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CHRNS: Cryogenic Goniometer

Studying the structure, dynamics, and electronic/magnetic properties of single crystals and thin films often necessitates a combination of low or ultra-low temperatures and magnetic fields and simultaneous control of the crystal orientation with respect to the neutron beam and instrument detector system. The control of crystal orientation is mostly performed outside the sample environment needed to achieve the temperature and field and held with a fixed vertical axis with sample rotations in the horizontal plane only possible by rotating the entire cryostat. On the occasion that the crystal orientation is not perfect and the desired scattering plane is not accurately oriented, the sample would need to be removed, realigned, and replaced in the cryostat, which results in wasting significant neutron time in re-preparing the system and limiting the range of reciprocal space available to an experimenter at a given time resulting in constraining the scientist’s response to the experiment in progress. To allow unprecedented experimental flexibility and maximize efficiency, we have developed a system using a sample goniometer inside the sample environments that allows on-the-fly realignment of the sample and maintains the experiment temperature and magnetic field conditions.

ANR240_ANR101 Instrument

The prototype design of the low-temperature goniometer (Figure 1(a)) can operate at temperatures as low as 10 mK and under external magnetic fields to 20 T and has a horizontal rotation axis.  It has been successfully used for several low-temperature magnetic neutron experiments, but only in the largest cryostat at the NCNR. With experience using the device, we improved several aspects to enhance the application and useability. These upgrades include:

  • Reducing the size of the goniometer (Figure 1(b)) to fit in most cryogenic equipment, including:
    • 50 mm helium dilution refrigerator inserts,
    • 10 T and 11 T cryo-magnets
    • All other helium cryostats
    • Top loading CCR for the 7 T cryo-magnet
  • Moving the rotation axis of the new goniometer to a different orientation in the horizontal plane, which extends experimental capabilities
  • Improving the sample thermalization.
    • Testing indicated a considerable thermal lag after driving the goniometer so the goniometer was placed inside a vacuum can with thin aluminum walls (Figure 2(a)) sealed in a helium atmosphere which provides excellent sample thermalization at a wide range of temperatures (Figure 2(b)).
cold plate instrument

We are now working to implement communication of the goniometer with the instrument control software (NICE) for CHRNS-MACS to allow a seamless integration into an experimental protocol for both goniometers, which should be available to users soon.

Figure 3: Cryogenic Goniometer Control Program

Over the coming year, we will work to improve the thermalization of the new goniometer in the smallest dilution fridges using the vacuum can method demonstrated above. This is challenging due to minimal space inside the 50 mm dilution refrigerator vacuum chamber.

The new sample goniometer will allow easy adjustment of sample tilt and scattering plane switch for single crystals samples, enabling quick access to large range of momentum-space for the study of quantum magnetism, superconductivity, and other frontiers of condensed matter physics with neutron scattering.

U.S. Provisional Patent Application
Serial number 63/327,172

Created April 26, 2022, Updated June 16, 2023