TEA CO2激光器不同放电电路放电过程的比较

 利用像增强CCD相机对脉冲CO₂激光器的放电区进行观测,获得了放电辉光的发展过程,由此研究了长脉冲放电电路和短脉冲放电电路对放电过程的影响。发现普通电容放电电路（长脉冲放电电路）存在与自持放电阶段相对应的二次辉光;采用磁压缩开关的短脉冲放电电路,预电离出现较晚,但预电离辉光峰值和主放电辉光峰值之间间距较短,不存在自持放电阶段,只观测到一次强辉光。长脉冲放电电路与短脉冲放电电路在放电的后期均存在一个阴极位降区形成的过程。短脉冲放电电路有利于产生更窄的脉宽和更高的峰值功率。     

小型球形脉冲氙灯光谱分析与实验测定

作为分析仪器和医疗仪器光源,脉冲氙灯的光谱特性直接影响着仪器的整体性能。为了研究脉冲氙灯放电回路参数及几何参数对其光谱特性的影响,利用气体放电理论分析了脉冲氙灯发光过程,设计了光谱检测系统,实验测定了脉冲氙灯在不同放电参数下的光谱特性。结果表明：脉冲氙灯光谱由连续谱和线状谱组成,连续谱有离子复合和韧致辐射产生,线状谱由电子能级跃迁产生。相对光谱辐射能量随着放电电压升高呈近似线性增长、并随着储能电容的变大而变大。在放电电压较低时,弧长较短时相对光谱辐射能量较大;在放电电压较大时,弧长越长相对光谱辐射能量越大。对于脉冲氙灯工作参数选取以及应用生产具有重要的意义。     

利用密度反馈实现离子源长脉冲放电

 介绍了等离子体密度对离子源放电的影响,为了获得长脉冲放电,采用朗缪尔探针测量等离子体密度并反馈调节离子源放电。基于朗缪尔探针测量,设计了控制部分硬件与软件构架,建立了离子源等离子体密度反馈控制系统,并成功地应用于离子源等离子体放电实验,通过反馈调节实验进气,得到了长达4.5 s的长脉冲放电,为中性束注入稳态运行提供了依据。     

脉冲束流引出时的等离子体鞘层变化

采用一维无碰撞的动力学鞘层模型计算了脉冲等离子体在恒压引出时的等离子体鞘层厚度变化,分别对短脉冲和长脉冲放电时的离子源发射面演变进行了分析。结果表明:对于短脉冲放电,发射面位置的变化相对等离子体密度的变化存在一定时间的延迟;对于长脉冲的上升沿和直流放电的开启阶段,鞘层厚度变化的速度与离子初始速度相关,稳定后发射面的位置与离子初始速度和等离子体密度的乘积相关。     

大气压空气纳秒脉冲板-板放电中逃逸电子产生机理

经典放电理论(Townsend和流注理论)解释纳秒脉冲气体放电存在局限性,近年来基于高能电子逃逸的纳秒脉冲气体放电理论研究受到广泛关注.但是目前对大气压空气纳秒脉冲板-板放电中逃逸电子产生机理研究仍较少,严重阻碍了纳秒脉冲放电等离子体的应用发展.本文利用一维粒子模型,对幅值为20 kV的纳秒脉冲电压驱动下,间隙长为1 mm的板-板电极之间的大气压空气放电中逃逸电子的产生机理进行了数值模拟研究..结果表明,在空间电荷动力学行为的影响下,板-板电极之间出现了增强电场区域,使得电子可以满足电子逃逸判据而进入逃逸模式.此外,还观察到放电通道前逃逸电子的预电离效应导致了二次电子崩的产生,随着二次电子崩与放电通道不断汇聚,引导并加速了放电通道的发展,最终导致气隙击穿.本研究进一步揭示了纳秒脉冲板-板放电机理,拓展了纳秒脉冲气体放电基础理论,为纳秒脉冲放电等离子体的应用和发展开辟了新的机会.     

空气中纳秒脉冲介质阻挡放电高速摄影

使用上升沿40 ns、脉宽70 ns的重复频率单极性纳秒脉冲电源,采用双水电极结构产生大气压空气中介质阻挡放电。测量了纳秒脉冲下介质阻挡电压和电流,并获得长曝光时间和ns级曝光时间的放电特性,采用曝光时间为2 ns的高速摄影拍摄放电发展过程。结果表明:大气压空气中,水电极结构纳秒脉冲介质阻挡放电能够产生稳定均匀的放电等离子体,且存在二次放电。高速摄影对放电发展过程的拍摄结果表明:放电首先由电极中部开始发展,径向扩展至整个电极范围。     

High speed imaging of nanosecond-pulse dielectric barrier discharge in atmospheric air

使用上升沿40 ns、脉宽70 ns的重复频率单极性纳秒脉冲电源,采用双水电极结构产生大气压空气中介质阻挡放电.测量了纳秒脉冲下介质阻挡电压和电流,并获得长曝光时间和ns级曝光时间的放电特性,采用曝光时间为2 ns的高速摄影拍摄放电发展过程.结果表明:大气压空气中,水电极结构纳秒脉冲介质阻挡放电能够产生稳定均匀的放电等离子体,且存在二次放电.高速摄影对放电发展过程的拍摄结果表明:放电首先由电极中部开始发展,径向扩展至整个电极范围.     

