Abshoct-High-power klystrons, coqpled-cavity traveling-wave tubes (TWT's), and hybrid tabes, all of which utilize the microwave cavity as the basic circuit element, are described These amplifiers are used in communications, radars, electronic countermeasures, and other applications at power levels from a f e w hondred watts to megawatts, at frequencies from dtmhigh frequency on up, and are particularly suited for high average powers. High gain, 30 to 60 dB, is normally achieved, and bandwidth usually lies m the 1-*percent range. Elementary theory of operation is desaibed, together with design considerations and systems interface information. Typical tube designs and data are presented. Recent developments are disprovements in bandwidth, periodic focusing, and beam control electrodes. Most of the basic design techniques are well developed, and emphasis is being shifted to improvements m the detailed performance characteristics such as gain and pbase response ripples, noise, and the sensitivities to operating voltages and currents. cossed, including h i g techniques ( t o 75 percent), im-All linear-beam tubes consist of a n electron gun and focusing structure used to generate a long cylindrical electron beam, an RF structure which provides gain and power output by interaction with the beam, and a collector where the unused beam energy is converted to heat. Tubes differ one from another principally in the characteristics of the interaction circuit. Its function may be described by the interaction impedance it presents to the beam as shown in Fig.

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A 10 MW, 1.3 GHz multiple beam klystron (MBK) has been developed for the DESY X-FEL and International Linear Collider projects. The device uses six electron beams set off-axis on a large bolt circle which interact with a combination of higher-order-mode and conventional klystron cavities to efficiently produce high power RF. Extensive two and three dimensional simulations were used to design the device. Recent test results have validated the basic design concepts and procedure. Ten megawatts of peak and 150 kW of average power have been stably generated with 59% efficiency and 48 dB of gain.

A compact periodic permanent magnet focused 9290 MHz klystron is described that produces 2.7 MW of output power with 52 dB of gain and 43% efficiency. Three klystrons have been manufactured that exhibited a high degree of repeatability and robustness with all meeting the performance requirements. The goal of a first-time-through design success was met through the use of extensive multidimensional modeling of all aspects of the klystron. Agreement between simulated and measured performance was very good.