Paramagnetic centers in boron and aluminum borides

The electron spin resonance spectra of crystalline and amorphous boron and aluminum dode-caboride samples have been recorded on a Q-band spectrometer. The parameters of the spectra have been determined, and the concentration of paramagnetic centers has been estimated. It has been found that the concentration of the paramagnetic centers in amorphous boron is high and exceeds the corresponding value in crystals by two orders of magnitude. The spectra of boron powders enriched in ¹¹B and ¹⁰B isotopes have been measured. It has been established that the difference between the hyperfine interactions of the unpaired electron with the ¹¹B and ¹⁰B nuclei manifests itself as a change in the width of the structureless electron spin resonance spectra.     

K-line X-ray fluorescence from highly charged iron ions under dense astrophysical plasma conditions

In the present work, we report an investigation of plasma environment effects on the atomic parameters associated with the K-vacancy states in highly charged iron ions within the astrophysical context of accretion disks around black holes. More particularly, the sensitivity of K-line X-ray fluorescence parameters (wavelengths, radiative transition probabilities, and Auger rates) in Fe XVII–Fe XXV ions has been estimated for plasma conditions characterized by an electron temperature ranging from 10⁵ to 10⁷ K and an electron density ranging from 10¹⁸ to 10²² cm⁻³. In order to do this, relativistic multiconfiguration Dirac-Fock atomic structure calculations have been carried out by considering a time averaged Debye-Hückel potential for both the electron–nucleus and electron–electron interactions.     

Controlled doping of rf sputtered germanium films

Germanium films have been rf sputter deposited on a variety of substrates. A new techniques has been developed to control doping concentrations of the films at predetermined levels for bothp-type as well asn-type films. The hole concentrations of these films could be varied from 10¹⁵ to 2×10¹⁸/cm³ while the electron concentrations could be varied from 10¹⁵ to 5×10¹⁷/cm³ using this technique. Transmission electron microscope studies have been made to study the crystalline quality of the films.     

Estimation of various scattering parameters and 2-DEG mobilities from electron mobility calculations in the three conduction bands Γ, L and X of gallium arsenide

The electron drift mobility in Γ conduction band of GaAs has been calculated before, but for the first time, we have made attempts to estimate the electron mobilities in higher energy L and X minima. We have also calculated the value of mobility of two-dimensional electron gas needed to predict hetero-structure device characteristics using GaAs. Best scattering parameters have been derived by close comparison between experimental and theoretical mobilities. Room temperature electron mobilities in Γ, L and X valleys are found to be nearly 9094, 945 and 247 cm²/V-s respectively. For the above valleys, the electron masses, deformation potentials and polar phonon temperatures have been determined to be (0.067, 0.22, 0.39m ₀), (8.5, 9.5, 6.5 eV), and (416, 382, 542 K) as best values, respectively. The 2-DEG electron mobility in Γ minimum increases to 1.54 × 10⁶ from 1.59 × 10⁵ cm²/V-s (for impurity concentration of 10¹⁴ cm⁻³) at 10 K. Similarly, the 2-DEG electron mobility values in L and X minima are estimated to be 2.28 × 10⁵ and 1.44 × 10⁵ cm²/V-s at 10 K, which are about ∼4.5 and ∼3.9 times higher than normal value with impurity scattering present.      

Electron scattering based on a novel internal target technique: SCRIT

A novel technique for forming internal targets, named SCRIT (Self-Confining RI Ion Target), has been developed, which can make electron scattering off short-lived radioactive nuclei possible in an electron storage ring. SCRIT confines the ions of interest by utilizing the “ion trapping” phenomenon in the electron storage ring. Approximately 10⁷ stable ¹³³Cs ions were trapped in a three-dimensional configuration along the electron beam axis at an electron beam current of 75mA. The angular distribution of the electrons scattered from the trapped ¹³³Cs ions was successfully measured, and a collision luminosity of 10²⁶/(cm² s) was achieved.     

Density dependence of recombination in the electron cooler of CRYRING

The electron-ion recombination rates of Ne¹⁰⁺ and D⁺ have been measured as a function of relative energy and electron density. We found a strong enhancement of e-Ne¹⁰⁺ recombination over expected radiative recombination rates below 1 meV relative energies, reaching a factor of 4 close to zero relative energy. Remarkably, the measured rate coefficients decrease as a function of electron density for both systems. Studies of recombination of D⁺ indicate that this density dependence may be due to temperature variations of the electron beam with the electron density.     

