the year draws to its end with a positive balance and it is time to get prepared for the cryogenics events planned for 2018. In February there will be the Big Science Business Forum in Copenhagen, in April the European Space Cryogenics Workshop in Noordwijk. We all look forward to the ICEC 27-ICMC 2018, on September 3 in Oxford! Check regularly our website to keep informed on upcoming events.
We wish you happy holidays and a productive New Year and for those who have not yet registered, we hope to count you among our members in 2018!
PhD Thesis in 2017
We congratulate Dr. Tiemo Winkler and Dr. Diego Paixao Brasiliano for completing the doctoral degree in cryogenics in 2017. Please find below the abstracts of their dissertations.
We take the chance to solicit your contribution to render the CSE an increasingly exhaustive source of literature for anybody active in cryogenics. Please send us editorial material for the Website at firstname.lastname@example.org, be it an abstract of a particularly interesting publication, the review of a text book or a recently defended PhD thesis.
Title:Helium II heat transfer in LHC magnets Author: T. Winkler Referees: Prof. Dr. H.J.M. ter Brake & Prof. Dr. H.H.J. ten Kate (University of Twente, the Netherlands). Date: June 9, 2017 Abstract: Today’s large particle accelerators like the LHC at CERN are using superconducting materials as a construction material for magnets. These magnets need to be cooled constantly to temperatures below the critical surface of the superconducting material. In the LHC this is achieved by using liquid Helium at a temperature of 1.9K. At this temperature Helium is in a liquid state that is called Helium II, which is characterized by its low viscosity and its high effective thermal conductivity.
In this work heat transfer in Helium II between the superconductor and the He II bath is investigated in steady-state as well as in transient conditions. The geometry investigated in this work is a result of the design requirements of the LHC and consists of microchannels formed by the polyimide insulation of the superconducting Rutherford cable. As results of the work it is found that two distinct channels are formed by the polyimide insulation, where one channel has a significant contribution at low heating power and the second channel becomes dominant at higher heating power. To further confirm this result the cable experimental data is obtained in the temperature range 1.7K to 2.1K and the heating power is varied between 0.61 mW/cm3 and 4.9 mW/cm3.
Additionally a model is developed for the effective thermal conductivity of He II in order to replicate the measurement data. In this effective thermal conductivity model a critical temperature gradient in introduced to model the transition between the laminar heat transfer regime and the turbulent heat transfer regime. The experimental data can be reproduced very well using a two channel model for the geometry and the effective thermal conductivity model.
Title: Etude et réalisation d'une désaimantation adiabatique spatiale 4K-50mK Author: Diego Paixao Brasiliano Referees: Prof. Grégoire Bonfait (Universidade Nova de Lisboa, Portugal), Prof. Thomas Mazet (University of Lorraine, France) Date: May 15th, 2017
Abstract: Highly sensitive detectors required for astrophysics missions demand temperatures of about 50 mK to operate with the targeted sensitivity. This PhD work is dedicated to the research and development of Adiabatic Demagnetization Refrigerators (ADR) for space in the 4 K - 50 mK range. In particular, this cryocooler is required to be efficient with optimized mass.
The key points of this work are the development of a method that allows the identification of highly efficient paramagnetic materials and the improvement of gas-gap heat switches. Among the studied materials, YbGG (Yb3 Ga5 O12 ) was identified to have a great potential as a magnetic refrigerant in the 1.5 K - 0.4 K range, which was confirmed by its characterization. Transient thermal short circuits may appear on the gas-gap heat switches under the working conditions of this cryocooler. This study allowed us to sup- press or to considerably attenuate this effect. Finally, a cryocooler prototype consisting of 3 ADR stages was designed and built.
New CSE Member
We would like to welcome the University of Twente (the Netherlands) among our members. The activities on cryogenics are led by the Chair of Energy, Materials and Systems (EMS), which is part of the Faculty of Science and Technology (TNW), and in particular by Prof. Marcel Ter Brake, CSE Chairman. The research of EMS is application oriented and greatly benefits from its internationally recognized expertise and unique infrastructure on applied superconductivity and cryogenics.
The membership fee for Universities and research institutions, as non-profit entities, is a bargain! Consider joining us and allowing students and personnel full access to the restricted area of the CSE website.