VUV emission model of REB-heated plasma

VUV emission model of a hygrogen plasma with oxygen impurity (T _e=tens of eV,n _e 10¹⁴–10¹⁶ cm^–3,ⁿimp=1–3 % n_e) is constructed in order to judge different possibilities of plasma diagnostics (especiallyT _e measurements) in the REBEX experiments. Two sets of calculations based on the nonstationary corona model are performed: time dependent continuous and line spectra in the range 5 eV—5 keV in the constantT _e approximation (discussion ofT _e measurements by the filter-method) and time dependent intensities of selected spectral lines (2s-2p type) of ionsO ²⁺–O⁵⁺ at variableT _e (including plasma heating by REB and radiative cooling). A possibility of plasma energy content determination from radiation losses is shown.We would like to acknowledge many helpful discussions with dr. P. unka; we thank also dr. J. Ullschmied for comparing our results with diamagnetic measurements.     

Anomalous plasma phenomena of hollow cathode arc discharge

Magnetically confined argon plasma produced by hollow cathode arc discharge has been studied in different experimental conditions, with discharge current from 10–50 A, vessel argon pressure between 10^–3 and 10^–4 torr (1 torr=133·32 Pa) and axial magnetic field up to 0·12 T. The plasma density measured by a cylindrical Langmuir probe is found to be 10¹⁹ to 4 × 10¹⁹ m^–3 and the electron temperatureT _e varies between 2·5 and 4·8 eV. When an external axial magnetic field is applied the plasma temperature decreases with the increase in the magnetic field intensity until it reaches a minimum value at 0·075T and then increases with the same rate. This has been interpreted as high frequency waves excitation due to electron beam-plasma interaction, which explains the electron density jumps with the magnetic field intensity. Enhanced plasma transport across the magnetic field is studied and classified as anomalous diffusion.     

Characterization of vacancy-related defects introduced into silicon during heat treatment by deep-level transient spectroscopy and gamma-ray diffraction techniques

Vacancy-related defects introduced into n-Si during annealing or aluminium diffusion at high temperature (1000–1250°C) have been studied. Different ambients (argon, nitrogen, vacuum and chlorine-containing atmosphere) were used to create a vacancy supersaturation during heat treatments. Three deep-level centers whose formation is governed by the presence of vacancies have been identified. They were characterized by the following temperature dependences of the thermal emission rate:e3 = 7.92 × 10⁷ T ² × exp(– 0.455/kT),e ₅ = 2.64 × 10⁶ T ² × exp( – 0.266/kT),e ₇ = 7.26 × 10⁶ T ² × exp (– 0.192/kT). The influence of different factors, such as heat-treatment conditions, concentration of oxygen and doping level in initial crystals, on center formation was studied. An asymmetric diffuse-ray scattering was observed near the surface of a crystal irradiated by thermal neutrons and annealed in a chlorine-containing atmosphere. This scattering is related to the formation of structural defects of the vacancy type. In the same region of the crystal, the concentration of the E7 center was one order of magnitude higher than that of other deep-level centers. Comparison of the-ray diffraction and deeplevel transient spectroscopy (DLTS) data suggests that the formation of the center occurs under the conditions of Si supersaturation with vacancies.     

Effect of nuclear structure on the single particle β− transitions in deformed nuclei

In the framework of the Nilsson model the calculations of the so called shape factor for the first forbidden ^– transitions 5/2^{+ 241}Pu 5/2^{– 241}Am and 7/2^{+ 177}Lu 7/2^{– 177}Hf are carried out. The dependence on the Nilsson potential parameters is studied. It turns out that for the transitions considered the calculated shape factor depends linearly on the electron energy and its slope is 10^–3 per 20 keV. This can affect the analysis of electron spectra if the endpoint energy is sufficiently large.     

Collisional broadening of Ba I line (553.5 nm) by He or Ar

The Doppler-free line shape of the 6s ^{2 1} S ₀ – 6s ¹6p ^{1 1} P ₁ transition at 553.5 nm in natural Ba in the presence of an argon or helium buffer gas has been measured at 744 K for gas pressures from 0.2 to 100 Torr. Using the measured data for pressures above 5 Torr, the broadening rate coefficients for the half width at half maximum (HWHM) are determined to be (4.9±0.5)10^–9 and (5.0±0.5)10^–9 s^–1 cm^–3 for helium and argon respectively.     

