Weak gravitation shielding properties of composite bulk YBa2Cu3O7−x superconductor
Weak gravitation shielding properties of
composite bulk YBa2Cu3O7−x superconductor
below 70 K under e.m. ﬁeld
- Moscow Chemical Scientiﬁc Research Centre
- 113452 Moscow - Russia
A high-temperature YBa2Cu3O7−x bulk ceramic superconductor with composite structure has revealed weak shielding properties against gravitational force while in a levitating state at temperatures below 70 K. A toroidal disk with an outer diameter of 275 mm and a thickness of 10 mm was prepared using conventional ceramic technology in combination with melt-texture growth. Two solenoids were placed around the disk in order to initiate the current inside it and to rotate the disk about its central axis. Samples placed over the rotating disk initially demonstrated a weight loss of 0.3-0.5%. When the rotation speed was slowly reduced by changing the current in the solenoids, the shielding eﬀect became considerably higher and reached 1.9-2.1% at maximum.
74.72.-h High-Tc cuprates.
The behavior of high-Tc ceramic superconductors under high-frequency magnetic ﬁelds is of great interest for practical applications. Crystal structure seems to be the key factor determining all physical properties of bulk superconductors, and the interaction of this structure with external and internal e.m. fields might result in quite unusual effects. Despite a large number of studies [1,2,3] the nature of these interactions still remains unresolved. Our recent experimental work  clearly indicated that under certain conditions single-phase bulk, dense YBa2Cu3O7−x revealed a moderate shielding effect against gravitational force. In order to obtain more information about this unusual phenomenon, a new installation was built, enabling operation with larger disks (275 mm in diameter), in magnetic ﬁelds up to 2 T and frequencies up to 108 Hz at temperatures from 40 to 70 K.
A new experimental technique was employed to modify the structure of the ceramic superconductor. All these efforts yielded a larger value of the shielding effect (up to 0.5% in stationary conditions and to 2.1% for shorter periods), providing good hopes for technological applications. A gravitational shielding effect of this strength has never been previously observed, and its implications present serious theoretical difficulties (see  for references and an analysis of some hypotheses). Thus, great attention was devoted to the elimination of any possible source of systematic errors or of spurious non-gravitational effects. The small disturbances due to air flows pointed out by some authors [9,10] were eliminated by weighing the samples in a closed glass tube (see Section 4). The entire cryostat and the solenoids were enclosed in a stainless steel box. But probably the best evidence for the true gravitational nature of the effect is that the observed weight reductions (in %) were independent of the mass or chemical composition of the tested samples (Section 6). This work is organized as follows. Sections 2 and 3 describe our experimental setup. Section 2 summarizes the main steps in the sinterization of the composite ceramic disk and contains information about the final properties of the disk (Tc for the two layers, Jc for the upper layer, etc.) and about the microscopic structure of the material. Section 3 describes how we obtain and control the levitation and rotation of the disk, up to an angular speed of about 5000 rpm.
In Section 4 we describe the weight measurement procedure and analyze in detail possible error sources and parasitic effects. Several checks were performed to exclude any influence of spurious factors (Section 5). In Section 6 we give the maximum % shielding values obtained in dependence on the rotation speed of the disk and on the frequency of the applied magnetic field. Finally, Sections 7 and 8 contain a short discussion and our conclusions. According to public information, a NASA group in Huntsville, Alabama, is now attempting to replicate our experiment. This is a difficult task, especially in view of the sophisticated technology involved in the construction of the large ceramic disk and in the control of its rotation. We are also aware, through unofficial channels, that other groups are working on similar experiments with smaller disks.
to be continued