In the last 20 years, 2-stage cryocoolers have been found to provide an optimum solution for a wide range of applications like low temperature physics, superconducting cold electronics, cryopumping and superconducting magnets. For a proper design of helium cryostats with significant cold masses connected to the first and second stages of cryocoolers, it is important to have a load map (also called "working field") in order to estimate cool-down and warm-up time periods. Such load maps are either not presented in the open literature sources for "high" temperature ranges, or just given by manufacturing companies for general information but without any guarantee. In the present paper, the load map of a 2-stage Sumitomo 415DP cryocooler in the wide temperature range of 40-400 K is presented.
The Vuilleumier (VM)-type pulse tube cryocooler is a novel kind of cryocooler used to obtain liquid helium temperature, which has been experimentally verified. However, the overall efficiency is not satisfying. Based on previous work on a low pressure ratio system, numerical investigations that explore the effect of high pressure ratios on cooling performance are presented in this paper. The research system is cryogen-free in which a Stirling type pulse tube cryocooler is used to provide the required cooling power for the thermal compressor and makes it adjustable for pre-cooling temperature to achieve optimum efficiency. First, after increasing the displacer swept volume to increase the pressure ratio, the dimensions of the main components were optimized with the lowest no-load temperature as the optimization target. Then the dependence of system performance on average pressure, displacer swept volume, frequency and cold HX temperature were studied considering the heat transfer temperature difference of the thermal bridge. Compared with the previous low efficiency under low pressure ratio, when the heat transfer temperature difference of the thermal bridge is 0 K, a higher relative Carrot efficiency of 1.29% and a cooling power of 250 mW at 4.2 K were predicted with an average pressure of 3 MPa, a frequency of 3 Hz and a pressure ratio of 1.67. Further optimization is underway.
Baby-IAXO is a new helioscope, a demonstration version of the proposed full-size IAXO, the International Axions Observatory. It is currently under design and once installed it will search via the Primakoff effect for axions or axion-like particles (ALPs) originating in the Sun. Axions can transform into photons in the presence of a significant magnetic field, and then be detected. The superconducting magnet for Baby-IAXO comprises two 10 m long racetrack coils, spaced by 0.8 m, operated in a quadrupole configuration and generating an average magnetic field of 2.1 T in the two 700 mm diameter free bores for axion-to-photons decay positioned in between the coils. Cool down and operational cryogenic requirements are handled by a combination of single and double stage cryocoolers. For the cool down of the 18.5 t cold mass within 22 days and for current leads cooling, the use of powerful single stage cryocoolers is of paramount importance. The cooling power is distributed across the cold mass and thermal shield using helium gas flow enforced by cryocirculators. The design of the 10 kA conduction cooled current leads is presented as well, since at 70 K these represent the dominant heat load. The cryogenic system allows for a constant heat load of 1.2 kW at the first stage and 8.5 W at the 4.2 K cold mass. Alternatively, the magnet may be operated in persistent mode, thereby reducing the heat load and the number of cryocoolers. It requires a more complex cooling circuit, implementation of a 10 kA persistent mode switch, and a delicate balance of energizing and operational heat loads.
The new Cryogenic Flux Capacitor (CFC) technology employs nano-porous aerogel composites to store large quantities of fluid molecules in a physisorbed solid-state condition at moderate pressures and cryogenic temperatures. By its design architecture, a CFC device can be "charged" and "discharged" quickly and on demand according to standby/usage requirements. One of three main application areas is the CFC-Life for breathing air or oxygen supply to meet new demands in life support systems. Through the Liquid Oxygen Storage Module (LOXSM) Project, the National Institute for Occupational Safety and Health, and Cryogenics Test Laboratory have partnered to test the feasibility of applying the CFC technology to Closed-Circuit Escape Respirators (CCER), or respirators operating on the closed-circuit principle in general. The envisioned Cryogenic Oxygen Storage Module (COSM) is an innovative concept to store oxygen in solid-state form, according to physisorption processes at any cryogenic temperature, and deliver it as a gas using the CFC as the core storage element. Gaseous oxygen would be admitted into the breathing loop of the CCER by introducing heat into the storage module. Potentially replacing the gaseous or chemical based oxygen supply used in today's closed-circuit respirators, the COSM is a high capacity, conformal, small-size solution for future life support equipment of all kinds. In particular, are the CCER devices that must to be carried on the person, ready to be quickly deployed and used for escape in an emergency. Initial test data for physisorption of oxygen in aerogel materials and CFC core modules are presented. The basic operational parameters for charging and discharging are summarized through prototype testing of the cryogenic oxygen storage module.
With end of year 2018 the LHC has completed its second physics run and started its second two-years long shut down period dedicated to planned consolidation, maintenance and upgrade activities. The run2 - four-year physics operation period started in spring 2015 - was used mainly for luminosity production but also to allow the optimization and adaptability of the cryogenic system capacity to compensate for generated operational heat loads. Several tests and qualifications were studied and applied to the configuration of the available equipment in order to reach a deep understanding of the real operation limits. Dedicated global improvements were implemented in the control system, especially in regards of handling the beam induced dynamic heat load during transitory operational states. Adequate modifications were also applied for the Inner Triplet magnets control system to compensate for dynamic heat load related to secondaries, close to the interaction points of the ATLAS and CMS detectors. This paper will give a general overview of the LHC cryogenics operation with specific information on encountered operational difficulties and applied solutions on the system. Helium inventory management, including process use and leaks, as well as the system overall availability indicators will be presented.
