Superconducting Gravity Gradiometers:Principle, Design and Applications
Ho Jung Paik ( University of Maryland)
Sensitive superconducting accelerometers and gravity gradiometers have been developed for tests of laws of gravity, searches for new forces and particles, and gravity survey. These devices utilize benign properties of superconductors, as well as the enhanced mechanical stability of materials at cryogenic temperatures. By differencing the responses of two linear accelerometers in a superconducting circuit, an in-line-component gravity gradiometer, which is insensitive to platform vibrations, has been constructed. Likewise, by differencing the responses of two angular accelerometers in a similar circuit, a cross-component gradiometer has been constructed.
A sensitive superconducting gravity gradiometer (SGG) was used to perform a null test of Newton’s law of gravitation. This experiment set the best limit for the inverse-square law at 1 m: two parts in 104. Presently, a new test of the inverse-square law is being carried out at 100 micrometer range by using an apparatus working on the same principle. The SGG can also be used to map the gravity field of the Earth and other planets. The original SGG, fully developed in the 1990’s, had mechanically suspended test masses, which limited the sensitivity to 2 × 103 E Hz1/2 (1 E 109 s2). Magnetically levitated test masses will improve the sensitivity by two orders of magnitude. A mission based on this technology represents improvement in gradient sensitivity by two orders of magnitude over the gravity missions already flown.
【报告人简介】
Professor Paik is an internationally recognized leader, who has pioneered in gravitational-wave detection and precision tests of the laws of gravity. He received his Ph.D. in physics at StanfordUniversity in 1974. Since 1978, he has been a faculty member at the University of Maryland. He has published over 120 scientific papers on precision gravity experiments and measuring instruments.
In 1978, he proposed a new, null test of the inverse-square law (ISL), based on Gauss's law. To carry out this experiment, he invented and developed a superconducting gravity gradiometer (SGG) with support from NASA. The Maryland SGG is the world’s most sensitive operating low-frequency gravity sensor. With this instrument, Paik and his coworkers carried out the null test of Newton’s law in the laboratory and have set the best limit for the ISL at 1 m distance. Presently, he is carrying out a cryogenic experiment to test the inverse-square law at a 100-micrometer range, which has a potential sensitivity of improving the limit by two orders of magnitude.
In 1992 through 1996, Professor Paik was invited to serve in the Science Teams for the STEP (Satellite Test of the Equivalence Principle) mission. He made major contributions in understanding the errors of the STEP differential accelerometer and improving the design of STEP. Professor Paik has received international recognition for his many contributions and accomplishments in experimental gravitation. He was a recipient of Sloan Fellowship in 1981-83 and was elected as a Fellow of the American Physical So-ciety in 2004. He served in numerous NASA and ESA committees. From 2004 to 2007, he served as a Distinguished Visiting Scientist at NASA’s Jet Propulsion Laboratory.