Polarized 3He Gas Research Articles

Optically pumped polarized [formula omitted]He[formula omitted] ion source development for RHIC/EIC

The proposed polarized 3He++ acceleration in RHIC and the future Electron-Ion Collider will require about 2×1011 ions in the source pulse. A new technique had been proposed for production of high intensity polarized 3He++ ion beams. It is based on ionization and accumulation of the 3He gas (polarized by metastability-exchange optical pumping and in the 5T high magnetic field) in the existing Electron Beam Ion Source (EBIS). A novel 3He cryogenic purification and storage technique was developed to provide the required gas purity. An original gas refill and polarized 3He gas injection to the EBIS long drift tubes, (which serves as the storage cell) were developed to ensure polarization preservation. An infrared laser system for optical pumping and polarization measurements in the high 3–5T field has been developed. The 3He polarization 80–85% (and sufficiently long ∼30min relaxation time) was obtained in the “open” cell configuration with refilling valve tube inlet and isolation valve closed. The development of the spin-rotator and 3He4He absolute nuclear polarimeter at 6MeV 3He++ beam energy is also presented.

Absolute [formula omitted]He polarimetry for a double-chambered cell using transmission of thermal neutrons

We present an absolute 3He polarimetry method based on thermal neutron transmission for a double-chambered cell. This method utilizes the fact that a 3He nucleus has a large absorption cross section and a spin dependence for thermal neutrons. The cell had a pumping chamber and a target chamber. Polarized 3He gas was produced in the pumping chamber by SEOP and then diffused into the target chamber. The 3He polarization in the target chamber was determined by comparing the neutron transmissions with the polarized and unpolarized targets. The measurement was performed at the RIKEN Accelerator-Driven Compact Neutron Source. The 3He polarization in the target chamber was determined with a statistical error of 1.8% and systematic uncertainty of 0.6%. This method can be used to obtain high-precision data of spin observables in few-nucleon scattering for the investigation of nuclear forces.

A High-Density Polarized 3He Gas–Jet Target for Laser–Plasma Applications

A laser-driven spin-polarized 3He2+-beam source for nuclear–physics experiments and for the investigation of polarized nuclear fusion demands a high-density polarized 3He gas-jet target. Such a target requires a magnetic system providing a permanent homogeneous holding field for the nuclear spins plus a set of coils for adjusting the orientation of the polarization. Starting from a transport vessel at a maximum pressure of 3 bar, the helium gas is compressed for a short time and can be injected into a laser–interaction chamber through a non-magnetic opening valve and nozzle, thus forming jets with densities of about a few 1019 cm−3 and widths of about 1 mm. The target comprises a 3D adjustment system for precise positioning of the jet relative to the laser focus. An auxiliary gas system provides remote target operation and flushing of the gas lines with Ar gas, which helps to reduce polarization losses. The design of the target, its operation procedures and first experimental results are presented.

A concept for polarized [formula omitted]He targets for high luminosity scattering experiments in high magnetic field environments

We present the conceptual design of a polarized 3He target to be used for high luminosity scattering experiments within high magnetic field environments. This two-cell target will take advantage of advancements in optical pumping techniques at high magnetic field to create 60% longitudinally polarized 3He gas in a pumping cell within a uniform magnetic field above 1T. By transferring the polarized gas to a cryogenic target cell, the gas density is increased to create a target thickness suitable for high luminosity applications. We discuss the general design of this scheme, and plans for its application in Jefferson Lab’s CLAS12 detector.

Development and application of a [formula omitted]He Neutron Spin Filter at J-PARC

We are developing a neutron polarizer with polarized 3He gas, referred to as a 3He spin filter, based on the Spin Exchange Optical Pumping (SEOP) for polarized neutron scattering experiments at Materials and Life Science Experimental Facility (MLF) of Japan Proton Accelerator Research Complex (J-PARC). A 3He gas-filling station was constructed at J-PARC, and several 3He cells with long spin relaxation times have been fabricated using the gas-filling station. A laboratory has been prepared in the MLF beam hall for polarizing 3He cells, and compact pumping systems with laser powers of 30 W and 110 W, which can be installed onto a neutron beamline, have been developed. A 3He polarization of 85% was achieved at a neutron beamline by using the pumping system with the 110 W laser. Recently, the first user experiment utilizing the 3He spin filter was conducted, and there have been several more since then. The development and utilization of 3He spin filters at MLF of J-PARC are reported.

Enhanced polarization of low pressure [formula omitted]He through metastability exchange optical pumping at high field

We report high steady-state nuclear polarization of 1torr 3He gas nuclei via metastability exchange optical pumping at magnetic fields above 2T. The introduction of highly polarized 3He gas into Brookhaven’s Electron Beam Ion Source would enable a new, polarized 3He ion source for use at the Relativistic Heavy Ion Collider and a future Electron–Ion Collider facility. By adapting recent developments in high field metastability exchange optical pumping for higher pressure gas, we have successfully polarized 1torr 3He sealed cells in the EBIS solenoid. Through careful manipulation of the RF discharge parameters, polarizations above 80% were attained at 2, 3 and 4T, with 89% being reached at 3T with a 664s relaxation time.

