Population inversion between the ground and first excited states in a recombining hydrogen plasma

Plasma conditions for generating a population inversion between the ground and first excited states in a recombining hydrogen plasma have been investigated on the basis of the CR model. Population inversion can be expected when three-body recombination plays a dominant role; the required regions of electron density and temperature are specified. It is shown that upper bounds exist for the ground-state population density at given electron density and temperature. Larger inversion densities can be obtained between the ground and first excited states than between excited levels. Numerical results are presented.     

Optical Emission of Molecular Hydrogen in a Recombining Hydrogen Plasma

We observed optical emission of molecular hydrogen in a recombining hydrogen plasma with an electron temperature of 0.1 eV and an electron density of 3 × 10¹²cm^–3. The optical emission intensities of molecular hydrogen in the recombining plasma were roughly 10%–45% of those in an ionizing plasma with an electron temperature of 4 eV. The ratio was greater for a transition line originated from an excited state with a larger vibrational quantum number. Because of the low electron temperature of 0.1 eV, the production processes of excited states are not considered electron impact excitation in the recombining plasma. Possible recombination processes are discussed which produce excited states of molecular hydrogen in the recombining plasma (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Population inversion in optically thick,recombining hydrogen plasmas

The plasma condition is investigated theoretically for population inversion between the first two excited states of hydrogen atoms in a recombining plasma. The rate equation, including atom-atom collision terms, is solved consistently with the optical escape factors. The upper bound of the ground level population density (n₁)_max necessary for inversion in the optically thick plasma at specified electron density and temperature is nearly inversely proportional to the mean radius of the plasma r_O. With a decrease in the atom temperature, the upper bounds increase in the optically thin plasma but decrease in the optically thick plasma.     

Experimental study of a drifting low temperature plasma extracted from a magnetized plasma column

In a new divertor simulator, a very cold recombining plasma is produced after transverse electric extraction from a dense magnetized plasma column. The plasma is characterized using probes, spectroscopic measurements, and ultra-fast imaging of spontaneous emission. This new technique is shown to be very useful for the investigation of the recombination processes.     

Simulation and experiment on detached plasmas in the linear divertor simulator NAGDIS-II

We have performed two dimensional fluid B2 simulations on detached recombining plasmas to compare with experimental observations in a linear divertor plasma simulator. In detached helium plasmas associated with volumetric electron-ion recombination (collisional radiative recombination), an electron-ion energy exchange process followed by ion-neutral charge exchange is found to be a key to reduce the electron temperature along the magnetic field to be less than leV. The structural change of detached plasmas associated with molecular activated recombination has been also discussed in detail.     

Observation of population inversions in a freely expanding helium plasma

Population inversion on He I is experimentally investigated in a recombining helium plasma. Experimental results confirm that population inversions for n = 3–4 and 3–5 levels of the He I singlet system are larger than for the triplet system. The difference between the two systems is discussed by using rate equations.     

Infrared recombination lasers pumped by low energy Nd: YAG and excimer lasers

24 infrared laser lines on atomic and ionic transitions have been observed in recombining plasmas by vaporizing and ionizing Cd, Pb, Sn, Zn, and Mg with low energy Nd:YAG or excimer pump-lasers. For operation and optimization of the recombination lasers separated plasma spots and a plasma confinement have been used. The operation of shorter wavelength systems by isoelectronic scaling is discussed.     

Lowering of the Populations of Excited Hydrogen and Helium Atoms in Plasmas Irradiated by a Laser Beam

The populations of excited hydrogen and helium atoms in non-L.T.E. plasmas have been calculated for two different physical situations, namely (i) no external radiation field present, and (ii) strong superposed radiation originating from a CO₂, Ruby or Argon Ion Laser. The radiation field intervenes in the collisional-radiative model via two new terms: Photoionization and stimulated recombination induced by the Laser radiation field. The solutions of the rate equations yield a lowering of the populations when a plasma is irradiated by a Laser beam. The lowering is different for cold recombining and hot diffusion-dominated plasmas. At high radiation densities a saturation effect occurs, since the photoionization rate becomes equal to the rate of stimulated recombination. Measurements of the populations of excited H and He atoms in a glow discharge irradiated by a CO₂ Laser beam of power density 10⁵ W/cm² are in broad agreement with the theoretical predictions.     

对应于铜离子X射线激光条件下的等离子体基本参数和光谱结构

本文是在复合泵浦类钠铜软X射线激光系统实验基础上,对该体系的等离子体参数、光谱结构进行测量和分析,给出了类钠铜离子粒子数反转,增益系数与等离子体参数及发射谱结构的内在联系。文中也给出了不同激光功率对各种等离子体参数、光谱结构的影响。     

类锂铝复合机制产生X光激光的等离子体状态

本文从速率方程出发,讨论了类锂铝复合等离子体的激发态结构,衰减常数,反转率和小信号增益等表征介质增益特性的物理量以及它们随电子温度,电子密度和光子逃逸几率的变化。找到了进行类锂铝离子通过复合机制产生X光激光设计应创造的等离子体状态目标区域。还讨论了这些物理量随原子序数变化的定标律。     

Recombination of hydrogen atoms on fine-grain graphite

The probability of recombination of hydrogen atoms on surfaces of fine-grain graphite EK98 was investigated as a function of surface roughness. The source of hydrogen atoms used in this experiment was weakly ionised plasma created with an inductively coupled radiofrequency generator at pressures from 30 Pa to 175 Pa in hydrogen. Hydrogen atom density was measured by means of fibre optic catalytic probes. The recombination coefficient of the graphite samples was determined by observing their impact on the spatial distribution of the atom density in a closed side-arm of the reactor. Smith's diffusion model was used to calculate the values of the recombination coefficient. The measured recombination coefficient was found to increase much faster than the measured effective surface. This discrepancy is explained by the fact that on a surface which is not perfectly flat, there is a finite probability for multiple collisions. Impinging atoms collide more than once with the surface before they are reflected into the surface, which results in a larger probability of recombination.     