The effect of low-temperature electron irradiation on the transition temperature of YBa2Cu3O7−δ superconductors

Measurements of the complex susceptibility =–i of electron-irradiated YBa₂Cu₃O_7– show a strong influence of the electron irradiation dose, ·t on the transition temperatureT _c . For irradiation doses of ·t=2.2·10¹⁹ e^–/cm² we find a damage rate of T _c /(·t)=–1.6·10^–19 K/(e^–/cm²). It is assumed that the decrease ofT _c is mainly a bulk effect due to the production of atomic defects like vacancies and interstitials in the Cu–O–Cu chains and in the basal planes of the unit cells.     

Hydrogen-like recombination X-ray lasers using ps pulse drivers

We propose a scheme for producing high gain recombination X-ray lasers on hydrogen-like Balmer transitions by irradiating fibre targets with a 2 ps Chirped Pulse Amplification CPA beam of a Nd-glass laser facility. Very high gain coefficients for H-like C, N, O, F, Na Balmer transitions are predicted. The optimum electron density and temperature for maximum gain operation scale approximately asN _e 4 × 10¹³ Z ⁷ cm^–3 and T_e 7 × 10^–3 Z ⁴ eV, respectively, at the time when maximum lasing gain appears. Significant improvement in gain performance of recombination X-ray lasers is predicted by using CPA ps pulse drivers.     

Optical Emission Spectroscopy Used to Study the Characteristics of the Capacitive Radio-Frequency Discharge in Argon

Capacitively coupled radio-frequency (13.56 MHz) glow discharge in argon at low pressure (200 mTorr) has been studied by optical emission spectroscopy (OES) and electrical probe. Increasing power density resulted in lowering of the electron temperature T _e and increase of the electron density n _e. The to transition in this case takes place smoothly. The intensity (I _750.4) of the emission line at 750.4 nm due to 2p₁1s₂ transition closely follows the variation of n _e with power density. Calculation of the electron-energy probability function shows that electron occupation mainly changes in the high-energy tail, which explains close resemblance of I _750.4 to n _e. At moderate pressures, only OES method was applied to observe - transition which is abrupt in this pressure range.     

Interaction of Growth Steps on the Surface of InAs Epitaxial Layers in Vapor-Phase Epitaxy

The influence of concentrations of vapor-phase growth components on the structure of singular, vicinal, and nonsingular growth surfaces of InAs epitaxial layers grown in the In–AsCl₃–H₂ system is investigated by the methods of electron microscopy. It is established that the average distance between steps in the echelon increases as the input pressure P _AsCl3 increases in the range 70–700 Pa and then approaches a constant value when P _AsCl3 > 700 Pa. The observed dependences (P _AsCl3) are explained within the framework of the model of diffusion interaction of steps.     

Determination of the Concentration of Electrons in the Laser Plasma of Helium

The dependence of the Stark width of the spectral line of He II P 468.6 nm on the electron concentration in the laser plasma of helium for the range of electron densities N _e = (1–10)·10²³ m^–3 and electron temperatures of the order of 60 kK has been measured. The results obtained correspond well to Griem's theoretical data. An empirical relation is suggested which makes it possible to reliably determine the electron concentration from measured halfwidths in the investigated range of N _e.     

The influence of superradiant relaxation on associative ionisation yield of laser excited potassium atoms

The influence of superradiant relaxation of excited 7P _1/2 potassium atoms on their associative ionisation yield has been investigated. The excitation was carried out by a laser pulse in a tube containing potassium vapour with concentration 10¹⁴ cm^–3. A seven-fold drop of ionisation yield was found and spontaneous luminescence pulse distortions by superradiance (SR) were measured in the wide interval of excited atoms densities N _e ⁰ 10⁸–10¹³ cm^–3. The values of associative ionisation rate constant and SR threshold atomic densities are obtained, and the shapes and quantum yields of SR pulses are evaluated from the experimental results.     

