Development of 394.6 GHz CW Gyrotron (Gyrotron FU CW II) for DNP/Proton-NMR at 600 MHz

Abstract

Gyrotron FU CW II with an 8 T liquid He free superconducting magnet, the second gyrotron of the THz Gyrotron FU CW Series, has been constructed and the operation test was successfully carried out. It will be used for enhancing the sensitivity of 600 MHz proton-NMR by use of Dynamic Nuclear Polarization (DNP). The designed operation mode of the gyrotron is TE2,6 at the second harmonic. The corresponding frequency is 394.6 GHz. The real operation frequency is 394.3 GHz at TE06 mode, because of fabrication error of the diameter of the cavity. The operation is in complete CW at the output power of around 30 W or higher at the TE06 cavity mode. There are many other operation modes at the fundamental and the second harmonic. Typical output power of the fundamental and the second harmonic are higher than 100 W and 20 W, respectively. The highest frequency observed up to the present is 443.5 GHz at the second harmonic operation of TE6,5 mode. The measured results are compared with the theoretical consideration

Resonant Cavities for Frequency Tunable Gyrotrons

“…This mode has been chosen because it is relatively well separated from the neighboring competing modes at both fundamental and second harmonics. Moreover, it was corroborated experimentally that the parameters of the beam generated by the electronoptical system of FU CW II are appropriate for excitation of this mode and ensure stable operation [7]. The radius and length of the central straight section of this cavity are 2.36 mm and 15 mm, respectively.…”

“…Here however we present only one illustrative example. It is pertinent to the cavity of the gyrotron FU CW II which is optimized for operation on TE 26 mode at second harmonic of the cyclotron frequency [7]. This mode has been chosen because it is relatively well separated from the neighboring competing modes at both fundamental and second harmonics.…”

“…The second device that belongs to the same series is FU CW II. It utilizes an 8 T liquid He free magnet and has been developed as a radiation source for NMR spectroscopy [7].…”

“…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.…”

Performance Test of CW 300 GHz Gyrotron FU CW I

“…FU CW II delivers 394.6 GHz radiation of tens of Watts [14]. It will be used as a power source of DNP-NMR for protein analysis.…”