Comparison of pulse-modulated and continuous operation modes of a radio-frequency inductive ion source

The paper describes an experimental study of the characteristics of a pulse-modulated radiofrequency(RF)discharge sustained at low pressures,typical of the operating modes of RF gridded ion sources.The motivation for the study is the question of whether the RF pulsemodulated mode can increase the efficiency of the ion source.The ion current values extracted from an RF inductive ion source operating in continuous and pulse-modulated modes were compared.The experimental data were also compared with the parameter calculations based on a0D numerical model of the discharge.The measurements showed that the pulse-modulated operation mode of the RF ion source had a noticeable advantage when the power of the RF generator was 140 W or lower.However,as the generator power increased,the advantage was lost because the pulse-modulated operation mode,having a higher RF power instant value,entered the region of existence sooner than the continuous mode,where the ion production cost begins to grow with RF power.

Temporal evolution of atmospheric cascade glow discharge with pulsed discharge and radio frequency discharge

Atmospheric cascade discharges with pulsed discharge and radio frequency(RF)discharge were experimentally investigated by the temporal evolution of discharge spatial profile and intensity.The indium tin oxide(ITO)coated glass was employed as the transparent electrode to capture the discharge distribution above the electrode surface.It is demonstrated that in the pulsed discharge with dielectric barrier,the first discharge at the rising edge of pulse voltage is uniformly ignited and then forms an expanding plasma ring on the ITO electrode surface,which shrinks to the same diameter as that of bare stainless steel electrode with the generation of second discharge at the falling edge of pulse voltage.The discharge profiles along the electrode surface and discharge gap of the successive RF discharge are dependent on the intensity and spatial distribution of residual plasma species generated by the pulsed discharge,which is determined by the time interval between the pulsed discharge and RF discharge.It is demonstrated that the residual plasma species before the RF discharge ignition help to achieve the stable operation of RF discharge with elevated intensity.

Modeling of the nanoparticle coagulation in pulsed radio-frequency capacitively coupled C_2H_2 discharges

The role of pulse parameters on nanoparticle property is investigated self-consistently based on a couple of fluid model and aerosol dynamics model in a capacitively coupled parallel-plate acetylene（C2H2） discharge. In this model, the mass continuity equation, momentum balance equation, and energy balance equation for neutral gas are taken into account.Thus, the thermophoretic force arises when a gas temperature gradient exists. The typical results of this model are positive and negative ion densities, electron impact collisions rates, nanoparticle density, and charge distributions. The simulation is performed for duty ratio 0.4/0.7/1.0, as well as pulse modulation frequency from 40 kHz to 2.7 MHz for pure C2H2 discharges at a pressure of 500 mTorr. We find that the pulse parameters, especially the duty ratio, have a great affect on the dissociative attachment coefficient and the negative density. More importantly, by decreasing the duty ratio, nanoparticles start to diffuse to the wall. Under the action of gas flow, nanoparticle density peak is created in front of the pulse electrode,where the gas temperature is smaller.

Ignition dynamics of radio frequency discharge in atmospheric pressure cascade glow discharge

A cascade glow discharge in atmospheric helium was excited by a microsecond voltage pulse and a pulse-modulated radio frequency(RF) voltage, in which the discharge ignition dynamics of the RF discharge burst was investigated experimentally. The spatio-temporal evolution of the discharge, the ignition time and optical emission intensities of plasma species of the RF discharge burst were investigated under different time intervals between the pulsed voltage and RF voltage in the experiment. The results show that by increasing the time interval between the pulsed discharge and RF discharge burst from 5 μs to 20 μs, the ignition time of the RF discharge burst is increased from 1.6 μs to 2.0 μs, and the discharge spatial profile of RF discharge in the ignition phase changes from a double-hump shape to a bell-shape. The light emission intensity at 706 nm and 777 nm at different time intervals indicates that the RF discharge burst ignition of the depends on the number of residual plasma species generated in the pulsed discharges.

