Strictly axisymmetric turbulence, i.e., turbulence governed by the Navier-Stokes equations modified such that the flow is invariant in the azimuthal direction, is a system intermediate between two-and three-dimensional turbulence. We investigate statistically steady states of this system by direct numerical simulation using a forcing protocol, which allows the injected energy in the toroidal and in the poloidal directions to be tuned independently. A sharp transition between a two-dimensional two-component (2D2C, nonswirling) flow and a two-dimensional three-component (2D3C, swirling) flow is observed. We derive a statistical model which reproduces this transition.
At the China Spallation Neutron Source (CSNS), we have developed a custom gas-filling station, a glassblowing workshop, and a spin-exchange optical pumping (SEOP) system for producing high-quality 3He-based neutron spin filter (NSF) cells. The gas-filling station is capable of routinely filling 3He cells made from GE180 glass of various dimensions, to be used as neutron polarizers and analyzers on beamlines at the CSNS. Performance tests on cells fabricated at our gas-filling station are conducted via neutron transmission and nuclear-magnetic-resonance measurements, revealing nominal filling pressures, and a saturated 3He polarization in the region of 80%, with a lifetime of approximately 240 hours. These results demonstrate our ability to produce competitive NSF cells to meet the ever-increasing research needs of the polarized neutron research community.
Polarized 3 He neutron spin filters (NSFs) can be used as a vital tool for neutron polarization production and analysis. The China Spallation Neutron Source (CSNS), as one of the major neutron facilities in China, has committed resources to the development of a polarized 3 He NSF program to support its growing polarized neutron research. A spin-exchange optical pumping (SEOP)-based polarized 3 He system and other necessary hardware for NSF transport has been recently developed. The performance of the system is benchmarked using an in-house developed cell named "Trident". Neutron beam measurements yield a 3 He polarization of 77% with over 200 h of on-beam relaxation time. Combining this newly developed SEOP system with the recently reported cell fabrication station, CSNS is now capable of the fully self-sustained production of 3 He NSFs that shall support its future neutron polarization research.
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