电子对Cl2的离解附着

在电子平均能量为3—5电子伏的范围内,测定了Ar/Cl₂混合物中,电子对Cl₂的离解附着速率常数。结果表明,电子平均能量为3.5电子伏时,离解附着速率常数为(3.2±0.4)×10^-10厘米³/秒,并考察了速率常数与电子平均能量的关系。这些实验结果与最近Los Alamos国家实验室研究者们的类似工作的结果是一致的。 关键词：     

Plasma wave field effect transistor as a resonant detector for 1 terahertz imaging applications

The possibility of using plasma wave field effect transistor in a time domain terahertz (THz) spectroscopy setup is presented. We demonstrate that High Electron Mobility Transistors (HEMTs) is an efficient device for detection of pulsed terahertz electric fields generated with a femtosecond laser oscillator. The response was observed in the frequency range of about 1 THz, far above the cutoff frequency of the transistors at room temperature. We show that the physical mechanism of the detection is related to the plasma waves excited in the transistor channel and that significant improvement of the active device can be achieved by increasing the drain current. The two-dimensional terahertz imaging applications clearly demonstrate that plasma wave nanometer HEMT should be employed as efficient future detectors in a matrix configuration.     

Lengthening the Lifetime of Long Plasma Channel in Air Generated by Femtosecond Laser Pulse

We theoretically investigate the lifetime of self-guided plasma channel in air by launching an auxiliary delayed long-pulsed laser beam following an ultrashort laser. A detailed model makes the electron-ion recombination, the attachment of electrons on neutral particles, and particularly the impact ionization and electron-detachment mechanism incorporate. The calculated results show that the temporal evolution of electron density is greatly flattened and broadened. When the auxiliary laser intensity exceeds the threshold 3.32 × 10^4 Wcm^-2, the channel lifetime is distinctly prolonged from nanosecond to microsecond, or even longer due to the electrical field enhancement. Furthermore, with the laser intensity up to 109 Wcm^-2, the impact ionization overwhelms the detachment in effect. Thus, it is an effective way to extend the channel lifetime and provides a real opportunity for applications.     

Simulation of turbulence

The linear theory of propagation of a spherical wave layer is used to treat the principles of simulating turbulent process and the criteria of its similarity. The mechanism of turbulence is given for a flat channel defined by two walls and for a square tube. We use this channel as an example to demonstrate the effect of the wave layer properties on velocity pulsations, as well as the effect of the characteristics of a sequence of disturbances on the structure of pulsations. The model is used to describe the structure of a plasma channel developed by a Bessel beam of laser radiation. The Mathematica-4 language is used for simulation.     

Amplifying discharge instabilities in the emission channel of a plasma electron emitter

We consider the amplification of oscillations of the plasma parameters in the emission channel of an electron source with a plasma emitter. The relationship between the modulation level of the emission current and the oscillations of the concentration and potential of the emitting plasma is determined. The amplification of the discharge instabilities is seen to be a function of the ratio of the size of the boundary layer in the channel to the channel radius. The amplification factor is calculated as a function of the emission current and the accelerating voltage. The change in the plasma parameters at the emission boundary for a plasma shift in the channel is taken into account.Tomsk Academy of Control Systems and Electronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 73–76, Feburary, 1994.     

Macroscopic Stability of Charged Particle Streams

We compare the analysis of macroscopic instabilities of pinch systems based on classical hydromagnetic theory with an analysis based on two-fluid electromagnetic hydrodynamics. In contrast to the predictions of the hydromagnetic theory, where the sausage-type instability is thought to predominate, the two-fluid electromagnetic hydrodynamics approach indicates that filamentation of the current channel is the most important mechanism at work. We conclude that macroscopic instabilities are not insurmountable obstacles for the laboratory realization of the electromagnetic collapse; that is, the contraction of plasma by the magnetic field of its own current to the condense state.     

Stabilizing dicyanoacetylene anions in planetary atmospheres: quantum dynamics of its transient negative ions

Quantum computations that follow the electron-attachment process at low energies (<10 eV) to the NCCCCN gaseous molecule are carried out in order to understand the role of transient negative ions (TNIs) which act as “doorway states" to molecular stabilization and/or fragmentation after resonant attachment of an environmental electron. The computed behaviour of the found TNIs suggests that an NCCCCN^*- intermediate could be formed under conditions which justify and explain the existence of stable carbonaceous anions in the interstellar medium, while further anionic fragments of the title molecule, already seen in laboratory experiments, are also identified by the present calculations.     

