Design and Testing of 100 mK High-voltage Electrodes for AEgIS

AbstractThe AEgIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) experiment at CERN has as main goal to perform the first direct measurement of the Earth's gravitational acceleration on antihydrogen atoms within 1% precision. To reach this precision, the antihydrogen should be cooled down to about 100 mK to reduce its random vertical velocity. This is obtained by mounting a Penning trap consisting of multiple high-voltage electrodes on the mixing chamber of a dilution refrigerator with cooling capacity of 100μW at 50 mK. A design of the high-voltage electrodes is made and experimentally tested at operating conditions. The high-voltage electrodes are made of sapphire with four gold sputtered electrode sectors on it. The electrodes have a width of 40mm, a height of 18mm and a thickness of 5.8mm and for performance testing are mountedto the mixing chamber of a dilution refrigerator with a 250μm thick indium foil sandwiched inbetween the two to increase the thermal contact. A static heat load of 120nW applied to the top surface of the electrode results in a maximum measured temperature of 100mK while the mixing chamber is kept at a constant temperature of 50mK. The measured totalthermal resistivity lies in the range of 210-260cm2K4W−1, which is much higher than expected from literature. Further research needs to be done to investigate this

A miniature Joule-Thomson cooler for optical detectors in space

The utilization of single-stage micromachined Joule-Thomson (JT) coolers for cooling small optical detectors is investigated. A design of a micromachined JT cold stage–detector system is made that focuses on the interface between a JT cold stage and detector, and on the wiring of the detector. Among various techniques, adhesive bonding is selected as most suitable technique for integrating the detector with the JT cold stage. Also, the optimum wiring of the detector is discussed. In this respect, it is important to minimize the heat conduction through the wiring. Therefore, each wire should be optimized in terms of acceptable impedance and thermal heat load. It is shown that, given a certain impedance, the conductive heat load of electrically bad conducting materials is about twice as high as that of electrically good conducting materials. A micromachined JT cold stage is designed and integrated with a dummy detector. The JT cold stage is operated at 100 K with nitrogen as the working fluid and at 140 K with methane. Net cooling powers of 143 mW and 117 mW are measured, respectively. Taking into account a radiative heat load of 40 mW, these measured values make the JT cold stage suitable for cooling a photon detector with a power dissipation up to 50 mW, allowing for another 27 to 53 mW heat load arising from the electrical leads

Optimization of the working fluid in a Joule-Thomson cold stage

Vibration-free miniature Joule–Thomson (JT) coolers are of interest for cooling a wide variety of devices, including low-noise amplifiers, semiconducting and superconducting electronics, and small optical detectors used in space applications. For cooling such devices, coolers are needed which have operating temperatures within a wide temperature range of 2–250 K. In this paper, the optimization of the working fluid in JT cold stages is described that operate at different temperatures within that range. For each temperature, the most suitable working fluid is selected on the basis of the coefficient of performance of the cold stage, which is defined as the ratio of the gross cooling power to the change in Gibbs free energy of the fluid during compression. In addition, a figure of merit of the heat exchange in the counter-flow heat exchanger is evaluated that depends only on the properties of the working fluid

Micromachined Joule-Thomson cold stages operating in the temperature range 80 - 250 K

Micromachined Joule-Thomson (JT) coolers can be used for cooling small electronic devices. For this application, two types of micromachined JT cold stages with dimensions of 60.0 × 10.0 × 0.7 mm3 were developed and tested that were designed for operation with nitrogen at 100 K. A theoretical analysis is developed to investigate the application of these cold stages in the temperature range 80–250 K. This analysis shows that the cold stages can be operated with various working fluids. Experiments of both JT cold stages operating with nitrogen and methane as working fluids were done to validate this analysis. The cooling power and the temperature profile along the length of the counter-flow heat exchanger were measured. In this paper, the theoretical analysis is described and the measuring results are presented and discussed