Compressing ultrafast electron pulse by radio frequency cavity

An ultrafast electron diffraction technique with both high temporal and spatial resolution has been shown to be a powerful tool to observe the material transient structural change on an atomic scale.The space charge forces in a multi-electron bunch will greatly broaden the electron pulse width,and therefore limit the temporal resolution of the high brightness electron pulse.Here in this work,we design an ultrafast electron diffraction system,and utilize a radio frequency cavity to realize the ultrafast electron pulse compression.We experimentally demonstrate that the stretched electron pulse width of14.98 ps with an electron energy of 40 keV and the electron number of 1.0 ×10;can be maximally compressed to about0.61 ps for single-pulse measurement and 2.48 ps for multi-pulse measurement by using a 3.2-GHz radiofrequency cavity.We also theoretically and experimentally analyze the parameters influencing the electron pulse compression efficiency for single-and multi-pulse measurements by considering radiofrequency field time jitter,electron pulse time jitter and their relative time jitter.We suggest that increasing the electron energy or shortening the distance between the compression cavity and the streak cavity can further improve the electron pulse compression efficiency.These experimental and theoretical results are very helpful for designing the ultrafast electron diffraction experiment equipment and compressing the ultrafast electron pulse width in a future study.

Effect of Duty Cycle on the Characteristics of Pulse-Modulhted Radio-Frequency Atmospheric Pressure Dielectric Barrier Discharge

Using a one-dimensional fluid model, the pulse-modulated radio-frequency dielectric barrier discharge in atmospheric helium is described. The influences of the pulse duty cycle on the discharge characteristics are studied. The numerical results show that the dependence of discharge characteristics on the duty cycle is sensitive in the region of around 40% duty cycle under the given simulation parameters. In the case of a larger duty cycle, the plasma density is higher, the discharge becomes more intense, but the power consumption is higher. When the duty cycle is lower, one can get a weaker discharge, lower plasma density and higher electron temperature in the bulk plasma. In practical applications, in order to get a higher plasma density and a lower power consumption, it is more important to choose a suitable duty cycle to modulate the RF power supply.

Radio-frequency compressed electron pulse-width characterization by cross-correlation between electron bunches and laser-induced plasma

A method is proposed to determine the temporal width of high-brightness radio-frequency compressed electron pulses based on cross-correlation technique involving electron bunches and laser-induced plasma. The temporal evolution of 2-dimensional transverse profile of ultrafast electron bunches repelled by the formed transient electric field of laser-induced plasma on a silver needle is investigated, and the pulse-width can be obtained by analyzing these time-dependent images.This approach can characterize radio-frequency compressed ultrafast electron bunches with picosecond or sub-picosecond timescale and up to 105 electron numbers.

The characteristics of negative corona discharge and radio interference at different altitudes based on coaxial wire-cylinder gap

The corona discharge from transmission lines in high-altitude areas is more severe than at lower altitudes. The radio interference caused thereby is a key factor to be considered when designing transmission lines. To study the influence of altitude on negative corona characteristics, an experimental platform comprising a movable small corona cage was established: experiments were conducted at four altitudes in the range of 1120-4320 m, and data on the corona current pulse and radio interference level of 0.8-mm diameter fine copper wire under different negative voltages were collected. The experimental results show that the average amplitude, repetition frequency and average current of the corona current pulse increase with increasing altitude. The dispersion of pulse amplitude increases with increase in altitude, while the randomness of the pulse interval decreases continuously. Taking the average current as an intermediate variable,the relationship between radio interference level and altitude is obtained. The result of this research has some significance for understanding the corona discharge characteristics of ultra-highvoltage lines.