On the nature of emissions of polymethyl methacrylate excited by an electron beam of subnanosecond or nanosecond duration

The results of studies of the physical nature of emissions produced in polymethyl methacrylate excited by electron beams of a subnanosecond or a nanosecond duration are presented. The spatial, amplitude, and spectral-kinetic properties of emissions have been examined under an electron beam energy density varying from 10^–4 to 4 × 10^–1 J/cm². It has been found that cathodoluminescence is the primary type of emission under low energy densities of the electron beam. When the energy density of a nanosecond electron beam and/or the number of pulses of excitation by a subnanosecond electron beam were increased, an electrical breakdown of polymethyl methacrylate occurred in the irradiated region. This process was accompanied by a burst of emission of dense, low-temperature plasma.     

Asymmetry of the Hβ central part measured in a T-tube

The asymmetry parameter δI of the H_β central part has been measured as a function of the plasma electron density. The results are compared with recently published theories and measurements. The plasma source was a small electromagnetic T-shaped shock tube. The electron density varied between 0.7 x 10²³ and 3 x 10²³m^-3, while the temperatures were 20,000 K and more.     

Atomic populations and temperatures in mixed plasmas

Atomic populations and temperatures have been measured in a mixed plasma formed by a mercury-lead-iodide arc in a quartz lamp. The excited levels observed for the mercury atom show a Boltzmann distribution when the electron density is above 4 × 10¹⁵ cm^-3. Departures from this distribution occur when the temperature falls below 0.25 eV with an electron density around 2 × 10¹⁵ cm^-3.     

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：     

Excitation of He+ in a hollow cathode arc discharge

Population densities of the excited He(II) levels i=4 to i=10 in hollow cathode arc discharge have been determined and compared with those calculated from a collisional-radiative model. In the experiment the electron temperature was about 2x10⁵K and the electron density about 3x10¹⁹ m^-3. The observed population densities agree within 50% with those calculated by Drawin and Emard, but differ by a factor 4–6 from the ones found by McWhirter and Hearn. The results of the present experiment suggest that near the threshold energies the cross sections for electronic excitation of He⁺ levels from the He⁺ ground state are half those expected from the calculations of Burgess. We conclude that Drawin and Emard's calculations should preferably be employed for the determination of the electron density and the electron temperature from observed population densities.     

Three-dimensional simulation of laser–plasma-based electron acceleration

A sequential three-dimensional (3D) particle-in-cell simulation code PICPSI-3D with a user friendly graphical user interface (GUI) has been developed and used to study the interaction of plasma with ultrahigh intensity laser radiation. A case study of laser–plasma-based electron acceleration has been carried out to assess the performance of this code. Simulations have been performed for a Gaussian laser beam of peak intensity 5 × 10¹⁹ W/cm² propagating through an underdense plasma of uniform density 1 × 10¹⁹ cm^− 3, and for a Gaussian laser beam of peak intensity 1.5 × 10¹⁹ W/cm² propagating through an underdense plasma of uniform density 3.5 × 10¹⁹ cm^− 3. The electron energy spectrum has been evaluated at different time-steps during the propagation of the laser beam. When the plasma density is 1 × 10¹⁹ cm^− 3, simulations show that the electron energy spectrum forms a monoenergetic peak at ~14 MeV, with an energy spread of ±7 MeV. On the other hand, when the plasma density is 3.5 × 10¹⁹ cm^− 3, simulations show that the electron energy spectrum forms a monoenergetic peak at ~23 MeV, with an energy spread of ±7.5 MeV.     

Field electron emission from Ge-Si nanostructures with quantum dots

Self-assembled arrays of Ge-Si clusters with sizes of ～ 10 nm and a density of ～ 10¹⁰ cm^?2 have been grown by molecular beam epitaxy. Stable steady-state field electron emission from such clusters has been observed and studied. The emission is characterized by resonance current peaks, which are explained by the quantization of the electron energy in nanoclusters. The estimation of the ground level energy from their emission measurements coincides with estimates obtained by other methods.     

