用远红外HCN激光干涉仪测量等离子体电子密度

在大多数托克马克上，远红外激光干涉仪是等离子体诊断中的一种重要的装置。本文介绍了用远红外ＨＣＮ激光干涉仪测量等离子体电子密度的原理和激光干涉仪结构，并给了了首次在我国第一以大型超导托克马克ＨＴ－７装置上测到的中心弦等离子体电子平均密度。     

等离子体冕区电子密度陡变和凹陷的研究

从等离子体二维流体方程出发,假定在柱对称电子密度分布的等离子体中,在激光辐射场的区域内,径向电子热压与径向有质动力在稳态情况下平衡,推导出了由有质动力引起的临界密度面附近轴向电子密度轮廓陡变和有场区径向电子密度凹陷结构的解析结果,此结果与266.0nm紫外激光探针所测到的实验结果相符合。     

微波共振探针在测量等离子体密度中的应用

本文介绍了一种可以测量局部等离子体电子密度的微波共振探针法，并给出了它的测量原理、设计方法和实验结果。实验结果表明：由于微波共振探针不受鞘层的影响，因此它比通常的朗谬静电探针对等离子体密度的测量要精确得多。微波共振探针的空间分辨率与它的几何尺寸有关。     

利用金属外探针探测激光等离子体的电学效应

利用Nd:YAG脉冲激光烧蚀Cu靶,实验研究了空气中激光等离子体电学效应在金属探针上产生的电信号的形成机制与演变规律,对探针与烧蚀点之间的距离对电信号的影响进行了测试。结果表明:信号结构与探测距离密切相关,探针距离较近时(<3mm),信号具有正负双极分布结构,距离较远时(>3mm),则仅表现为负脉冲单峰结构,且信号幅值与探针距离之间满足Ia∝d-2。对该信号进行详细分析后得出:从等离子体区域出射的高速电子和离子到达探针是信号形成的主要机制,并对信号幅值随探针距离的变化关系进行了合理解释。     

朗缪尔探针诊断脉冲激光锡等离子体特性

激光作用锡靶等离子体极紫外光转换效率与等离子体特性密切相关。为了对等离子体特性进行诊断,设计了一种用于激光等离子体诊断的朗缪尔探针,取得了不同激光能量下产生的锡等离子体电子温度与电子密度的时间演化。结果表明,能量为58.1mJ的激光产生的等离子体峰值电子密度约为4.5×1011cm-3,最大电子温度为16.5eV,均随激光能量减少而降低,与发射光谱法所测的电子温度演化趋势一致。该研究为激光等离子体极紫外光源提供了一种新的简单快速诊断方法,有利于对激光等离子体的极紫外光源的参量进行优化。     

激光诱导Al等离子体中电子密度的实验研究

用Nd:YAG脉冲激光器产生的1.06μm激光,在低压环境下烧蚀金属Al靶获得等离子体,并观测其空间分辨发射光谱;利用AlⅠ的两条发射谱线的Stark展宽计算了Al等离子体电子密度,研究了电子密度随空间的演化规律。结果发现:在靶面附近电子密度达到最大值,随着离靶面距离的增加,电子密度逐渐减小,从微观物理机制的分析推断:激光诱导等离子体的复合辐射是电子密度减少的主要原因。另外,还探讨了激光能量的变化对等离子体电子密度的影响。     

有限宽全息干涉技术对等离子体电子密度的诊断

利用Nd:YAG激光器产生的1064 nm激光束(光斑直径为100μm,脉冲能量为60 m J,脉冲宽度为200 ps)聚焦击穿大气形成激光大气等离子体。采用全息干涉技术对激光击穿空气等离子体的电子密度分布进行了诊断,获得的无限宽条纹图直观反映了位移量的等位线,从有限宽条纹图获得了电子密度的分布,结果表明激光大气等离子体中各种离子和电子呈橄榄形分布,即沿激光束方向不对称,而垂直激光束方向对称分布,且最大电子密度为1018cm-3量级。     

纳秒紫外激光空气电离及等离子体导电实验研究

为了验证纳秒紫外激光大气等离子体通道技术的可行性,采用实验方法研究了248nm远紫外激光与实验室空气的相互作用,测试了相应的电离击穿阈值;尝试建立了连续的激光等离子体电离通道,并进行了激光等离子体通道直流电传输实验,得到的数据显示,在180m J单脉冲能量作用下,连续闪光柱长度8mm,可导电区长度约20mm。结果表明,纳秒紫外激光建立连续激光等离子体导电通道是可行的。     

激光诱导Al等离子体中电子密度和温度的实验研究

激光烧蚀等离子体在微量元素分析方面有着重要的应用背景，而缓冲气体的种类及压力对激光等离子体的特性有重要影响。报道了以氦气、氩气、氮气和空气作为缓冲气体，实验测定了不同气压下Nd：YAG激光烧蚀Al靶产生的等离子体中的时间分辨发射光谱，利用发射谱线的Stark展宽和相对强度计算了等离子体中的电子密度和温度，得到了在不同缓冲气体中激光诱导Al等离子体的电子密度随延时、气压的演化规律，同时得到了电子温度的时间演化特性。实验结果表明，电子密度的数量级约为10^17cm^-3，电子温度测量值约为10000K，二者都是在激光脉冲后随时间快速衰减，直到4μs以后达到一个较低的水平并缓慢变化，其中以氩气作为缓冲气体时等离子体中的电子密度最大。     

Measurement of ion density in a plasma torch using a plane probe

The plasma density of the flame of a plasma torch has been determined from the current to a plane probe using two theories. One includes only the ion flow motion; the other includes only the ion thermal motion. Comparison with spectroscopic results suggests that both motions should be included.     

