High-power linear-beam tubes

Abstract

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.

Terahertz quantum-cascade lasers

“…The permittivity can be rewritten as 18) where the susceptibility χ is due only to the intersubband oscillator. If the approxi-mation ω ≈ ω 10 is made, the imaginary part of the susceptibility is given by…”

Applications of advanced materials technologies to vacuum electronic devices

“…Such structures, consisting of waveguide steps and transitions that create impedance transformations and reflections, cancel the normal window reflections over some bandwidth. One example of the latter configuration, known as a "pillbox" window [10], [11], is shown schematically in Fig. 2, along with an equivalent transmission line model.…”

“…Thus, windows composed of high-strength diamond can be made thinner than those of BeO, which will reduce reflections in unmatched window applications and increase the bandwidth in pillbox configurations [11]. The dielectric constant of diamond is somewhat smaller than that of BeO, which is also advantageous.…”

“…Numerous references describing theoretical and experimental correlations between the process variables and the heat transfer coefficient can be found in the literature [37], [38], so we will not cover the details here. Instead, we will summarize by stating that an effective heat transfer coefficient, , (MKS units Wm K ) relates the difference between the wall temperature and the bulk fluid temperature to the heat flux according to (10) The heat transfer coefficient is related to a dimensionless quantity known as the Nusselt number, , according to (11) where is the fluid thermal conductivity. The Nusselt number is the ratio of convection for a fluid in motion to the thermal conduction through a motionless fluid layer.…”

“…The local heat transfer coefficient can be estimated from the Kar-Dybbs [50] correlation for the Nusselt number (18) and (11). In the computation of using (11) and the Reynolds number, the value of should be set equal to the mean pore diameter.…”