基于DCS的EAST内置低温泵监控系统设计

内置低温泵是EAST装置中为防止杂质从偏虑器靶板附近进入等离子体核心的关键部件之一,可以为EAST长脉冲放电试验提供持续的排灰能力实现装置长脉冲放电。主要在EAST低温控制系统基础上,基于DCS结构设计内置低温泵的监控系统,从而实现低温泵阀箱冷却、运行、回温整个过程的自动监控。     

重复频率脉冲流注放电演变现象与机制研究进展

重复频率脉冲流注放电是低温等离子体前沿应用的关键使能因子,然而,高重复频率脉冲作用下流注放电呈现复杂的不稳定和记忆效应现象,放电基础演变机理和调控方法尚不完善,极大影响应用的安全性和放电特性调控的有效性。综述了重复频率脉冲流注放电演变现象与机制的研究进展。首先归纳了重复频率脉冲流注放电的强非线性和渐进式演变特征,然后分析不同类型放电记忆效应因子对后续流注起始和传播的作用机制,最后总结了脉冲波形参数对重复频率脉冲流注放电的影响规律。凝练了重复频率脉冲流注放电演变机制研究的若干挑战,对脉冲放电等离子体机理研究具有一定的借鉴作用。     

大功率脉冲氙灯的放电研究

利用转镜式高速摄影机分幅摄影技术,对脉冲氙灯放电中的沟道扩展和熄灭过程进行了摄影和分析.放电时沟道扩展速度很快,呈树枝状,沟道熄灭过程长于扩展过程,且呈斑状.同时研究了预电离放电对沟道扩展和熄灭过程的影响,当预电离存在时,脉冲氙灯放电的沟道扩展的时间要长.结果表明,预电离有利于放电沟道的形成,提高氙灯的发光效率,且有助于减小主放电能量对管壁材料的冲击.     

HL-1装置硬X射线能谱及长脉冲放电与硬X射线的发射关系

在HL-1装置上初步测硬(?)射线能谱,能量达5MeV。实验观测到长脉冲放电与硬(?)射线的关系,并得到逃逸电子的径向扩散。     

纳秒脉冲气体放电中逃逸电子束流的研究

经典的放电理论(Townsend和流注理论)不能很好地解释纳秒脉冲放电中的现象,近年来基于高能量电子逃逸击穿的纳秒脉冲气体放电理论研究受到广泛关注,有研究发现,高能逃逸电子是纳秒脉冲气体放电中的新特征参数,本文研制了用于测量纳秒脉冲放电中逃逸电子束流的收集器,并对脉宽3—5ns、上升沿1.2—1.6 n8激励的大气压纳秒脉冲气体放电中逃逸电子束流进行了测量,收集器采用类似法拉第杯的原理,利用金属极收集纳秒脉冲放电中的高能电子,并转换为电信号后由示波器采集,为了获得更好的逃逸电子束流波形,对逃逸电子束流收集器进行了优化设计,提高了收集器的阻抗匹配特性,基于上述的逃逸电子束流收集器,研究了纳秒脉冲气体放电中逃逸电子的特征,实验结果表明,所设计的收集器可以有效地测量到逃逸电子束流,改进设计后收集器测得的逃逸电子柬流的时间分辨率和幅值均得到提高,施加电压约80 kV时,大气压空气中的逃逸电子束流幅值可达160 mA,脉宽小于1ns,多个脉冲激励放电的结果表明逃逸电子束流收集器具有较好的可靠性,其瞬态响应与时间分辨率比较稳定。     

HL-1装置中的相对论性非热辐射

在垂直于大半径方向用两个固定频率((?)0和(?)5GHz)的毫米波段外差接收机研究了在HL-1装置中等离子体的非热辐射。根据这些辐射与等离子体密度的关系,HL-1装置的放电可分为4种类型,并得到两个临界密度。这些辐射特性被认为是与逃逸放电性质和逃逸动力学不稳定现象有关。在实验中还观察到了与这种不稳定性有关的一系列等离子体宏观现象以及由此引起的逃逸损失。     

Observation of Runaway Electron Behaviour During Disruptions in LHCD Discharges in the HT‐7 Tokamak

