Magnetic field, achievement

In all cases, an optical isolator must be interposed between the Laser and the experiment, to prevent the return beam from perturbing the Laser (a X/4 plate or a Faraday glass in an axial magnetic field achieves this). 

It is suggested though that even more precise sizing of cracks with complex cross-sections and unknown shapes could be achieved using the distribution of the leakage magnetic field along two lines positioned above the surface of the sample and parallel to the direction of the applied field at the same distance from the centre of the crack and from its closer end. 

It is occasionally desirable to retain a small proportion of molecular orientation, in order to quantitate the dipolar interactions present, whilst minimizing their contribution to the linewidth. Partial orientation may be achieved by using a nematic solvent. In large, magnetically anisotropic molecules it may occur naturally at the highest magnetic fields. 

Figure B2.4.6. Results of an offset-saturation expermient for measuring the spin-spin relaxation time, T. In this experiment, the signal is irradiated at some offset from resonance until a steady state is achieved. The partially saturated z magnetization is then measured with a kH pulse. This figure shows a plot of the z magnetization as a fiinction of the offset of the saturating field from resonance. Circles represent measured data the line is a non-linear least-squares fit. The signal is nonnal when the saturation is far away, and dips to a minimum on resonance. The width of this dip gives T, independent of magnetic field inliomogeneity.

Once the primary electron beam is created, it must be demagnified with condenser lenses and then focused onto the sample with objective lenses. These electron lenses are electromagnetic in nature and use electric and magnetic fields to steer the electrons. Such lenses are subject to severe spherical and chromatic aberrations. Therefore, a point primary beam source is blurred into a primary beam disk to an extent dependent on the energy and energy spread of the primary electrons. In addition, these lenses are also subject to astigmatism. AH three of these effects ultimately limit the primary beam spot size and hence, the lateral resolution achievable with sem. 

The problem with all the mirror approaches is that none has achieved the degree of confinement quaUty that the closed systems have. Closed systems ate characterized by magnetic field lines that close on themselves so that charged particles following the field lines remain confined within the system. 

Fig. 20. Scaling of channel enthalpy extraction for the various MHD faciUties discussed in text ( ) achieved, and (e) predicted where O is the average gas conductivity in mho/m B, the average magnetic field in T M, the channel Mach number E, the average channel active length, m and P, the average...

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