A DCN laser interferometer for electron density measurements of plasmas

The main characteristic of this interferometric system is such that the systems can be used for DCN laser (=195m, 190m) and also for HCN laser (=337m) by changing the work medium, regulating the temperature of tube wall and adjusting the optic path, without changing any optic element.     

High sensitivity HCN laser interferometer for plasma electron density measurements

This paper describes a high sensitivity 337 μm HCN laser interferometer for plasma electron density measurements. The plasma phase shift is transferred to a low frequency signal obtained by slightly shifting the frequency of the 337 μm radiation in the reference beam of the interferometer. The frequency shift is produced by diffracting the radiation of a cylindrical rotating blazed grating. A phase shift is deduced from the time variation of the zero crossings of the low frequency signal, giving a result which is independent of amplitude fluctuations. Using pyroelectric detectors, the interferometer has a time resolution of 100 μsec and a sensitivity of 10^-2 fringe.     

A vibrationally compensated far infrared laser interferometer for plasma density measurements

A modulated far-infrared laser interferometer which is presently operating on the PDX experiment at Princeton is described. The interferometer geometry permits the characterization of inside D, outside D as well as circular discharges. To achieve this versatility, a titanium corner cube reflector, mounted inside the PDX vacuum vessel is used in conjunction with a second visible wavelength interferometer for vibration corrections. In addition, the use of room temperature quasi-optical Schottky diodes in the far-infrared interferometer is reported. The minimum detectable line average density of the system is 5×10¹¹ cm^–3.     

First gravity measurements using the mobile atom interferometer GAIN

We present the compact Gravimetric Atom Interferometer (GAIN), based on laser-cooled ⁸⁷Rb atoms, and discuss its first measurements of the local gravitational acceleration. In this context, we also describe an active vibration isolation system and a tip-tilt stage, which allow for a suppression of vibrational noise and systematic effects like the Coriolis force due to Earth’s rotation.     

A DC probe diagnostics for fast electron temperature measurements in tokamak edge plasmas

The tunnel probe is a new kind of Langmuir probe for use in the tokamak scrape-off layer. It provides simultaneous measurements of electron temperature and parallel ion current density with high frequency at the same point in space. We describe ongoing work to characterize the ion flows within the probe, and to calibrate the diagnostics using 2D kinetic simulations. Presented at 5th Workshop “Role of Electric Fields in Plasma Confinement and Exhaust”, Montreus, Seitzerland, June 23–24, 2002.     

Temperature and density spectroscopic measurements in different laser-generated plasmas

A pulsed Nd:Yag laser, at intensities of the order of 10¹⁰ W/cm², is employed to irradiate different thick metallic targets (Ti, Fe, Ag, and Ni) placed in vacuum. The obtained non-equilibrium plasmas are investigated with various analytical techniques. An electrostatic ion energy analyzer and different ion collectors are employed to monitor in situ the ions ejected from the plasma and to determine the core plasma temperature, the ion energy distributions and the ion angular emission. An optical spectrometer is employed to analyze the plasma corona emitted light vs. wavelength and to identify the emitted characteristic lines. The optical spectroscopy permitted to evaluate the electron temperatures and densities. Results show strong temperature and density gradients occurring in the laser-generated plasma plume.     

Nonlinear shielding and electron density enhancement in moderately coupled plasmas

As the plasma coupling grows, the electron density in the vicinity of the central ion increases appreciably, and the atomic reaction rates evaluated with the free Maxwell distribution for weakly coupled plasmas require modifications. The Maxwell–Boltzmann distribution, expressed in terms of the screened ionic potential, provides a simple way to correct for the density change. Several adjustments of the distribution are considered, including the nonlinear shielding, the quantum effect, the charge neutrality condition, and electron–electron correlation. The nonlinear coupling is shown to add to the linearly shielded potential a new component with much stronger shielding and generally reduces the strength of the linear potential. A simple model for the density enhancement is then constructed for moderately coupled plasmas, which may be applied to approximately correct the existing rates which were obtained in the weak coupling limit.     

A new multi-channel heterodyne polarimeter for plasma current and electron density measurements

A spatially-scanning phase-sensitive heterodyne far-infrared (FIR) polarimeter/interferometer for measurement of plasma current and electron densities is described. The instrument utilizes a rotating diffraction grating wheel for the dual purpose of spatially scanning the plasma cross section and providing a Doppler frequency offset for heterodyne detection purposes. Only two detectors are required to obtain accurate interferometric and polarimetric information for 15 discrete spatial chords. A novel approach to the optical processing of the initially linearly polarized probe beam allows the Faraday rotation of the vibrational ellipse to be unambiguously encoded as a phase modulation on the intermediate frequency carrier signals extracted from the two detectors. The plasma birefringence can be recovered from the corresponding amplitude modulation.     

