Second-harmonic Gyrotron Research Articles

Design of a high-efficiency low-voltage axially modulated cusp-injected second-harmonic X-band gyrotron amplifier

We present the theoretical design of a second-harmonic small-orbit gyrotron amplifier which utilizes the interactions between a 35-kV 4-A beam and a TE/sub 011/ cavity to produce over 70 kW of amplified power at 9.9 GHz in a 1.83-kG magnetic field. One of the novel features of this device is that the electron gun produces an axially streaming annular beam which is velocity modulated by a short TM/sub 0n0/ input cavity. Perpendicular energy is imparted to the beam via a nonadiabatic magnetic transition at the end of a 13-cm drift region. An electronic efficiency of 53% is predicted with a large signal gain near 20 dB by a single particle code which takes into account nonideal effects associated with finite beam thickness and finite magnetic field transition widths.

Operation of a stable 200-kW second-harmonic gyro-TWT amplifier

The experimental results are reported for a stable second-harmonic gyrotron traveling wave amplifier, which generated a record-breaking 207-kW output power based on the principle that the weaker harmonic interactions are more stable to spontaneous oscillations than at the fundamental, and therefore, capable of generating higher output power. The high-power amplifier was kept completely (zero-drive) stable by employing a mode-selective interaction circuit and web-matched directional input and output couplers, and choosing an amplifier interaction length shorter than the start-oscillation length for gyrotron backward-wave oscillations. The single-stage Ku-band amplifier utilized an 80-kV 20-A /spl upsi//sub /spl perp////spl upsi//sub /spl par//=1.1 electron beam from a magnetron injection gun and yielded an efficiency of 12.9%, an output phase variation of 10/spl deg//kV, a saturated bandwidth of 2.1%, a large-signal gain of 16 dB, and a detuned small-signal gain of 38 dB.

Phase-locking of a second-harmonic gyrotron oscillator using a quasi-optical circulator to separate injection and output signals

Phase-locking in a 34.5-GHz special complex cavity gyrotron oscillator operating at the second harmonic of the electron cyclotron frequency was studied. Injection of the locking power was made via a quasi-optical circulator connected to the gyrotron output. Locking bandwidth was measured by comparing the phase of the injection signal and output signal using a balanced mixer. Locking was observed with input power level as low as 40 dB below the gyrotron output power. The locking bandwidth is, however, narrower than in gyrotrons operating at the fundamental cyclotron frequency which may be attributed to the longer resonant cavity in the second harmonic gyrotron and the corresponding larger value of external quality factor. The measurements are roughly in agreement with predictions of Adler's phase-locking equation which is given for our system in terms of powers propagating in the output waveguide toward and away from the gyrotron cavity. >

Development of submillimeter wave gyrotron for plasma diagnostics

Abstract A high frequency second-harmonic gyrotron using a 12 T superconducting magnet is described. It has achieved second-harmonic operations whose frequencies are varied up to 636 GHz (corresponding to a wavelength of 472 μm). The output powers are several hundred watts. Experimental results on the amplitude modulation of the output of the gyrotron are presented. 100% modulation of the output at frequencies up to several hundred kilohertz has been achieved under anode modulation levels of only a few per cent. The gyrotron is useful for plasma diagnostics as a medium power frequency-step-tunable millimeter to submillimeter wave source.

Long-pulse, low-voltage infrared free-electron laser

Free-electron lasers (FEL's) have been developed as powerful IR sources at several sites around the world. This paper considers the design of a relatively compact, low-cost, tunable IR FEL based on a 3-MeV electrostatic accelerator and a submillimeter-wavelength electromagnetic wiggler. The system should be sufficiently portable for use in the field, and applications such as remote sensing and industrial processing are envisioned. The wiggler is powered by a second-harmonic quasioptical gyrotron. A prescription for optimizing the gain of an electromagnetic wiggler FEL is derived and the nonlinear regime is treated by relating the electromagnetic wiggler FEL to the universal normalized FEL equations. A point design is given showing accelerator, gyrotron, and output parameters for a system capable of operating over the entire 3-13-/spl mu/m wavelength atmospheric windows. A wide range of output characteristics is available. >

Development of a high-frequency, second-harmonic gyrotron tunable up to 636 GHz

In this Letter, a high-frequency, second-harmonic gyrotron using a 12 T superconducting magnet is described. It has achieved a maximum frequency of 636 GHz (corresponding to a wavelength of 472 μm). Operating at both the fundamental and the second harmonic of the electron cyclotron frequency enables the gyrotron to act as a high power (several 100 W), step tunable, millimeter to submillimeter wave source in the wide frequency range from 150 to 630 GHz.

Powerful second-harmonic gyrotron oscillator

Experimental results from a study of second-harmonic gyrotron oscillator are reported. A steady second-harmonic cavity emission has been observed at 28 GHz and waveguide mode TE/sub 02/. A peak power of approximately 30 MW has been reached with approximately 9% efficiency. For better understanding of the generation mechanism additional gyrotron experiments have been carried out with a similar cavity without a cutoff section at the exit, operating at the fundamental cyclotron harmonic. >