Speaker
Description
The University of New Hampshire Nuclear Physics Polarized Target Group operates an advanced polarized target system for high-precision nuclear physics experiments. These experiments require a combination of low-temperature cryogenic operation, strong magnetic fields, nuclear magnetic resonance polarimetry, and a dedicated millimeter-wave microwave system for dynamic nuclear polarization. A major challenge in operating such systems is the high consumption and increasing cost of liquid helium, which is essential for maintaining the cryogenic environment required for polarized target operation. To address this challenge, UNH has integrated a dedicated closed-loop helium liquefier system that captures, purifies, and re-liquefies helium gas exhausted from the target cryostat. This system allows helium to be recovered and reused, reducing dependence on external helium supply and supporting more sustainable long-term target operations. In parallel, the UNH polarized target program has developed and operated a specialized solid-state millimeter-wave microwave system for dynamic nuclear polarization. Compared with traditional continuous-wave microwave extended interaction oscillator systems, the solid-state millimeter-wave approach can provide a more compact, stable, and efficient microwave source with reduced heat load on the target, which is especially important for maintaining low-temperature operation near 1 K. This presentation discusses the technical design and operational performance of the UNH closed-loop helium liquefier system and its role within the broader polarized target infrastructure. We also highlight the connection between cryogenic stability, microwave delivery, target heat load, and polarization performance in dynamic nuclear polarization studies. By transitioning from a traditional “boil-off to atmosphere” model to a sustainable internal helium recovery cycle, the UNH system significantly reduces helium waste, lowers operational risk associated with helium supply volatility, and supports reliable operation of polarized targets for nuclear physics research. The combined development of sustainable cryogenics and low-heat-load polarized-target microwave technology provides a model for how medium-scale university laboratories can support advanced nuclear physics instrumentation while improving efficiency, reducing environmental impact, and maintaining the demanding conditions required for high-precision spin-physics experiments.