Solid-State Dynamic Nuclear Polarization at 263 GHz: Spectrometer Design and Experimental Results

Dynamic Nuclear Polarization (DNP) experiments transfer polarization from electron spins to nuclear spins with microwave irradiation of the electron spins for enhanced sensitivity in nuclear magnetic resonance (NMR) spectroscopy. Design and testing of a spectrometer for magic angle spinning (MAS) DNP experiments at 263 GHz microwave frequency, 400 MHz 1H frequency is described. Microwaves are generated by a novel continuous-wave gyrotron, transmitted to the NMR probe via a transmission line, and irradiated on a 3.2 mm rotor for MAS DNP experiments. DNP signal enhancements of up to 80 have been measured at 95 K on urea and proline in water–glycerol with the biradical polarizing agent TOTAPOL. We characterize the experimental parameters affecting the DNP efficiency: the magnetic field dependence, temperature dependence and polarization build-up times, microwave power dependence, sample heating effects, and spinning frequency dependence of the DNP signal enhancement. Stable system operation, including DNP performance, is also demonstrated over a 36 h period.National Institutes of Health (U.S.) (NIH grant EB-002804)National Institutes of Health (U.S.) (NIH grant EB-002026

The Mars Atmosphere and Volatile Evolution (MAVEN) Mission

The MAVEN spacecraft launched in November 2013, arrived at Mars in September 2014, and completed commissioning and began its one-Earth-year primary science mission in November 2014. The orbiter’s science objectives are to explore the interactions of the Sun and the solar wind with the Mars magnetosphere and upper atmosphere, to determine the structure of the upper atmosphere and ionosphere and the processes controlling it, to determine the escape rates from the upper atmosphere to space at the present epoch, and to measure properties that allow us to extrapolate these escape rates into the past to determine the total loss of atmospheric gas to space through time. These results will allow us to determine the importance of loss to space in changing the Mars climate and atmosphere through time, thereby providing important boundary conditions on the history of the habitability of Mars. The MAVEN spacecraft contains eight science instruments (with nine sensors) that measure the energy and particle input from the Sun into the Mars upper atmosphere, the response of the upper atmosphere to that input, and the resulting escape of gas to space. In addition, it contains an Electra relay that will allow it to relay commands and data between spacecraft on the surface and Earth