T. Morokuma

Absolute determination of the magnetic flux quantum using superconducting magnetic levitation

The current status of our superconducting magnetic levitation experiment for determining the magnetic flux quantum is described. The flux-up system has been improved significantly by using a Josephson voltage standard. Studies are also in progress to improve the mechanical measurement relevant to the floating body with the goal of reducing the uncertainty to less than 1 ppm. >

Evaluation of equilibrium trajectory of superconducting magnetic levitation system for the future kg unit of mass

The superconducting magnetic levitation system for absolute determination of magnetic flux quantum /spl Phi//sub 0/, which is aimed at the future replacement of the kilogram unit of mass, has been developed at the National Research Laboratory of Metrology (NRLM) with a small floating body of approximately 25 g mass. The consistency of the relation between potential energy of the floating body and the electromagnetic energy of the superconducting magnetic levitation system has been evaluated with 1 ppm order resolution. In this paper, the results of the evaluation as well as the improvements made in the apparatus in recent years at NRLM are described.

Vertical displacement determination of a levitated superconducting mass

The determination of the vertical displacement of the center of gravity of a levitated superconducting body in the National Research Laboratory of Metrology (NRLM) superconducting magnetic levitation project, which is aimed at establishing a new definition of the unit of mass based on the fundamental constants, is discussed. The translation displacement (three degrees of freedom) and the attitude change (three degrees of freedom) of the measuring point, which is the optical center of the cube corner prism O/sub C/ of the floating body, are measured using a newly developed optical measuring system. To determine the vertical displacement of the center of gravity of the floating body G/sub C/ the relative position of G/sub C/ with respect to O/sub C/ is required, which is determined using the energy relation between the electromagnetic energy and the gravitational potential energy under levitating conditions.

Mechanism for levitated superconductor experiment

A mechanism for a levitated superconductor experiment has been proposed and is being developed with the final target of defining the kilogram in terms of fundamental constants. Improving the stability of the levitated object by means of introducing a superconducting linear bearing is the aim of the work reported in this paper. The strategy of this development, results of the preparatory experiments, and further prospects are discussed.

Present status of the NRLM superconducting magnetic levitation system for absolute determination of the magnetic flux quantum

The NRLM superconducting magnetic levitation is based on the concept of quasi-static energy injection process, where the energy injected from external source to the coil system is equal to the sum of the increase in magnetic energy and gravitational potential energy. The levitation system uses a niobium coil and floating body with mass of 25 g. The measurement consists of two processes: (1) to increase the magnetic flux through the coil in terms of the Josephson voltage which we call flux-up, (2) to measure the coil current and the vertical displacement of the center of gravity of a floating body in equilibrium. By the repetition of these processes, the relation which we call equilibrium trajectory is obtained. The absolute value of the magnetic flux quantum is calculated in terms of the energy equation using the trajectory data. Hence, a quasi-static process is not vital. The levitation system has been developed at NRLM and the reproducibility of magnetic flux and vertical displacement in equilibrium at 0.1 ppm level was confirmed including Meissner effect of the superconductive material. In this paper, we report a recent improvements concerning mechanical energy determination as well as the changes to the electrical system.

Optics for five-dimensional measurement for correction of vertical displacement error due to attitude of floating body in superconducting magnetic levitation system

An improved optical system for five-dimensional measurement has been developed for the correction of vertical displacement error due to the attitude change of a superconducting floating body that shows five degrees of freedom besides a vertical displacement of 10mm. The available solid angle for the optical measurement is extremely limited because of the cryogenic laser interferometer sharing the optical window of a vacuum chamber in addition to the basic structure of the cryogenic vessel for liquid helium. The aim of the design was to develop a more practical as well as better optical system compared with the prototype system. Various artifices were built into this optical system and the result shows a satisfactory performance and easy operation overcoming the extremely severe spatial difficulty in the levitation system. Although the system described here is specifically designed for our magnetic levitation system, the concept and each artifice will be applicable to the optical measurement system for an ...

Vertical displacement determination in the NRLM superconducting magnetic levitation system

The vertical displacement of the gravity center of the floating body is estimated by solving energy equations. To calculate it, all the six degrees of freedom of the floating body are measured by using a optical measurement system.

Development of a new levitated-mass mechanism toward replacing the kilogram

A new superconducting levitated-mass mechanism is now being developed with the final target of replacing the kilogram in terms of the fundamental constants. Improving the stability of trajectory by means of introducing a superconducting linear bearing is the issue in question for this development. The strategy of the development, experimental results and further prospects are discussed.

Improvements of NRLM superconducting magnetic levitation system for absolute determination of /spl Phi//sub 0/

The NRLM superconducting magnetic levitation system is now refining for the determination of Magnetic Flux Quantum /spl Phi//sub 0/ with small 25 g mass floating body. Recent study to investigate error sources and improvements are described in this paper.