Plasma disruption is often an unavoidable aspect of tokamak operations. It may cause severe damage to in-vessel components such as the vacuum vessel conductors, the first wall and the divertor target plates. Two types...Plasma disruption is often an unavoidable aspect of tokamak operations. It may cause severe damage to in-vessel components such as the vacuum vessel conductors, the first wall and the divertor target plates. Two types of disruption, the hot-plasma vertical displacement event and the major disruption with a cold-plasma vertical displacement event, are simulated by the DINA code for HL-2M. The time evolutions of the plasma current, the halo current, the magnetic axis, the minor radius, the elongation as well as the electromagnetic force and eddy currents on the vacuum vessel during the thermal quench and the current quench are investigated. By comparing the electromagnetic forces before and after the disruption, we find that the disruption causes great damage to the vacuum vessel conductors. In addition, the hot-plasma vertical displacement event is more dangerous than the major disruption with the cold-plasma vertical displacement event.展开更多
针对多用户扩频水声通信中的强多址干扰导致解码性能不佳的问题,提出一种基于广义正弦调频(generalized sinusoidal frequency modulation,GSFM)信号的多用户M元扩频水声通信调制方案。GSFM信号可以通过改变参数和频率反射技术产生大量...针对多用户扩频水声通信中的强多址干扰导致解码性能不佳的问题,提出一种基于广义正弦调频(generalized sinusoidal frequency modulation,GSFM)信号的多用户M元扩频水声通信调制方案。GSFM信号可以通过改变参数和频率反射技术产生大量占据同一频带且彼此近似正交的波形,建立合适的优化模型可以从众多波形中优化得到所需数目的最佳波形构建正交波形集,解决M元码分多址(code division multiple access,CDMA)水声通信系统选码困难的问题。接收端采用复杂度较低的M元能量检测器(M-ary energy detector,MED)算法完成各用户的解码。仿真结果表明,该方案在保证较高频带利用率的同时可以较好地抑制多址干扰,验证了方案的有效性和鲁棒性。该方案为多用户扩频水声通信中的强多址干扰问题提供了有效解决方案,具有应用价值。展开更多
目的:对M序列编码激励提高磁声信号信噪比的处理方法进行研究,进一步解决目前磁声成像单脉冲激励方法信噪比低、磁声成像质量受到限制以及叠加平均改善磁声信号信噪比方法限制成像速率的问题。方法:通过仿真计算和磁声信号的实验测量,...目的:对M序列编码激励提高磁声信号信噪比的处理方法进行研究,进一步解决目前磁声成像单脉冲激励方法信噪比低、磁声成像质量受到限制以及叠加平均改善磁声信号信噪比方法限制成像速率的问题。方法:通过仿真计算和磁声信号的实验测量,对不同码长下M序列编码的磁声信号的信噪比、峰值旁瓣水平、采集处理时间进行研究,并采用单层石墨纸模型进行信号检测实验。结果:对于单层石墨纸实验模型,在未进行波形叠加平均条件下,相比于单脉冲激励方式,7、31和127 bit M序列编码处理方法可提高磁声信号信噪比19.4、29.6和40.4 d B;3种码长的M序列编码激励磁声信号平均距离旁瓣水平分别为14.1、10.0和7.6 d B,峰值距离旁瓣水平分别为26.3、24.3和21.3 d B;将信噪比提升40 d B,采用127 bit M序列编码激励,相比于单脉冲激励结合波形平均处理方法,其采集处理时间由53.1 s缩短为0.520 s。结论:M序列编码激励的磁声成像信号处理方法对于提高磁声信号信噪比、改善成像质量、提高整体成像速率具有重要意义。展开更多
基金Supported by the China ITER Plan Project Foundation under Grant Nos 2013GB113001 and 2014GB110004
文摘Plasma disruption is often an unavoidable aspect of tokamak operations. It may cause severe damage to in-vessel components such as the vacuum vessel conductors, the first wall and the divertor target plates. Two types of disruption, the hot-plasma vertical displacement event and the major disruption with a cold-plasma vertical displacement event, are simulated by the DINA code for HL-2M. The time evolutions of the plasma current, the halo current, the magnetic axis, the minor radius, the elongation as well as the electromagnetic force and eddy currents on the vacuum vessel during the thermal quench and the current quench are investigated. By comparing the electromagnetic forces before and after the disruption, we find that the disruption causes great damage to the vacuum vessel conductors. In addition, the hot-plasma vertical displacement event is more dangerous than the major disruption with the cold-plasma vertical displacement event.
文摘针对多用户扩频水声通信中的强多址干扰导致解码性能不佳的问题,提出一种基于广义正弦调频(generalized sinusoidal frequency modulation,GSFM)信号的多用户M元扩频水声通信调制方案。GSFM信号可以通过改变参数和频率反射技术产生大量占据同一频带且彼此近似正交的波形,建立合适的优化模型可以从众多波形中优化得到所需数目的最佳波形构建正交波形集,解决M元码分多址(code division multiple access,CDMA)水声通信系统选码困难的问题。接收端采用复杂度较低的M元能量检测器(M-ary energy detector,MED)算法完成各用户的解码。仿真结果表明,该方案在保证较高频带利用率的同时可以较好地抑制多址干扰,验证了方案的有效性和鲁棒性。该方案为多用户扩频水声通信中的强多址干扰问题提供了有效解决方案,具有应用价值。
文摘目的:对M序列编码激励提高磁声信号信噪比的处理方法进行研究,进一步解决目前磁声成像单脉冲激励方法信噪比低、磁声成像质量受到限制以及叠加平均改善磁声信号信噪比方法限制成像速率的问题。方法:通过仿真计算和磁声信号的实验测量,对不同码长下M序列编码的磁声信号的信噪比、峰值旁瓣水平、采集处理时间进行研究,并采用单层石墨纸模型进行信号检测实验。结果:对于单层石墨纸实验模型,在未进行波形叠加平均条件下,相比于单脉冲激励方式,7、31和127 bit M序列编码处理方法可提高磁声信号信噪比19.4、29.6和40.4 d B;3种码长的M序列编码激励磁声信号平均距离旁瓣水平分别为14.1、10.0和7.6 d B,峰值距离旁瓣水平分别为26.3、24.3和21.3 d B;将信噪比提升40 d B,采用127 bit M序列编码激励,相比于单脉冲激励结合波形平均处理方法,其采集处理时间由53.1 s缩短为0.520 s。结论:M序列编码激励的磁声成像信号处理方法对于提高磁声信号信噪比、改善成像质量、提高整体成像速率具有重要意义。
