强流质子直线加速器低能束流传输线束流脉冲化技术研究

Research on Beam Pulsing Technology of Low Energy Beam Transport Line for Proton Linear Accelerator

  • 摘要: 束流脉冲化技术作为加速器物理领域的核心调控手段,通过优化时域束流结构可显著提升束流品质,在实现时间分辨测量、抑制空间电荷效应及增强加速器系统灵活性等方面具有关键作用。以中国原子能科学研究院强流质子直线加速器的低能束流传输线为研究对象,系统分析了其核心组件的束流动力学特性。基于FPGA的时序控制系统,构建了包含束流切割器与聚束器的协同工作架构,并针对窄脉冲(100 ns)与微脉冲(10 ns)两种工作模式开展专项设计。通过双电极静电偏转切割器的创新设计实现了100 ns窄脉冲模式输出;采用LC分布式聚束器与束流切割器的联合调控方案,最终获得脉宽3.99 ns微脉冲模式。

     

    Abstract: Beam pulsing technology serves as a critical methodology in modern accelerator systems, offering substantial improvements in beam quality enhancement, time-resolved measurement capabilities, space charge effect mitigation, and operational flexibility optimization. In this paper, the low energy beam transport (LEBT) line of the proton linear accelerator at the China Institute of Atomic Energy was taken as the research object, and the beam dynamics characteristics of its core components were systematically analyzed. In addition, in order to meet the injection requirements of the experimental terminal and the annular accelerator, the beam needs to be cut into different time structures. Based on the FPGA-based timing control system, a collaborative working architecture including a chopper and a buncher was constructed, and special designs were carried out for two working modes: the narrow pulse (100 ns) mode and the micro-pulse (10 ns) mode. The theoretical design, simulation calculation, and mechanical structure design of chopper and buncher were carried out sequentially. Dual-deflection electrode was employed by the chopper, with a working frequency of 1 MHz and a chopping voltage of 6 kV. The deflection electric field intensity was enhanced by means of inclined plates. The distance between the plates was maintained at 1.2 times the beam envelope, and the plate width was set to 1.5 times the longitudinal envelope of the beam. The minimization of capacitive load was achieved by tapering the electrode width, while the uniformity of the field intensity was improved with the inclined structure. The buncher adopted a double-drift gap structure with an external inductance coil, working at a frequency 3 times that of the chopper and with a bunching voltage of 12 kV. Due to the low working frequency and the operational constraints of electronic components, the resonant cavity structure and the AC power supply are not suitable for the generation of bunching voltage. The LC resonant circuit of buncher was employed by the matching inductance coil outside the bunching cavity, so that the buncher is enabled to work at a lower operating frequency (3 MHz) with a smaller volume structure. The entire system was controlled by the FPGA, which could avoid phase slippage caused by asynchronous triggering, guaranteeing the stability and reliability of the operation of the whole system and ensuring the accuracy of the coordinated work of each component. In this paper, the design process of the LEBT beam pulsing technology was systematically expounded. The output of the 100 ns narrow pulse mode is achieved through the innovative design of a dual-electrode electrostatic deflection chopper. An LC-distributed buncher has been developed to operate in conjunction with the chopper to achieve a 3.99 ns micro-pulse mode operation.

     

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