Vitaliy Mykhaylyk

Sample cooling in vacuum environment

 A number of technical challenges needed to be solved for the MX experiment in vacuum to become a viable tool for structural biology. One such challenge is the necessity to provide efficient cooling of protein samples below 100 K. In a vacuum environment, cooling is controlled by thermal conductivity only. As a protein sample should be mounted on the goniometer in a holder, there will be several dissimilar materials and interfaces (i.e. metal - ice - protein) involved in heat transfer. The interfaces create breaks in the continuity of the cooling, resulting in a temperature jump across the joint. This is due to the thermal contact conductance (TCC), which in many cases is a primary factor limiting cooling efficiency. Therefore, the studies into the thermal conductivity through a system comprising several materials and interfaces constitute an integral part of the development of the procedure for handling the protein crystal in a vacuum environment.

             Systematic investigations of the TCC of uncoated and Au-plated Cu-Cu joints allowed to suggest a model that consistently explains the observed temperature dependencies [1]. The results were then used to design a demountable sample holder assembly with a magnetic joint that ensures good thermal conductivity. Extensive tests have shown that this type of demountable joint provides adequate and reliable solution for applications that require swift and frequent exchange of sample holders in vacuum, while preserving a high thermal contact conductivity, consistently over extended periods of operation.

Non-contact thermometry for application at synchrotron sources

Temperature is an important parameter affecting the state of any system in nature. For many areas of science and technology, temperature monitoring is vital, especially in cases where it has a strong impact on the material properties, specifically those influencing the system’s functionality, reliability and lifespan. It must be therefore accurately monitored during experiments aiming to characterise the system, especially when the property to be characterized exhibits a temperature dependence. As an example, temperature is a very important parameter when aiming to protect biological samples from radiation damage during experiments that utilise powerful ionising radiation produced by modern synchrotron light sources. There are numerous evidences that intense irradiation applied to samples of microscopic size can significantly increase their temperature, which in turn causes sample degradation. This effect is likely to have even higher impact owing to the even higher brilliance that will result from planned upgrades of synchrotrons.

A novel method for remote, non-contact, in situ monitoring of protein crystal temperatures has been developed for the I23 beamline at the Diamond Light Source (DLS) dedicated to macromolecular crystallography with soft X-rays. The beamline operates in a vacuum in which properties of microscopic (ca. 0.01 mm³) samples of protein crystals, cooled to temperatures below 100 K, are measured. The temperature is derived from changes in the luminescence decay characteristics of a Bi₄Ge₃O₁₂ scintillation sensor [1]. The schematics of the measurement technique is displayed in Fig. 1

Fig. 1 Schematics of the luminescence lifetime thermometry system: M1-M3 mirrors, L1 – objective lens UV LED – ultraviolet light emitting diode, W – optical window, PMT – photomultiplier tube, CCD – camera, DAQ – data acquisition, PC – personal computer, WG - waveform generator.

The method was extensively tested and the results obtained demonstrated the feasibility and usefulness of the approach as well as the reliability and level of accuracy of the method. In the temperature range of beamline operation (30 – 150 K) the error of temperature determination using a BGO scintillator is ±1.6 K. The principal advantage of the non-contact thermometry system is the elimination of any electrical connection between the sensor and the readout systems. This feature makes it fully compatible with the vacuum environment of the beamline, and a necessity of swift replacement and manipulation (transfer, mounting, rotation) capability of the samples. Furthermore, non-contact measurements allow easy minimization of systematic errors due to unavoidable heat transfer in wired sensors. The application of this technique at I23 underpins the optimisation of the sample cooling and transfer processes that was previously done through the laborious and time-consuming trial-and-error repeats.

                Furthering these researches an elegant concept of megahertz thermometry that uses the time structure of synchrotron radiation has been tested recently [3]. It is demonstrated that temperature can be derived by measuring decay time profile of ultrafast scintillations excited by synchrotron X-ray pulses in narrowband semiconductors. The initial experiments have proved the principal feasibility of the temperature measurements based on this approach and the studies commenced to facilitate reliable temperature monitoring using this method.

1. V. B. Mykhaylyk et al. Thermal contact conductance of demountable in vacuum copper-copper joint between 14 and 100 K Rev. Sci. Instr. 83 (2012) 034902.

2. V. B. Mykhaylyk et al. Non-contact luminescence lifetime cryothermometry for macromolecular crystallography, Journal of Synchrotron Radiation 24 (2017) 636-645.

3. V. B. Mykhaylyk et al. Megahertz non-contact luminescence decay time cryothermometry by means of ultrafast PbI₂ scintillator, Scientific Reports 9 (2019) 5274.

Joint project  with Prof. Hans Kraus (University of Oxford, UK): “Application of a particle detection technique for in situ temperature monitoring in synchrotron beamline end stations” (STFC, miniPIPS, 2012-2016).

Collaboration with Dr. Y. Zhydachevskyy (Institute of Physics, Polish Academy of Science, Poland) "Non-contact thermometry using oxide crystals".

Collaboration with Prof. V. Kapustyanyk  (Centre of Low  Temperature Studies, Lviv National University, Ukraine) "Studies of scintillation properties of materials at low temperatures"

Collaboration with Prof. M. Saliba (Technical University of Darmstadt, Germany) "Cryogenic perovskite scintillators"

Link to Google Scholar citations

Vitaliy Mykhaylyk was appointed as a Beamline Scientist on beamline I23 in 2010. Prior to this he was in charge of the  development of cryogenic techniques and instrumentation for detection of ionizing radiation at the University of Oxford. He is now developing the procedure of sample handling in a vacuum environment, as well as protein tomography for I23.