Millimeter-wave Sources for DNP-NMR

Advances in both solid-state and vacuum-electron-based sources at frequencies greater than 200 GHz have been a key factor in the recent improvements in solid-state dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) instrumentation. The current state of the art in solid-state sources and vacuum-electron devices (VEDs), such as extended interaction oscillators (EIOs), extended interaction klystrons (EIKs), and gyrotrons for DNP applications are described. The key features and design aspects of gyrotrons, which are presently the most promising DNP sources for high-field NMR systems, are detailed. In addition, the current capabilities of high-performance DNP gyrotron sources are illustrated. The status of ongoing research efforts in DNP gyrotrons and future directions are discussed.