Ultra-High Vacuum Systems for Experiments with Cold Atoms in Space

Abstract

Dual-species atom interferometry, with Bose-Einstein condensates, is a promising technique for ultra-precise and accurate measurements for spaceborne applications, such as inertial sensing, future detection of gravitational waves, earth observation, and testing fundamental physics. An ultracold atom experiment on a future satellite mission could improve the precision of testing general relativity, with the test of the universality of free fall. The technology discovery of such a complex and challenging experiment, requires a multitude of space qualified technologies and developments.

The MAIUS-2/3 (Matter-Wave Interferometry Under Microgravity) missions, within the QUANTUS (Quantum Gases in Microgravity) consortium, aims to perform the first dual-species atom interferometer with ultracold rubidium and potassium atoms on a sounding rocket. It is used as a pathfinder mission to further develop the technologies which enable future cold atom missions. Space suitable ultra-high vacuum (UHV) systems are one of the enabling technologies for missions on long-duration microgravity platforms, such as the International Space Station or a satellite.

The scientific payload MAIUS-B, flying on both missions MAIUS-2 and MAIUS-3, is introduced in this thesis. The payload is sheltered within seven RADAX (radial-axial) hull segments, and is divided into five subsystems; electronics, physics package, laser system, laser electronics, and batteries. The newly developed thermal control system and ground support equipment is capable of accounting for an internally produced heat load of 707.6 W and a temperature rise by aerodynamic drag during launch. The mass and size was continuously optimized, with a final mass of 335.3 kg and a length of 2.8 m, which is within the limits of 340.0 kg and 3.0 m. A load assessment of the new suspension system showed that the payload is capable of carrying the MAIUS-B payload up to 981ms^(−2) (100 g0) within a reasonable safety margin. A new umbilical and sealing concept was implemented, providing the payload until lift-off with power, data, and cooling liquid connections.

The UHV system was redesigned to fit within the mass and size requirements. Two titanium sublimation pumps and one ion getter pump are maintaining a pressure of 2 × 10^(−11) hPa. This is one order of magnitude better than the experiment required pressure of 5 × 10^(−10) hPa. Several vacuum components, such as the differential pumping stage, the oven design, and the pumps itself, were modified or redesigned. The physics package, including the UHV system, was qualified for a vibration level of 19.6ms^(−2) RMS (2.0g0RMS), compared to the maximum flight level of 17.7ms^(−2) RMS (1.8 g0RMS) throughout a sounding rocket mission. The UHV system is capable of regaining the required pressure within 19 s.

To investigate the influence of static loads on the leakage rate of ConFlat (CF) seals, a test setup was built. The tests were performed to indicate the influence on the tightening torque (10Nm, 12.5Nm, 15Nm), the flange material (aluminum [AluVaC®], stainless steel [316LN-ESR, 14429-ESU]), and different oxygen free high conductivity (OFHC) copper gaskets (annealed, non-annealed). The presented results provide the first data set on the leakage rate for CF DN40 flange connections tested up to a applied force of 1 950N.