Electron-transition stimulated plasma chemical reactions on surfaces with nanostructures

A mechanism is proposed for dissipating the energy of the heterogeneous recombination of atoms from low-temperature plasma. The mechanism considers accommodation of the energy of the reaction through an electron channel. The results from simulations using the Monte Carlo method for gas-surface systems with metal nanodots are reported. It is demonstrated that in wide-gap solids with metal nanodots, the electron channel can determine the rate of the plasma-chemical reaction and the epitaxial growth of a semiconductor or a nanowhisker.     

Radiative electron-attachment spectra of O3 and SO2

Several aspects of radiative electron-attachment processes are discussed and the corresponding photon energy spectra computed for O₃ and SO₂. In both cases the vibrational stretching mode is significantly excited. The calculated electron attachment spectrum of SO₂ is compared with the laser photo-detachment spectrum of SO₂ ^-. The computed electron affinities and changes in geometry between natural and negative ion are in good agreement with the experimental data.     

Excitation of accelerating wakefields in inhomogeneous plasmas

The excitation of the wakefields in an inhomogeneous plasma by a short laser pulse is investigated theoretically. A general equation for the wake excitation in transversely nonuniform plasma is derived. This equation is applied to the step-function density profile model of hollow channel laser wakefield accelerator. A more realistic model, in which the transition between the evacuated channel and the homogeneous surrounding plasma occurs over a finite radial extent, is then analyzed. It is shown that the excited channel made can interact resonantly with the plasma electrons inside the channel wall, leading to secular growth of the electric field. This eventually results in wavebreaking and the dissipation of the accelerating mode. We introduce an effective quality factor Q for the hollow channel laser wakefield geometry. This resonance limits the number of electron bunches that can be accelerated in the wake of single laser pulse     

等离子体通道中的自生磁场

研究了超短脉冲强激光在等离子体通道中传播时产生的自生磁场．利用相对论动量方程和泊松方程及安培定律得出自生磁场的一个基本公式，在此基础上解析并数值研究了通道中产生的自生磁场的特性和结构，初步探讨了超短脉冲强激光在等离子体中传播时形成的排空效应对自生磁场的影响，并分析了产生自生磁场的机制 关键词：     

A Source for Fuel Supply to a Fusion Reactor Core

We present the results of studies of the plasma source based on the coaxial accelerator with the slothole channel geometry for plasma acceleration and working gas inlet into the accelerator via the electrodynamic valve. The plasma parameters at the output of the accelerator are measured. The slot-hole channel of the accelerator created higher jet pressure, as compared to the coaxial channel, especially at large distances from the source. The jet pressure reached 10⁶ N/m² at a distance of 0.7 m. The source created moderately pure plasma for a current below 80 kA. The density was (2.5–5) × 10²² m^–3, which was higher than the density obtained with the coaxial gun.     

Parametric amplification of laser-driven electron acceleration in underdense plasma

A new mechanism is reported that increases electron energy gain from a laser beam of ultrarelativistic intensity in underdense plasma. The increase occurs when the laser produces an ion channel that confines accelerated electrons. The frequency of electron oscillations across the channel is strongly modulated by the laser beam, which causes parametric amplification of the oscillations and enhances the electron energy gain. This mechanism has a threshold determined by a product of beam intensity and ion density.     

空气中激光等离子体通道导电性能的研究

超强飞秒激光在大气中传输时，可以形成很长的等离子体通道.对通道电阻率和测量电极与等离子体通道间的接触电阻进行了测量，并对影响等离子体通道电阻率的主要因素进行了研究分析.提出减小等离子体通道电阻的方案. 关键词： 等离子体通道 电阻率 接触电阻     

A plasma channel scheme for the interaction of an intense femtosecond laser pulse with a deuterium cluster jet

We propose a plasma channel scheme to obtain an improved table-top laser driven fusion neutron yield as a result of explosions of large deuterium clusters irradiated by an intense laser pulse. A cylindrical plasma channel is created by two moderate intensity laser prepulses at the edge of a deuterium cluster jet along which an intense main laser pulse propagates several nanoseconds later. With the aid of this plasma channel, the main laser pulse will be allowed to deposit its energy into the central region of the deuterium gas jet where the cluster sizes are larger and the atomic density is higher. The plasma channel formation and its impact on the deuterium ion energy spectrum and the consequent fusion neutron yield have been investigated. The calculated results show that a remarkable increase of the table-top laser driven fusion neutron yield would be expected.     

