Residual magnetic field

Anomalies in the power wiring are a common cause of stray magnetic fields in commercial buildings and hospitals. Neutral-to-ground connections downstream of the main bonding connection cause some of the neutral current to return via the ground path. This path is not predictable and results in residual magnetic fields due to mismatch in the supply and return currents to the various electrical circuits in the... 

Figure 4.15 Relative transmission T (called here the collecting efficiency ) of a CMA as a function of the kinetic energy of the electrons. The solid curve guides the eye through the experimental data. For energies higher than 4eV the transmission is constant, below this value it drops to zero (the cut-off effect due to disturbances in the performance of the analyser caused by residual magnetic fields and inhomogeneities of electrical fields, see Sections 4.5.2 and 4.5.3). Reprinted from J. Electron Spectrosc. Relat. Phenom., 15, Samson, 257 (1979) with kind permission of Elsevier Science - NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.

Disturbances due to inhomogeneities in electric fields and to residual magnetic fields on electrons of low kinetic energy also occur in this mode of operation. They... 

Although the resonance Is shifted by Zeeman- and motional Stark-effects due to a residual magnetic field of about 75 G in the transition region, the results are promising and lead to the expectation of improved precision in future excited state experiments. 

At the same time, the residual magnetic field can be expressed as the vertical derivative of the residual electric field Ey using the equation... 

Residual magnetic fields with a component in the radial plane will couple the radial and axial motions of the ions. The effect of the cyclotron motion on the resonance frequencies co+ can be judged by considering the simpler single-ion situation. Here, the coupled equations of motion read... 

For a typical residual magnetic field of ca 1 Gauss (if, for example, the Earth s magnetic field is not compensated for), the corresponding cyclotron frequency co, of the ions is ca 2n x 100 Hz. Hence, with (oJ2n being typically of the order of 100 kHz, the relative change in frequency is only of the order of 10" . A similar result can be found for co+. ... 

In this laboratory, the amplitude of the residual magnetic field can be reduced readily to 0.1 Gauss, meaning that the effect of the magnetic field can be reduced to a level of 10". ... 

Measurement of the velocity distribution and the laser-induced changes to it is most easily done by observing the fluorescence from atoms excited by a second, very weak laser propagating nearly parallel to the atomic beam in a region where there is zero magnetic field. Because of the Doppler shift, the absorption and hence the intensity of this fluorescence will depend on the atomic velocity, and a slow scan of this laser s frequency will result in a fluorescence signal that reflects the velocity distribution. This second, probe laser should be sufficiently weak that it doesn t perturb the atomic velocity distribution, and should cross the atomic beam sufficiently far away from the end of the solenoid that there is no residual magnetic field from it. 

There is another rotation associated with the absorption line called Faraday rotation. This is only present when there is a magnetic field parallel to the light. Faraday rotation in a known magnetic field is used to calibrate rotation measurements, but Faraday rotation due to residual magnetic fields is a potential source of systematic error that is carefully guarded against. 

---