Design of a low-power high-frequency gyrotron for DNP-enhanced NMR spectroscopy

Summary form only given as follows. We report on a design of a modular low-power (10-50 W) high-frequency gyrotron (200-530 GHz) for DNP-enhanced NMR spectroscopy. For covering this wide range of frequencies a 9.5 T helium-free superconducting magnet (SCM) with a warm bore diameter of 75 mm is foreseen. Considering the wide frequency range, the SCM field level is compatible with an operation of the gyrotron at both the fundamental or second harmonic of the electron cyclotron frequency. The gyrotron design is based on a triode electron gun (V_k=15 kV, I_b=100 mA, V_a= plusmn5 kV) which is very flexible for adapting the electron beam properties to a wide variety of cavities operating at the fundamental or at the second harmonic. The gyrotron is designed for an axial output and a quasi-optical mode-converter to a Gaussian mode will be placed after the gyrotron window. The reference parameters for the first application of DNP-enhanced NMR spectroscopy on a 400 MHz (¹H) spectrometer are: frequency = 263.5 GHz, frequency tunability = 0.12%, RF-power = 10-50 W. The modularity of the gyrotron refers to the possibility to change only some elements like the cavity-uptaper system to be adapted to the wide range of NMR spectrometers existing at EPFL.