Optimal design of basic pulse waveforms for THSS UWB radio systems

Ultrawide bandwidth (UWB) radio, a very promising technique carrying information in very short basic pulses, has properties that make it a viable candidate for short-range wireless communications. In this paper, several short-pulse waveforms based on Gaussian genetic monocycle as well as Gaussian pulse waveform, as candidates of basic UWB pulse waveforms, are firstly proposed and investigated. Their spectrum characteristics, bit transmission rate (BTR), and bit error rate (BER) performance in AWGN channel using time hopping spread spectrum (THSS) and pulse position modulation (PPM) are simulated and evaluated. The numerical results are compared and show that the basic pulse waveforms determine the spectrum characteristics of UWB signals and have much effect on the performance of UWB radio system. The performance of UWB radio system achieved by the proposed basic pulse waveforms is much better than that of UWB radio system realized by other used basic pulse waveforms under the uniform conditions. Also, the polarity of these short basic pulses does not affect the performance of UWB radio system.

Pulse Compression Technique of Radio Fuze

The advantages of using phase-coded pulse compression technique for radio fuze systems are evaluated. With building mathematical models a matched filter has been implemented successfully. Various simulations for pulse compression waveform coding were done to evaluate the performance of fuze system under noisy environment. The results of the simulation and the data analysis show that the phase-coded pulse compression gets a good result in the signal identification of the radio fuze with matched filter. Simultaneously, a suitable sidelobe suppression filter is established by simulation, the suppressed sidelobe level is acceptable to radio fuze application.

A study of the strong pulses detected from PSR B0656+14 using the Urumqi 25-m radio telescope at 1540 MHz

We report on the properties of strong pulses from PSR B0656＋14 by analyzing the data obtained using the Urumqi 25-m radio telescope at 1540 MHz from August 2007 to September 2010.In 44 h of observational data,a total of 67 pulses with signal-to-noise ratios above a 5σthreshold were detected.The peak flux densities of these pulses are 58 to 194 times that of the average profile,and their pulse energies are 3 to 68 times that of the average pulse.These pulses are clustered around phases about 5-ahead of the peak of the average profile.Compared with the width of the average profile,they are relatively narrow,with the full widths at half-maximum ranging from 0.28 ° to 1.78 °.The distribution of pulse-energies follows a lognormal distribution.These sporadic strong pulses detected from PSR B0656＋14 have different characteristics from both typical giant pulses and its regular pulses.

基于Wnt/β-catenin信号通路探讨雷公藤甲素联合脉冲射频对大鼠神经性疼痛模型抗炎镇痛的作用机制

目的 探讨雷公藤甲素联合脉冲射频对大鼠神经性疼痛模型的抗炎镇痛作用及相关机制。方法 将SD大鼠随机分为假手术组、脊神经结扎组、雷公藤甲素组、脉冲射频组、雷公藤甲素联合脉冲射频组。构建脊神经结扎模型大鼠,检测大鼠疼痛行为学变化;蛋白质印迹法检测坐骨神经组织中Wnt-3α、β-catenin、frizzled7蛋白表达;聚合酶链式反应检测坐骨神经组织中Il-1β、Cox-2、Tnf-α、p65 Nf-κB mRNA表达;免疫组织化学检测坐骨神经组织中SP和C-fos蛋白表达。结果 除假手术组外,其余各组机械性缩足反射阈值在术后第1天急剧下降,术后第5天脊神经结扎组的机械性缩足反射阈值趋于稳定,各治疗组的机械性缩足反射阈值逐渐上升。除假手术组外,其余各组热缩足反射潜伏期在术后前3天急剧下降,术后第3天各组热缩足反射潜伏期开始升高,各治疗组的升高速度均高于脊神经结扎组。蛋白质印迹法结果显示术后第3、7、14天,脊神经结扎组Wnt-3α、β-catenin、frizzled7蛋白表达升高。与脊神经结扎组比,术后第3天各治疗组Wnt-3α、β-catenin、frizzled7蛋白表达差异较小,术后第7天和第14天各治疗组蛋白表达均降低,且雷公藤甲素联合脉冲射频组的相对表达量最低。聚合酶链式反应结果显示术后第3、7、14天,与假手术组比,脊神经结扎组的Il-1β、Cox-2、Tnf-α、p65 Nf-κB mRNA表达升高。与脊神经结扎组比,术后第7天和第14天各治疗组的mRNA表达均降低,且雷公藤甲素联合脉冲射频组表达最低。免疫组织化学结果显示脊神经结扎组中SP和C-fos蛋白表达高于假手术组,且随着时间的延长两种蛋白表达逐渐升高。与脊神经结扎组比,各治疗组SP、C-fos蛋白表达水平随治疗时间的延长均降低,且雷公藤甲素联合脉冲射频组降低最明显。结论 雷公藤甲素联合脉冲射频治疗通过调控Wnt/β-catenin信号通路减轻大鼠神经性疼痛模型炎症和疼痛反应。

