Department of Chemistry, Colorado State University, Fort Collins, Colorado
The idea of combining cylindrical coils for producing a longitudinal gradient with respect to the MAS axis with quadrupole (straight wire) magnetic-field-gradient coils for producing two transverse gradients for 3D MAS and CRAMPS imaging has been demonstrated. A modified set of a double Maxwell pair and two sets of quadrupole (eight wire) coils were combined in a compact way and adapted for a 5 mm MAS rotor, achieving gradients of high efficiency (4.3 and 2.9 G/cm*A for longitudinal and transverse coils, respectively), low inductance (3.5 and 1.9 uH, respectively), and very good linearity (1%). A 60 um spatial resolution in a TREV-CRAMPS imaging experiment on solid polyethylene oxide was demonstrated; gradient pulses of 12 us duration were generated by applying currents of 2.3 and 1.5 A to longitudinal and transverse coils, respectively. This magnetic-field-gradient-coil configuration could also be appled in other areas of NMR where time-dependent gradients are required.