Design of Lightweight Superconducting Magnets for a Rotating Gantry With Active Shielding

In order to reduce the weight of superconducting magnets used in a rotating gantry for heavy particle radiotherapy, the design study of a cosine-theta superconducting magnet with active shielding was conducted. The superconducting magnet with active shielding was composed of a dipole coil and an active shield coil. The cross-section of each coil was designed, based on a cosine-theta current distribution made by the arrangement of a superconducting wire with NbTi filaments. The result of the design study indicated that the designed coil cross-sections can meet the requirements regarding the magnetic field distribution and the load factor for the magnet operation. Additionally, the weight of the superconducting magnet with active shielding was evaluated while comparing that of the superconducting magnet with an iron yoke. As a result, the superconducting magnet with the active shielding has a possibility to reduce the weight significantly

Residual Strain Dependence on Matrix Structure in RHQ-Nb3Al Wires by Neutron Diffraction Measurement

We prepared three types of non-Cu RHQ-Nb3Al wire samples with different matrix structures: an all-Ta matrix,a composite matrix of Nb and Ta with a Ta inter filament, and an all-Nb matrix. Neutron diffraction patterns of the wire samples were measured at room temperature in J-PARC "TAKUMI". To obtain residual strains of materials, we estimated lattice constant a by multi-peak analysis in the wire. Powder sample of each wire was measured, where the powder was considered to be strain-free. The grain size of all the powder samples was below 0.02 mm. For wire sample with the all-Nb matrix, we also obtained lattice spacing d by a single-peak analysis. Residual strains of Nb3Al filament were estimated from the two analysis results and were compared. Result, residual strains obtained from the multi-peak analysis showed a good accuracy with small standard deviation. The multi-peak analysis results for the residual strains of Nb3Al filament in the three samples were all tensile residual strain in the axial direction, they are 0.12%, 0.12%, and 0.05% for the all-Ta matrix, the composite matrix, and the all-Nb matrix, respectively. Difference in the residual strain of Nb3Al filament between the composite and all-Nb matrix samples indicates that type of inter-filament materials show a great effect on the residual strain. In this paper, we report the method of measurement, method of analysis, and results for residual strain in the tree types of non-Cu RHO-Nb3Al wires.Comment: 7 pages, 8 figure

Development of Radiation-Tolerant HTS Magnet for Muon Production Solenoid

Superconducting magnets are widely used in accelerator science applications. Muon production solenoids are applications that have recently attracted considerable public attention, after the approval of muon-related physics projects such as coherent muon to electron transition or muon-to-electron-conversion experiments. Based on its characteristics, muon production solenoids tend to be subjected to high radiation exposure, which results in a high heat load being applied to the solenoid magnet, thus limiting the superconducting magnet operation, especially for low-temperature superconductors such as niobium titanium alloy. However, the use of high-temperature superconductors may extend the operation capabilities owing to their functionality at higher temperatures. This study reviews the characteristics of high temperature superconductor magnets in high-radiation environments and their potential for application to muon production solenoids

Multi-Pole Components of Magnetic Field in Dipole Magnets Wound With High T-c Superconductor Tape and Feasibility of Their Accelerator Applications

Applications of high T-c superconductors to accelerator magnets are attractive from the viewpoint of cooling cost reduction and that of generating very high magnetic field at low temperature. However, in magnets using cosine-theta like coils, three-dimensional shape of coil ends and magnetic field quality might be concerns, because most of practical high T-c superconductors are with flat tape shape. We studied the field quality of dipole magnets wound with high T-c superconductor tapes. Case studies on magnetic field design were made for dipole magnets wound with coated conductors: we designed two magnets and calculated multi-pole components of the magnetic field to evaluate their field qualities. The torsion/bending tolerance of coated conductors was studied experimentally to clarify the feasibility of three-dimensional winding. The influence of the shielding current in high T-c superconductor tapes on field quality was discussed based on the numerical electromagnetic field analysis of superconductors

Influence of gamma ray irradiation on thermal conductivity of bismaleimide-triazine-based insulation tape at cryogenic temperature

近年、大強度加速器を利用した素粒子物理の研究実施を実現するため、MGy級の高放射線環境下で使用可能な超伝導磁石システムが要求されている。この要求に対し、我々は、機械的特性の面において100MGyの耐放射線性を有するエポキシ樹脂とビスマレイミドートリアジン(BT)樹脂を基材としたガラス繊維強化絶縁テープを開発している。一方、絶縁テープ材の熱伝導率は、磁石システム動作中の超伝導コイル温度に影響を及ぼす重要なパラメータの一つである。そこで本報では、熱伝導率測定装置を開発するとともに、ガンマ線照射後の絶縁テープの熱伝導率変化を調べた。その結果、5MGyまでの照射において顕著な熱伝導率の変化は見られず、BT樹脂を用いた絶縁テープが超伝導磁石システムに適用可能であると結論を得た