EID study on the system platinum-hydrogen

Electron induced desorption of hydrogen on polycrystalline platinum has been studied in continuation of former work. The results remain consistent with a supposed adsorption model implying that electron induced H⁺ emission is restricted to hydrogen adsorbed only at particular sites occupying not more than 1 per cent coverage. These sites are ascribed to characteristic and stable surface impurities which are not influenced by the improved target treatment applied. Depletion of sites by sputter cleaning is cancelled by recovery during annealing. The highest observed H⁺ yield (all available sites filled with hydrogen) is 2 · 10⁻⁵ ions per electron. The total cross section for desorption by electron impact is 2 · 10⁻¹⁷ cm². Complex interaction phenomena between the electrons and the hydrogen covered platinum surface have been observed.     

Rotating relativistic electron beam-plasma interaction and formation of a field-reversed configuration

Experimental results on interaction of a rotating relativistic electron beam with plasma and neutral gas are presented. The rotating relativistic electron beam has been propagated up to a distance of 150 cm in a plasma. The response of the plasma to the rotating electron beam is found to be of magnetic diffusion type over a plasma density range 10¹¹–10¹³ cm⁻³. Excitation of the axial and azimuthal return currents by the rotating beam and subsequent trapping of the azimuthal return current layer by the magnetic mirror field are observed. A field-reversed configuration has been formed by the rotating relativistic electron beam when injected into neutral hydrogen gas. We have observed field reversal up to three times the initial field in an axial length of 100 cm.     

Spectroscopic studies of a helium plasma generated near ceramic surface at pressures below 1000 hPa

Spatially resolved line intensity measurements from a plasma generated near ceramic surfaces have been performed. Disk-shaped helium plasmas of diameter 20 mm and thickness 0.9 mm have been studied in a pressure range of 2×10³–10⁵ Pa. On the basis of line intensity measurements and applying an appropriate collisional-radiative model for a helium plasma, the distributions of electron density and electron temperature have been evaluated.     

Shift and oscillator strength of Xe(I) lines emitted from an alectric pulse discharge

An electric pulse discharge has been used to generate Xe plasmas with equilibrium temperatures of the order of 10⁴ K and electron densities between 10¹⁷ and 10¹⁸ cm^-3. Spectroscopic measurements were made in the range between 455 and 475 nm. The shift of the observed lines was found to vary linearly with electron density even at the highest N_e values reached. Oscillator strengths were estimated for the lines at 462.4, 467.1 and 473.4 nm on the basis of a computer reconstruction of the appropriate spectral region.     

托卡马克微波预电离等离子体

使用回旋管系统产生的电子回旋波段的大功率微波在托卡马克中得到无电流等离子体。其电子密度达8×10¹²cm^-3,电子温度达50eV,粒子约束时间约为0.5ms,加热效率达25％以上。研究了对环向击穿的影响及加热机制。     

Schlieren diagnostics of pulsed electron beam ablation of polymethyl-methacrylate

The investigation of the interaction of pulsed electron beams with PMMA (polymethylmethacrylate) targets is reported. The electron beam of some 10^–8 s in duration is produced in a pulsed low-pressure gas discharge. The beam power density of up to 10⁸ W/cm² leads to a surface plasma formation similar to that of the pulsed laser ablation process. The propagation of the ablated material and the shock wave inside the PMMA target are observed by means of Schlieren diagnostics. An electron density gradient of over 3×10¹⁹ cm^–4 has been observed in the expanding plasma up to 1.5 s after the plasma formation. During the early stage of expansion, the expansion velocity of the plasma plume as determined by the steep electron density gradient is around 10⁵ cm/s. The pressure behind the shock front inside the PMMA target as determined from the shock velocity exceeds 0.3 Gpa.     

Thomson Scattering Applied to a Noisy Radiative Plasma

Thomson scattering with a 1.5 ms long pulse mode 20 J ruby laser has been applied to a radiative argon plasma with electron densities n_e from 2.5 10¹⁹ m^?3 to 1.5 10²⁰ m^?3 and an electron temperature T_e of about 3 eV. Photon counting techniques have been used. The accuracy of n_e and T_e to be reached is about 5% after 10 shots. The signal to noise ratio S/N has been optimized by the use of optical filters and a special purpose grating. The effects of these elements on S/N have been calculated. The entrance angle, transmission and quantum efficiency have also been optimized. A comparison between 5 possible laser systems, including a normal mode and a Q-switched mode ruby laser, has been carried out.