Time-multiplexing generates a diode laser beam with high beam quality

The beams of four pulsed high-power laser diodes are time-multiplexed resulting in a laser beam of high quality. A combination of polarization switches and filters forming a digital time-multiplexer is utilized to guide laser pulses produced by the individual laser diodes onto a common optical path. A resulting beam with an optical power of 10 W and a beam quality comparable with that of a single laser diode at a wavelength of 960 nm is obtained.     

Electron beam generation in a magnetron diode with metal secondary-emission cathode

The effects of electric and magnetic field intensities, the triggering-pulse droop rate, and the electrode diameter on the processes of electron beam formation and generation were studied experimentally. The results of mathematical simulation of the secondary-emission multiplication of the electron flow are presented. Tubular electron beams with a wall thickness of 1.5–2 mm, a current density of 1–70 A/cm², and a particle energy of 5–100 keV were obtained. It was shown that several electron bunches could be obtained during a single voltage pulse.     

Electron transport properties of lithium and phase transitions at high pressures

The electric resistivity and thermopower of lithium have been precisely measured at high pressures (up to 8 GPa) and temperatures from room temperature to 100°C. Transition to the fcc phase of lithium has been analyzed. The hysteresis of the direct and inverse transitions is 0.3 GPa at room temperature, decreases slightly with an increase in the temperature, and is almost independent of the prehistory of the sample. The phase transition line on the P-T diagram has a positive slope of dP/dT = 0.03 GPa/K. It is assumed that the fcc phase of lithium, which is stable at a high pressure, can appear for kinetic regions from the 9R phase, which is intermediate in energy between the bcc and fcc modifications.     

Operation of the EGA electron gun at high gas pressures

Summary This paper presents experimental results on the effects of increasing gas pressure on electron gun operations. The electron gun used is the gun EGA which has been developed for the TSS-1 mission. Various gases have been used with pressures in the range from 10⁻⁶ to a few times 10⁻³ mbar. The measurements, taken in a vacuum chamber, show a steady increase in the slope of theI–V characteristics of the gun when the pressure is increased, as a consequence of ionization phenomena induced by the electron beam. Further measurements have been taken of the overall current on a target at some distance from the gun itself. An attempt is also made at a theoretical calculation of the effects observed, based on simplified models.     

Electron temperature measurement in a surface-wave-produced argon plasma at intermediate pressures

The main objective of this work is to obtain the electron temperature in an argon surface-wave-produced plasma column at intermediate gas pressures. After proving that argon upper excited states remain in Excitation Saturation Balance, the value of electron temperature along the plasma column has been obtained using a modified Saha equation and a corrected Boltzmann-plot. Moreover, the electron energy distribution function has been verified to be nearly Maxwellian in a 0.8-2.8 torr intermediate pressure range. Received 24 July 2000 and Received in final form 19 January 2001     

Electron beam formation in an anomalous glow discharge

Scaling parameters that account for the efficient formation of electron beams in sources based on an anomalous glow discharge are considered, and the processes leading to the violation of scaling laws are analyzed. Estimates show that the working pressure range in such sources can be increased significantly. The results obtained can be used to optimize discharge regimes with required electron beam parameters. It is demonstrated that sources with plane-parallel continuous electrodes can operate at pressures as high as 100 Torr (which is one to two orders of magnitude higher than that in similar existing electron beam sources), provided that parasitic spark breakdowns at the insulator near the discharge cathode are suppressed. The sources designed can be used for direct excitation of laser working media or their preionization by soft X-rays.     

Electron beam induced formation of carbon nanorods

Electron beam induced formation of carbon nanorods was realized in situ under high resolution scanning electron microscopy (HRSEM). When a CVD deposited carbon nanotube sample was irradiated with an electron beam in an HRSEM, progressive etching of the sample, expanding of the nanotubes, and formation of additional nanorods have been observed. Transmission electron microscopy study revealed typical nanorods of 20 nm in diameter and with amorphous structure. The direct observation of the synthesis of nanorods under electron microscopy manifests the possibility of nano-machining of such nanomaterials using electron beams. This may lead to future integration and networking of nanostructures of different functionalities, which is crucial for nanotechnology.     

Iron at high negative pressures

With the object of verifying the presence of a region of anomalous iron compressibility at negative pressures, as predicted by the ab initio calculations, the reflection of compression pulses from the surfaces of iron single crystals was detected. No evidence of the expected formation of rarefaction shock waves was observed in the range of attained tensile stresses up to 7.6 GPa. The breaking stresses achieved 25-50% of the theoretical iron ultimate strength for a load duration of ～10^?8 s. The dependence of breaking strength on the extension rate did not reveal any singularities in the region of assumed anomaly in iron compressibility.     

