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激光打靶驱动惯性约束聚变的过程中会产生大量的带电粒子,如高能电子[1]、X射线[2]、带电离子[3],进而产生大量的强电磁脉冲[4]。脉冲信号的瞬态强度高达几百MV/m,频域分布在几百MHz到几个GHz[5-7]。电磁辐射特性与靶材和靶型有关,掺杂不同含量Ti的靶产生的脉冲强度不同[8],激光与不同靶型包括真空球腔靶、真空柱腔靶、平面靶、金球靶、网格靶、半黑腔靶、充气球腔靶、桶腔靶等作用产生的电磁波形也有很大差异,波形时间演变规律与激光能量有关[9]。文献[10]的研究结果表明黑腔靶的开口尺寸会影响电磁辐射的强度。距离靶室中心不同距离处的电磁辐射测量结果表明,靶室内的电磁波形极为复杂,应该是多个辐射与震荡过程的混合信号,靶室内外信号强度差异较大[11]。这些电磁脉冲信号对物理诊断和数据采集造成干扰,同时脉冲信号耦合进传输线后会对其他线缆产生串扰影响。探究激光打靶过程中串扰信号造成的影响和如何进行减小串扰信号,能够有效提高实验诊断结果的准确性。
电磁辐射环境下的线缆信号串扰现象普遍存在,如动车和地铁里的传感器连接的线缆放置在金属沟槽当中,沟槽的金属结构对线缆的分布参数产生影响,进而影响线缆的串扰情况[12-14];飞行器里的电子设备使用不同种类的线缆,会存在串扰[15-16];在实验室环境下,不同放置方式下不同种类线缆会产生串扰[17-18]。在强激光物理实验中,准确测量电磁辐射的分布有助于深刻理解激光与靶耦合的物理过程,但围绕靶室周围的各种诊断设备线缆必然受到强电磁脉冲的影响,造成信号串扰。因此,对强激光打靶过程中产生的电磁脉冲耦合线缆造成串扰的规律进行深入系统的探讨,揭示关键影响因素,设计合理的屏蔽,具有重要的理论与工程价值。本文通过传输线理论[19-20]建立串扰等效模型,并使用CST 2019电缆工作室建立平行线缆模型[21],馈入神光II升级靶场中一发实际测得的电磁脉冲信号,研究了不同线缆间距、线缆长度对串扰信号幅值的影响,并探讨了添加金属屏蔽层后对串扰的衰减机制。
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电信号在电缆中传输泄露电磁辐射,这个现象可以通过传输线原理来研究。由于同轴线缆芯线与屏蔽层之间有分布式电感、电容和电阻,每条电缆之间也有互电感和互电容,因此线缆信号耦合时会受到这些参数的影响,线缆的性质也会对串扰信号产生很大的影响。图1为两根平行线缆串扰的传输线模型,馈入信号的线缆是信号源线缆,受串扰信号影响的是接收线缆,其中L1、L2、C1、C2、R1、R2分别是单位长度信号源线缆和接收线缆的自电感、自电容和内阻,LM、CM是单位长度线缆之间的互电感和互电容。
两条平行线缆的传输线方程可以表示为:
$$ \frac{{\text{d}}}{{{\text{d}}x}}{\boldsymbol{V}}(x) = - \left( {{\boldsymbol{R}} + {\text{j}}\omega {\boldsymbol{L}}} \right){\boldsymbol{I}}(x) $$ (1) $$ \frac{{\text{d}}}{{{\text{d}}x}}{\boldsymbol{I}}(x) = - {\text{j}}\omega {\boldsymbol{CU}}(x) $$ (2) 式中,V(x)和I(x)可以表示为:
$$ {{\boldsymbol{V}}}(x) = \left[ {\begin{array}{*{20}{c}} {{{{\boldsymbol{V}}}_1}(x)} \\ {{{{\boldsymbol{V}}}_2}(x)} \end{array}} \right] $$ (3) $$ {{\boldsymbol{I}}}(x) = \left[ {\begin{array}{*{20}{c}} {{{{\boldsymbol{I}}}_1}(x)} \\ {{{{\boldsymbol{I}}}_2}(x)} \end{array}} \right] $$ (4) L、C、R分别是由线缆的分布式电感、电容、电阻确定的矩阵,表示为:
$$ {\boldsymbol{L}} = \left[ {\begin{array}{*{20}{c}} {{{\boldsymbol{L}}_1}}&{{{\boldsymbol{L}}_M}} \\ {{{\boldsymbol{L}}_M}}&{{{\boldsymbol{L}}_2}} \end{array}} \right] $$ (5) $$ {\boldsymbol{R}} = \left[ {\begin{array}{*{20}{c}} {{{\boldsymbol{R}}_1}}&{\boldsymbol{0}} \\ {\boldsymbol{0}}&{{{\boldsymbol{R}}_2}} \end{array}} \right] $$ (6) $$ {\boldsymbol{C}} = \left[ {\begin{array}{*{20}{c}} {{{\boldsymbol{C}}_1} + {{\boldsymbol{C}}_M}}&{ - {{\boldsymbol{C}}_M}} \\ { - {{\boldsymbol{C}}_M}}&{{{\boldsymbol{C}}_2} + {{\boldsymbol{C}}_M}} \end{array}} \right] $$ (7) 如果已知信号源线缆和接收线缆的分布式参数,那么可以通过传输线方程来计算串扰信号的大小。计算机仿真技术软件CST电缆工作室是通过计算电缆之间的各种电参数,并基于传输线理论来进行建模仿真。
Simulation of Cable Crosstalk Generated by Electromagnetic Induced by High-Power Laser Shooting Targets
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摘要: 以在神光II升级靶场使用九路激光打靶实测的电磁脉冲信号为输入源,建立平行线缆模型,研究电磁脉冲耦合电缆产生的串扰现象,揭示不同线缆间距、线缆长度受串扰的规律,以及线缆长度对串扰信号频率的影响机制。同时探讨铜箔屏蔽处理后对串扰信号的衰减。结果表明,增大平行线缆的间距有利于抑制串扰,增大线缆长度抗干扰能力减弱,谐振频率降低;屏蔽处理能有效抑制信号串扰,为高功率激光装置安全精确的开展各类物理诊断提供实验与理论支持。Abstract: In this study, the electromagnetic pulse (EMP) signals were measured at the Shenguang II Upgrade Range and used as the input source to establish a parallel cable model to reveal the crosstalk phenomenon generated by the EMP coupled cables. The law of crosstalk induced by varying cable distances and cable lengths were investigated, and the influence of cable length on the frequency of crosstalk signals was also unraveled. Meanwhile, the attenuation of the cable to the crosstalk signal after the copper foil shielding is discussed. The results indicate that increasing the distance between parallel cables is beneficial for suppression of crosstalk, while increasing the length of parallel cables reduce the anti-interference ability and lower resonance frequency. Therefore, proper shielding can effectively suppress signal crosstalk and provide experimental and theoretical support for implementing various physical diagnostics safely and accurately.
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Key words:
- cable crosstalk /
- electromagnetic pulse /
- laser /
- shielding
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