Magnetic field drift

Lock or field/ A method for accurately maintaining frequency lock (locking) the static magnetic field at a fixed value. The frequency of a nuclear magnetic resonance signal - commonly deuterium from a deuterated solvent - is held at constant value by a field/fre-quency feedback loop to compensate for any magnetic field drift during an experiment. 

The transport of particles in the plasma is diffusive or convective for the neutrals, whereas the charge carriers move under the influence of the external and internal electric and magnetic fields. The drift velocityv of the charged particles is proportional to the electric field E ... 

This deleterious effect can be obviated by introducing additional components of magnetic field, causing the field lines to circumscribe the toms without ever closing on themselves. The net magnetic field is then composed of a major, or toroidal, field component produced by the current cods, plus a smaller poloidal component which gives the desired twist to the lines. Particle drifts weaken or nullify the harmful electrical field and the plasma no longer tends to move to the wads. 

Assuming that the current in the gas is carried mostly by electrons, the induced electric field uB causes transverse electron motion (electron drift), which, being itself orthogonal to the magnetic field, induces an axial electric field, known as the Hall field, and an axial body force, F, given by... 

Also in 1950 Sakliarov and Tamm proposed an idea for a controlled thermonuclear fusion reactor, the TOKAMAK (acronym for the Russian phrase for toroidal chamber with magnetic coiF ), which achieved the highest ratio of output power to input power of any fusion device of the twentieth centuiy. This reactor grew out of interest in a controlled nuclear fusion reaction, since 1950. Sakharov first considered electrostatic confinement, but soon came to the idea of magnetic confinement. Tamm joined the effort with his work on particle motion in a magnetic field, including cyclotron motion, drifts, and magnetic surfaces. Sakharov and Tamm realized that... 

If your experiment is short, you don t need to worry about field drift. Modem magnets are quite stable and can be used for at least a few minutes without drifting too far. The disadvantage with this approach is that shimming is normally performed on the deuterium signal and you will need to shim your sample differently if there is no deuterium in the sample. 

In order to better illustrate these points, consider, for example, a magnet such as the one described in Section III.D. It reaches the maximum field of 1.143 T, corresponding to 48.7 MHz of Larmor frequency, with a current of 400 A. It follows that for a very low magnetic field corresponding to, let us say, 1 kHz, one has to set a current of just 8 mA. In order to do that, one should be able to control the current with a precision and resolution of about 20 ppm of the maximum value. The required absolute precision is therefore of the same order of magnitude as the current offsets and thermal drifts of even the best analog electronic components. 

By revealing all aspects of the signal, the phase detector makes evident all instrumental artifacts which would not be observable with another type of detection. On an FFC instrument, this typically includes thermal field drifts (see Section IV.D) and field instabilities associated with the large dynamic bandwidth of the switching magnet system. 

Development of Dosimeter Materials. - 4.2.1 Quantitative ESR and Intensity Standards of Mn1+ and CuS04.5H20. An ESR spectrometer consists of vacuum tube amplifier and a Klystron oscillator with thermal noise and frequency drift. Hence, an inherent standard of Mn2+ was used in ESR dating of carbonate stalactites,8 and patented as a standard in ESR radiation dosimetry in 1980.102 The standard sample of MgO with Mn2+ is frequently used for calibration of -factor and the magnetic field as well as for radiation dosimetry.103... 

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