Conceptual Design Study of a Novel Gyrotron for NMR/DNP Spectroscopy

Resonant Cavities for Frequency Tunable Gyrotrons

“…The numerical experiments predict tunability bandwidth of 2 GHz [29]. The same approach has been followed also in the conceptual design of another gyrotron for NMR/DNP spectroscopy at 395 GHz [11].…”

“…Therefore, while for the conventional water cooled gyrotron cavities made of copper it is enough to uphold the local wall losses at levels below 2.0 kW/cm 2 in the case of piezo elements the thermal loading must be significantly lower. The estimates made for the cavity of a 395 GHz gyrotron [11] and metallization of gold with electrical conductivity 6.3×10 7 Ω -1 m -1 gives a skin depth about 0.1 μm and Ohmic Q factor around 12000. Evaluation of the density of absorbed power due to Ohmic heating in the cavity optimized for TE 04 mode [11] at output power 10 W is 2.6 W/cm 2 .…”

“…The estimates made for the cavity of a 395 GHz gyrotron [11] and metallization of gold with electrical conductivity 6.3×10 7 Ω -1 m -1 gives a skin depth about 0.1 μm and Ohmic Q factor around 12000. Evaluation of the density of absorbed power due to Ohmic heating in the cavity optimized for TE 04 mode [11] at output power 10 W is 2.6 W/cm 2 . The thickness of the metallization is usually 1.0 μm for thin-film electrodes and 10 μm for thick-film electrodes [36].…”

“…It is pertinent to a gyrotron cavity for a new gyrotron for DNP enhanced NMR spectrometer for protein studies, which is under development now. The resonant cavity of the gyrotron is optimized for operation on TE 04 mode at 395 GHz and supports a sequence of axial modes as demonstrated in [11]. The length of the piezoelectric tube is 16.26 mm and the radius is 1.6094 mm.…”

“…These are two gyrotrons operating at fundamental cyclotron frequency (140 GHz and 250 GHz and embedded in 200 MHz and 380 MHz spectrometers, respectively) and 470 GHz second harmonic gyrotron for 700 MHz spectrometer. Similar project is in progress now at FIR FU Research Center [7,11,12]. The main challenge is to achieve a stable operational performance (several days of CW regime) with constant (within 1 %) amplitude of the output power (about 10 W) and broadband continuous frequency tuning in an interval of ±0.5 GHz around the frequency of 395 GHz, which corresponds to 600 MHz NMR resonance for a proton.…”