Richard Down

Cryogen-free low temperature sample environment for neutron scattering based on pulse tube refrigeration

Recent rapid progress in cryogen-free technology has become possible due to a new generation of commercial cryo-coolers developed during the last decade. The most successful example is the pulse tube refrigerator (PTR). A unique feature of the PTR is the absence of cold moving parts. This considerably reduces the generated noise and vibration and increases the reliability of the cold head, as expensive high-precision seals are no longer required and the cold head can be operated without service inspection. In this paper we present preliminary test results of a development system, based on the PTR, which provides a low temperature sample environment for neutron scattering experiments. The main aim of the development is to create a cryogen-free system suitable as a substitute for the conventional ILL-type Orange cryostat, the cryogenic workhorse of the neutron community for many years.

Absence of low temperature anomaly in the Debye-Waller factor of solid He-4

The mean-square atomic displacement in hcp-phase solid {sup 4}He has been measured in crystals with a molar volume of 21.3 cm{sup 3}. It is temperature independent from 1 K to 140 mK, with no evidence for an anomaly in the vicinity of the proposed supersolid transition. The mean-square displacement is different for in-plane motions (0.122{+-}0.001 A{sup 2}) and out-of-plane motions (0.150{+-}0.001 A{sup 2})

Cryogen free low temperature sample environment for neutron scattering experiments

Recent increase in liquid helium cost caused by global helium supply problems rose significant concern about affordability of conventional cryogenic equipment. Luckily the progress in cryo-cooler technology offers a new generation of cryogenic systems with significantly reduced consumption and in some cases nearly complete elimination of cryogens. These cryogen-free systems also offer the advantage of operational simplicity and require less space than conventional cryogen-cooled systems. The ISIS facility carries on an internal development program intended to substitute gradually all conventional cryogenic systems with cryogen free systems preferably based on pulse tube refrigerators. A unique feature of this cryo-cooler is the absence of cold moving parts. This considerably reduces vibrations and increases the reliability of the cold head. The program includes few development projects which are aiming to deliver range of cryogen free equipment including top-loading cryostat, superconducting magnets and dilution refrigerators. Here we are going to describe the design of these systems and discuss the results of prototypes testing.

Cryogen free high magnetic field sample environment for neutron scattering

Cryogenic equipment can be found in the majority of neutron scattering experiments. Recent increases in liquid helium cost caused by global helium supply problems lead to significant concern about affordability of conventional cryogenic equipment. However the latest progress in cryo-cooler technology offers a new generation of cryogenic systems in which the cryogen consumption can be significantly reduced and in some cases completely eliminated. These systems also offer the advantage of operational simplicity, require less space than conventional cryogen-cooled systems and can significantly improve user safety. At the ISIS facility it is possible to substitute conventional cryostats with cryogen free systems. Such systems are based on the pulse tube refrigerator (PTR) which possesses no cold moving parts. Oxford Instruments in collaboration with ISIS have developed new high magnetic field sample environment equipment based on re-condensing technology. This project includes 9T wide angle chopper magnet for spectrometry and 14T magnet for diffraction. The main advantage of these systems is that all magnet operating procedures, for example cooling, running up to the field and quenching remain the same as for a standard magnet in a bath cryostat. This approach also provides a homogeneous temperature distribution, which is crucial for optimum magnet performance.

Cryogen free sample environment for neutron scattering experiments at ISIS

Most neutron facilities have a fleet of cryostats providing low temperature and high magnetic fields for sample environment. This large scale usage of cryogenic equipment requires significant resources and can create a number of problems including health and safety issues and the considerable cost of the required cryogens. The last problem has become more significant due to the increasing costs of liquid helium caused by global helium supply problems. The ISIS facility has an internal development programme intended to gradually substitute all conventional cryogenic systems with cryogen free systems preferably based on the pulse tube refrigerator. The programme includes a number of development projects which are aiming to deliver a range of cryogen free equipment including a top-loading 1.5 K cryostat, superconducting magnets in re-condensing cryostats and cryogen free dilution refrigerators. Here we are going to describe the design of these systems and discuss the results of prototype testing.

Cryogenic sample environment on TOSCA

We have developed a new top-loading cryogenic insert that forms part of the integrated cryogenic sample environment for the Tosca spectrometer at the ISIS Facility. New advanced cryo-coolers and optimised design of the cryogenic insert allowed us to dramatically decrease system cool down time from 20 to 7 hours, sample cooling time from 3 hours to 45 minutes and also reduce the base temperature of the insert from 12 K to 4.5 K in the continuous regime and ~1.5 K in the single shot regime. We have also reduced the number of cold heads from three to two. This lets us save the significant cost of the third cold head maintenance and has cut electricity consumption by ~30%. A much lower base temperature of 4.5 K has opened new opportunities for molecular spectroscopy studies on Tosca.