Gas-puff Z-pinch experiment

The fast linear Z-pinch was experimentally investigated using a high-current pulse generator (10·8 F, 5–10 kJ, 150–250 kA) and pulse injection of argon and neon. Measured electrical characteristics of the discharge (current shape and risetime, inductance) and calculated dynamic parameters of plasma implosion (accelerated mass, radial plasma velocity) are presented. X-ray diagnostics with temporal resolution (vacuum X-ray diodes, semiconductor detectors) were utilized. The temperature and the density of pinch plasma (T_e 50 eV, n_e 1·4 × 10²⁶ m^–3) as well as its other parameters (size, lifetime) were estimated. Total energy emitted by the pinch in ultra-soft X-ray region (hv<1 keV) during 200 ns pulse achieves 125 J/4.The author is grateful to P. unka for stimulating discussions and also to V. ****Piffi and J. Rau for their help concerning X-ray detectors.     

MPD arcs as plasma sources for recombination lasers

In this study the decay of argon plasmas ejected from a MPD thruster described in a previous paper is investigated. Various parameters, e.g. the electron densityN _e , the electron temperatureT _e , and the absorption coefficient of the ArII-488 nm transition are measured by different experimental techniques. Axial and radial profiles ofN _e andT _e are determined, and used to decide on the relevant recombination mechanism. In spite of the fact that the dominant three-body recombination favours the population of the high-lying energy levels, population inversions have been observed even with the most sensitive method only in plasmas ejected from a reduced aperture of the MPD thruster. The theoretical analysis shows that the ranges ofT _e andN _e , in which recombination-lasing may be expected, are narrow. In addition, the mechanisms that limit the population inversions in discharge tubes of conventional Ar⁺-lasers restrict the dimension of the plasma perpendicular to the resonator axis. From these facts and the described measurements on population inversions we conclude that the initial diameter of the plasma has to be reduced. We therefore propose a new discharge configuration where extended regions of constant plasma parameters can be expected. With this arrangement it should be possible to reach population inversions required for laser oscillations in ArII.Polish Academy of Sciences, Gdansk, Poland     

The Yang-Lee edge singularity in spherical models

The density of Yang-Lee zeros in the thermodynamic limit is discussed for ferromagnetic spherical models of general dimensionalities and arbitrary range of interaction. In all cases the zeros lie on the imaginary axis in the complex magnetic field planeH=H+iH with a density (H) that exhibits a square root singularity(H) (H-H ₀), with=1/2, as the edge of the gap atH=H ₀(T) is approached forT>T _c. WhenTT _c one hasH ₀(T)(TT _c ) with critical exponent=+.Supported by the National Science Foundation in part through the Materials Science Center at Cornell University.     

Two-temperature channel model of a direct current arc

A relatively simple method is proposed for computing the gas and electron temperatures in an arc plasmotron channel within the framework of the self-consistent two-temperature channel model of an arc discharge. This method affords the possibility of obtaining the gas and electron temperature distribution with good enough accuracy for given discharge parameters (current intensity in the discharge, power inserted in the discharge, etc.) as a function of the radial coordinate in both nonequilibrium (T_e T_ai) and quasi-equilibrium (T_e = T_ai within the current conducting channel) cases. The results obtained can be utilized in model computations to estimate the gas and electron temperatures as well, possibly, as in a number of engineering computations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 80–86, July, 1990.The author is grateful to L. A. Rachevskii for useful discussion of results of the research.     

Elementary particle states based on the Clifford algebraC 7

The lepton isodoublet (e ^–,v _e ), the bare nucleon isodoublet (n,p), and their antiparticles are shown to constitute a basis of the irreducible representation of the Clifford algebraC ₇. The excited states of these doublets, i.e., ( ^–, ), ( ^–, ),..., and (s ⁰,c ⁺),(b⁰,t⁺) are generated by the products (e ^–,v _e )a and (n,p)a, wherea2^–1/2(e ^– e ⁺+v _e v _e ) has the same quantum numbers as the photon state. The bare baryonss, c, b, t carry the strangeness, charm, bottom, and top quantum numbers. These lepton and bare baryon states are in one-to-one correspondence with the integrally charged colored Han-Nambu quarks, and generate all the observedsu(3) andsu(4) hadron multiplets.     

