A LOW-TEMPERATURE NMR PROBE FOR USE IN A DILUTION REFRIGERATOR

We report an NMR probe that we use in ultra low temperature experiments in a top-loading dilution refrigerator. The probe is thermally anchored to the 1.2 K pumped He-4 pot and is thermally isolated from the sample located inside a Kel-F cup containing liquid He-3. The probe is adapted from a standard double resonance probe, using air trimmer capacitors, a lambda/4 cable, a homemade saddle coil, and metal film resistors. The double resonance design breaks the probe's tuning ranges into two bands. The high frequency band tunes from 100 to 150 MHz covering all the nuclei with large gyromagnetic ratios, H-3, F-19, H-1, He-3. The low frequency band tunes for 17 to 54 MHz covering all nuclei with gyromagnetic ratios between Cs-133 and Sn-119. The air trimmer capacitors have an open structure that allows efficient pumping and the metal film resistors are used to reduce the Q of the probe. This probe has been successfully used for a wide range of nuclei including H-1, F-19, He-3, Sn-119, Sn-117, Sn-115, B-11, C-13, Si-29, Al-27, and H-2.