Formation of extended directional breakdown channels produced by a copper wire exploding in the atmosphere

Experimental data for switching initiated by the electrical breakdown of air gaps up to 1.9 m long with an arbitrary geometry that are produced by an exploding copper wire 90 μm in diameter are presented. At an initial voltage of 11 kV, the stored energy equals 100–2100 J. Two channel formation conditions are possible: explosion of a wire without electrical breakdown and electrical breakdown in a channel produced by an exploding wire with a delay (current pause) no longer than 250 μs. Current and voltage waveforms across the discharge gap, as well as the resistivity values, under the electrical breakdown conditions are shown. Mechanisms and conditions for streamer initiation at a mean electric field strength in the discharge gap of 5.3–17.0 kV/m are discussed. The geometrical dimensions of plasma objects in the forming channel, the run of the electrical current under breakdown, and the formation mechanism of wire explosion products are found from color microphotographs. The formation mechanism of large aerosols in the form of tiny spherical copper and copper oxide (CuO, Cu₂O) particles under wire explosion conditions is discussed.     

Spectroscopic diagnostics for an electrical discharge plasma in a liquid

We conducted spectroscopic studies of an electrical discharge plasma in a liquid, used for synthesis of nanosized particles of metals and their compounds. From the intensity ratio of the copper lines, we estimated the electron temperature, and from the Stark broadening of the hydrogen lines H _α we determined the electron density in the electrical discharge plasma. Information about the concentration of copper atoms in the discharge was obtained from analysis of the spectra in the region of resonance lines of copper. We carried out a comparative analysis of the plasma parameters for spark and arc discharges in water, ethanol, and air. Based on the equation of state for an ideal plasma, taking into account the Debye correction, we estimated the pressure in the plasma channel.     

Formation of plasma channels in the interaction of a nanosecond laser pulse at moderate intensities with helium gas jets

We report on a detailed study of channel formation in the interaction of a nanosecond laser pulse with a He gas jet. A complete set of diagnostics is used in order to characterize the plasma precisely. The evolution of the plasma radius and of the electron density and temperature are measured by Thomson scattering, Schlieren imaging, and Mach-Zehnder interferometry. In gas jets, one observes the formation of a channel with a deep density depletion on axis. Because of ionization-induced defocusing which increases the size of the focal spot and decreases the maximum laser intensity, no channel is observed in the case of a gas-filled chamber. The results obtained in various gas-jet and laser conditions show that the channel radius, as well as the density along the propagation axis, can be adjusted by changing the laser energy and gas-jet pressure. This is a crucial issue when one wants to adapt the channel parameters in order to guide a subsequent high-intensity laser pulse. The experimental results and their comparison with one-dimensional (1D) and two-dimensional hydrodynamic simulations show that the main mechanism for channel formation is the hydrodynamic evolution behind a supersonic electron heat wave propagating radially in the plasma. It is also shown from 2D simulations that a fraction of the long pulse can be self-guided in the channel it creates. The preliminary results and analyses on this subject have been published before [V. Malka et al., Phys. Rev. Lett. 79, 2979 (1997)].     

Study of the gas-filled injector of a plasma opening switch

A plasma injector with pulsed gas filling is investigated experimentally. Interferometric measurements of the formation dynamics of the plasma channel are carried out. Under optimal operating conditions, the injector is capable of producing a plasma channel 4 cm in diameter with an electron density of ∼10¹⁷ cm⁻³. The effect of the cathode diameter of the plasma opening switch on the conductivity of the plasma channel is studied. It is shown that the current flowing through the plasma channel of a single injector attains 400 kA.     

Self-Focusing and Channeling of Wave Beams in a Nonuniform Magnetic Field under Conditions of Ionization Nonlinearity

We study experimentally the effect of ionization self-channeling of waves at the whistler frequencies in a nonuniform magnetic field. It is shown that the formed plasma nonuniformity localizes the radiation from a short high-frequency source inside a discharge channel stretched along an external magnetic field. We found a possibility to control the parameters of the formed plasma-wave channel as well as the dispersion characteristics and structure of wave fields in wide limits by varying the magnetic field in a specified spatial region. We propose a method for the formation of a plasma resonator and test this method in the laboratory experiment. The spatial plasma and field distributions in this resonator are similar to those along a geomagnetic field tube of the magnetospheric resonator. We reveal the plasma instability in such a resonator in the vicinity of the frequency of electron bounce oscillations between magnetic mirrors.