[en] Nonstationary behaviour of a virtual cathode at the plasma-vacuum boundary in the oscillating beam regime was investigated using the REBEX high-current electron accelerator. Emitted electromagnetic waves and the modulation of transmitted and reflected electron beams were measured in the frequency band 2 to 12 GHz. Beam current radial profiles were recorded by means of a tiny movable current probe. The modulation frequency correlated with the frequency of radiated waves, increasing linearly with the increasing beam current. The observed frequencies lay slightly above the calculated maximum beam plasma frequency, within the range predicted by numerical simulations of a reflected beam. (J.U.). 1 fig., 2 refs

[en] The transfer of energy of a relativistic electron beam into an inhomogeneous magnetized plasma is studied in the beam current and beam injection modes. Both propagating and oscillating beam modes can be implemented thanks to a special experimental arrangement. Beam-to-plasma energy transfer efficiency is evaluated from diamagnetic measurements. For a fix mode (propagating or oscillating beam) the total energy was deposited in plasma scales proportionally to the beam current. The maximum heating efficiency (30%) and the maximum stored energy (2.5x10¹⁹ eVcm^-1) were found in the oscillating beam modes with the shortest plasma columns available. The waveforms of diamagnetic signals reflected a complex nature of the energy deposition and dissipation processes. The regular damped oscillations of the diamagnetic signals were shown to be magnetoacoustic oscillations of the whole plasma column. From their period and damping rate the local plasma density and temperature could be estimated. (J.U.)

[en] The energy distribution of electrons in a plasma heated by a high-current relativistic electron beam was studied experimentally using X-ray plasma diagnostics. Plasma X radiation in the energy range from 100 eV to 10 keV was detected with a special four-channel silicon surface barrier detector and the spectrum was roughly analyzed using a set of foil filters. A high-energy component was found in the bremsstrahlung from a carbon target placed in the plasma periphery. The best fit for the experimental data was obtained with the electron distribution function inversely proportional to the electron energy. The energy contained in the observed part of the energy spectrum is some 10 per cent of the injected beam energy. The high-energy electrons live a surprisingly long time after the beam injection. (J.U.)

No abstract available

[en] The apparatus used for measurements of Balmer line profiles at the REBEX experiment is described in detail. The illuminating optical system transmits light from a plasma to the spectroscopic part of the instrument. The spectral analysis is performed by a six-channel polychromator based on mirror monochromator SPM-2 with a plane grating. The key part of the detection system is a light pipe head supplied with six optical strip lines coupled to photomultipliers. The evaluating part consists of fast digitizers and a computer-controlled data processing system. The spectral and time resolution of the apparatus is 0.084 nm per channel and 10 ns, respectively. (J.U.). 3 figs., 3 refs

[en] To achieve a better time resolution in measurements of profiles of plasma emission lines by means of an intracavity laser spectroscopy method, a new dye laser pumped by the second harmonic of a Q-switched Nd:YAP laser has been built. The laser part of the apparatus, which consists of a laser generator, amplifier, second harmonic generator and a dye laser, is described in detail, and the results of measurements of the laser output energy (typically 30 mJ/70 ns) are presented. As for the detection part, the diffraction-grating spectrograph tested earlier will be used, in combination with an upgraded digital readout system, the key part of which will be a triggerable CCD camera. (J.U.) 3 figs., 11 refs

[en] The angular beam velocity spread of the injected relativistic electron beam in the REBEX machine reduced in order to achieve a higher plasma heating efficiency. For this purpose, the guiding magnetic field in the diode region was increased to 1.5 T and ultrathin anode foils were used. Simultaneously, the length of the interaction region was shortened and a new plasma source with a transient reversed magnetic field was installed. In the experiments the beam energy deposition efficiency was calculated on the basis of measurements of local plasma diamagnetism. Both the single transit and the reflected beam regimes were studied. In the former case the energy deposition rate increased along the beam path in accordance with the theory, while in the latter the longitudinal profile of the deposited energy had a reversed slope and the overall beam deposition efficiency was up to 3 times higher. (J.U.) 8 figs., 7 refs

[en] Non-linear non-stationary oscillations of a magnetized plasma column, the driving force of which is the transient kinetic and magnetic pressure produced by the injection of a high-current electron beam, are modelled on the basis of the numerical solution of the equation of plasma boundary motion. The results of the computations are used in the interpretation of diamagnetic, optical and neutral-particle measurements at the REBEX machine. (author) 10 figs., 23 refs

No abstract available

[en] The problem of the effective energy deposition of the injected relativistic electron beam (REB) in a plasma remains traditionally in the focus of the experimental investigations, especially at GOL (Novosibirsk) and REBEX (Prague) devices. Recently the experimental way to the dense (10¹⁵cm^-3) bulk plasma heating by the microsecond intensive (50-70 kJ) REB was paved. The generation of the overthermal electrons is the other interesting phenomenon experimentally demonstrated in REB-plasma systems. Ten per cent of the injected REB energy can be transformed into the high current density, low impedance (100kA, 10kV) electron stream applicable in further for classical collisional heating of a dense plasma. Search for the optimal conditions of the overthermal plasma electrons generation in REB-plasma system is one of the aims of the proposed experiment at REBEX machine. Consequently the relatively small experimental devices with the injection of a nanosecond REB (1-10 kJ) into a magnetized plasma could be used for heating of dense gaseous targets or very thin foils to study the matter in extreme conditions (high ionized states of ions) in the future. (author) 3 refs., 1 fig