Continuous emission of argon,krypton and xenon plasmas

Emission coefficients of shock-tube plasmas have been measured as functions of the plasma parameters in the visible spectrum. The plasma state was determined by dual-wavelength interferometry and high accuracy of the ξ-factors was achieved. The results are compared with theoretical and other experimental data. In particular, the dependence of ξ on the plasma state is discussed.     

Multispectral imaging of continuum emission for determination of temperature and density profiles inside implosion plasmas

In inertial confinement fusion experiments, implosion of a cryogenic hydrogen isotope-filled capsule produces a plasma with a high-temperature, low-density core (the hot spot) surrounded by a low-temperature, high-density main fuel layer. Experimental measurements of temperature and density profiles in the hot spot are critical for implosion diagnosis. In this paper, we propose a simple technique for measuring core temperature and density profiles in cryogenic implosion plasmas. This technique uses absolutely calibrated continuum emission spectroscopy coupled with two-dimensional imaging to allow temperature and density profiles to be measured directly. We develop the technique analytically, and validate it using synthetic data and hydrodynamics simulation results. We find that the technique should be sufficiently accurate to measure central temperatures and densities to better than 20%. The technique may also find application to the diagnosis of other types of plasmas.     

Studies of continuum radiation from nitrogen,oxygen and carbon dioxide plasmas in the vacuum ultraviolet region

The spectral distribution of the radiation intensities of nitrogen, oxygen and carbon dioxide plasmas have been measured at atmospheric pressure and temperatures of 10,000–13,000 K within the spectral range 110–250 nm. Analysis of our results and literature data shows a continuum produced by the formation of negative ions and the importance of photoattachment in the total radiation intensities of nitrogen and oxygen plasmas. Photodetachment cross sections of N^- and O^- have been determined. Calculations were made on the assumption of LTE in the plasma. The applicability of this assumption under the conditions of the experiments is discussed.     

Charged particle emission from transient plasmas

When a voltage pulse is applied to an interelectrode vacuum gap, bunches of transient plasma are formed on the cathode which are efficient emitters of charged particles. The present review gives the results of investigations of the cathode-plasma emissivity, the stability conditions of the high-voltage discharge phase, the mass-charge composition of the cathode plasma and its relationship to the threshold current of the cathode material, and the conditions for forming an anode plasma and its influence on the duration of the high-voltage discharge phase. Examples are given in which the results are used to create a wide range of electron and ion beams and current beakers.Institute of Power Electronics, Siberian Branch, Russian Academy of Sciences. G. P. Bazhenov Institute of Electrophysics, Urals Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 83–99, March, 1994.     

X-ray emission from short-pulse laser plasmas

Highly intense picosecond and subpicosecond laser pulses interacting with solids can create hot and dense plasmas which emit x-ray pulses in a broad spectral range from 100 eV up to MeV. The duration of these x-ray pulses depends on the transient behaviour of the relaxation and recombination mechanisms, as well as on the lifetime of energetic electrons produced via nonlinear processes in the plasma. This paper reports experiments using a 1.5-ps laser pulse with high constrast ratio (up to 10¹⁰) and intensities up to 10¹⁸ W cm^-2 irradiating solid targets. Both the line spectrum characteristics of a magnesium plasma, recorded using crystal spectrometers with high spectral resolution, and kinetic calculations have allowed the deduction of plasma parameters in the process of plasma evolution. In addition, hard x-ray pulses from a tantalum plasma were measured and their scaling was explained as bremsstrahlung emission from energetic electrons. Absolute dose values of x-ray pulses are given.     

Ion emission from arc discharge plasmas

Results are presented from studies of the ion-emission properties of the anode plasmas of low-pressure contracted arc discharges and vacuum arcs. It is shown that creating a longitudinal magnetic field in the anode region of a discharge changes the plasma parameters significantly and facilitates a large increase in the ion current. Space charge limited ion current in a vacuum arc leads to a reduction in the noise level of the total ion current and of its components with charges of up to +3, while creating Penning discharge conditions ensures that ions of different gases can be generated in this discharge system at fractions as high as 90%, depending on the type of plasma forming gas.Institute of High-Current Electronics, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vuzov, Fizika, No. 3, pp. 24–33, March, 1994.     

