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An intense relativistic electron beam with energy of 550 keV, current of 3 kA and duration of 12 ns was injected into a periodical slow-wave structure and interacted with backward wave. With trapezoidal energy and current pulse profile, microwave pulses with frequency of 5 GHz, duration of 5 ns and output power of 300 MW was observed. The simulated results suggested that the radiation was caused by superradiance. [ABSTRACT FROM PUBLISHER]

Experiments on transformation of energy and beam current waveforms of an intense relativistic electron beams with cavities located in the drift tube were carried out. An intense electron beam with energy of 550 keV, current of 3 kA and duration of 12 ns was injected into a drift tube. A coaxial cavity connected with the drift tube via a gap was utilized to transform the time evolution of electron energies of the beam. With duration of the round trip time for light of the cavity, the former part of the beam lost the energy and following part of the beam gained the energy. A cylindrical cavity with large diameter whose space-charge limiting current was smaller than the injected current was located behind the coaxial cavity to change the current waveform of the beam. The beam current was decreased gradually to the limiting current by elongating the cavity length. Trapezoidal waveforms of injected electron energy and beam current were transformed to the time-increasing waveforms after the cavities. [ABSTRACT FROM PUBLISHER]

New diagnostic, “electron-beam-shadowgraph”, is examined for taking the spatial distribution of transient fields in a plasma. It is applied to the unmagnetized plasma, which is perturbed by an intense relativistic electron beam (IREB). Strong deflection is observed with duration of about 1 µs just after the IREB injection. The shadowgraph image is characterized by presence of aggregate holes. The size of the hole is changed with the plasma density, and corresponds to the 15 – 60 Debye lengths. Important agreements are observed between the experiment and the strong Langmuir turbulence theory. [ABSTRACT FROM PUBLISHER]

Automodulation of an intense relativistic electron beam was reexamined experimentally to obtain trains of subnanosecond electron bunches. Transmission line theory suggested that the round trip time for the electromagnetic wave in the cavity must be comparable with the rise time of the beam current to obtain high voltage at the gap. Single cavity experiments were carried out using the beam with current rise time of 6 ns. Cavities whose round trip time was less than 6 ns were utilized. The longer cavity resulted in the higher gap voltage and the higher current modulation. For high-frequency current modulation for a beam with slow rise time, we propose a series of cavities with decreasing lengths to improve the current rise time. [ABSTRACT FROM PUBLISHER]

Experiments and simulations for the propagation of intense relativistic electron beams that pass through a gap are carried out. The radius of the drift tube increases at the gap entrance and it returns to the initial radius after the gap length. Though the injected beam current into the gap is larger than the space charge limiting current at the gap, it passes through the gap without loss when the gap length is short. A criterion is proposed for the gap length through which the beam current passes without loss. [ABSTRACT FROM PUBLISHER]