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We present the results of studies of the active compressor of 3-cm wavelength microwave pulses, which uses a high-Q storage Bragg resonator excited at the H 01 mode and new types of plasma switches. Phase variation during a compressed pulse and phase correlation of the input and compressed microwave pulses are studied both experimentally and theoretically. Using a singlechannel compressor excited at the megawatt power level by the magnicon radiation with frequency 11.4 GHz, a power amplification factor equal to 9 was reached for an output-pulse duration of 40-50 ns and a peak power of up to 25 MW.

Results obtained in several experiments on active rf pulse compression at X band using a magnicon as the high-power rf source are presented. In these experiments, microwave energy is stored in high-Q TE 01 and TE 02 modes of two parallel-fed resonators, and then discharged using switches activated with rapidly fired plasma discharge tubes. Designs and high-power tests of several versions of the compressor are described. In these experiments, coherent pulse superposition was demonstrated at a 5-9 MW level of incident power. The compressed pulses observed had powers of 50-70 MW and durations of 40-70 ns. Peak power gains were measured to be in the range of 7:1-11:1 with efficiency in the range of 50%-63%.

We consider an axisymmetric microwave cavity for an accelerator structure whose eigenfrequency for its second lowest TM-like axisymmetric mode is twice that of the lowest such mode, and for which the fields are asymmetric along its axis. In this cavity, the peak amplitude of the rf electric field that points into either longitudinal face can be smaller than the peak field which points out. Computations show that a structure using such cavities might support an accelerating gradient about 47% greater than that for a structure using similar single-mode cavities, without an increase in breakdown probability.

For the upper electron cyclotron wave launcher on the international thermonuclear experimental reactor (ITER), the use of a ‘remote steering antenna’ based on the imaging properties of square waveguides is planned. To characterize launchers of this type, low-power experiments on a four-side corrugated square waveguide, with a scanning mirror at the input of the waveguide, were performed in the frequency range 140–160 GHz.It is shown that elliptical polarization, which is necessary for the electron cyclotron current drive (ECCD), can be transmitted without depolarization and that the usable steering range of the antenna is at least 20°.Low-power measurements demonstrate that mitre bends can be integrated into the waveguide, practically without extra loss. Detailed calorimetric measurements for this set-up confirm this statement for the polarization perpendicular to the scanning plane, whereas excess loss is measured for the parallel polarization. Various modifications of mitre bends are investigated and results are discussed.

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