基于分数阶傅里叶滤波的数字信道化储频

现代战场环境电磁日趋密集和复杂,各类信号相互混迭,同时各种相参雷达采用脉冲压缩技术以及相参处理方法,抗噪声和抗干扰能力大大增强,特别是采用线性调频(LFM)信号满足了雷达大威力、低截获的功能设计需求,抗干扰能力也得到提高。常规的数字储频(DRFM)采用宽带采集,在数字上对宽带信号进行调频、叠加等调制处理,在瞬时带宽内调制样式、参数是相同的,此处理方式导致瞬时带宽内多信号时,无法针对性施加不同的调制样式,以致干扰粗放、不够精确。为实现精确、有效的干扰相参脉冲压缩雷达,文中提出了采用频域子带处理与分数阶傅里叶滤波的数字信道化干扰设计,增强LFM信号去噪能力,通过DRFM技术形成假目标干扰信号,实施有效干扰。

某型射频接收机强电磁耦合的仿真预测

针对强电磁环境下射频接收机仿真预测的问题,开展强电磁脉冲信号构建、射频接收机建模、场路结合方式预测等研究,得到射频接收机内部监测点场强、壳体表面电流、接收机线缆耦合电压等仿真结果,实现对某型射频接收机电磁防护的优化设计,为射频接收机强电磁防护实施提供支撑。

Numerical solution to the Bloch equations:paramagnetic solutions under wideband continuous radio frequency irradiation in a pulsed magnetic field

A novel nuclear magnetic resonance （NMR） experimental scheme, called wideband continuous wave NMR （WB-CW-NMR）, is presented in this article. This experimental scheme has promising applications in pulsed magnetic fields, and can dramatically improve the utilization of the pulsed field. The feasibility of WB-CW-NMR scheme is verified by numerically solving modified Bloeh equations. In the numerical simulation, the applied magnetic field is a pulsed magnetic field up to 80 T, and the wideband continuous radio frequency （RF） excitation is a band-limited （0.68-3.40 GHz） white noise. ~lrthermore, the influences of some experimental parameters, such as relaxation time, applied magnetic field strength and wideband continuous RF power, on the WB-CW-NMR signal are analyzed briefly. Finally, a multi-channel system framework for transmitting and receiving ultra wideband signals is proposed, and the basic requirements of this experimental system are discussed. Meanwhile, the amplitude of the NMR signal, the level of noise and RF interference in WB-CW-NMR experiments are estimated, and a preliminary adaptive cancellation plan is given for detecting WB-CW-NMR signal from large background interference.