用离焦4f差分干涉仪测量等离子体壳层电子密度

将环型横向剪切干涉仪置于两个镜头之间,由此设计出一种新型的离焦4f差分干涉仪,该干涉仪同时具有分离光路的剪切量和条纹空间频率分别可调的优点以及共光路结构的稳定性和易于调节的优点,使得在测量大密度梯度等离子体的密度分布时,可以在不降低空间分辨率的条件下仍保证干涉条纹可读。在DPF装置上进行了实验,获得了等离子体壳层的干涉图样,计算了等离子体的径向电子密度分布,在内电极端面上方测量到的最高电子密度约为1.2×1019 cm-3,外围等离子体壳层的电子密度约为2×1018 cm-3。     

用离焦4f差分干涉仪测量等离子体壳层电子密度

 将环型横向剪切干涉仪置于两个镜头之间,由此设计出一种新型的离焦4f差分干涉仪,该干涉仪同时具有分离光路的剪切量和条纹空间频率分别可调的优点以及共光路结构的稳定性和易于调节的优点,使得在测量大密度梯度等离子体的密度分布时,可以在不降低空间分辨率的条件下仍保证干涉条纹可读。在DPF装置上进行了实验,获得了等离子体壳层的干涉图样,计算了等离子体的径向电子密度分布,在内电极端面上方测量到的最高电子密度约为1.2×10¹⁹ cm^-3,外围等离子体壳层的电子密度约为2×10¹⁸ cm^-3。     

Determination of critical electron density for the establishment of LTE in argon plasmas

Oscillator strengths of Ar I lines were measured in a certain interval of electric currents in an argon cascade are in order to determine the critical electron density necessary for the establishment of LTE in argon plasmas.     

一种新的线成像激光干涉测速系统

设计并搭建了一种新的线成像激光干涉测速系统,用于小样品材料的冲击波诊断或飞片速度测量。系统采用梳状干涉条纹做为信号载体,利用1维光纤阵列＋光电倍增管＋数字示波器替代变像管扫描相机作为记录设备,记录伪推挽四路干涉信号,实现1 ns时间分辨和86 μm空间分辨。用它测量了脉冲激光驱动铝膜飞片的速度场,获得对比度较好的信号,数据处理结果揭示了飞片加速过程将近20 ns,飞片的平面度为14.8 mrad。实验证明,该线成像激光干涉测速系统具有一定实用性。     

一种新的线成像激光干涉测速系统

 设计并搭建了一种新的线成像激光干涉测速系统,用于小样品材料的冲击波诊断或飞片速度测量。系统采用梳状干涉条纹做为信号载体,利用1维光纤阵列＋光电倍增管＋数字示波器替代变像管扫描相机作为记录设备,记录伪推挽四路干涉信号,实现1 ns时间分辨和86 μm空间分辨。用它测量了脉冲激光驱动铝膜飞片的速度场,获得对比度较好的信号,数据处理结果揭示了飞片加速过程将近20 ns,飞片的平面度为14.8 mrad。实验证明,该线成像激光干涉测速系统具有一定实用性。     

A modified Marton-type electron interferometer

It is shown that the original Marton-type electron interferometer is based on the Fresnel diffraction of two coherent beams by a crystal. The modified Marton-type electron interferometer presented here is based on the Fraunhofer diffraction. The advantages of the proposed interferometer are given in the text along with a simplified sketch of the major components.     

非理想氩等离子体电子密度和平均离化度理论研究

用SHM模型计算了非理想Ar等离子体在温度T为2.0eV、密度ρ为0.01~0.5g•cm-3的电子密度和平均离化度。研究了非理想Ar等离子体电子密度和平均离化度随温度、密度的变化规律,得到了在温度T为2.0eV、密度ρ为0.01~0.5g•cm-3非理想Ar等离子体的平均离化度小于0.5的结果。这表明非理想Ar等离子体的平均离化度非常低,大量的Ar仍然处于非电离状态。计算的结果还显示了平均离化度随等离子体密度ρ增加而减小的特征,并分析了减小的原因。     

Oscillation correction to the electron density of an atom

The oscillation correction to the electron density of an atom in the Thomas-Fermi model is calculated with the help of the method of Green's functions and continuous integration. This correction has a nonanalytic dependence on Planck's constant and cannot be obtained by the usual methods, which employ an expansion in terms of a small parameter proportional to .The author is deeply grateful to L. Ya. Kobelev for suggesting this subject and supervising the work.     

用马赫贞德干涉仪测量喷气式Z箍缩等离子体密度

 为了研究喷气式Z箍缩（gas-puff Z-pinch）等离子体的内爆特性，研制了一套马赫-贞德干涉系统，并在小型喷气式Z箍缩装置(充电电压23kV,放电峰值电流210kA)上进行了试验，获得了清晰的干涉图像。根据干涉图上条纹的移动数目，计算得到该装置内爆早期等离子体的平均电子密度为10¹⁷~10¹⁸/cm³。     

An atom interferometer for measuring loss of coherence from an atom mirror

We describe an atom interferometer to study the coherence of atoms reflected from an evanescent wave mirror. The interferometer is sensitive to the loss of phase coherence induced by the defects in the mirror. The results are consistent with and complementary to recent measurements of specular reflection.Received: 3 August 2004, Published online: 26 October 2004PACS: 03.75.Be Atom and neutron optics - 03.75.Dg Atom and neutron interferometry - 39.20. + q Atom interferometry techniques The Laboratoire Charles Fabry is part of the Federation LUMAT, FR2764 du CNRS.     

A Michelson interferometer using electron waves

An electron interferometer of the Michelson type is realized. Monoenergetic 25 keV electrons emitted from a line source 1000 Å in width are deflected by 90 ° in a magnetic Castaing prism and reflected on two mirrorsM ₁ andM ₂ held at a potential ΔU _m negative with respect to the cathode. In the experiment the mirrors are represented by height differences on the surface of an silvered glass plate. The reflected electrons are once more deflected by the magnetic prism behind which the coherent partial beams 1 and 2 reflected on the mirrorsM ₁ andM ₂, respectively, are superimposed using an electrostatic biprism to form two-beam interferences. The observed fringe shift indicates a phase shift due to differences in height between the equipotentials reflecting the partial beams 1 and 2. It is estimated that path differences less than the electron wavelength of 0.08 Å can be observed.