to operate the accelerator with minimizing beam instability and beam loss. Particularly, time-varying field quality during a period of the beam injection is an important subject to be understood. A possible reason of the time-varying magnetic field is the change of the superconductor magnetization due to local magnetic field change induced by redistribution of imbalance current in superconducting cables. In order to clarify and to evaluate the mechanism, experimental studies and their evaluations with computer simulations were performed.<br />   Magnetic field measurements of the superconducting quadrupole magnets (MQXAs) developed by KEK for the CERN/LHC insertion regions were carried out. The measurements at the beam injection current were performed by using a set of rotating harmonic coils after pre-excitations of the magnet. The periodic patterns of the magnetic field along the magnet axis, of which pattern length is equal to the cable twist pitch, was observed. The amplitude of the periodic pattern was decreased with time. The average field over the even number of the wave-length of the periodic pattern corresponding to the effective field quality, was also changed with time. It was thought that the decrease of amplitude is caused by equalization of imbalance currents in cables, and the change of average is caused by re-magnetization of superconducting filament. From the measurements of 18 magnets, it was clarified that the behaviors of the amplitude and the average indicate strong dependences on the pre-excitation.<br />   A change of superconductor magnetization due to external field change was experimentally evaluated. By using a vibration sample magnetometer (VSM), the magnetization of superconductor used in the LHC magnets was measured. The behavior of re-magnetization of filaments induced by the external magnetic field with arbitrary direction was clarified.<br />   In order to evaluate the mechanism of time-varying magnetic field, a simulation program was developed. At first, the numerical model of re-magnetization was developed. In this model, persistent current, which flowed in a superconductor filament, was assigned as “nested cosine theta current distribution” in coaxial shell as division of filament. Magnetization behavior calculated by cosine theta model indicated good agreement with results measured by VSM. As the next step, a numerical model of imbalance currents was developed. The imbalance currents were ascribed as zigzag currents given randomly. The amplitude of periodic pattern induced by the zigzag currents was evaluated by means of Monte Carlo simulation. To reproduce the measured periodic pattern amplitudes, current imbalance with a level of hundred amperes was required in calculation.<br />   A 3-dimensinal full coils model based on the LHC magnet was developed as extension of above programs. Imbalance currents in cables were assigned as zigzag current models on each cable position. Magnetic field in the magnet bore induced by the zigzag currents was computed, and a sinusoidal field pattern along the longitudinal axis was given. The local magnetic field at the strand in the coils was also calculated. Magnetization change of the superconductor filament in the coils, due to the local magnetic field change induced by zigzag current change, were computed by using the cosine theta model. Finally, the magnetic field in the bore induced by each magnetization of superconductor filaments in the coils was calculated. The simulation reproduced the magnetic field change in the magnet bore, by assuming the change of the zigzag currents which was needed to induce the periodic pattern consistent with measured results. It has been understood that magnetization change due to local magnetic field change induced by imbalance current redistribution causes the time-varying magnetic field during a period of beam injection in accelerator operation.<br />   In conclusion, the field measurement of the magnets showed the strong dependencies on periodic pattern amplitude and the average field to the pre-excitation history. The computation model for superconductor magnetization by cosine theta distribution was developed, and the calculation agreed with the VSM measurements. The simulation for the imbalance currents in the cables has shown the periodic pattern similar to the hat observed in the measurement. It has been understood that the simulation combining the magnetization and the imbalance currents has shown that the magnetization change due to the local field change induced by the decay of the imbalance currents are in good agreement with that observed in the measurement.
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