Testing at low pressure

It was a challenge to find a vacuum bell large enough to fit our experiment into. We finally found the perfect setup at the University of Antwerp (Experimental Solid State and Laser Physics lab of prof. Wenseleers). Using a rotary vane pump and a diffusion pump a pressure of 0.05 kPa has been achieved.

When our experiment operates in a low pressure environment (~1kPa) we saw some bad behaviour at the HV area. At a pressure corresponding to an altitude of 30 km we saw a corona discharge taking place between the resistors, as shown below! Occasionally some arcs jumped outside the HV area and damaged other components on the PCB. Such discharges identify themselves by a drop in the reference voltage and the absence of any counts on the Geiger-Müller tubes. The HV area has been moved completely onto a daughter board and has been coated in order to reduce the strength of the discharges and push the effect to a lower pressure.

Since the Geiger-Müller tubes are pressure vessels, this vacuum test was also important to verify the mechanical integrity and stability of these tubes. Fortunately nothing imploded or exploded!

At the same time we callibrated the pressure sensors of the experiment using a manual manometer, to be sure that we will measure the right pressure during the flight.