Results 1 - 10 of 382
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[en] The stability of the millimeter-wave gyrotron-traveling-wave-tube (gyro-TWT) amplifier can be effectively improved via controlling the propagation characteristics of the operating modes using lossy dielectric-lined (DL) waveguide. Self-consistent nonlinear theory of the electron cyclotron maser (ECM) interaction in lossy DL circuit is developed based on a full-wave study of the propagation characteristics of the DL waveguide. This nonlinear theory fully takes into consideration the waveguide structure and the lossy dielectric characteristics. It is capable of accurately calculating the ECM instability between a cyclotron harmonic and a circular polarized mode, and effectively predicting the nonlinear stability of the DL waveguide-based gyro-TWT. Systematic investigation of a Ka-band TE01 mode DL waveguide-based gyro-TWT is carried out, and numerical calculation reveals a series of interesting results. This work provides a basic theoretical tool for further exploring the application of the lossy DL waveguide in millimeter-wave gyro-TWTs.
[en] A high-power X-band traveling-wave tube (TWT) amplifier has been designed. A disk-loaded circular waveguide is used as the slow wave structure (SWS) for wave interaction with a 450 kV, 80 A solid electron beam. From Pierce theory, the predicted gain at 9.7 GHz is 1.94 dB/cm with an instantaneous bandwidth of 5% and a phase advance of π/2 for the TM01 mode. Cold dispersion measurements show good agreement with the simulation
[en] Forerunning wave and wakefield induced by a non-relativistic, charged Gaussian bunch moving along a wide-bandwidth, periodic structure have been simulated in time domain. Unusual waveform of the potential function is compared to theoretical predictions and time-domain, multi-mode analytical solution. The numerical experiment demonstrated anomalously high magnitude of the precursor wave. A specific case, when the group velocity is equal to the bunch velocity, is discussed as well. Potential applications include diagnostics, sensors, and probing tools for metamaterials and photonic crystals
[en] This paper presents the results of a survey study that analyzed the possibility of using a magnetic coupled disk-loaded waveguide as an accelerating structure in travelling wave (TW) regime. The electrodynamics parameters of such a structure at various modes in C-band for a wide range of phase velocities as a function of aperture radii and coupling slot sizes are presented. This accelerating structure is applicable for forward or backward wave operation modes. The version of a 10 MeV combined accelerator with a standing wave (SW) coupler and a TW magnetic coupled accelerating structure is proposed.
[en] The authors report results from experiments studying X-Band amplification in both cylindrical traveling wave tube (TWT) and coaxial drift tube geometries. In the TWT geometry 800-900 kV, 1-2 kA, 50-100 ns electron beams are injected into cylindrical guides containing slow wave structures. The amplifiers operate in the TM01 mode. With single stage ripple wall slow wave structures gains of order 30 dB have been obtained with output powers of 100 MW. Using a dielectric loaded TWT amplifier gains of 30 dB have also been measured, although at lower output powers of 35 MW. In the coaxial geometry a 9 cm diameter annular, 400 kV, 7 kA, 50 ns electron beam is injected through a 16 cm dielectrically loaded cavity, and an X-Band magnetron provides frequency locking of the interaction. The interaction processes involved in these devices have been studied analytically and also simulated with the MAGIC code. These studies show significant electron energy spreads result from the amplification process in the TWT devices. A magnetic spectrometer has been built to analyze the output energy spectrum of the accelerated electrons. Preliminary results from this experiment show evidence of a change in the electron distribution at the amplifier output when the r.f. power is present
[en] A wideband low-voltage millimeter-wave gyro-traveling wave tube (gyro-TWT) amplifier operating in the TE10 rectangular waveguide mode at the fundamental cyclotron frequency is discussed. The device incorporates precise axial tapering of both the magnetic field and the interaction circuit for broadband operation. Experimental results of a wide (>20%) instantaneous bandwidth with a high gain (> 25dB) and a saturated efficiency of >15% has been achieved and shown to be in good agreement with the theory. (author)
[en] In two-beam accelerators, the reacceleration of a modulated drive beam can enable high conversion efficiency of electron beam energy to rf energy. However, the stability issues involved with the transport of high current electron beams through rf extraction structures and induction accelerator cells are critical. The author reports on theoretical studies and computer simulations of a two-beam accelerator design using traveling-wave extraction structures. Specific issues addressed include regenerative and cumulative transverse instabilities
[en] High gradient performance of a travelling wave X-band accelerating structure 20 cm long was examined. Various observables were measured such as RF pulse waveform at various positions, dark current versus accelerating field level, energy spectra of emitted electrons downstream and so on. The field level of 80 MV/m at the input coupler cell was obtained after 500 hours' conditioning at a typical repetition rate of 10 pps. This field level is equivalent to 70 MV/m accelerating field in 20 cm long structure. Peak dark current decreased down to 1 μA level at accelerating field of 50 MV/m at the input coupler cell. (Author) 5 refs., 7 figs., tab
[en] At output powers in excess of 100 MW the authors have noted the development of sidebands in many TWT structures. To address this problem an experiment using a narrow bandwidth, two-stage TWT is in progress. The TWT amplifier consists of a dielectric (e = 5) slow-wave structure, a 30 dB sever section and a 8.8-9.0 GHz passband periodic, metallic structure. The electron beam used in this experiment is a 950 kV, 1 kA, 50 ns pencil beam propagating along an applied axial field of 9 kG. The dielectric first stage has a maximum gain of 30 dB measured at 8.87 GHz, with output powers of up to 50 MW in the TM01 mode. In these experiments the dielectric amplifier output power is about 3-5 MW and the output power of the complete two-stage device is ∼160 MW at the input frequency. The sidebands detected in earlier experiments have been eliminated. The authors also report measurements of the energy spread of the electron beam resulting from the amplification process. These experimental results are compared with MAGIC code simulations and analytic work they have carried out on such devices