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

The 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