Production of runaway electrons during disruptions has been observed in the HT‐7 Tokamak. The runaway current plateaus, which can carry part of the pre‐disruptive current, are observed in lower‐hybrid current drive (LHCD) limiter discharges. It is found that the runaway current can mitigate the disruptions effectively. We can use gas puffing to increase the line‐averaged density to restrain the runaway electrons and rebuild the plasmas after the disruptions. Detailed observations are presented on the runaway electrons generated following disruptions in the HT‐7 tokamak discharges. The results indicate that the magnetic oscillations play a significant role in the loss of runaway electrons in disruptions. There are two important preconditions to rebuild plasmas by runaway electrons after the disruptions. One of them are weak magnetic oscillations; another one are LHWs (lower‐hybrid waves) (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

HL-1托卡马克中逃逸电子的最高能量和光致中子

本文描述我们在实验观察到每次放电结束之前或大破裂之后,强烈的高能X射线出现,同时伴随着较强的光致中子辐射。其时逃逸电子的最大能量,在考虑到回旋辐射损失及逃逸电子速度的径向分量引起的回旋半径变小等情况后经计算可达50-62MeV,光致中子的强度为2.5×10~(10)s~(-1),与JET在破裂条件下的经验定标关系大致相符。     

Study of runaway electron behaviour during electron cyclotron resonance heating in the HL-2A Tokamak

During the current flat-top phase of electron cyclotron resonance heating discharges in the HL-2A Tokamak, the behaviour of runaway electrons has been studied by means of hard x-ray detectors and neutron diagnostics. During electron cyclotron resonance heating, it can be found that both hard x-ray radiation intensity and neutron emission flux fall rapidly to a very low level, which suggests that runaway electrons have been suppressed by electron cyclotron resonance heating. From the set of discharges studied in the present experiments, it has also been observed that the efficiency of runaway suppression by electron cyclotron resonance heating was apparently affected by two factors: electron cyclotron resonance heating power and duration. These results have been analysed by using a test particle model. The decrease of the toroidal electric field due to electron cyclotron resonance heating results in a rapid fall in the runaway electron energy that may lead to a suppression of runaway electrons. During electron cyclotron resonance heating with different powers and durations, the runaway electrons will experience different slowing down processes. These different decay processes are the major cause for influencing the efficiency of runaway suppression. This result is related to the safe operation of the Tokamak and may bring an effective control of runaway electrons.     

Runaway Electron Beam Instability in Slide-Away Discharges in the HT-7 Tokamak

Slide-away discharges are achieved by decreasing the plasma density or ramping down the plasma current in runaway discharges in the HT-7 tokamak. In the case of plasma current ramp down, the ratio of the electron plasma frequency to the electron cyclotron frequency is higher than in the stationary pulses when the discharge goes into a slide-away regime. The instability regime is characterized by relaxations in the electron cyclotron emission due to relativistic anomalous Doppler effect which transfers energy from parallel to perpendicular motion. The triggering of relativistic anomalous Doppler effect at higher density by ramping down of plasma current may provide a alternative runaway energy control scenario.     

Experimental observation of increased threshold electric field for runaway generation due to synchrotron radiation losses in the FTU Tokamak

The threshold electric field for runaway generation has been investigated during runaway suppression experiments by means of electron-cyclotron-resonance heating in the flattop phase of FTU discharges. Runaway suppression has been experimentally found to occur at electric fields substantially larger than those predicted by the relativistic collisional theory of runaway generation, ER=nee3lnΛ/4πε0(2)mec2. These experimental results are consistent with an increase of the critical electric field due to the electron synchrotron radiation losses. No runaway electrons are found in FTU experiments below the radiation threshold. These results support evidence for a new threshold electric field for runaway generation that accounts for the effect of the synchrotron losses, and which should be considered when making predictions on runaway generation and mitigation in devices such as ITER.     

Investigation of the effect of electron cyclotron heating on runaway generation in the KSTAR tokamak

Wave enhanced runaway generation is expected to play an important role in the conversion of plasma current into runaway current during major disruptions. The fast electrons created by electron cyclotron heating (ECH) were used to study this issue in KSTAR. It is found that the fast electrons driven by ECH can enhance runaway production in the flat top phase with high loop voltage. The runaway current in disruptions was not enhanced by the ECH produced fast electron population due to the strong magnetic fluctuations which inhibited the generation of runaway electrons. It is found that a complete loss of existing REs during thermal quench has occurred in KSTAR limiter configuration discharges.     

Negative edge plasma currents in the SINP tokamak

A tokamak plasma discharge having an increase in duration accompanied with enhanced runaway electron flux has been experimentally studied in this paper. The discharges have been obtained by controlling the applied vertical magnetic field (B_v^applB_{\rm{v}}^{\rm{appl}}) to below a critical value. Such discharges have been observed to have ‘negative edge plasma currents’, detected using an internal Rogowskii coil (IRC). We have tried to correlate the runaway behaviour with the negative edge plasma currents and have explained that these observations are a result of beam plasma instabilities.