What Are Cryostat Temperatures and How Do They Work?

Cryostat temperature control is pivotal for cryogenics and low-temperature research. But maintaining and regulating cryostat temperature is a complex process, one requiring efficient and effective cooling and control systems. Difficulties in gaining access to low-temperature cooling can create bottlenecks in research programs and innovation. Thus, for companies and research groups conducting low-temperature testing and experiments, having ready access to effective cryostat solutions is essential.

What is cryostat temperature?

From medicine and MRI machines to space technology and quantum computers, cryostats are essential components to a wide range of devices and fields of research.

The types of cryostats employed for each application vary, and temperatures range depending on the required cooling states. Histology, for example, only needs temperatures to go down to -20°C to -30°C, while the cryopreservation of biological samples takes place at around -180°C (93 Kelvin). Going even lower, the cryostat in an MRI keeps the machine’s superconducting magnet at around four Kelvin, and in some forms of condensed matter physics and in some implementations of quantum computing technology, temperature is measured in millikelvins—mere thousandths of a Kelvin above absolute zero.

kiutra has cryogenic platforms to suit a variety of research needs, offering both cryostat cooling systems as well as Cryogenics as a Service for companies and research groups to outsource their low-temperature measurement needs.

Definition and concept

Essentially, a cryostat is an insulated chamber, typically a vacuum, which serves to keep the interior object protected from heating by the exterior environment and it incorporates shielding layers of reflective material to maintain the cooling.

• Open-cycle versus closed-cycle cryostats: Open-cycle cryostatsuse a continuous flow of a cryogenic gas like helium or a helium mixture to cool an environment. The process involves compression and subsequent expansion for cooling and a heat exchanger to absorb heat from the cooling environment. Closed-cycle cryostats also involve gas compression and expansion but in a closed system, meaning that the circulated gas is not lost but recovered for continuous compression and expansion (i.e., cooling).
• Bath cryostats are a type of cryostat that immerses the object to be cooled in a cold liquid for direct cooling, which allows for achieving low temperatures quickly.
• Flow cryostats, as the name suggests, allow a cold fluid to flow through a system to remove heat, often in situations where there’s a need for cooling external objects or systems rather than enclosed samples.
• Dilution cryostats are closed-loop systems for reaching extremely low (sub-Kelvin or milli-Kelvin) temperatures. They use the de-mixing of isotopes, often helium-3 and helium-4, to reduce temperatures.

Units of measurement

For cryostats, precise measurement is key, not only in the use of thermocouples to determine temperature but also in pressure gauges, which measure in pascals, flowmeters such as mass flow controllers, measuring in units such as liters per minute, and voltage and current meters.

Factors affecting cryostat temperature

Several factors can affect the temperature within a cryostat and influence the stability and uniformity of the process.

External factors

Having effective thermal insulation is an obvious concern for cryostats, where the quality of the vacuum space, the reflective shields and insulating materials are all crucial to maintaining low temperatures. Radiation shields are also needed to prevent heat transfer by radiation, and even vibrations and physical disturbances outside the cryostat need to be minimized, as they can create heat by friction and stress.

Internal factors

Cryostats require high-grade purity coolants, as added impurities can significantly impact stability and the cooling process. Air or other gases in the coolant can create insulation and limit the coolant’s ability to absorb heat, while other dissolved substances such as nitrogen can negatively impact the gas flow, thereby affecting cooling power and temperature control.

Heat generated by electronic devices and mechanical components operating within a cryostat can also impact temperature, as can the accuracy of a cryostat’s control systems which serve to monitor temperature and regulate cooling rates.

How to measure cryostat temperature

Thermocouples are common for measurement. These consist of two different metals joined at one end, where the setup produces a voltage proportional to the temperature difference. Cryostats measure the voltage and convert it to a temperature reading.

At Kelvin and sub-Kelvin temperatures, cryostats commonly involve resistive temperature devices (RTDs).

Importance of maintaining cryostat temperature

Impact on Experimental Results

For researchers using cryostats, precise and accurate temperature control is crucial. Quantum mechanical effects such as superconductivity and superfluidity, for example, occur at extremely low temperatures, so scientists need access to cryostats with precise temperature regulation to test materials.

