Developing New Q-meters for NMR Measurements of Polarized Solids

Abstract

Enhanced polarization of target nuclei can be measured via the complex impedance of a resonant circuit coupled to the target while sweeping the circuit through the nuclear Larmor frequency, observing the absorption or emission of energy by the spins in the material. For decades, solid polarized targets at Jefferson Lab have relied upon continuous-wave Nuclear Magnetic Resonance polarization measurements using Liverpool Q-meter systems. These Liverpool Q-meters are no longer produced, and replacing the aging components is becoming increasingly difficult. The polarized target group at Bochum has produced replacement Q-meters in the Liverpool style using modern components, and we are following their example while researching improvemnts to the technique. We discuss our efforts to produce improved Q-meters for upcoming experiments utilizing solid polarized targets in Jefferson Lab's Hall B.

First Use of a Longitudinally Polarized Target with CLAS12

“…In order to reach the center of the solenoid and avoid interference with the CLAS12 Central Detector and its electronics, the target cryostat must be approximately 3 m long. The target is inserted into the spectrometer using a rail-mounted cart that also supports a 140 GHz microwave system for DNP at 5 T, NMR electronics for measuring the polarization, a roots pumping set for the horizontal 4 He evaporation refrigerator, and all other electronic equipment for monitoring and controlling the system. The compact, self-contained nature of the target system was chosen so that it could be fully assembled and tested in the JLab Target Group laboratory and installed in the experimental hall in only two weeks.…”

“…Coarse tuning of the frequency is performed using a computer-controlled DC motor that adjusts the length of the oscillator cavity, while fine tuning is accomplished by applying a DC bias to the cathode. The polarization is measured by CW-NMR using series-tuned Q-meters recently developed at Jefferson Lab [4]. There is one Q-meter used for proton NMR at 212.9 MHz and one for deuteron NMR at 32.7 MHz.…”