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由于回旋加速器引出的束流能量为固定能量,治疗时为了实现能量自由选择,要求能量调制系统中的二极磁铁电源工作在有序触发模式,即针对病人病灶的不同深度采用不同能量的束流进行治疗;在加速器束流调试阶段,为了保证磁铁的励磁特性,电源需要工作于直流和周期脉冲模式。图1和图2所示为电源有序触发模式和周期脉冲模式的工作原理图。
在治疗前,技术人员会为每位患者制定治疗计划,用不同能量的束流照射病人癌细胞的不同层。物理人员再根据每一层的束流能量计算出治疗时电源需要输出的电流值,并将这些电流值作为给定电流提前下发至电源中进行保存,当电源接收到触发信号时,按照顺序依次输出这些电流值,每个电流值的保持时间由治疗计划决定。图1为电源工作于有序触发模式时的一个电流波形的例子,图中五个不同的电流值(I1 ~ I5)对应治疗需要的五种不同的束流能量,It为平顶电流值,该值一般为电源的额定输出电流值。电源工作时首先将电流由0升至It;当t1时刻收到第一个触发信号时,将电流调整至第一个电流值I1;t2时刻收到第二个触发信号时,将电流调整至第二个电流值I2;最后,在t6时刻收到第六个触发信号时,将电流降到0电流,结束治疗,此为一个完整的有序触发工作周期。
图2给出了周期脉冲模式的电流工作波形,其中Ic为平顶电流值,该值不大于电源的额定输出电流值,T为波形周期。当电源工作于周期脉冲模式时,电源输出连续的周期脉冲电流。
根据医用回旋加速器能量调制与束流输运系统二极磁铁的工作要求,提出了如表1所列的电源技术参数。为了保证输出电流精度,直流模式下,要求长期稳定度小于50×10–6,电流纹波小于0.001;有序触发和周期脉冲模式下,要求输出超调量小于100×10–6。
表 1 电源技术参数表
参数名称 参数规格 磁铁线圈电阻 202 mΩ 磁铁线圈电感 716 m 额定输出电流 500 A 长期稳定度 < 50×10–6 电流纹波 < 0.001 超调量 < 100×10–6
Design of Non-single Operation Mode Dipole Magnet Power Supply Controller for Medical Accelerator
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摘要: 近年来,离子治疗技术在国内外发展迅速。为满足加速器调试和不同治疗方案对医用回旋加速器装置的不同束流能量要求,二极磁铁电源要求工作在可相互切换的直流、有序触发和周期脉冲三种模式。使用中国科学院近代物理研究所自主研发的集成盒装式控制器,实现了对电源的控制和保护功能。为了适应调试和治疗两种不同场合的需求,控制器还支持本地和远程控制两种不同的网络协议,可通过触摸屏的控制按钮完成两者的切换。电源主回路和控制器设计并装配完成后,对各项指标进行了测试。测试结果表明,电源可正常工作在不同模式下,额定电流下长期稳定度达到了21×10–6,电流纹波小于万分之四,超出了设计指标。Abstract: In recent years, ion therapy technology has developed rapidly in China and abroad. To meet the demands of the accelerator commissioning and the energy requirements of the different treatment scheme for the accelerator facility, the power supplies of the dipole magnets in the energy selection and beam transport system are required to work in the modes of DC, in-order trigger and periodic pulse. Using the integrated box controller independently developed by the Institute of Modern Physics, Chinese Academy of Sciences, the control and protection function of the power supply are realized. In order to meet the requirements of commissioning and treatment working modes, the controller has been designed to support the local and remote control network protocols, between which the switch can be achieved through the button on the touch screen. The power supply specifications has been tested after the main circuit and controller were designed and assembled. The test results indicate that the power supply can work well under the different modes, the long-term stability of current rating reached 21 ppm, and the current ripple was less than 0.000 4, exceeding the design index.
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Key words:
- ion therapy /
- magnet power supply /
- power supply controller /
- non-single operation mode
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表 1 电源技术参数表
参数名称 参数规格 磁铁线圈电阻 202 mΩ 磁铁线圈电感 716 m 额定输出电流 500 A 长期稳定度 < 50×10–6 电流纹波 < 0.001 超调量 < 100×10–6 -
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