新的高能注量电子束二极管系统

为“闪光二号”加速器研制了新的二极管系统, 其电子束能注量比原二极管系统大3倍多。该系统由带滑闪开关的二极管、漂移管、脉冲磁场和真空靶室等部分组成, 通过减小阴极直径、增大轴向磁场强度和磁透镜比,调节滑闪开关距离和预脉冲开关气压等技术措施, 使二极管具有高能注量电子束输出的稳定工作状态, 在Marx发生器充电电压70kV条件下,在距阴极22cm的靶上获得了总能量21.5kJ、束斑直径52mm和能注量1.01kJ/cm2的电子束输出。     

新的高能注量电子束二极管系统

 为“闪光二号”加速器研制了新的二极管系统, 其电子束能注量比原二极管系统大3倍多。该系统由带滑闪开关的二极管、漂移管、脉冲磁场和真空靶室等部分组成, 通过减小阴极直径、增大轴向磁场强度和磁透镜比,调节滑闪开关距离和预脉冲开关气压等技术措施, 使二极管具有高能注量电子束输出的稳定工作状态, 在Marx发生器充电电压70kV条件下,在距阴极22cm的靶上获得了总能量21.5kJ、束斑直径52mm和能注量1.01kJ/cm²的电子束输出。     

Breakdown threshold in the microwave field at low and high pressures in electronegative gas mixtures

The dependence of the critical value of the microwave field amplitude in electronegative mixtures, which corresponds to the local equality of the ionization frequency and the dissociation attachment frequency, is investigated theoretically in a wide range of pressures with allowance for electron temperature pulsations. The resultant values are compared with the critical value for the static field. The range of pressures in which electron temperature pulsations become significant is determined, and the excess of the critical amplitude over the value in the static field is calculated in the high-pressure limit. Simple formulas are recommended for estimating the critical value of the microwave field amplitude.     

Anharmonicity in aluminum hydride at high pressures

Aluminum hydride has been predicted to be a superconductor with a transition temperature of 24 K at 110 GPa, in disagreement with the experimental observation. In this work, it is shown that the bulk of the electron–phonon coupling can be associated with modes that are highly anharmonic according to frozen phonon calculations. This large anharmonicity could partially explain the origin of the disagreement between previous predictions and experiments.     

Effect of the amplitude and rise time of a voltage pulse on the formation of an ultrashort avalanche electron beam in a gas diode

The effect of the amplitude and rise time of a voltage pulse from a RADAN-303 pulser on the formation of an ultrashort avalanche electron beam (UAEB) in a gas diode is experimentally investigated. It is shown that, when the open-circuit voltage of the pulser exceeds an optimum value, the beam current amplitude and the gap voltage under which the UAEB is generated decrease.     

Electric strength of rocks at a pulsed voltage under high pressures at high temperatures

The electric strength of rocks (granite, limestone, and sandstone) for the first time has been measured under the simultaneous effect of the pressure up to 35 MPa and temperature up to 120°C in the system of rod-rod electrodes arranged on one sample surface and point-plane electrodes in the liquid medium of a drilling agent. With the simultaneous increase in pressure and temperature, the electric strength of rocks for point-plane electrodes continuously increases (especially rapidly in the pressure range of 10–24 MPa and temperature range of 35–85°C), while for rod-rod electrodes arranged on the same sample surface, the electric strength varies with a maximum at pressures of 5–12 MPa and temperatures 20–35°C.     

Spectroscopy at very high pressures—XXV: The IR spectrum of ferrocene at high pressures

The IR spectrum of ferrocene has been examined up to 50kbar under approximately hydrostatic conditions in a gasketed diamond anvil cell, and also under shear stress without gaskets. The results provide evidence in support of Duecker and Lippincott's claim of a phase transition at about 11.5 ± 0.5 kbar which is sluggish except under shear stress. Thermal strain and phonon self-energy contributions to the temperature-induced frequency shifts were analysed but no general pattern emerged.     

Thermopower of calcium at high pressures

Calcium at megabar pressures undergoes numerous structural transitions and has a complex phase diagram. At the same time, according to the recent theoretical investigations, an anomalous behavior of many physical properties, including a transition to the state of a narrow-gap semiconductor, can be expected even in the region of stability of the normal-pressure phase of calcium with the fcc structure at moderate pressures P ～ 5–15 GPa. Data on the thermopower of calcium in the pressure range up to 9 GPa have been reported. The thermopower in this pressure range is positive, has a smooth maximum at 5–6 GPa, and decreases quite rapidly at higher pressures. The absolute values of the thermopower (5–12 μV/K) indicate that calcium in this pressure range is a metal. The difference between the thermopowers in the direct and inverse passages in the range of 5–7.5 GPa is fairly noticeable (～10%). The possible reasons for such an anomalous behavior, as well as new calculations of the band structure of calcium, have been discussed.     

Polyhedral carbon nanoparticles at high pressures

JETP Letters - The solid-phase transformations of polyhedral nanoparticles at a pressure of 8.0 GPa and various temperatures have been investigated by X-ray diffraction, small-angle X-ray...