Dual-jet plasmatron for medical applications

We present a design for a dual-jet arc plasmatron operating at a frequency of 66 kHz in an argon flow at atmospheric pressure. We present the results of determination of the temperature, electron concentration, and electrode erosion obtained by atomic emission spectral analysis. The proposed convenient design for a dualjet plasmatron and the low erosion of the copper electrodes in the plasma make it possible to use it for medical purposes. Report given at the Fifth International Conference on Plasma Physics and Plasma Technologies (PPPT-5), 18–22 September 2006, Minsk, Belarus. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 139–140, January–February, 2007.     

Chiral invariant phase space event generator

The Geant4 CHIPS model simulates both decay and nuclear capture of negative muons. In hadron level models the muon is captured by a proton, p(μ,ν_μ)n , and the neutron transfers to the nucleus only 5MeV, which is not enough to split a nucleon from the nucleus, while the measured spectra of emitted nucleons reach 80MeV. In CHIPS, which considers asymptotically free quark-partons, the muon can be captured by a quark, u(μ,ν_μ)d , and transfers 52MeV to the nucleus. This capture mechanism fits the main part of the nucleon spectra, while the high-energy part of the spectra is not fitted. A precise fit of the high-energy part of the nucleon spectra can be made if the muon decay μ → dˉν_μ is taken into account.     

Small amplitude ion-acoustic double layers with cold electron beam and q-nonextensive electrons

Small amplitude ion-acoustic double layers in an unmagnetized and collisionless plasma consisting of cold positive ions, q-nonextensive electrons, and a cold electron beam are investigated. Small amplitude double layer solution is obtained by expanding the Sagdeev potential truncated method. The effects of entropic index q, speed and density of cold electron beam on double layer structures are discussed.     

太赫兹GaAs肖特基混频二极管高频特性分析

在太赫兹波段,存在几种新的高频效应会限制混频二极管的高频特性.应用热电子发射理论和隧道理论,研究了外延层肖特基二极管的高频特性,并以截止频率为品质因数对二极管进行优化设计.研究表明,当二极管工作频率大于等离子频率时,二极管相当于一个电容,失去了混频性能;提高基底掺杂浓度可以减小基底等离子共振效应;外延层等离子频率非常重要并且在研究外延层等离子共振效应时必须考虑传输时间效应;减小阳极直径、减小外延层厚度、提高外延层掺杂浓度可以提高二极管的工作频率.这对太赫兹波段室温混频器件的研制具有重要的参考价值.     

ICP等离子体鞘层附近区域发光光谱特性分析

为了独立控制鞘层附近区域离子密度和离子能最分布,采用光发射谱(OES)测量技术,对不同射频功率、放电气压和基底偏压下感应耦合等离子体鞘层附近区域辉光特性进行了研究.原子谱线和离子谱线特性分析表明,在鞘层附近区域感应耦合等离子体具有较高的离子密度和较低的电子温度.改变放电气压和射频功率,对得到的光谱特性分析表明,鞘层附近区域离子密度随射频功率的增大而线性增大,在低压下随气压的升高而增大.低激发电位原子谱线强度增加迅速,高激发电位原子谱线强度增加缓慢,而离子谱线强度增加很不明显.改变基底直流偏压,对得到的发射光谱强度变化分析表明,谱线强度随基底正偏压的增加而增大.随着基底负偏压的加入,谱线强度先减小而后增大;直流偏压为-30 V时,光谱强度最弱.快速离子和电子是引起Ar激发和电离过程的主要能量来源.     

Study of plasma parameter’s distribution upon electrical wire explosion

Experimental results on electrical explosion of wires in vacuum with current density  A/m², current rise rate (dI/dt) ~ 50 A/ns and current pulse with amplitude ∼10 kA are presented. The structure of the discharge channels in vacuum has been studied using laser shadow and schlieren imaging with 7 ns frames, UV pinhole images with 5 ns frames and X pinch X-ray backlighting. The information on the dense core material and the conducting plasma distributions was obtained in our experiments by analyzing and comparing the results obtained from all diagnostics.     

