Automated sample exchange and tracking system for neutron research at cryogenic temperatures

An automated system for sample exchange and tracking in a cryogenic environment and under remote computer control was developed. Up to 24 sample “cans” per cycle can be inserted and retrieved in a programed sequence. A video camera acquires a unique identification marked on the sample can to provide a record of the sequence. All operations are coordinated via a LABVIEW™ program that can be operated locally or over a network. The samples are contained in vanadium cans of $6–10mm$ in diameter and equipped with a hermetically sealed lid that interfaces with the sample handler. The system uses a closed-cycle refrigerator (CCR) for cooling. The sample was delivered to a precooling location that was at a temperature of $∼25K$⁠, after several minutes, it was moved onto a “landing pad” at $∼10K$ that locates the sample in the probe beam. After the sample was released onto the landing pad, the sample handler was retracted. Reading the sample identification and the exchange operation takes approximately $2min$⁠. The time to cool the sample from ambient temperature to $∼10K$ was approximately $7min$ including precooling time. The cooling time increases to approximately $12min$ if precooling is not used. Small differences in cooling rate were observed between sample materials and for different sample can sizes. Filling the sample well and the sample can with low pressure helium is essential to provide heat transfer and to achieve useful cooling rates. A resistive heating coil can be used to offset the refrigeration so that temperatures up to $∼350K$ can be accessed and controlled using a proportional-integral-derivative control loop. The time for the landing pad to cool to $∼10K$ after it has been heated to $∼240K$ was approximately $20min$⁠.