Depth profiling of semiconductor structures by X-ray microanalysis using the electron probe energy variation technique

Depth profiling of semiconductor structures by X-ray microanalysis using the electron probe variation technique followed by mathematical processing of the measurement results is described. Experimental dependences of the relative X-ray intensity on the energy of the electron probe were compared to the Monte Carlo simulation results. Concentration depth profiles were estimated using a priori assumptions, and numerical parameters of the depth distributions were determined from the best fit of calculated curves to the experimental data. The technique was applied to determine Al depth profiles in SiC and GaN samples.

     

Studies of the electron spectrum in structures with InGaN quantum dots using photocurrent spectroscopy

Structures with InGaN/GaN quantum dots have been studied using photocurrent spectroscopy. The dynamic range of measurements is found to amount to four orders of magnitude under preservation of the signal-to-noise ratio at a level higher than ten. Within the experimental accuracy, the shape of the spectrum is independent of an applied reverse external bias, whereas the spectrum itself shifts to shorter wavelengths, which is attributed to the Franz-Keldysh effect. Variation of the temperature brings about a change in the spectrum shape. This effect is found to be different for structures grown under different conditions. This behavior can be attributed to homogeneous broadening of the electronic states, the statistics of charge carriers at the levels of quantum dots, and the effect of temperature on the position of these levels.     

Measurements of electron density and plasma current distributions in Tokamak plasma

A submillimeter-wave, phase-modulated polarimeter/interferometer is used for simultaneous time-dependent measurement of line-averaged electron density and poloidal field-induced Faraday rotation along chords of the plasma column in ISX-B tokamak. Heterodyne detection and hollow dielectric waveguide are utilized to achieve the high sensitivity required for the multichord experiment. A data analysis code has been developed to reconstruct the asymmetric distributions of plasma density. The validity of the code is examined, and the result shows good agreement with density profiles measured by Thomson scattering.     

Surface-wave probe for measuring electron densities in a gaseous plasma

A dielectric rod enveloped in gaseous plasma can act as a supporting structure for electromagnetic surface waves. The dielectric constant of the plasma and hence the electron number density in the vicinity of the rod may be determined from measurements of the phase-change coefficient of the EH11 mode supported by the plasma-clad rod. Measurements of radial density distribution have been carried out in an unmagnetised argon afterglow plasma at 35Gc/s and compared with double-probe measurements.     

Continuous measurement of electron density in unmagnetised plasmas by a self-oscillating probe

We show experimentally that it if possible to measure continuously the electron plasma density using a mutual impedance probe working in a self-oscillating mode at the plasma frequency. The comparison of the experimental curves obtained in unmagnetised plasmas either in a classic sweep-frequency mode or in a self-oscillating mode emphasises the excellent accuracy of this new diagnostic method.     

大气压电子束等离子体密度诊断实验

大气压电子束等离子体密度诊断用微波法和光谱法较为合适,根据微波在等离子体中的传播特性,利用微波透过等离子体时透射能量衰减和相位变化,计算等离子体密度,并与光谱诊断结果进行比较,2种方法诊断结果基本一致。在微波诊断等离子体实验研究中,发现空气湿度对大气压等离子体密度有显著影响,利用大气化学模型仿真研究湿度对等离子体密度影响规律,获得与实验测试一致的结果。     

High-resolution laser interferometer for measurement of electron density in transient plasma

A laser interferometer of the Mach-Zehnder type based on the use of a single-mode frequency-stabilised He-Ne gas laser, 6329 ? in wavelength and with 100 ?V output, has been used to measure accurately electron densities in the range 1014?1015cm?3 in a transient mercury-vapour plasma. An `amplitude? (intensity) modulation system is employed in order to obtain a wide dynamic range. The interferometer system is mounted on a massive movable table in order to obtain the spatial distribution of electron density by means of sequential discharges. The experimental results show clearly that there are definite time delays between the peak of current in the discharge and the maximum value of the (average) electron density. The results are in good agreement with the values of electron densities obtained by the extrapolation from microwave measurements.     

朗谬尔探针法测量横流CO_2激光器的电子密度

本文讨论了探针在流动等离子体中的鞘层变化,在厚鞘层情况下,用朗谬尔探针测量了在不同偏压和主放电电流下的离子电流,并计算出不同放电电流下的电子密度,给出了电子密度的顺流分布。