No abstract available

No abstract available

No abstract available

[en] Results are reported on the dependence of the current of a pulsed ion beam produced in a reflex triode upon the applied resistive voltage in the range 0.6 to 1.3 MV. The measured peak ion current at the maximum voltage tested is 20 kA, corresponding to a current density of 200 A/cm³

No abstract available

[en] A rotating relativistic beam of energy 500 keV and current 20-40 kA is injected into a preformed plasma of density n/subp/ between 10¹² and 10¹⁴ cm^-3. It is observed that optimum coupling of beam energy to the plasma occurs at n/subp/very-much-greater-thann/subb/, where n/subb/ is the beam density. The peak plasma temperature is about 1 keV. The heated plasma undergoes radial oscillations characteristic of the magnetosonic mode. The results are interpreted with a new theoretical model

[en] Initial measurements on a millimeter-wave collective free-electron laser (FEL) experiment have demonstrated very high-power superradiant emission in the range 60-100 GHz. This emission corresponds to an instantaneous conversion efficiency of electron beam kinetic energy into millimeter-wave radiation of 2.5%, an order of magnitude improvement over that seen in previous experiments. Computer simulations and experimental measurements have shown the beam quality to be sufficient to sustain a collective free-electron-laser interaction. In addition, the experiment has shown a regular parametric dependence of emission amplitude on guide and pump magnetic fields, both above and below gyroresonance, that had not been previously reported. This behavior agrees well with predictions based on single particle orbits and collective interaction theory. Initial spectral measurements have produced emission spectra that agree well with predictions. Coupling has been observed to the two lowest order modes of the overmoded circular waveguide. Moderate linewidths in the range of 6% to 15% have been measured, demonstrating the broad gain bandwidth of the interaction. Also, the predicted simple broadband tuning of the FEL interaction has been observed for the first time, with tuning demonstrated over a 50% range of frequencies through variation of the axial electron velocity by means of changing the strength of the wiggler field

[en] The authors present a progress report on a program to develop a high-power X-band magnicon amplifier for accelerator applications. The goal of the program is to generate 50 MW at 11.4 GHz with 50% efficiency, using a 200 A, 500 keV electron beam produced by a cold-cathode diode on the NRL Long-Pulse Accelerator Facility. The initial experiment, designed to study the gain from the first (driven) deflection cavity to a second (passive) deflection cavity, has recently begun

[en] The experiment has been fabricated and cold tested. In initial experimental operation, free-running oscillation at 35 GHz has been observed at about 5 MW output power. The TE₁₁₂ mode of the bunching cavities has been observed to oscillate early in the pulse, but generally not during the voltage flattop, so that is should not interfere with the phase-locking process. Phase-locking experiments are under way

[en] The millimeter-wave free-electron laser is a relativistic fast-wave device that offers the possibility of reaching extremely high powers (10/sup 9/ W) at high efficiencies. Operating as an amplifier in the collective regime, this device offers the capability of very high gain with a broad instantaneous gain-bandwidth, is broadly tunable, and can have intrinsic efficiencies of order 10%. Previous results have been reported for this device operating in a superradiant configuration, that is as an amplifier of spontaneous emission. In that configuration, it has produced a record power of 75 MW at a frequency of 70 GHz with 6% experimental efficiency in a 15 nsec pulse, and has demonstrated tunability of this emission at high power over the entire range 25-100 GHz. In this mode of operation, the free-electron laser has also demonstrated the unique capability to produce air breakdown in full atmospheric pressure air with intense millimeter-wave emission