title: Towards a beyond 1 GHz solid-state nuclear magnetic resonance: external lock operation in an external current mode for a 500 MHz nuclear magnetic resonance.
abstract: Achieving a higher magnetic field is important for solid-state nuclear magnetic resonance (NMR). But a conventional low temperature superconducting (LTS) magnet cannot exceed 1 GHz (23.5 T) due to the critical magnetic field. Thus, we started a project to replace the Nb(3)Sn innermost coil of an existing 920 MHz NMR (21.6 T) with a Bi-2223 high temperature superconducting (HTS) innermost coil. Unfortunately, the HTS magnet cannot be operated in persistent current mode; an external dc power supply is required to operate the NMR magnet, causing magnetic field fluctuations. These fluctuations can be stabilized by a field-frequency lock system based on an external NMR detection coil. We demonstrate here such a field-frequency lock system in a 500 MHz LTS NMR magnet operated in an external current mode. The system uses a (7)Li sample in a microcoil as external NMR detection system. The required field compensation is calculated from the frequency of the FID as measured with a frequency counter. The system detects the FID signal, determining the FID frequency, and calculates the required compensation coil current to stabilize the sample magnetic field. The magnetic field was stabilized at 0.05 ppm∕3 h for magnetic field fluctuations of around 10 ppm. This method is especially effective for a magnet with large magnetic field fluctuations. The magnetic field of the compensation coil is relatively inhomogeneous in these cases and the inhomogeneity of the compensation coil can be taken into account.
authors.affiliation: RIKEN Systems and Structural Biology Center, Yokohama, Kanagawa 230-0045, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Takahashi
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Ebisawa
authors.forename: Konosuke
authors.initials: K
authors.lastname: Tennmei
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Yanagisawa
authors.forename: Masami
authors.initials: M
authors.lastname: Hosono
authors.forename: Kenji
authors.initials: K
authors.lastname: Takasugi
authors.forename: Takashi
authors.initials: T
authors.lastname: Hase
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Miyazaki
authors.forename: Teruaki
authors.initials: T
authors.lastname: Fujito
authors.forename: Hideki
authors.initials: H
authors.lastname: Nakagome
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Kiyoshi
authors.forename: Toshio
authors.initials: T
authors.lastname: Yamazaki
authors.forename: Hideaki
authors.initials: H
authors.lastname: Maeda