Schematic of the experimental setup used to characterize the HTS coil as a function temperature (T HTS) and applied static magnetic field (B 0). The resonance frequency ( f 0) and the quality factor (Q) of the HTS coil were extracted from the reflection coefficient (ρ) at the output port of an inductively coupled loop probe. T HTS was set by controlling the pressure (P LN2) and temperature (T LN2) equilibrium in a liquid nitrogen (LN2) bath. A pressure instruction (P IN) was sent to a pressure regulator with output pressure (POUT) to control P LN2 through a vacuum line with a pressure loss ΔP. T HTS was offset from T LN2 by temperature gradient ΔT along a sapphire cold finger. The cryostat was placed in the fringe field of a MRI magnet bore around 10 m from the electronics.
The liquid nitrogen cryostat: (a) schematic and (b) secondary vacuum chamber opened with the HTS coil mounted on the sapphire cold finger. Superinsulation layers cover all surfaces of the chamber other than the sapphire window.
The RF characterization setup with the loop probe coaxially aligned with the HTS coil.
Resonance frequency ( f 0) and quality factor (Q) of the HTS coil as a function of the applied magnetic field B 0 in parallel and orthogonal orientations without pumping (HTS-coil temperature of 80 K).
(a) Quality factor (Q) and (b) resonance frequency ( f 0) of the HTS coil as a function of temperature and applied magnetic field in both parallel or orthogonal orientations.
(a) Relative improvement of the RF sensitivity (S RF) in decibels (dB), as compared to S RF at 80 K in earth's field and (b) detuning effect (Det) with the HTS coil as a function of temperature and applied magnetic field in both parallel or orthogonal orientations. The horizontal dashed lines represent the lower and upper limits of the acceptably tuned domain, corresponding to a –3 dB attenuation of the resonance frequency curve.
Decline of the HTS coil quality factor in the presence of static magnetic field (B 0) reported in the MRI literature involving different HTS coil temperatures (T HTS) and HTS materials.
Article metrics loading...
Full text loading...