Cooling of electrically insulated high voltage electrodes down to 30 mK: Dynamic measurements

AEgIS [1] is an antimatter experiment, using high voltage electrodes at 100 mK. Two possible principles to cool these electrodes with a dilution refrigerator are investigated: the Rod and the Sandwich. Both designs are described in detail in [2]. The Sandwich design is discussed in the present work. It consists of an electrically insulating sapphire plate covered with indium on both sides. Dynamic measurements are performed in order to estimate the influence of time depending heat loads on different Sandwich designs. From these data the Sandwich’s thermal diffusivity is derived and compared to previous measurements using a static heat load. The lowest resistivity of the Sandwich is achieved with an indium vapor deposition onto polished sapphire (26 cm2K4/W at 30 mK). The same sandwich shows the best, i.e. highest thermal diffusivity (0.23 mm2/s at 70 mK). However, the results of the static and the dynamic measurements show some interesting and contrary tendencies.