Kakuyūgō kenkyū

A dispersion relation is derived for an ion beam-plasma system located in a cylinder with perfectly conducting wall. There are able to be many waves formed of the eigen modes. One of these eigen modes can be unstable though the velocity of the ion beam is greater than that of the ion acoustic wave. The frequency region in which the wave becomes unstable jumps from higher to lower mode with increasing the length of the cylinder. A growth rate of the unstable wave is large for a large value of β_{m, n}/a, here a and β_{m, n} are a radius of the cylinder, the nth root of Bessel function J_m, respectively. The experimental results agree qualitatively with the theory.

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An experiment is carried out to prove a new principle for a high-power microwave pulse source utilizing a superconducting cavity for energy storage. The stored energy in the cavity can be released, in a short time, by changing the coupling between the cavity and an output circuit.
A stainless steel cryostat of 112 cm height and 45 cm outer diameter is designed and constructed. Inside the cryostat, a TE₀₁₁ mode cylindrical cavity made of copper is installed. Inner surface of the cavity is electroplated by lead at a thickness of the order of 20 μm. The resonant frepuency of the cavity at 4.2 K is 2.876 GHz, and the internal Q value is greater than 10⁶. The microwave power of 30 mW is incident on an input port to store the energy. At an output port, a circular waveguide which includes a movable center conductor is connected. An impulse current is given to a magnetic coil to hit up the conductor. The quick movement of the conductor causes a rapid change in the coupling between the cavity and the output circuit. We obtain microwave pulses which exceed considerably the input power, and time width of the pulse is of the order of 1 msec. It is emphasized that the output power will increase by improving the parameters of the apparatus.

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