逃逸电子和不稳定性波反常多普勒共振实验研究

利用电子回旋辐射诊断系统并结合其他相关诊断研究了HL-2A托卡马克中逃逸电子与波间的反常多普勒共振作用.结果显示:欧姆放电下提高等离子密度能抑制逃逸电子束的不稳定性,但等离子密度的再次降低导致逃逸电子又会激发不稳定性波,并耦合不稳定性波发生二次反常多普勒共振作用.利用统计方法分析了HL-2A上不同放电阶段逃逸电子反常多普勒共振阈值(ωpe/ωce)区间大致都在0.17-0.54范围内.此共振机制导致逃逸电子在速度空间被波散射,平行能量转化到垂直能量,pitch角增加,同步辐射功率增强,逃逸电子能量限制在反常多普勒效应的阈值能量附近.基于反常多普勒共振的逃逸抑制能有效减轻逃逸电子对装置第一壁的损坏.     

托卡马克等离子体逃逸放电中的驰豫振荡与电子回旋激射不稳定性

我们研究了托卡马克等离子体进制电子引起的电子回旋激射不稳定性发生的条件，发现由反常多普勒效应及切伦科夫效应确定的准稳态速度分布又会激发电子回旋激射不稳定性，且其对本底电子回旋辐射的放大频段低于回旋频率，这与ＨＬ－１实验观察一致。     

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.     

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.     

Experimental study of electron-beam interaction with H-type resonator decelerating structure

Electron-beam interaction with an H-type resonator was used to study the anomalous Doppler effect at the electron cyclotron frequency with excitation in an electron beam of slow cyclotron waves, the anomalous Doppler effect at the plasma frequency with excitation of slow plasma waves, the energy relations for slow plasma waves, and the effect of reflected electrons and cyclotron absorption on the development of instabilities.Khar'kov Physicotechnical Institute, Academy of Sciences of Ukraine. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, Nos. 3, 4, pp. 334–346, March–April, 1992.     

HT-7托卡马克slide-away放电充气对等离子体行为的影响

本文研究了slide-away放电条件下的等离子体约束性能;分析了充气对等离子体约束性能以及反常多普勒共振不稳定性的影响.研究了等离子体密度的提升对slide-away放电过程中逃逸电子辐射行为的影响.研究结果发现:slide-away放电充气可以抑制逃逸电子反常多普勒不稳定性,但是使得等离子体约束状态变差,逃逸电子辐射增强.     

On the amplification mechanism of the ion-channel laser

The amplification mechanism of the ion-channel laser (ICL) in the low-gain regime is studied. In this concept, a relativistic electron beam is injected into a plasma whose density is comparable to or lower than the beam's density. The head of the electron beam pushes out the plasma electrons, leaving an ion channel. The ion-focusing force causes the electrons to oscillate (betatron oscillations) about the axis and plays a role similar to the magnetic field in a cyclotron autoresonance maser (CARM). Radiation can be produced with wave frequencies from microwaves to X-rays depending on the beam energy and plasma density: ω~2γ^3/2ω_pe, where γ is the Lorentz factor of the beam and ω_pe is the plasma frequency. Transverse (relativistic) bunching and axial (conventional) bunching are the amplification mechanisms in ICLs; only the latter effect operates in free-electron lasers. The competition of these two bunching mechanisms depends on beam velocity ν_0z; their dependences on ν_0z cancel for the cyclotron autoresonance masers. A linear theory is developed to study the physical mechanisms, and a PIC (particle-in-cell) simulation code is used to verify the theory. The mechanism is examined as a possible explanation for experimentally observed millimeter radiation from relativistic electron beams interacting with plasmas     

托卡马克中等离子体频率附近的增强辐射现象

实验提出托卡马克中的等离子体频率附近的增强辐射现象与高能逃逸电子有关,但是辐射的机制尚未完全弄清。本文讨论了两种可能的机制。一种是诱发辐射,这是来自逃逸电子与波的反常迴旋共振。另一种是自发辐射,主要来自契仑柯夫共振。前者要求逃逸电子的能量比后者为大,因此,自发辐射理论更引人注意。在很宽的参数变化范围内对辐射率作了数值计算。对于等离子体频率大于迴旋频率的情况也作了讨论。 关键词：     

Electron cyclotron resonance in a weakly magnetized radio-frequency inductive discharge

The evolution of the electron energy distribution function (EEDF) over a weak magnetic field range is investigated in magnetized radio-frequency (rf) inductive discharges under a collisionless regime where an anomalous skin effect and electron cyclotron resonance (ECR) can occur. A significant change in the low-energy range of the EEDF is found in the ECR condition during the evolution. The observed result reveals the low-energy electrons are efficiently heated by the rf ECR in the presence of the anomalous skin effect. The calculated result of the electron distribution based on kinetic theory is in good agreement with the experiment.     

Fluorescence excited in a thunderstorm atmosphere by relativistic runaway electron avalanches

The spectrum and spatiotemporal evolution of the fluorescence of an atmospheric discharge developing in the regime of relativistic runaway electron avalanche (RREA) generation have been calculated without involving the relativistic feedback. The discharges generating narrow bipolar pulses, along with the discharges responsible for terrestrial gamma-ray flashes, are shown to be relatively dark. Nevertheless, the fluorescence excited by a discharge involving RREAs can be recorded with cameras used to record high-altitude optical phenomena. A possible connection between a certain class of optical phenomena observed at the tops of thunderclouds and RREA emission is pointed out.     

