Research to built a compact system to shape irradiation field for the particle cancer therapy

为了建立一个紧凑的粒子癌症治疗照射系统，我们制作了一个磁体，在垂直于光束轴的平面上扫描光束。磁铁由两组空芯线圈组成。我们使用了Bi2223材料的高温超导线，它在工作温度上有很大的余量。在设计中，对磁场、冷却系统和支撑架对电磁力的影响进行了数值分析。通过单级GM冷却器的传导冷却，线圈在10小时内显示出超导性。在20K时测得线圈临界电流大于250A，符合预期。在绕组过程中未观察到损坏。沿着每个线圈的中心线测量磁场。结果与数值计算结果吻合较好。交流电源由逆变器、感应电动机和发电机组成。线圈与冷凝器串联励磁。在10、15和20 Hz下测量线圈的交流功率损耗。每周期的功率损耗与频率无关。这表明损耗是高温超导体所特有的滞回损耗。损耗显示2.4^< >功率依赖于激励电流。这种现象与报道的低磁场电缆相同。关于高磁场下交流损耗的研究报道很少。目前的结果为未来在癌症治疗系统、加速器等方面的应用提供了宝贵的信息。

In order to build a compact irradiation system for the particle cancer therapy, we fabricated a magnet to scan the beam in a plane perpendicular to the beam axis. The magnet consists of two sets of air core coils. We used the high temperature superconducting wire of the material Bi2223 which has a large margin in operating temperature. In the design, numerical analyses were performed on the magnetic fields, the cooling system and supporting frame against the electromagnetic force. Coils showed superconductivity in10 hours by conduction cooling with a single stage GM cooler. Critical currents of coils were measured to be higher than 250A at 20K as expected. No damages were observed during winding. Magnetic field was measured along the center line of each coil. The results agreed very well with the numerical calculations. An alternating current (AC) power supply was constructed with an inverter, an induction motor and a generator. Coils were excited in series with condensers. The AC power loss of coils was measured at 10, 15 and 20 Hz. The power loss per cycle is independent of the frequency. This shows the loss is the hysteretic one which is characteristic to high temperature superconductors. The loss shows 2.4^<th> power dependence on exciting currents. This phenomenon is same as that reported for low magnetic field cables. There have been few reports on the AC loss studies at high magnetic fields. Present results give the invaluable information towards future applications in cancer therapy systems, accelerators, etc.