Well-posedness of continuum models for weakly ionized plasmas

Continuum fluid models of weakly ionized plasmas are useful in the design and control of plasma-assisted deposition and etching processes. The equations in these models are numerically stiff. Their stiffness is affected by the imposed boundary conditions. In this work, a DC discharge model is studied and the effect of the boundary conditions on the model solution is investigated. It is established, both analytically and numerically, that depending on the choice of boundary conditions the model may range from being ill-posed to being solvable with standard software. It is also established that excessive truncation error maybe present in numerical simulations which appear to qualitatively capture plasma structure. Accurate numerical simulations of the considered model, with alternate boundary conditions, are shown to capture many characteristics of a DC discharge, albeit at lower values of applied voltage than those reported in the literature. Finally, model shortcomings are discussed     

高Z等离子体辐射的非平衡特性

 对激光直接加热和X光辐射加热Au等离子体的非平衡特性进行了实验研究，探讨了它们的物理机制。为此，提出了一种新型的锥盘靶结构，并在神光 II装置上进行了实验，结果表明：锥盘靶很好地避免了激光加热区的等离子体喷射和散射光对X光加热区的影响，改善了辐射加热场的干净性。对锥盘靶激光和辐射加热进行了模拟计算，所得结果与实验的结果符合较好。     

高Z等离子体辐射的非平衡特性

对激光直接加热和X光辐射加热Au等离子体的非平衡特性进行了实验研究,探讨了它们的物理机制。为此,提出了一种新型的锥盘靶结构,并在神光 II装置上进行了实验,结果表明：锥盘靶很好地避免了激光加热区的等离子体喷射和散射光对X光加热区的影响,改善了辐射加热场的干净性。对锥盘靶激光和辐射加热进行了模拟计算,所得结果与实验的结果符合较好。     

Oxygen impurity radiation from Tokamak-like plasmas

We have constructed a nonhydrodynamic coronal model for calculating radiation from impurity atoms in a heated plasma. Some recent developments in the calculation of dielectronic recombination rate coefficients and collisional excitation rate coefficients are included. The model is applied to oxygen impurity radiation during the first few milliseconds of a TFR Tokomak plasma discharge, and good agreement with experimental results is obtained. Estimates of total line and continuum radiation from the oxygen impurity are given. It is shown that impurity radiation represents a considerable energy loss.     

Measurements of the glass-to-plasma boundary-layer influence on continuum radiation in a T-tube

The influence of the glass-to-plasma boundary layers on the continuum radiation of hydrogen plasma has been experimenally checked at the H_β wavelength by introducing an additional number of boundary layers into the observed plasmas produced inside of a T-shaped electromagnetic shock tube. In the first case (case A), the plasma was observed (by using a monochromator) with the two usual boundary layers. In the second case (case B), four additional boundary layers were created by introducing two glass plates into the plasma. During the first microsecond, after the reflected shock front had passed the point of observation, no major differece was noted between the continuum intensities in cases A and B. At 1.5 μs and later, the difference amounted to about 10 to 20% with case B being more intense, depending on time, that is on the plasma parameters and boundary-layer thickness.     

Neutron emission from KSTAR Ohmically heated plasmas

An un-calibrated sensitive ³He detector was used to monitor the KSTAR neutron rate during Ohmically heated discharges. Neutrons were detected for every shot. If the neutrons were from D-D reactions then there should be a dependence on the ion temperature. We obtained ion temperature, electron density, Ohmic heating input power measurements, etc. from standard diagnostics. The study shows no observable dependence on the Ohmic power, ion temperature, or calculated source strength. It appears that the neutrons are from sources other than D-D reactions. The most probable source is high-energy runaway electrons.     

Directionality of terahertz emission from photoinduced gas plasmas

Forward and backward terahertz emission by ionizing two-color laser pulses in gas is investigated by means of a simple semianalytical model based on Jefimenko's equations and rigorous Maxwell simulations in one and two dimensions. We find the emission in the backward direction has a much smaller spectral bandwidth than in the forward direction and explain this by interference effects. Forward terahertz radiation is generated predominantly at the ionization front and is thus almost not affected by the opacity of the plasma, in excellent agreement with results obtained from a unidirectional pulse propagation model.     

Continuum emission from recombining oxygen and nitrogen plasmas

The quantum defect method is used to obtain photoionization cross-sections for some 40(55) levels of OI (NI) over a range of electron energies from threshold to one Rydberg. These cross-sections are then incorporated into a model that predicts the total radiative emission resulting from radiative recombination and bremsstrahlung in the presence of singly ionized oxygen (nitrogen) atoms. Modified emission coefficients are presented for the wavelength region extending from the visible to the long wave infrared for a variety of temperatures.     

Soft X-ray emission of continua from laser produced plasmas

Plasmas produced irradiating plane targets of low Z elements with moderate energy (3–10 J) lasers emit considerable amounts of free-free and free-bound continua in the soft X-ray region (10–100 Å) of the spectrum. With intensity calibrated grazing incidence spectrographs an intensity of the order of 10⁸ W sr^–1 Å^–1 cm^–2 emitted by the densest portion of the plasma inside the crater formed at the interaction was determined. This is in good agreement with theoretical predictions for a plasma of predetermined parameters. In case of high Z elements the continuum emitted has a very smooth wavelength dependence.