Boosted excitation of the fifth cyclotron harmonic based on frequency multiplication in conventional gyrotrons.

We discovered a specific property of the eigenmodes of a cylindrical waveguide, due to which efficient mode excitation at ultrahigh (s=4n+1, n is integer) multiples of the gyrofrequency can be provided by a polyhelical weakly relativistic electron beam, standardly used for gyrotron operation. In the proof-of-principle experiment with a V-band gyrotron driven by a 25-keV, 2-A beam, about 100 mW radiation power at the fifth cyclotron harmonic (0.22 THz) has been detected in the cw regime. Based on the gyrotron theory, we demonstrate in simulations that, using parameters of existing gyrotrons, this method can be applied for producing cw radiation at a power level of up to several watts in the terahertz gap.

High-power sub-terahertz source with a record frequency stability at up to 1 Hz.

Many state-of-the-art fundamental and industrial projects need the use of terahertz radiation with high power and small linewidth. Gyrotrons as radiation sources provide the desired level of power in the sub-THz and THz frequency range, but have substantial free-running frequency fluctuations of the order of 10-4. Here, we demonstrate that the precise frequency stability of a high-power sub-THz gyrotron can be achieved by a phase-lock loop in the anode voltage control. The relative width of the frequency spectrum and the frequency stability obtained for a 0.263 THz/100 W gyrotron are 4 × 10-12 and 10-10, respectively, and these parameters are better than those demonstrated so far with high-power sources by almost three orders of magnitude. This approach confirms its potential for ultra-high precision spectroscopy, the development of sources with large-scale radiating apertures, and other new projects.

A novel THz-band double-beam gyrotron for high-field DNP-NMR spectroscopy.

We present the first experimental results of the study on a novel second harmonic THz-band double-beam gyrotron. The tube has demonstrated a stable single-mode operation with output parameters that are appropriate for the next-generation 1.2 GHz dynamic nuclear polarization-nuclear magnetic resonance spectroscopy. Besides the design mode (TE8,5), a series of other fundamental and second harmonic modes have been excited. This makes the new gyrotron a versatile radiation source, which can be used also in other applications of the high-power science and technologies.