Assembly and performance of a 6.4 T cryogen‐free dynamic nuclear polarization system

Abstract

We report on the assembly and performance evaluation of a 180-GHz/6.4 T dynamic nuclear polarization (DNP) system based on a cryogen-free superconducting magnet. The DNP system utilizes a variable-field superconducting magnet that can be ramped up to 9 T and equipped with cryocoolers that can cool the sample space with the DNP assembly down to 1.8 K via the Joule-Thomson effect. A homebuilt DNP probe insert with top-tuned nuclear magnetic resonance coil and microwave port was incorporated into the sample space in which the effective sample temperature is approximately 1.9 K when a 180-GHz microwave source is on during DNP operation. C DNP of [1- C] acetate samples doped with trityl OX063 and 4-oxo-TEMPO in this system have resulted in solid-state C polarization levels of 58 ± 3% and 18 ± 2%, respectively. The relatively high C polarization levels achieved in this work have demonstrated that the use of a cryogen-free superconducting magnet for C DNP is feasible and in fact, relatively efficient-a major leap to offset the high cost of liquid helium consumption in DNP experiments.

Dissolution DNP using trityl radicals at 7 T field

“…Originally, most polarizers operated at a static magnetic field of 3.4 T corresponding to an electron Larmor frequency of 94.5 GHz due to the ready availability of microwave sources at this frequency. Going to static magnetic fields higher than 3.4 T has shown the potential to achieve higher polarization values [25][26][27][28][29] .…”

A multisample 7 T dynamic nuclear polarization polarizer for preclinical hyperpolarized MR

“…Although zero boil‐off “wet” magnets are now standard in MR, because of the technological advances of cryocoolers, which can be utilized for recondensing evaporated helium, recently developed conduction‐cooled superconducting dry magnets provide an attractive option to simplify DNP polarizers and completely remove the need for the input of liquid helium. The recent DNP polarizer designs include a high field (9, 9.4 or 10.1 T) dry magnet . The design presented herein displays how a conduction‐cooled 7 T magnet was anchored to the 1‐K plate, the temperature of which always stays below 3 K during standard operation, thereby minimizing the risk of an accidental quench.…”

A cryogen-consumption-free system for dynamic nuclear polarization at 9.4 T

“…The apparatus described by Yoshihara, Can, Karlsson, Lerche, Schwitter, and Comment operates at B0 = 7 T [6]. The system designed by Kiswandhi, Niedbalski, Parish, Wang, and Lumata [7] utilizes a variable-field "cryogen-free" superconducting magnet that can be ramped up to B0 = 9 T but was only used at B0 = 6.7 T and is equipped with cryo-coolers that can cool the sample space and DNP assembly down to T = 1.8 K via the Joule-Thomson effect. The DNP system described in a lecture by Bowen, Rybalko, Petersen and Ardenkjaer-Larsen is also based on a dry magnet and can in principle be used at B0 = 3.35, 6.70, and 10.05 T [8].…”