THz Gyrotron and BWO Designed for Operation in DNP-NMR Spectrometer Magnet
- PDF / 311,476 Bytes
- 10 Pages / 439.37 x 666.142 pts Page_size
- 73 Downloads / 158 Views
THz Gyrotron and BWO Designed for Operation in DNP-NMR Spectrometer Magnet V. L. Bratman & A. E. Fedotov & Yu. K. Kalynov & P. B. Makhalov & A. Samoson
Received: 26 June 2013 / Accepted: 22 August 2013 # Springer Science+Business Media New York 2013
Abstract Dynamic nuclear polarization (DNP) in high-field nuclear magnetic resonance (NMR) spectroscopy requires medium-power terahertz radiation, which nowadays can be provided basically by gyrotrons with superconducting magnets. As the electron cyclotron frequency is very close to the frequency of electron paramagnetic resonance for the same magnetic field, under certain conditions the gyrotron can be installed inside the same solenoid used for NMR spectrometer. This eliminates the need for an additional superconducting magnet, results in a shorter terahertz transmission line, and can make DNP systems practical. In addition to an extremely low-voltage gyrotron (“gyrotrino”), we analyze also advantages of strong magnetic field for a slow-wave electron device as an alternative terahertz source. Keywords Gyrotron . Backward-wave oscillator . DNP-NMR spectroscopy . Superconducting magnet
1 Introduction Dynamic nuclear polarization (DNP) is a powerful method of sensitivity enhancement in the spectroscopy of nuclear magnetic resonance (NMR) [1–3]. DNP is based on pumping of electron spin polarization by microwave or terahertz irradiation at the frequency of electron paramagnetic resonance (EPR) and transfer of this polarization to nuclear spins by means of Overhauser effect, solid effect or cross effect. For modern 400-1000 MHz high field NMR spectrometers, electron paramagnetic resonance (EPR) frequencies are 260-650 GHz, respectively. Current probe design V. L. Bratman : A. E. Fedotov (*) : Y. K. Kalynov : P. B. Makhalov Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia e-mail: [email protected] V. L. Bratman Nizhny Novgorod State University, Nizhny Novgorod, Russia A. Samoson Tallinn University of Technology, Tallinn, Estonia A. Samoson Physics Department, University of Warwick, Coventry, UK
J Infrared Milli Terahz Waves
principles require terahertz radiation power in a range of 1-100 W for saturation of the electron spin polarization [3–5]. Since these power levels are beyond capacity of solid-state devices or conventional slow-wave vacuum electron tubes, gyrotrons as only practical option have been preferred [3–10]. The gyrotron operation is based on stimulated cyclotron radiation of electrons, which requires magnetic field slightly higher than target NMR is using for the expected power at teraherz frequencies. Despite remarkable development, use of high voltage gyrotrons with dedicated bulky and expensive superconducting magnets still deter the NMR community from a wide proliferation of the DNP technique. In current paper we outline alternative approach, namely, combining both, spectrometer and terahertz source, in a single magnet. Since the electron cyclotron frequency is very close to the EPR frequency for the same
Data Loading...
