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A quick and accurate method of locating the axis of a magnetic field of rotational symmetry is proposed. It is shown that the deviation of the field axis in direction or in position from the axis of a reference frame (the instrument axis) is found from the angular distribution of the transverse field component. This is detected by rotating a Hall probe on the instrument axis. Formulas for locating the axis of a uniform magnetic field and that of a periodic one for electron-beam focusing are derived, and have been experimentally confirmed. The instrument for the measurement is easily constructed, and the procedures are so simple that results can be obtained in a short time. Moreover, this can be done with error of less than a few percent and with resolution of the order of 10−4 rad in direction in case of uniform fields and of 10−4 in position (ratio to the inner radius of a magnetic field device) in case of periodic fields.

View the article online for updates and enhancements. Abstract. We have developed an electron beam ion source (EBIS) assembling three rings made of high-T C superconductor as a solenoid, which enables us to construct a "table-top" EBIS operated at the liquid N 2 temperature with a strong magnetic field. Optimizing a pulse field magnetization procedure, the assembly yielded a magnetic field as high as 0.8 T under a persistent mode, which stably lasted more than two days. An electron beam of 12 keV -50 mA was successfully compressed and guided by the magnetic field along the axis of the drift tube and "soft-landed" on an electron collector with a collection efficiency of more than 99 %. As a result, highly charged ions such as Ar 17+ and Xe 42+ have been produced and extracted.

The method, which was previously proposed by the authors, of locating the magnetic-field axis has been applied to measure the misalignment of the axes of a uniform magnetic field produced by a solenoidal coil and of a periodic one produced by a permanent-magnet stack. In the former the tilt of field axis has been detected with a resolution of the order of 10−3 rad. In the latter the displacement of the field axis has been detected with a resolution of the order of 10−2 mm, which is equal to about one part in 103 of the inner diameter of magnets. It has been found experimentally that even a slight local misalignment considerably influences electron-beam transmission.