Velocity Exchange Spectroscopy

Fig. 12. Radiofrequency and gradient pulse sequence for velocity exchange spectroscopy (VEXSY) in which successive PGSE pulse pairs (G, and G2X separated by a delay time t , are applied. For an unambiguous correlation, Gj and Gj are required to be collinear. Note the two orthogonal Fourier domains represented (schematically) by r, and tj- Fourier transformation with respect to the acquisition time leads to a third spectral dimension.

In velocity-change NMR the variables q and q 2 replace the axes ki and kz in Fig. 5.4.5, and ui and V2 replace r and r2 (Fig. 5.4.12). In a coordinate frame rotated by 45° the difference coordinate corresponds to acceleration a and the other to velocity v, so that this exchange experiment can be read as a velocity-acceleration correlation experiment. Following the coordinate transformations (5.4.21) for position-change spectroscopy, the following coordinate transformations apply for velocity-change spectroscopy. 

Fig. 8.6. Comparison between the measurements of toroidal plasma velocity by X-ray spectrometer and charge exchange recombination spectroscopy (CXRS) in the plasma center [3]...

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