[en] A mode analysis is presented for the case of a planar electron beam in a ridged waveguide slow-wave structure. By matching boundary conditions between a Fourier expansion of the mode between the ridges with a space-harmonic expansion of the mode in the region below the ridges, a dispersion relation for a traveling-wave interaction is found. The dispersion relation is numerically solved for both the case with and without beam. For the nominal geometry, gains as high as 30 dB/cm at 300 GHz are found for a 15 A, 155 keV beam

[en] The gyrotron traveling-wave tube (gyro-TWT) amplifier is known to be highly susceptible to spurious oscillations. This study develops a simulation approach to analyze the stability of a coaxial-waveguide gyro-TWT with distributed wall losses. The interplay among the absolute instabilities, the gyrotron backward-wave oscillations, and the circuit parameters is analyzed. Simulation results reveal that the distributed wall losses effectively stabilize spurious oscillations in the coaxial gyro-TWT. Furthermore, the wall resistivity of the center conductor is shown to be an additional effective mechanism for suppressing oscillations. Under stable operation conditions, the coaxial gyro-TWT with distributed losses is predicted to generate 435 kW in the Ka band with 31% efficiency, a saturated gain of 45 dB, and a bandwidth of 1.86 GHz (≅5.8%) for a 70 kV, 20 A electron beam with an α(=ν_{perpendicular})/ν_z)=1.0 and an axial velocity spread of Δν_z/ν_z=5%

[en] By delivering unprecedented power and gain, the gyrotron traveling-wave amplifier (gyro-TWT) offers great promise for advanced millimeter wave radars. However, the underlying physics of this complex nonlinear system is yet to be fully elucidated. Here, we report a new phenomenon in the form of nonlinearly driven oscillations. A zero-drive stable gyro-TWT is shown to be susceptible to a considerably reduced dynamic range at the band edge, followed by a sudden transition into driven oscillations and then a hysteresis effect. An analysis of this unexpected behavior and its physical interpretation are presented.

[en] A three-dimensional model has been developed for the investigation of the coupling of symmetric (TM₀₁) and asymmetric (HEM₁₁) modes in a high-power, high-efficiency traveling-wave amplifier. In the framework of a simplified model it is shown that the coupling between these two modes is determined by a single parameter that depends on the beam characteristics. For a specific set of parameters corresponding to operation at 35 GHz, simulations indicate that an initial HEM₁₁ power of 0.5 MW at the input end is sufficient to deflect electrons to the wall. The build-up of this parasitic mode is investigated over many round trips of the wave in the structure and a threshold criterion for self-sustain oscillation is established. Finally a way for suppressing the HEM₁₁ mode is analyzed. (c) 2000 The American Physical Society

[en] The CONDOR code is used to simulate the cold test and the beam-induced microwave amplification of an 11.4-GHz, six-cell, disk-loaded, traveling wave cavity. Cold test simulation results are in agreement with a modified Slater's theory. Power extraction at the output port is calculated by launching a train of Gaussian electron bunches through the structure. Results are consistent with recent relativistic klystron experiments using a similar TW output cavity. It is further shown that, depending on operating beam parameters, the power extraction efficiency can be maximized by modification of various cells in the TW structure

[en] Experimental results are presented on the first W-band gyrotron Traveling-Wave Tube (gyro-TWT) developed to exploit the 94 GHz atmospheric window for long-range, high-resolution radar applications. The gyro-TWT is designed to operate in the higher order TE₀₁ mode and is driven by a 100 kV, 5 A electron beam with a pitch angle of v_{perpendicular}/v_z=1 and velocity spread of Δv_z/v_z=5%. Large-signal simulations predict 140 kW output power at 92 GHz with 28% efficiency, 50 dB saturated gain, and 5% bandwidth. The stability of the amplifier against spurious oscillations has been checked with linear codes. To suppress the potential gyro-BWO interactions involving the TE₀₂, TE₁₁, and TE₂₁ modes, the interaction circuit with a cutoff frequency of 91 GHz has been loaded with loss so that the single-path, cold-circuit attenuation is 90 dB at 93 GHz. A coaxial input coupler with 3% bandwidth is employed with a predicted and measured coupling of 1 dB and 2 dB, respectively. The operating voltage is limited to below 75 kV because of oscillations encountered at higher voltages in this initial embodiment. Preliminary test at V_b=60 kV and I_b=3.7 A yielded 59 kW saturated output power at 92.2 GHz with 42 dB gain, 26.6% efficiency, and a 3 dB bandwidth of 1.2 GHz (1.3%)

[en] The invention broadly involves a method and means for generating a traveling wave laser pulse and is basically analogous to a single pass light amplifier system. However, the invention provides a traveling wave laser pulse of almost unlimited energy content, wherein a gain medium is pumped in a traveling wave mode, the traveling wave moving at essentially the velocity of light to generate an amplifying region or zone which moves through the medium at the velocity of light in the presence of directed stimulating radiation, thereby generating a traveling coherent, directed radiation pulse moving with the amplification zone through the gain medium. (U.S.)

No abstract available

[en] The accelerating cavity and coupler need to be tuned and matched after machining in order to meet requirement of RF transmission and accelerating electric field. Based on the development of a 10 MeV travelling wave electron linear accelerating tube, the RF adjusting method was illustrated in this paper. The plunger-probe method was used to tune uniform cavities, and the resonance approximation method was used for the non-uniform cavities, which reduces complexity of tuning. The three-frequency-point method and shifting load method were used to match input coupler. The tuning and matching result can meet the requirement. (authors)

[en] In view of the strong correlation between amplitude and phase characteristics of Traveling Wave Tube Amplifier (TWTA) analog predistortion technology, a dual-branch vector synthesis predistortion linearizer is proposed, which consists of branch line hybrid couplers, an adjustable attenuator and a reflective diode-based predistortion circuit. This linearizer is fabricated and measured according to the theoretical analysis and simulation results. The measurement results show that the linearizer can compensate the nonlinearity of the TWTAs. Once the two branches bias voltages are rationalized, the phase expansion can change 30 degrees, while the change of the amplitude expansion is less than 1 dB, which effectively reduces the correlation between the amplitude and the phase characteristics of the analog predistortion linearizer. (authors)