DC SQUID-based position detector for gravitational experiments

Experiments like the test of the weak equivalence principle at the Bremen drop-tower, Germany, and STEP (Satellite Test of the Equivalence Principle) require a position detector with an extremely high resolution to measure tiny displacements of free falling test bodies. In order to develop a SQUID position detector numerous configurations of test bodies and pick-up coils with different geometries were tested experimentally. As a function of the position of the test body the inductance of the pick-up coil was measured with a commercial LCR meter as well as with a LTS DC SQUID system. This SQUID system, which is developed and manufactured at the Jena University, provides high sensitivity and extremely low intrinsic noise, especially at low frequencies. This contribution will also discuss some recent results in measuring the motion of one body during its free fall over 109 m at the Bremen drop-tower. (C) 1999 Elsevier Science Ltd. All rights reserved.