强流质子加速器低能段束流损失探测方法可靠性改进的研究

The damage caused by lost beam is more significant for RF cavity and other key components in the low energy section of high intensity proton accelerator. The dose produced by the lost beam in the low energy section is lower than that in the high energy section, in addition, the shielding effect caused by the large accelerator structure will result in that the traditional ion chamber type beam loss monitor (BLM) cannot detect the effective signal near the accelerator. Limited by the bad radiation resistance, the scintillator type BLM is usually used as the relative measurement tool. However, we will use the scintillator type BLM as an absolute measurement tool considering the dose level in the low energy section of the high intensity proton accelerator. An analogous experiment using radioactive source will be carried out to verify our assumptions with the support of the fund. We also research the differential beam current type BLM based on the hardware platform to further improve the measurement reliability of beam loss in the low energy section. Through combining the two methods, the beam loss measurement reliability will be greatly improved.

在强流质子加速器低能段，束流损失对高频腔等关键设备伤害尤为严重。而在这个束流能量区间，质子束损失产生的剂量比高能束低，同时由于加速结构的“屏蔽效应”，使得传统的电离室型束损测量系统无法工作。闪烁体型探头限于它较差的抗辐照性能一般用作相对测量的工具，然而考虑到强流质子加速器低能段的剂量水平，我们将闪烁体型束损探头用作绝对测量。在基金支持下，我们要通过放射源模拟试验验证我们的设想。为了进一步提高束损测量可靠性，我们还研究基于硬件平台判断的束流流强测量系统的流强差来进行束损探测。通过这两种方法的研究，将极大提高强流质子加速器低能段束损探测的可靠性。

塑料闪烁体型探测器是一种有效的束损探测器件。由于其耐辐照性差，此类型探测器被视为束流损失相对测量器件。我们选用EJ-244M、BC-440M 、EJ-208、BC-412作为实验样品，经过γ射线、中子束的照射试验，得到了在γ射线累积剂量小于2000Gy，中子通量小于2.67 *10^14n/cm^2情况下，这四种塑料闪烁体发射谱、透射谱等性能变化均小于10%，其中EJ-244M、BC-440M的性能更加稳定。对强流质子加速器低能段（小于20MeV）正常运行时的剂量进行多种方法评估后，可以看到这几种塑料闪烁体在此区段均可长期可靠的使用，其探测信号可以参与机器保护。课题中研制的带聚乙烯慢化体结构的BF3气电离室探测器，在负氢15MeV区段，束损探测灵敏度高氩气电离室至少2个量级以上，但其响应速度及灵敏度需要更加均衡优化研究。通过大量数据的评价，我们得到了流强测量系统的测量精度。基于FPGA平台的差分流强束流损失判断系统，可以在束流损失超过10%的状况下“正确”保护加速器的安全，为加速器提供另一种束损保护方式。通过多种方式的组合，可以完善强流质子加速器低能段的保护功能，延长加速器的寿命。