THz Dynamic Nuclear Polarization NMR

Abstract

Dynamic nuclear polarization (DNP) increases the sensitivity of nuclear magnetic resonance (NMR) spectroscopy by using high frequency microwaves to transfer the polarization of the electrons to the nuclear spins. The enhancement in NMR sensitivity can amount to a factor of well above 100, enabling faster data acquisition and greatly improved NMR measurements. With the increasing magnetic fields (up to 23 T) used in NMR research, the required frequency for DNP falls into the THz band (140–600 GHz). Gyrotrons have been developed to meet the demanding specifications for DNP NMR, including power levels of tens of watts; frequency stability of a few megahertz; and power stability of 1% over runs that last for several days to weeks. Continuous gyrotron frequency tuning of over 1 GHz has also been demonstrated. The complete DNP NMR system must include a low loss transmission line; an optimized antenna; and a holder for efficient coupling of the THz radiation to the sample. This paper describes the DNP NMR process and illustrates the THz systems needed for this demanding spectroscopic application. THz DNP NMR is a rapidly developing, exciting area of THz science and technology.

Experimental study from linear to chaotic regimes on a terahertz-frequency gyrotron oscillator

“…12 The gyrotron system used in this work has been designed with the aim of maximizing its frequency tunability via longitudinal mode competition for dynamic nuclear polarization (DNP)-nuclear magnetic resonance (NMR) applications. 3,25 The uncoupled dispersion relation for the gyrotron system parameters is shown in Fig. 1.…”

Triode Magnetron Injection Gun for 132 GHZ Gyrotron for 200 MHZ DNP-NMR Application

“…[6,7]. Since last one decade, huge efforts are made by researchers todevelop the sub-THz and THz gyrotrons specifically for the application of NMR (Nuclear Magnetic Resonance) spectroscopy [8,9]. The sub-THz/THz gyrotronsare used to pump tens of watt RF power at a particular frequency (decided by the proton frequency in NMR) into the NMR spectroscopic system to enhance the sensitivity of experiments via a technique called Dynamic Nuclear Polarization (DNP).…”

“…for different proton frequency NMR systems and the present development status of DNP gyrotrons isgiven in Refs. [8,9]. The main design and technological challenges for such gyrotrons are the superconducting magnet system of very high magnetic field value, frequency tunability of few GHz (generally from 2-5 GHz) and highly stable operation of the device [8,10,11].…”

“…The main design and technological challenges for such gyrotrons are the superconducting magnet system of very high magnetic field value, frequency tunability of few GHz (generally from 2-5 GHz) and highly stable operation of the device [8,10,11]. These technological features of DNP gyrotrons make the design and development of the device slightly different from high power fusion gyrotrons [2,6,8,9]. 30-50 watt RF power at 132 GHz frequency is required for dynamic nuclear polarization in 200 MHz NMR spectrometer.…”

“…The basic specifications of this gyrotron are summarized in Table 1. To obtain the smooth frequency tuning of 2-3 GHz, a series of cavity axial modes is excited during the beam wave interaction in the interaction cavity [8]. In this process the magnetic field values at cavity center and emitter are changed continuously.…”