A TE21 second-harmonic gyrotron backward-wave oscillator with slotted structure

Abstract

Second-harmonic gyrotron backward-wave oscillator ͑gyro-BWO͒ with a reduced magnetic field strength is a tunable source in the millimeter wave regime, but it has long been impeded by the severe mode competition as a result of low efficiency and narrow bandwidth. This study employs a slotted structure functioning as a mode selective circuit to suppress the lower order transverse modes. In addition, a two-step tapered waveguide is adopted to stabilize the higher-order transverse modes and axial modes. Some important characteristics of the slotted gyro-BWO will be analyzed and discussed. As a calculated result, the interaction efficiency is improved and the stable tuning range is broadened. A stable, Ka-band, slotted second-harmonic gyro-BWO is capable of producing an efficiency of 23% with a 3 dB tuning bandwidth of 9% at 5 A and 100 kV.

Broadband conversion of TE01 mode for the coaxial gyrotron at low terahertz

“…Consider the case of symmetrically arranged coupling apertures that are applied on the coaxial outer conductor and form a slotted boundary. 6,11 The symmetry condition requires that the coupling waves have the same wave power and equal phase difference 2pm=N between the adjacent apertures, where N is the number of apertures and m is an integer and is zero for the coupling of coaxial/circular TE 01 mode. The rf field of the TE mode under this slotted boundary is composed of an infinite number of azimuthal component C that satisfies the value of m þ jN, 11 where j ¼ 0; 61; 62; :::.…”

“…To achieve high frequency and high power simultaneously, however, the gyrotron is inevitably operated in a high-order mode, which tends to induce severe mode competition in an overmoded system. Many mode selective circuits [3][4][5][6][8][9][10][11][12][13][14] have been studied to alleviate mode competition. The circular TE 01 mode associated with low wall dissipation and a purely azimuthal surface current mode selectivity in a transversely sliced structure for a gyro-BWO to achieve a wide stable tuning range of 15.3% at ka-band.…”

Theoretical Study of a Fourth-Harmonic 400-GHz Gyrotron Backward-Wave Oscillator

“…The theoretical investigation in this paper aims at enhancing the interaction, realizing broadband tuning, and simultaneously suppressing mode competitions. The technique of upstream tapered circuit is widely used to enhance beam-wave interaction efficiency of a gyro-BWO in both theoretical study and experiments [16], [28]- [30]. The TE (4) 41 mode gyro-BWO is inherently with relatively low beam-wave coupling strength due to high-harmonic interaction, and, accordingly, it is challenging to achieve high-efficiency interaction.…”

A magnetic cusp gun for terahertz gyro-devices

“…Fortunately, higher cyclotron harmonic (s:? : 2) interaction allows a lower magnetic field strength, only equaling 1/ s of the fundamental scheme [3]. Hence, higher harmonic ECM promises gyrotron a booming future as a kind of important high power terahertz radiation source.…”

“…Serious competition from lower harmonics challenges the system stability, and leads to low interaction efficiency in general. A solution, proposed from the beginning of harmonic gyrotron research until the most recent frontier THz gyrotron development, is to use a mode-selective axis-encircling electron beam, or called Large Orbit Beam (LOB) [3][4][5][6][7][8], where the sth harmonic selectively and efficiently excites the TEmn mode only, where �. Figures l(a) and I (b) comparatively display transverse views of a small orbit electron beam in fundamental harmonic gyrotron and a LOB in sth harmonic gyrotron.…”