The use of the "negative mass" regime provides stabilization of longitudinal size of dense photoinjector electron bunches moving through a long undulator. This allows one to increase significantly the power capabilities of a terahertz source based on coherent spontaneous emission from a short bunch. However, such type of emission is produced if the bunch length is comparable with the radiation wavelength. This work discusses the use of the negative mass regime to provide effective compression of dense bunches down to "terahertz" lengths.
Abstract. A continuous flow dynamic nuclear polarization (DNP) employing the Overhauser effect at ambient temperatures can be used among other methods to increase sensitivity of magnetic resonance imaging (MRI). The hyperpolarized
state of water protons can be achieved by flowing aqueous liquid through a
microwave resonator placed directly in the bore of a 1.5 T MRI magnet. Here
we describe a new open Fabry–Pérot resonator as DNP polarizer, which exhibits a larger microwave exposure volume for the flowing liquid in
comparison with a cylindrical TE013 microwave cavity. The
Fabry–Pérot resonator geometry was designed using quasi-optical theory and simulated by CST software. Performance of the new polarizer was tested
by MRI DNP experiments on a TEMPOL aqueous solution using a blood-vessel
phantom. The Fabry–Pérot resonator revealed a 2-fold larger DNP enhancement with a 4-fold increased flow rate compared to the cylindrical
microwave resonator. This increased yield of hyperpolarized liquid allows
MRI applications on larger target objects.
Abstract. A continuous flow dynamic nuclear polarization (DNP) employing the Overhauser effect at ambient temperatures can be used among other methods to increase sensitivity of magnetic resonance imaging (MRI). The hyperpolarized state of water protons can be achieved by flowing aqueous liquid through a microwave resonator placed directly in the bore of a 1.5 T MRI magnet. Here we describe a new open Fabry-Pérot resonator as DNP polarizer, which exhibits a larger microwave exposure volume for the flowing liquid in comparison with a cylindrical TE013 microwave cavity. The Fabry-Pérot resonator geometry was designed using quasi-optical theory and simulated by CST software. Performance of the new polarizer was tested by MRI DNP experiments on a TEMPOL aqueous solution using a blood-vessel phantom. The Fabry-Pérot resonator revealed a 2-fold larger DNP enhancement with a 4-fold increased flow rate compared to the cylindrical microwave resonator. This increased yield of hyperpolarized liquid allows MRI applications on larger target objects.
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