Abstract
A high-harmonic Large Orbit Gyrotron and a low-voltage gyrotrino placed inside a spectrometer cryomagnet enable greatly simplify terahertz systems for magneto-resonance spectrometers. Large Orbit Gyrotrons provide a powerful third-harmonic generation at frequencies of 1 THz and 0.394 THz in pulsed and CW regimes, respectively, at significantly lower magnetic fields than conventional gyrotrons. According to simulations the gyrotrino with the voltage of 1.5 kV and frequency of 0.264 THz can generate a power of tens of watts; a possibility to operate at such a low voltage is demonstrated in the existing gyrotron with three-electrode magnetron-injection gun.
Highlights
THz medium power gyrotrons are in high demand for high-field DNP-NMR spectroscopy
A greater effect can be achieved in Large Orbit Gyrotrons (LOGs), capable of selective operation even at the third and fourth harmonics due to applying an axis-encircling electron beam [1,2,3,4,5], in contrast to a hollow poly-axis beam in a conventional gyrotron
In the 80-kV LOG (Fig. 2a) [4], a stable single-mode second- and third-harmonic generation with a power of 0.3–1.8 kW was obtained in 10-μs pulses at four frequencies in the range of 0.55–1.00 THz at magnetic fields 10.5–13.6 T
Summary
THz medium power gyrotrons are in high demand for high-field DNP-NMR spectroscopy. only few installations are equipped with such fairly expensive generators. In a LOG cavity (Fig. 1), an axis-encircling electron beam can excite only co-rotating modes with azimuthal indices equal to the number of the resonant cyclotron harmonic [1,2,3,4,5].
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