Preservation of samples and materials

Cryogenics is widely used in the cryopreservation of cells and tissues, the storage of biomolecules, chemical compounds and any materials that are sensitive to temperature and degradation, and thus, maintaining constant temperatures is central to preventing the chemical reactions that can cause instability for samples and materials.

Challenges in Controlling Cryostat Temperature

Low-temperature research demands accuracy and stability in controlling and maintaining temperatures, but the task is made more difficult by heat leaks from the exterior environment into the system, for example, by thermal radiation and mechanical vibration. Achieving distinct temperature gradients within the cooled environment provided by the cryostat is important, as are the precise calibration of temperature sensors and the ability to continually monitor and respond to changes in the cooling environment.

What is the temperature of a cryostat?

Cryostat temperatures depend on the research being conducted. For instance, investigating the spin-charge dynamics of a metallic system can be carried out at various temperatures. Some electronic and magnetic properties can be researched at room temperature (about 293 K) to the liquid nitrogen level at 77 K, while others, such as researching superconductivity may require cooling to liquid helium (4.2 K) levels. In still others, such as investigating quantum properties, quantum phase transitions and spin-charge separation phenomena require temperatures below 1 K.

kiutra’s cryostats employ both single, one-shot cooling environments but also continuous sub-Kelvin cooling provided by multiple configured units. Continuous adiabatic demagnetization refrigeration (cADR) units can give researchers long-lasting access to sub-Kelvin temperatures without the need of rare cryogens such as helium-3.

Methods for achieving and maintaining low temperature in cryostats

The choice of cooling system depends on the project, materials and required temperature ranges, and researchers have several available options. For reaching temperatures below 1 K, here are a few refrigeration techniques:

• Adiabatic demagnetization refrigeration (ADR) uses the magnetic properties of certain materials which through inducing changes in magnetic field and magnetic entropy produce a cooling effect. The cyclical process of isolation, adiabatic demagnetization, heat dumping and re-magnetization allows for the maintenance of constant temperature.
• Pulse tube refrigeration creates a pulsating flow of helium gas through cyclical compression and expansion to induce a thermal exchange to transfer heat between the gas and its surroundings.
• The helium dilution technique typically dilutes helium-3 in helium-4 to produce a cooling effect, with the continuous circulation, separation and mixing of isotopes working to maintain the low temperatures.

Cryostats can also be specialized and configured in many ways to suit a variety of research interests. For example, research investigating the magneto-optical properties of materials can employ magneto-optical cryostats, which feature low temperatures, optical access, and a high-field magnet for the application of strong magnetic fields. Optical cryostats can feature optical measurement probes, detectors and other tools for conducting optical experiments at super-low temperatures.

In terms of speed for reaching sub-Kelvin temperatures, kiutra’s L-Type Rapid cryostat can achieve cooling of 100 mK-300 mK in three hours.

Applications of cryostats at different temperatures

Researchers in many fields take advantage of the precision measurement and elimination of background noise afforded by using cryostats.

Superconductivity experiments

In areas from quantum computing to medicine, energy storage and beyond, superconductivity has become a central concept to drive research and innovation forward, and cryogenics is at the heart of the discipline. For example, cryostats are used to investigate properties of so-called high-temperature superconductors, to study superconducting qubits for quantum devices and computers and in the development of new superconductive magnets and materials.

Photonics and optics

In photonics and optics, researchers use cryostats to conduct research in areas such as low-temperature spectroscopy, infrared and terahertz photonics, quantum optics, superconducting photon detectors and some branches of astrophysics.

kiutra and our research partners are supporting new applications of cryogenics to push innovation forward, for example, in the field of quantum computing where we collaborates with industry partners on the testing of quantum computer hardware and control electronics.

Overall importance of cryostat temperature control

Cryogenics is featured in much of today’s research and innovation, and thus, cryostats for low temperature are key to experimentation and development across many fields. Maintaining and controlling cryostat temperature is a multifaceted procedure involving cooling systems and precise control systems. kiutra’s solutions can help deliver effective and impactful results for companies and labs incorporating cryogenics into their research programs.