Unusual Pathways of Triplet State Dynamic Relaxation in Meso-Aryl-Substituted Porphyrins and Their Chemical Dimers at 295 K

It was found that mono- and di-meso-phenyl substitution in octaethylporphyrins (OEP)and their chemical dimers with the phenyl ring as a spacer manifests itself in the dramatical shortening of T₁ state lifetimes at 295 K (from 1.5 ms down to 2–5 s in degassed toluene solutions). On the other hand, this substitution does not influence spectral-kinetic parameters of S₀ and S₁ states. The enhancement of the T₁ state non-radiative deactivation is explained by torsional librations of the phenyl ring around a single C-C bond in sterically encumbered OEP molecules leading to non-planar dynamic distorted conformations in the excited T₁ states. For these compounds with electron-accepting NO₂-groups in the meso-phenyl ring the strong non-radiative deactivation of S₁ and T₁ states (by 2–3 orders of magnitude) is observed upon the displacement of NO₂-group from para-to ortho-position of the phenyl ring. The S₁ state quenching is caused by the direct intramolecular electron transfer to low-lying CT state of the radical ion pair (the normal region, non-adiabatic case presumably, V = 130–190 cm^–1 in dimethylformamide). The additional deactivation of the T₁ state is connected with thermally activated transitions to upper-lying CT states as well as the strengthening of intersystem crossing probabilities.     

Approach to a theory for the masses of the electron,muon, and heavier charged leptons

The electron mass valuem=9.093 × 10^–28 g is shown to be obtainable from the QED self-energy formula amended to include gravitational selfenergy and restricted by the space-time equipartition lawm/n ₀=4/3. Held together by gravity, the electron has a radiusr _e =8Gm/9e ² c=2.588 × 10^–53 cm. An extension of the analysis yields the theoretical muon-electron mass ratio of 206.241 and predicts heavier charged leptons with mass values of 1.915 GeV, 15.67 GeV, and above.     

The temperatures of protons andπ − mesons in central nucleus-nucleus interactions at a momentum of 4.5 GeV/c per incident nucleon

An estimate of the temperature of protons and ^– mesons in central He–Li, He–C, C–C, C–Ne, C–Cu, C–Pb, O–Pb, Mg–Mg interactions is presented. The results indicate an increase of the proton temperature with increasing mass numbers of projectile and target nuclei (A _p ,A _T ) fromT _p =(118±3) MeV for He–Li toT _p =(141±2) MeV for C–Pb. The temperature of ^– mesons does not depend onA _P ,A _T andT 95 MeV. A satisfactory fit for ^– mesons in C–Cu, C–Pb, O–Pb, Mg–Mg collisions can be achieved by using a form involving two temperatures,T ₁ andT ₂. The relative yield of the high temperature component (T ₂) is 24% for C–Cu, C–Pb, and Mg–Mg interactions. The observed results forT _P in C–Ne, C–Cu and C–Pb collisions are consistent with the prediction of the thermodynamic hagedorn model.     

Radiation of the Plasma of a Transverse Discharge in a Helium–Krypton–Elegas Mixture

We carried out a spectroscopic investigation of the degradation of the active medium of a pulsed-periodic KrF emitter based on a He/Kr/SF₆ mixture (P = 10–150 kPa) with pumping by a transverse volumetric discharge. The plasma radiation spectra in the range 200–620 nm at different stages of degradation of the working mixture and the dynamics of the radiation of inert gases as well as of the products of decomposition of SF₆ molecules in the plasma are studied. It is shown that since the number of discharge pulses is 10⁴, rather effective formation of excited sulfur molecules is observed which decompose with emission in the spectral range 260–550 nm. This can be employed for developing a wideband lamp based on the system of KrF(B–X; D–X), S₂(B–X), and S₂(f–a) bands.