Solid-State Sources for DNP-NMR

Project Summary / Abstract Dynamic nuclear polarization (DNP) is a technique to boost the sensitivity of nuclear magnetic resonance (NMR) and has been successfully utilized to study numerous biological and biochemical processes. The heart of a DNP instrument is the microwave (MW) source. An ideal MW source has high output power and a wide tuning bandwidth, is capable of pulsing, can generate complex signals with frequency, phase, and amplitude modulation control, and is easy to use. The ideal MW source does not yet exist; however, through this proposal we will be significantly closer to realizing solid-state sources that have most of these desired features. This will be accomplished through mixer-based up-conversion to preserve signal integrity, where an arbitrary waveform generator will be used as the base signal that is up-converted. Additionally, high powered high frequency amplifiers will be used to amplify the signal once it has been up- converted. After amplification, frequency multipliers can be used to extend the technology to higher frequencies beyond the reach of the current amplifier technology, albeit with a reduction in power and some distortion of the signal. This research effort is focused on the development of the source technology for the key DNP frequencies of 263 GHz (400 MHz NMR) and 527 GHz (800 MHz NMR), with emphasis on the amplifier and multiplier technologies, as well as the packaging technologies required to achieve the power required for DNP through in-phase power combining. The Phase I effort includes design studies of the amplifier MMICs to determine how much per-chip power can be expected at ~130 GHz and ~260 GHz and to complete the initial layout of the MMICs for possible fabrication in Phase II. The multiplier designs for 263 and 527 GHz will also be upgraded, with the goal of improved doubling efficiency at the increased level of input power expected from the new amplifiers. A Phase I prototype source will be developed using presently available MMIC amplifiers at ~130 GHz and the doubler to 263 GHz. A high level of power combining will be applied to these components to increase the state-of-the-art power by a about factor of two. Lastly, a new doubler will be fabricated and tested, so that the source can be extended to 527 GHz. This prototype source will demonstrate increased DNP enhancement at 263 GHz due to the higher power, and achieve the first DNP measurements at 527 GHz with a frequency sweepable solid-state source with pulsing capabilities. These Phase I results will facilitate the Phase II goals, which include watt-level power at 263 GHz and 100's of mW at 527 GHz with control of the frequency, phase and amplitude of the output waveform.