Test results of long term operation of the superfluid-cooled cryostat for a 1 GHz NMR spectrometer

A superfluid cryostat for an 1 GHz-NMR magnet has been developed and its performance was tested. The magnet was successfully energized up to 21.6 T corresponding to a resonance frequency of 920 MHz this April. Before the 920 MHz operations, the magnet was operated for 5 months at the 900 MHz field to check the long-term reliability of the cryogenic system. Stable cryogenic performance has been confirmed through this operation. The HeII bath temperature was kept constant below 1.6 K without any trouble related to the cryostat. The resultant heat load at 1.6 K was 0.55 W. The total helium consumption rate was 800 cc/h.