Nuclear magnetic resonance radiation damping in inhomogeneous radio frequency fields: The toroid cavity detector

A theory is presented for radiation damping (RD) in the toroid cavity nucle ar magnetic resonance detector, a cylindrically symmetric inhomogeneous-rf field detector in which the magnitude of B-1 is inversely proportional to t he distance from the cylindrical symmetry axis. The equations of motion of the magnetization components are obtained and discussed. Numerical simulati ons of conventional- and composite-pulse experiments are presented, along w ith a discussion of the effects of RD on the evolution of magnetization. Pr eliminary simulations of RD in the presence of inhomogeneous line broadenin g are also presented. The signature effect of radiation damping in the TCD is the winding or unwinding of magnetization gratings that has recently bee n observed by other researchers. The observed magnitude of the effect is li nked to the effective filling factor, which currently appears to be limited by the stray inductance of the detection circuit. The results are of inter est in connection with recent findings regarding the interaction of RD with the dipolar demagnetizing field. (C) 2001 American Institute of Physics.