L波段全国产化2.5 kW级脉冲模块设计

随着国防和民用技术的迅速发展,高性能的L波段脉冲模块成为雷达和通信领域的关键组件。文章介绍了一个全国产化的2.5 kW级L波段脉冲模块的设计流程。该模块采用先进的射频放大技术和脉冲形成网络设计,结合本土材料和工艺技术的优势,实现模块的高性能和低成本生产。仿真和实验验证表明,设计的模块满足了所有预期的技术参数,包括功率水平、脉冲宽度和效率,通过了严格的质量控制和可靠性评估。

采用改进特征子空间投影的SAR脉冲式直达波干扰抑制方法

射频干扰(RFI)会污染合成孔径雷达(SAR)回波信号,增加SAR图像解译难度。脉冲式直达波干扰(PDWI)作为典型的RFI,在原始回波域以明亮条纹状掩盖SAR回波信息,对SAR成像质量产生严重影响。现有的干扰抑制方法中,传统的特征子空间投影(ESP)方法对整条含干扰脉冲进行干扰抑制,造成了脉冲中非干扰位置有用信号损失。为了保护有用信号,该文提出一种改进ESP的SAR脉冲式直达波干扰抑制方法。首先,通过两次检测干扰,获取PDWI在时域中的具体位置。其次,仅对检测的干扰位置数据,采用ESP将有用信号和干扰信号分离。最后,从原始数据中减去ESP重构的干扰数据以实现干扰抑制。仿真和实测数据处理表明,与现有方法相比,该方法能够有效避免SAR原始数据中有用信号的损失,抑制了脉冲式直达波干扰。

高速魔角旋转下基于组合π脉冲的射频驱动重耦同核双量子固体NMR相关实验研究

该文提出了一种改进固体核磁共振(NMR)实验中射频驱动重耦(RFDR)序列的方法。以组合π脉冲替代传统的单一矩形π脉冲作为RFDR序列的基本构成单元,并选择若干个适用于高速魔角旋转条件的组合π脉冲,在RFDR双量子实验中进行全面研究,通过数值模拟分析了影响RFDR双量子实验性能的两个关键因素——共振偏置和射频场不均匀性,并根据模拟结果确定了性能最优的组合π脉冲。结合六氟硅酸钠和L-组氨酸的一维和二维^(19)F或1H固体NMR实验,验证了在高速魔角旋转条件下选择适当的组合π脉冲的RFDR序列的优势。该方法不仅能确保较高的同核双量子激发效率,还能提高激发带宽,并且对射频场不均匀性更加不敏感。稳定高效的RFDR同核双量子相关实验为采用固体NMR分析强自旋耦合体系的核间相互作用提供了重要的技术支持。

基于脉组宽捷变的射频隐身雷达信号设计技术

射频隐身雷达能够从根本上提高雷达电子防御能力,是当前航空装备研究热点,而其重点是射频隐身信号设计。抗分选信号是一种重要的射频隐身信号,现在射频隐身信号设计领域的难点之一就是抗分选信号设计。通过分析雷达告警接收机等宽带实时电子侦察设备的主分选算法——序列差值直方图分选算法,指出该算法对于信号的脉冲重复间隔(PRI)大范围快速变化时会出现PRI估计错误的失效原理,提出基于脉组捷变的射频隐身雷达抗分选信号设计方法,即通过信号的脉组PRI大步进捷变,可以使RWR等实时宽带电子侦察设备的主分选算法输出出现较大误差,甚至完全错误。仿真及实验证明,基于上述方法设计的信号能有效对抗宽带实时电子侦察设备的主分选算法,实现雷达抗分选的目标。

ECCM schemes in netted radar system based ontemporal pulse diversity

For a netted radar system to counteract the deceptionelectronic countermeasure （ECM） signals, an effective electroniccounter countermeasure （ECCM） approach is proposed. The proposedapproach is realized based on the new signaling strategyfor the temporal pulse diversity, which makes use of transmittingpulses at each pulse repetition interval （PRI） with specific transmissionpulse block, and then following proper processing andinformation fusion. The existence of the deceptive ECM signal isconfirmed by one station, while the other stations in the nettedradar with same parameters applied the pulse diversity skillfully.Meanwhile, this method ensured that, pulse diversity can be appliedin netted radar. The performance assessment shows that theproposed solutions are effective in presence of ECM signals. Thisalgorithm has been demonstrated by simulations. The presentedsimulation results are in excellent consensus with theoretical predictions.