Appearance of a Hα Minimumat the Onset of Net Recombination in Hydrogen Plasmas

Hydrogen plasmas out of ionization equilibrium are either ionizing or recombining depending on the electron temperature T_e . Within the transition region between these two opposite states a minimum of the H_α emission is often experimentally observed. Simple cases were previously analyzed which could be interpreted assuming only a temperature variation, i.e the electron density was constant in the transition region. Here we discuss two examples in which both the density and the temperature vary at the transition. In the linear plasma generator PSI‐II a hydrogen plasma is cooled down by puffing additional gas. We find a minimum at T_min ≈ 1.1 eV. A second example is the effect of an ELM(edge localized mode) pulse propagating through a recombining divertor plasma in the tokamak ASDEX Upgrade. The H_α response shows a double peak which can be interpreted as a local minimum assuming a simultaneous rise of density and temperature during an ELM. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Forming characteristics of recombination properties of InSb MOS structures

Build-up processes of small-signal photo-emf and space-charge layer capacitance following cooling of the structure are investigated as well as the effect on them of fixed charge in the oxide and length of exposure to a voltage applied to the structure. It is shown that there are two types of recombination centers in the semiconductor which differ in the dependences of the concentrations and build-up times on the applied voltage. The centers of the first type determine the carrier recombination velocity in the weak inversion region, while centers of the second type are deep acceptors operating in the region of strong surface inversion. The latter are produced in the structure in the presence of an electric field. It is assumed that the recombinations centers originate from structural defects in the semiconductor and at the interface, whereby centers of the second type include indium vacancy and hydrogen. A mechanism of their emergence is proposed.     

Influence of Laser radiation on the collisional-radiative recombination and ionization coefficients

It is shown that irradiation of a plasma by a Laser beam lowers the collisional-radiative coefficient for recombination (α) and increases the one for ionization (S) compared to unirradiated plasmas. Numerical values ofα andS are given for a hydrogen plasma irradiated by CO₂, Ruby, and Ar-Ion Lasers. The calculations are based on a collisional-radiative model in which photoionization and stimulated recombination intervene. Stimulated recombination has an important effect and can lead to saturation of free-bound transitions at high power density of the Laser beam as long as multiphoton ionization effects and plasma heating by inverse bremsstrahlung remain negligibly small.     

Radiative cooling of tokamak plasmas due to multiply-charged Fe impurity ions

Calculations are presented for the rates of radiative energy loss from tokamak plasmas arising from radiation processes involving collisions between electrons and multiply-charged Fe impurity ions. The distribution of ionization states is determined from the steady-state corona model. The inclusion of dielectronic recombination raises the temperature at which each ion has its maximum equilibrium abundance. For certain nonhydrogenic ions, the dielectronic recombination rates obtained from previous calculations are found to be overestimated due to the neglect of autoionization into an excited state of the recombining ion. Electron impact excitation of resonance line radiation in the far ultraviolet and X-ray regions is the dominant radiative cooling mechanism at temperatures where ions with bound electrons are abundant. However, the radiation emitted during dielectronic recombination can be more important than direct recombination radiation and bremsstrahlung.     

Establishing an inverse population on mixing a hot plasma with a cold gas

A model in which the interaction between a hot plasma and a cold gas is used to create an inverse population is considered. Using hydrogen as an example it is shown that it is impossible to obtain an inversion at high electron concentrations (n₁= 10¹⁶ cm^?3). The conditions under which an inversion can occur are outlined.     

Laser-stimulated formation and stabilization of antihydrogen atoms

Laser-stimulated radiative transitions from states close to the ionization threshold to low-lying atomic levels are considered for protons (antiprotons) in a cold electron (positron) plasma and estimates for the resulting formation rate of hydrogen (antihydrogen) atoms in the ground state are given. The estimates apply to both laser-stimulated recombination and induced radiative stabilization of high Rydberg levels. First experiments concerning laser-stimulated recombination in merged beams of electrons and protons are discussed, which have confirmed the rate predictions for this process. In view of antihydrogen formation in a cold trapped positron plasma, the use of two successive stimulated transitions is considered for obtaining a high formation rate of ground-state atoms at relatively low radiation intensity.     

Structure and properties of zinc oxide films deposited in the recombination burning zone of a low-temperature plasma

The structure and refractive index of thin zinc oxide films grown in reactive gas-discharge plasma have been studied. Reactions on the substrate and film growth occur under conditions of complete or partial reagent ionization. The ion recombination and kinetic energies activate film growth. Thermal heating of the films is absent. Under certain concentration of recombining ions, the films are found to acquire new structural and electrooptic properties rather than being destructed. To a thickness of 1500 Å, the films are optically dense and have high mechanical and chemical resistance and changed interplanar spacing and refractive index as compared to the analogous properties of the ZnO films synthesized during thermal activation.     

A recombination laser from cooled hydrogen plasma (plasma dynamic laser)

Using our time-dependent model we calculate the inversion density and gain for a visible line (6563 Å) from hydrogen as a result of rapid cooling of a plasma. A visible plasma dynamic laser is shown to be possible under certain conditions.