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Pow
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atts
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Model Experimental Data
A device to allow the remote manipulation of a high power microwave beam was constructed. The instrument functions by using polarization, reflecting a fraction of the microwave, as a function of the rotation angle, into a heat sink.
Dynamic Nuclear Polarization
Motorized Grid Rotator
Above: the polarization control hardware. The polarizing grid acts as an adjustable beam splitter, allowing microwave power control.
Lock Installation
MicrowaveBeamPowerControlandNMRFrequencyLockforDynamicNuclearPolariza>onDonovanKelley,BiancaTrociewitz,WilliamBrey,ThierryDubrocaNa:onalHighMagne:cFieldLaboratory,Tallahassee,FL
NMR Frequency Lock Console Microwave Beam Power Control An NMR lock is an instrument that allows the correction of drift inherent to magnets over time. This correction capability permits significantly longer data averaging experiments.
Acknowledgements This work is supported by the National Science Foundation through DMR-1157490 and CHE-1229170, and the State of Florida. I’d like to thank the CIRL, Jose Sanchez particularly, and Karol Bicket for this internship.
References 1) Overhauser A., Phys. Rev. 92, 2 (1953)
2) Griffin R. et al., PCCP 12, 5737 (2010)
3) Nuclear Magnetic Resonance (NMR)
ooSpectroscopy, McGraw Hill Education
Motor
Polarizing Grid
Conclusions Over the course of this internship and the construction of these two devices I have gained a great deal of understanding about the necessity of documentation and systematic trial and error. In the future the power controller could be configured to run automated experiments and the lock can be set up to run independently of its’ accompanying console.
Lock
Magnet
Pre-Amp
NMR Console
Shim Control
Right: the lock is set up in a test configuration. It is connected to the magnet via a pre-amp which amplifies the NMR signal. The “shim control” is used as a current amplifier to correct the magnetic field.
Right: 16 NMR spectra of 1H water over 12 hours. A clear drift of the field is visible over this short period of time
Microwave power measured as a function of grid angle (diamonds). Calculated microwave power (solid line), based on a generalized Malus’ Law.
R2 Value = 0.998
Above: table of recorded recovery time after large field perturbation.
Below: software user interface developed in LabVIEWTM.
Overhauser1 (Liquid) DNP Solid DNP2
Microwave Source
Photograph of Dynamic Nuclear Polarization instruments at the National High Magnetic Field Lab
Lock Principle 1 2 3 4 5
Trial 1 2 3 4 5 AvgTime 50s 13s 47s 34s 45s 29s
Field(a.u.)
t=0hr
t=3hr
t=6hr
t=9hr
t=12hr
Left: lock signal as a function of time (red is the real part; green is the imaginary part). Five perturbations were introduced.
>me(s)
Magne>cField
Schema:cadaptedfromreference(3)