F. Plesescu

Measurement of Gravitomagnetic and Acceleration Fields around Rotating Superconductors

It is well known that a rotating superconductor produces a magnetic field proportional to its angular velocity. The authors conjectured earlier, that in addition to this so‐called London moment, also a large gravitomagnetic field should appear to explain an apparent mass increase of Niobium Cooper‐pairs. A similar field is predicted from Einstein’s general relativity theory and the presently observed amount of dark energy in the universe. An experimental facility was designed and built to measure small acceleration fields as well as gravitomagnetic fields in the vicinity of a fast rotating and accelerating superconductor in order to detect this so‐called gravitomagnetic London moment. This paper summarizes the efforts and results that have been obtained so far. Measurements with Niobium superconductors indeed show first signs which appear to be within a factor of 2 of our theoretical prediction. Possible error sources as well as the experimental difficulties are reviewed and discussed. If the gravitomagne...

Anomalous fiber optic gyroscope signals observed above spinning rings at low temperature

Precision fiber optic gyroscopes were mounted mechanically de-coupled above spinning rings inside a cryostat. Below a critical temperature (typically <30 K), the gyroscopes measure a significant deviation from their usual offset due to Earths rotation. This deviation is proportional to the applied angular ring velocity with maximum signals towards lower temperatures. The anomalous gyroscope signal is about 8 orders of magnitude smaller then the applied angular ring velocity, compensating about one third of the Earth rotation offset at an angular top speed of 420 rad/s. Moreover, our data shows a parity violation as the effect appears to be dominant for rotation against the Earths spin. No systematic effect was found to explain this effect including the magnetic environment, vibration and helium gas friction suggesting that our observation is a new low temperature phenomenon. Tests in various configurations suggest that the rotating low temperature helium may be the source of our anomalous signals.

Development of an Indium mN-FEEP Thruster

Future scientific satellites require precision pointing capabilities with thrust levels from sub-µN to the mN-range and very low thrust noise. Since 2004, a dedicated mN FEEP thruster based on the space-proven ARC Indium Liquid-Metal-Ion-Sources is under development. This paper gives an overview of the development program and its achievements. A mN FEEP thruster with a specific impulse close to 8000 s could be demonstrated with excellent efficiencies and a size comparable to present µN FEEP thrusters. Nomenclature e = electron charge f = beam divergence loss factor g = Earth’s gravitational acceleration ISp = specific impulse η = mass efficiency Droplet m & = ion mass flow

Investigation of Frame‐Dragging‐Like Signals from Spinning Superconductors using Laser Gyroscopes

The search for frame dragging around massive rotating objects such as the Earth is an important test for general relativity and is actively pursued with the LAGEOS and Gravity Probe‐B satellites. Within the classical framework, frame dragging is independent of the state (normal or coherent) of the test mass. This was recently challenged by proposing that a large frame‐dragging field could be responsible for a reported anomaly of the Cooper‐pair mass found in Niobium superconductors. In 2003, a test program was initiated at the Austrian Research Centers to investigate this conjecture using sensitive accelerometers and fiber optic gyroscopes in the close vicinity of fast spinning rings at cryogenic temperatures. This paper will discuss the measurements recently obtained with the fiber optic gyroscopes. They show, that the angular velocity applied to the superconductor can indeed be seen on the sensors below a critical temperature. The signal amplitude is about 8 orders of magnitude below the values applied ...

Consolidation of milli-Newton FEEP Thruster Technology based on Porous Tungsten Multiemitters

Recently, a highly integrated electric propulsion system for ultra-precise generation of thrust on spacecraft has been developed using a porous matrix through which liquid indium flows during operation. In an effort to further improve the performance of this so-called porous tungsten crown emitter by activating all available sites for ion emission, the process of rapidly manufacturing the emitters via micro powder injection moulding has been revisited and modified. Three variations of the material composition and manufacturing processes have been performed in order to study the influence of the pore size on the ratio of active emission sites. Variations include a change in tungsten grain size as well as changes to the sintering atmosphere. Results indicate that only the densest variation, using the smallest grain size is viable for a thruster with high specific impulse. The obtained peak thrust during testing exceeded 1 mN. Despite the large peak thrust, the multiemitters maintain sub-µN capability.

Precision angular velocity response of a fiber-optic gyroscope using a piezo-nano-rotation table

Modern fiber-optic gyroscopes are calibrated using the Earths rotation or stepper motor actuated rotation tables. We investigated the angular velocity resolution of the Optolink SRS-1000 fiber-optic gyroscope using a piezo-activated rotation table down to angular velocity steps of 1 × 10−7 rad s−1 with an accuracy of 1.5 × 10−8 rad s−1. To our knowledge, these are the smallest velocity steps resolved and reported in the literature so far. Our results show that such a gyroscope may be also used for nanopositioning purposes in addition to its usual navigation application.

Towards liquid metal ion source chips: Indium liquid metal ion source with glass microcapillaries

A liquid-metal-ion-source with indium propellant using an uncoated fused quartz glass microcapillary was manufactured and tested. The extremely thin capillary enabled a very low ignition voltage of 1000 V and a high electrical impedance ideal for clustering. However, low bonding forces between indium and glass resulted in a rather short lifetime of little more than 10 min. The use of pure glass as emitter material may enable liquid ion source chips with high current densities in the future.