中国散裂中子源反角白光中子源T0信号的精确扇出方法

The Accuracy Fan-out of T0 for Back-n White Neutron Facility at CSNS

反角白光中子源位于中国散裂中子源(CSNS),是以不同中子能量下的核数据测量为目标的大型物理实验装置,中子的能量是通过中子飞行时间(TOF)来获取的。实验中,将质子束流轰击钨靶的时刻作为TOF的起始时刻(T0),相应的电子学信号被用于触发整个电子学系统的运行。为了保证TOF测量的准确性和电子学系统各通道采集的同步性,需要对T0信号进行精确扇出。提出应用于反角白光中子源的T0信号两级精确扇出方法,将来自CSNS质子加速器的T0信号由T0扇出模块通过长电缆扇出到两个地下实验厅,扇出模块利用信号预加重技术来改善T0信号经过超过100 m长电缆的信号传输质量,从而使得扇出后的T0信号也拥有极快的信号上升前沿,以保证时间定时的精确性。电子学系统则对T0信号进行数字化编码,并利用PXIe读出机箱的高性能背板资源,从而完成T0信号的精准的全局同步扇出能力。实验结果表明,该扇出模块分发的T0信号的前沿抖动达到25 ps,机箱多通道的精度达到45 ps,TOF测量精度可达到248 ps,满足反角白光中子源对TOF测量的精度需求。

The Back-n White Neutron Source is located in China Spallation Neutron Source(CSNS).It aims to measure nuclear data under different neutron energies.The neutron’s energy is obtained by the Time Of Flight(TOF)of neutron.In experiment,the time when proton bunches hit the thick tungsten target is considered as the start point of TOF(T0),and the corresponding electronic signal is used to trigger the whole electronic system.The accuracy fan-out of T0 signal will have a significant influence on the accuracy of the TOF measurement and the synchronization of each channel of electronic system.A two-stage accuracy fan-out method of back-n T0 signal is proposed.The T0 signal from CSNS proton accelerator is fanned out by T0 fan-out module to two underground experiment station through long cable.The fan-out module uses signal pre-emphasis technology to improve the signal transmission quality of T0 signal through more than 100 m long cable and guarantee that the T0 signal has a very fast signal leading edge,so as to ensure the accuracy of time timing.The electronic system takes the advantage of the high-performance backplane resources of the chassis by PXIe,so as to realize the global precision and synchronous fan-out of T0 signal.The experimental results show that the leading edge jitter of the T0 signal distributed by the fan-out module reaches 25 ps,the multi-channel accuracy of the chassis reaches 45 ps,and the measurement accuracy of the TOF can reach 248 ps,which meets the requirements of the measurement accuracy of the neutron time of flight of the white light neutron source.