This paper presents the experimental results of the study of the Relativistic Electron Beam (REB) generated in a foilless diode and its transport at low pressure (lo-' torr-250 mtorr) in hydrogen gas. The typical beam parameters are 240 kV, 0.1-6 kA and pulse width (FWHM) from 10 to 65 ns. A mirror magnetic field has been used to minimise beam losses. It has been observed that the input beam parameters are functions of gas pressure, and a maximum peak beam current of 6 kA is observed at a pressure of 100 mtorr of hydrogen. The beam current and its width decrease as the gas pressure is increased. The amplification of the net current over the input beam current is observed for propagation distances of Z = 2 cm and Z = 15 cm. The ratio of peak transmitted current to the peak input current increases as the pressure is increased and at a distance of Z = 6 cm, there is an amplification of the peak beam transmitted current by a factor of 1.4 at a pressure of 200 mtorr. The analysis of the results shows that two stream instability may be operative in the pressure range studied and that there is also a possibility of formation of potential well and collective acceleration of ions.
Magnetic shielding and harmonic generation in a sintered Y,Ba,Cu,O,., tube, subjected to an incident AC magnetic field, has been studied. This study has shown that t h e onset of superconductivity in t h e specimen introduces a magnetic shielding of about 25 dB. Odd harmonics are generated during the propagation of the AC magnetic field. Flux trapping occurs in t h e specimen for frequencies less than 10 kHz. This trapped flux behaves as a superimposed oc magnetic field and results in a low shielding effectiveness and generation of even harmonics in the transmitted waveform.
Studies of the propagation of a n AC magnetic field through plasma sprayed superconducting Y,Ba,Cu,O,., coatings have been carried out in t h e incident field frequency and intensity ranges 100 Hz to 100 kHz and 0.01 to 3.5 mT respectively. Results show that the shielding effectiveness increases exponentially with decreasing field intensity. Shielding effectiveness increases with coating thickness and its density. Coatings thinner than 100 ,pm do not show any shielding. A non-linear dependence of critical magnetic fieid H* on both thickness and critical current density J, of the specimen has been observed.
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