Design of a frequency-tunable gyrotron for DNP-enhanced NMR spectroscopy

We report on the design of a modular low-power (10-50 W) high-frequency gyrotron (265-530 GHz) for DNP enhanced solid-state NMR spectroscopy. With the view of covering a wide range of frequencies, a 9.7 T helium-free superconducting magnet (SCM) is planned for the gyrotron operation on either 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 = 6-8 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 a lateral output with an internal Vlasov-type converter. The reference parameters for application of DNP-enhanced NMR spectroscopy on a 400 MHz (¹H) spectrometer are optimized with a RF frequency tunability corresponding to twice the proton NMR frequency. The modularity of the construction of the gyrotron allows for the possibility of changing only some elements like the cavity-uptaper system in order to adapt to the wide range of NMR spectrometers existing at EPFL.