Albannay, Mohammed M.

Ardenkjær-Larsen, Jan H.

Vinther, Joachim M.

Zhurbenko, Vitaliy

Microwave sample irradiation is essential to perform DNP. Waveguides provide an effective way of coupling the output of a microwave source to the electron spins. Indivertibly, the waveguide introduces a significant thermal heat load into the sample space of our dDNP probe. The use of a circular stainless steel waveguide with an internally electroplated layer of copper offers an effective, economical solution to address this problem

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Downloaded from orbit.dtu.dk on: Mar 30, 2019Low microwave attenuation and low thermal loss waveguides for dDNP probesAlbannay, Mohammed M.; Møllesøe Vinther, Joachim; Zhurbenko, Vitaliy; Ardenkjær-Larsen, Jan HenrikPublication date:2018Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Albannay, M. M., Vinther, J. M., Zhurbenko, V., & Ardenkjær-Larsen, J. H. (2018). Low microwave attenuationand low thermal loss waveguides for dDNP probes. Poster session presented at International Conference onNuclear Hyperpolarization 2018, Southampton , United Kingdom.Microwave irradiation is a requisite to transfer electronspin polarization to nuclear spins. Significant increase inNMR sensitivity by way of dissolution DNP (dDNP) [1] hasencouraged the development of multiple commercial andhome-built polarizers and dDNP probes [2-3].Engineering challengeThe length of waveguide neededto couple a microwave source tothe electron spins is dictated bythe dimensions of the polarizer,thereby influencing the totalwaveguide attenuation.The desire for higher magnetic fields (B0) has raised therequired microwave frequency to perform DNP, furtherlimiting the available power due to inefficient solid-statemicrowave sources.Corrugated waveguides improve microwave irradiation byreducing transmission losses, but are costly to procure[4]. Similarly, mode converters offer use of propagationmodes with reduced attenuation constants, but arechallenging to fabricate at higher frequencies and havesome insertion loss.We present a solution to achieve efficient microwaveirradiation whilst minimizing thermal loss.Solutions are pumped through the waveguide using aperistaltic pump. Once coated they are mechanicallypolished to reduce surface roughness, resulting in a shinypink finish. The waveguide is rinsed and then dried withan inert gas.Low microwave attenuation and low thermal loss waveguides for dDNP probesMohammed M. Albannay1, Joachim M. O. Vinther1, Vitaliy Zhurbenko1, Jan H. Ardenkjær-Larsen1,21Center for Hyperpolarization in Magnetic Resonance (HYPERMAG), Department of Electrical Engineering,  Technical University of Denmark, Kgs Lyngby, Denmark.2GE Healthcare, Brøndby 2605, DenmarkMohammed M.  AlbannayE-Mail:  mohalb@elektro.dtu.dkPhone:  +45 45255745[1] J. H. Ardenkjaer-Larsen et al., Proc. Natl. Acad. Sci., 100, 18, 10158-10163 (2003)[2] J. H. Ardenkjaer-Larsen et al., NMR Biomed., 24: 927-932 (2011)[3] Cremillieux et al., Appl. Magn. Reson., 43: 167-180 (2012) [4] E. de Rijk et al. Rev. Sci. Instr., 82, 066102 (2011).This work was financially supported by the European Union’s Horizon 2020 research and innovationprogramme under the Marie Sklodowska-Curie grant no. 642773 and the Danish National ResearchFoundation grant no. DNRF124AcknowledgementReferencesMicrowaves in DNP Thermal conduction vs. attenuation dDNP probeThe probe is permanently equipped with a waveguide,coupling the top flange to the cryogenically cooledsample space. The conducted thermal heat decreaseswith the waveguide’s cross-sectional area therefore a⌀4.16 mm circular stainless steel waveguide was selectedsince it offers the lowest attenuation for a givenperimeter (when compared to a rectangular waveguide).Ohmic losses are reduced by internally electroplating thewaveguide with a layer of copper.DNP-NMR experimentsWaveguide electroplatingWaveguide measurementsWaveguide attenuation wasmeasured using a 94 GHz sourceand a doubler or tripler. Thereliability of the measurementswere improved using an anti-cocking UG387 adapter and analignment flange.The effect of polarization using a  stainless steel and copper plated waveguide was investigated using a 100 μL 4.5 M [13C]urea (5:4:1 glycerol-d8, D2O, H2O & 40 mMTEMPOL) sample in a 6.7 T polarizer.1H polarization was observed using low flip angle pulses.The sample was irradiated with 188.06 GHz microwaves having afrequency modulation bandwidth of 50 MHz with a frequency of 1 kHz.Microwave sample irradiation is essential to perform DNP. Waveguides provide an effective way of coupling the output of a microwave source to theelectron spins. Indivertibly, the waveguide introduces a significant thermal heat load into the sample space of our dDNP probe. The use of a circularstainless steel waveguide with an internally electroplated layer of copper offers an effective, economical solution to address this problem.Thermal heat coupled by a coaxial cable can be significant(particular via the inner conductor). A compromise betweenelectrical loss and thermal loading can be achieved using acable with a stainless steel outer conductor.No chamfers or reflectors are employed in the overmoded cavity. Methods to improve irradiationefficiency are currently being explored.

Low microwave attenuation and low thermal loss waveguides for dDNP probes

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Low microwave attenuation and low thermal loss waveguides for dDNP probes

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