Compressing Spin-Polarized (3)He With a Modified Diaphragm Pump

Area of Science:

• Nuclear physics
• Atomic physics
• Materials science

Background:

• High nuclear spin polarization of helium-3 (3He) gas is essential for applications like neutron spin filters and MRI.
• Current methods like metastability-exchange optical pumping (MEOP) achieve high polarization but at low pressures (~0.1 kPa).
• A need exists for a method to increase the pressure of polarized 3He gas for practical applications.

Purpose of the Study:

• To develop a compact apparatus for compressing spin-polarized 3He gas to higher pressures.
• To evaluate the effectiveness of the compression method on 3He polarization.
• To assess the impact of temperature on gas density during compression.

Main Methods:

• Utilized a modified commercial diaphragm pump for gas compression.
• Employed metastability-exchange optical pumping (MEOP) to polarize 3He gas at ~0.25 kPa.
• Compressed the polarized 3He gas into a storage cell at ~100 kPa.
• Cooled the storage cell to liquid nitrogen temperature during compression.

Main Results:

• Achieved 20%–35% 3He polarization in pure 3He gas at 100 kPa.
• Obtained 35%–50% 3He polarization in 3He-4He mixtures at 100 kPa.
• Increased gas density by a factor of four by cooling the storage cell to liquid nitrogen temperature.

Conclusions:

• Successfully developed a compact compression apparatus for producing high-pressure nuclear spin-polarized 3He gas.
• The compression method maintains significant 3He polarization, making it suitable for applications requiring higher gas densities.
• The use of liquid nitrogen temperature further enhances the utility of the apparatus by increasing gas density.