No abstract available

[en] One of the main obstacles in achieving stable, efficient operation at the cyclotron harmonics in a gyrotron is mode competition with parasitic modes at the fundamental frequency. In this article, the nonlinear dynamics of mode interactions in such a system are studied using a multifrequency, time-dependent model. The results of numerical simulations for a second harmonic gyrotron are presented by considering two starting scenarios: (a) fast voltage rise or an instant turn-on case, and (b) slow voltage rise case. For the first case, it is demonstrated that for a certain range of operating parameters, the presence of a parasitic mode at the fundamental can be helpful in the excitation of the second harmonic operating mode. In the second case, it is found that the unstable operating region increases with the value of the rise time constant of the electrode voltages. Stable, efficient gyrotron operation at the second harmonic is demonstrated using the numerical study

[en] Simultaneous generation at the second and fourth cyclotron harmonics has been obtained from a single-cavity self-excited gyromultiplier. Output power of the short-wavelength radiation amounts to 100 W at a frequency of 75 GHz. The proposed scheme seems to be promising for the terahertz frequency range.

No abstract available

[en] Recently reported observations of electrostatic emissions in the first five harmonic bands of the electron cyclotron frequency, following a lithium release in the solar wind, are interpreted in terms of quasi-static waves with k perpendicular B (Bernstein waves), excited by photoionization of Li atoms in the magnetized, warm solar wind plasma. The observed distinct frequencies are selected from the excited broad band spectrum by the condition of zero group velocity in the satellite frame. copyright American Geophysical Union 1989

[en] We have proposed a double drift bunching scheme where one can obtain a bunching effect equal to that of a six-harmonic buncher by using only two harmonics mixed in optimum proportions. In this case one has to apply voltages with frequencies ω and 2ω (instead of only ω) on the first buncher and 2ω on the second buncher. The optimization of buncher parameters such as the voltage amplitudes of the various harmonics and the separation between the two bunchers has been carried out using linear programming technique

[en] Recently reported measurements of the electron cyclotron emission from the TFR Tokamak plasma are analyzed and compared to theoretical predictions. The line shape of an optically thick harmonic in a vertical observation is explained by wall reflections, plasma-detector arrangement and reabsorption. Non thermal emission at the electron plasma frequency is related to the presence of a high energy tail in the electron distribution function and might be the cause of the observed reduced runaway creation rate

[en] A formalism is presented for the analysis of polarization evolution in a magnetized plasma with dissipation due to kinetic effects. Such a plasma in addition to the Faraday and Cotton-Mouton effects also presents dichroism, namely anisotropic absorption. As expected this effect is significant near the cyclotron harmonics

[en] A comparative analysis between the fundamental and second cyclotron harmonics of gyrotron backward-wave oscillators (gyro-BWOs) is presented. The simulation results reveal that nonlinear field contraction is a common feature for both harmonic interactions. Besides, the electron transit angle, used to characterize the axial modes of the fundamental harmonic TE₁₁ mode at the start-oscillation conditions, is found to be applicable even for the second harmonic TE₂₁ mode. Each axial mode of either the fundamental harmonic TE₁₁ or the second harmonic TE₂₁ modes is maintained at a constant value of the electron transit angle while changing the operating parameters, such as magnetic field and beam voltage. Extensive numerical calculations are conducted for the start-oscillation currents and tuning properties. Moreover, single-mode operating regimes are suggested where the second harmonic TE₂₁ gyro-BWO could generate a considerable output power, comparing with the fundamental harmonic TE₁₁ gyro-BWO

[en] The first harmonic imperfection both in the central part as well as in the extraction region of the machine leads to beam off-centering, which in turn makes impossible to extract the internal beam from cyclotron. The magnetic field mapping in K500 superconducting cyclotron shows a strong first harmonic magnetic field imperfection of around 24-28 G at the central region (at radius of 100 mm) and around 45-50 G (at radius of 650-660 mm) at the extraction region of the machine. The paper describes the first harmonic correction at the central part of the machine to an accepted limit of few gauss (5-10 G level) and the correction scheme for the extraction part of the machine. Results of the optimization scheme developed for first harmonic correction in the extraction region has also been discussed in the paper. (author)