Vladimir Mikheev

A completely self-contained cryogen-free dilution refrigerator, the TritonDRTM

Oxford Instruments have developed a new dilution refrigerator for ultralow temperatures down to below 35mK. The TritonDRTM system is a continuous cryogenic cycle dilution refrigerator. The refrigerator is driven by a closed cycle cryocooler and hence requires no liquid cryogens. The system has a dedicated electronic control unit and software that provides full control of operation.

Adsorption pumping for obtaining ULT in 3He Cryostats and 3He-4He Dilution Refrigerators

Novel designs of3He Cryostats and Dilution Refrigerators (DR), based on adsorption pumping of3He gas, are described for obtaining temperatures well below 0.3K.Using a new technique, extremely low temperature3He refrigerators have been tested to T<235mK. The same technique enables the manufacture of a compact travelling3He system, that can move up to a distance of about 0.5m. The ability to travel from warm to cold zones can be important for sample preparation in ultra high vacuum and to carry out STM measurements.Also described is a continuously operating sorption pumped DR, that can be installed inside a transport dewar with a neck diameter of only 51mm. The cooling time of the mixing chamber from 4.2K down to 50mK is ∼2 hours. Removal of the insert from the cryostat requires approximately 30 minutes. The cooling power of the system is 40 microwatts at 100mK. With two miniature silver heat exchangers the mixing chamber temperature cools to a continuous temperature of 15mK.A key distinguishing feature of this DR is the absence of a traditional gas handling system and sealed helium-3 rotary pump. This makes it easy for transportation and quick commissioning at a new site within a few hours.

A self-contained 3He melting curve thermometer for dissemination of the new provisional low-temperature scale

Abstract We report progress in the development of a self-contained 3 He melting curve thermometer, designed to be both easy to construct and simple to operate. It is based on a cylindrical pressure gauge, with good linearity of pressure versus inverse capacitance making calibration straightforward. The gas handling system is compact and in principle automatic. The readout electronics is based on a tunnel diode oscillator circuit, since one of the capacitance plates of the gauge is necessarily grounded. We present preliminary data on the performance of the thermometer, which will allow convenient dissemination the new provisional low-temperature scale PLTS-2000.

A 3He cooled scanning tunneling microscope in UHV and high fields

We present a scanning tunneling microscope (STM) operating between 275 mK and room temperature in ultra-high vacuum (UHV) and in magnetic fields up to 14 T. The system features a compact STM fixed to a UHV compatible 3He insert fitting into a bottom loading cryostat with a superconducting magnet. Placing the cryostat on top of the UHV chamber allows a compact system design and an ideal thermalization of the STM, thus achieving a hold time of about 40 h at 275 mK. We show results obtained at 275 mK on a Bi2Sr2CaCu2O8+δ single crystal.

Chapter 11 – Cryogen Free Refrigeration to 270mK by Adiabatic Expansion of He3 Gas

Publisher Summary This chapter discusses the cooling performance and other features of two new types of He3 refrigerators that have been built at OIS. These refrigerators are constructed using the well-know phenomena of adiabatic expansion of gas and adsorption pumping. The first type operates in a liquid helium environment at 4.2K. The second design is cryogen free and uses a Pulse Tube Cryocooler. This ULT system is embodied in a commercial He3 Cryofree refrigerator Heliox AC-V, developed by Oxford Instruments. It is important to mention the reliability of the expansion refrigerator. Because current cryocoolers produce cooling down to <3K, this causes an extra liquid fraction by direct condensation into the He3 pot. However this temperature is close to the He3 critical point so any failure in the pulse tube and subsequent deterioration of the minimum temperature achieved by the PTR will completely stop the operation of a traditional He3 refrigerator. For these He3 systems this limit is much higher at 4.2K or even 5K, where adiabatic expansion of He3 still produces liquefaction of He3 and hence ultra low temperatures..