基于双向偏振态激光诱导荧光方法的离子速度分布函数测量

为了评估利用发散磁场构型双电层效应的紧凑式螺旋波等离子体推力器的离子加速效果,探索了一种双向偏振态激光诱导荧光测量方法来对螺旋波等离子体源近出口端的离子速度分布函数进行测量。实验中采用Ar作为螺旋波等离子体源工质,中心波长为611.662 nm的激光以轴向方式注入等离子体,以激励一价Ar离子获得波长为461.086 nm的诱导荧光光谱。为了消除磁化等离子体中逆塞曼效应对激光诱导荧光光谱带来的分裂影响,通过四分之一波片将入射激光分别调制为左旋和右旋圆偏振态,并对其诱导光谱进行了分别测量,结果发现不同磁场强度下两次测量结果的偏移值与理论高度吻合,证明了双向偏振态激光诱导荧光测量方法的理论可行性。进一步,采用高斯型滤波器反卷积算法从测量光谱中去除自然展宽和能量饱和效应,再通过对两次相反偏振态测量结果进行平移处理消除逆塞曼效应,从而分离得到实际的多普勒效应。测量了射频能量600 W,不同轴向位置、磁场大小以及气体压力下的螺旋波Ar等离子体激光诱导荧光光谱,结果表明在该实验条件下离子并没有因双电层效应而达到期望值的加速效果,离子速度的形成可能只是一种磁约束作用下的双极电场所导致,并不能产生好的推力性能。     

Angle-resolved x-ray photoelectron spectroscopy study of GeO_x growth by plasma post-oxidation

The growth process of GeO_x films formed by plasma post-oxidation(PPO) at room temperature(RT) is investigated using angle-resolved x-ray photoelectron spectroscopy(AR-XPS). The experimental results show that the distributions of the Ge~(4+)states, a mixture of the Ge_(2+)and Ge~(3+)states, and the Ge~(1+)states are localized from the GeO_x surface to the GeO_x/Ge interface. Moreover, the Ge~(1+)states are predominant when the two outermost layers of Ge atoms are oxidized.These findings are helpful for establishing in-depth knowledge of the growth mechanism of the GeO_x layer and valuable for the optimization of Ge-based gate stacks for future complementary metal–oxide–semiconductor(MOS) field-effect transistor(CMOSFET) devices.     

Production of long,laminar plasma jets at atmospheric pressure with multiple cathodes

Plasma jets from conventional non‐transferred arc plasma devices are usually operated in turbulent flows at atmospheric pressure. In this paper, a novel non‐transferred arc plasma device with multiple cathodes is introduced to produce long, laminar plasma jets at atmospheric pressure. A pure helium atmosphere is used to produce a laminar plasma jet with a maximum length of >60 cm. The influence of gas components, arc currents, anode nozzle diameter, and gas flow rate on the jet characteristics is experimentally studied. The results reveal that the length of the plasma jet increases with increasing helium content and arc current but decreases with increasing nozzle diameter. As the gas flow rate increases, the length of the plasma jet initially increases and then decreases. Accordingly, the plasma jet is transformed from a laminar state to a transitional state and finally to a turbulent state. Furthermore, the anode arc root behaviours corresponding to different plasma jet flows are studied. In conclusion, the multiple stationary arc roots that exist on the anode just inside the nozzle entrance are favourable for the generation of a laminar plasma jet in this device.     

Numerical and analytic study of rough surface morphology on the angular distribution of eroded impurity

The impact of rough surface morphology on the angular distribution of eroded impurities has been investigated with the three‐dimensional (3D ) rough surface code SURO and a newly developed analytic model. The property of the rough surface structure can be described by the shadow angle of the rough surface in SURO , which is defined as the ratio of the horizontal characteristic length to the initial surface roughness. The SURO simulation results show that the influence of the rough surface on the angular distribution of eroded impurities comes into play when the shadow angle is larger than a threshold value. The larger shadow angle of the rough surface leads to a stronger shift of the angular distribution of the eroded impurities. Different rough surface topographies have been used in the SURO code to check the angular distribution of the eroded impurities. It is found that the shift tendency of the angular distribution is similar for different structures of the rough surface. Based on the numerical modelling results, an analytical model has been developed to investigate the impact of the shadow angle on the angular distribution of the eroded impurities, which shows the consistent result as the SURO simulations.