电子迴旋激射不稳定性

本文分析了下述情况下的电子迴旋波的激射不稳定性:当相对性的单能高能电子斜向注入具有背景等离子体的磁场区域内,并且在电子等离子体频率与电子迴旋频率可以比拟时,考虑了背景等离子体密度远大于单能的高能电子的密度,以及与前者相反的两种情况。当单能的高能电子具有弱相对论性效应时,在电子迴旋频率的基频和二次谐波附近,分别有ο模和χ模的不稳定性存在。文中计算了这两种模的增长率,并作了讨论。 关键词：     

Ion energy distribution in a radio frequency sheath of plasma with Kappa electron velocity distribution

A hybrid model consisting of a one-dimensional radio frequency sheath model and an equivalent circuit model is used to investigate the effect of the non-Maxwellian plasma with enhanced electron tails on ion energy distribution (IED) at the plasma–wall interface. With the assumption that electrons obey the Kappa distribution in which the parameter κ characterizes the deviation from Maxwellian distribution, the bimodal shape of the IED can always be found with the decrease of κ under the condition of current experimental advanced superconducting tokamak (EAST) discharges during the ion cyclotron range of frequency wave heating. However, the height of the low-energy peak of the IED decreases, while the high-energy peak does not change significantly. In addition, the IED shifts towards the higher-energy regime, and the width of the IED expands with the decrease of κ . It is also shown that frequency and amplitude of the disturbance current, bulk plasma density, and ion temperature are the crucial parameters for determining the shape of IED even in the presence of super-thermal electrons.     

束—等离子体放电中低频等离子体波的非稳定性研究

本文采用非中性冷等离子体模型,研究了沿磁场入射的电子束和等离子体相互作用引起的低频等离子体波的非稳定性。计算表明,在束-等离子体放电情况下,振动频率和增长率都随电子束密度增加而增加,当束电流一定时,它们随l增加而略有增加。l=1时其频率数量级与离子迴旋频率相同。l≥3时,振动频率几乎不随k_z变化,其振动频率和增长率数量级与低混杂振荡频率相同,实质是低混杂漂移非稳定性。理论结果与实验一致。     

Experimental observation of interaction of runaway electrons with lower hybrid waves in slide-away regime in the HT-7 tokamak

The characters of slide-away regime in the HT-7 tokamak have been investigated, and evidences that lower hybrid waves (LHW) are excited in slide-away regime are presented based on local fast electron bremsstrahlung (FEB) emission profile and FEB emission spectrum. The interaction of high energy runaway electrons with those excited LHW via anomalous Doppler resonance is analyzed and the resonance energy is derived with which the behavior of those relevant signals in the experiment can be explained very well. It is shown that this interaction can provide an effective way to reduce the damage to the machine caused by runaway electrons.     

Simultaneous attainment of high electron and ion temperatures in discharges with internal transport barriers in ASDEX upgrade

Internal transport barriers have been demonstrated to exist also under conditions with T(e) approximately T(i) approximately 10 keV and predominant electron heating of the tokamak core region. Central electron cyclotron heating was added to neutral beam injection-heated ASDEX Upgrade discharges with a preexisting internal transport barrier, established through programmed current ramping leading to shear reversal. Compared to a reference internal transport barrier discharge without electron cyclotron resonance heating, the electron heat conductivity in the barrier region was found not to increase, in spite of a fivefold increase in electron heat flux, and also angular momentum and ion energy transport did not deteriorate.     

托卡马克等离子体中的电子回旋波电流驱动

通过将波迹方程与相对论情况下的完全Fokker-Planck方程联合进行求解,研究了寻常波基频电子回旋波从托卡马克等离子体中平面弱场侧发射时的电流驱动。数值结果表明:随着等离子体电子密度、温度的提高, 功率沉积和电流分布的位置将向等离子体的边缘方向偏移,并且产生的总的驱动电流随之减小;入射波极向发射角和环向发射角度的改变对功率沉积、电流分布及其大小产生明显的影响。     

发射波功率密度对电子回旋波电流驱动的影响

采用高斯光束的研究方法,结合Fokker-Planck方程,在堆级等离子体条件下模拟了发射波功率密度的改变对电子回旋波功率沉积以及电流驱动的影响。结果表明,高功率密度的波束会拓宽功率沉积剖面,使功率沉积的位置略有外移,电流驱动效率略有降低。     

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采用高斯光束的研究方法,结合Fokker-Planck方程,在堆级等离子体条件下模拟了发射波功率密度的改变对电子回旋波功率沉积以及电流驱动的影响。结果表明,高功率密度的波束会拓宽功率沉积剖面,使功率沉积的位置略有外移,电流驱动效率略有降低。     

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。     

Effect of relativistic elliptical beam modulation on excitation of surface plasma waves in a magnetized dusty plasma column with elliptical cross section

Abstract

The excitation of surface plasma waves due to the interaction of an elliptical relativistic density modulated electron beam with the magnetized dusty plasma column with elliptical cross-section has been studied. The dispersion relation of surface plasma waves has been retrieved from the derived dispersion relation by considering that the beam is absent and there is no dust in the plasma elliptical cylinder. It is shown that the Cherenkov and fast cyclotron interactions appear between the beam and eigen-modes of plasma column. The growth rate of the instability increases with the beam density and modulation index as one-third power of the beam density in Cherenkov interaction and is proportional to the square root of beam density in fast cyclotron interaction. The numerical results and graphs are presented, too.