A novel broad-band neutron spin filter based on dynamically polarized protons using photo-excited triplet states

The use of polarized protons as a broad-band neutron spin filter is an attractive alternative to the well-established neutron polarization techniques, namely polarized 3He gas and super mirrors, since the spin-dependent neutron proton scattering cross-section is large in a broad wavelength range. We have developed a novel neutron spin filter where we create the necessary large proton polarization in a solid with a recent method of dynamic nuclear polarization (DNP) that uses photo-excited triplet states. This requires only moderate experimental means and allows a compact design. In order to quantify the efficiency of the spin filter, we have measured the relevant spin-dependent and spin-independent terms of the neutron scattering cross-section of a naphthalene single crystal. The data allows to estimate the triplet spin filter performance over a broad wavelength range. With the recently achieved proton polarization of 80% the triplet filter compares well with a state of the art 3He filter.

A new magnetic field system for 3He polarization

The nuclear spin-polarized 3He gas has been in depth studied and widely used in various scientific experiments. The polarized 3He gas can be used as a polarized neutron target to study the reaction of neutrons with charged particles or photon beams. On the other hand, spin polarized 3He gas is a good probe for detecting the new interactions in the supernormal model, and has many other applications as follows:the spin-dependent interaction can be studied quantitatively by measuring the NMR frequency shift but the spin-dependent interaction can also be studied by measuring the relaxation time of polarized 3He gas; the polarized 3He gas can be applied to magnetometers and magnetic resonance imaging (MRI); the highly polarized 3He gas can be used as a neutron spin filter for neutron polarization and polarization analysis because of the high correlation between the absorption cross section of the neutron in polarized 3He nucleus and the spin orientation. At present, the three major domestic sources of neutron, CMRR, CARR, and CSNS, are used to study the neutron polarization and polarization analysis techniques based on spin polarized 3He gas. The longitudinal (or spin-lattice) relaxation time (i.e., T1) of 3He is a key parameter that limits the polarizability of 3He gas. In order to reduce the effect of magnetic field gradient on the longitudinal relaxation time of polarized 3He gas, large-sized Helmholtz coils are usually constructed to provide the main magnetic field where the uniformity in the magnetic field central region reaches 10-4 cm-1. To obtain enough magnetic field uniformity, some magnetic field systems even exceed 1.5 m in size. However, it is expected to have a small magnetic field configuration from the view of practicality and convenience. For the common size (3He cells, Merritt coil and Saddle coil can effectively reduce the size of the magnetic field apparatus. However, for electron scattering experiments of 3He cells, the chamber length can be 40 cm. The system length exceeds 1 m even by using the Merritt coil. In this work, a new six-coil system for 3He polarization is obtained. Within the coils, the magnetic field gradient satisfies the requirement that √|▽Bx|2+|▽By|2/B0 -4 cm-1 in more than 30% area, which is better than all the existing coils used in polarized 3He experiments and can be applied to the future 3He instruments. For other experiments that require magnetic field to have a large uniform area, the new six-coil system is also a good option.

Pickup coil optimization for polarized 3He system

Not only can polarized 3He gas work as neutron spin filters (NSF) but also search for spin-dependent new interactions beyond the standard model. For both cases, the relative polarization of the spin polarized noble gas needs to be measured precisely. Various NMR techniques are applied practically to monitor the 3He cell’s polarization. In this work, we tried to optimize the pickup coil for the spin exchange optical pump (SEOP) based 3He system. By optimizing the signal-to-noise ratio (SNR), we found that the coil should be wound by thin wire for a higher number of turns. The optimized sizes of the pickup coils depend on the detailed configurations. For a spherical 3He cell with radius a, we found the optimized coil radius is $\sqrt{5}(a+d)$ , where d is the coil to cell surface distance. For a cylindrical 3He cell with height h, for the configurations where the coils were placed either along or perpendicular to the longitudinal axis of the target cell, we derived the optimized sizes for the specific configurations. We believe these results are practically useful for designing pickup coils of polarized 3He systems.

Non-magnetic flexible heaters for spin-exchange optical pumping of 3He and other applications.

Spin polarized 3He gas is currently widely used in various scientific fields and in medical diagnosis applications. The spin polarization of 3He nuclei can be achieved by spin-exchange optical pumping (SEOP). In SEOP, the 3He gas is enclosed in a glass cell together with alkali metals and is then heated to maintain the alkali metal vapor pressures at the appropriate levels. However, polarized 3He gas is highly sensitive to any inhomogeneity in its magnetic field, and any small field gradients caused by the heaters may cause degradation of the 3He polarization. To overcome this conflict between the heating process and the magnetic field, we have developed electrical heaters that essentially cause no magnetic fields. These heaters are thin and are flexible enough to be bent to within a radius of a few centimeters. These carefully designed heater elements and a double layer structure effectively eliminate magnetic field generation. The heaters were originally developed for SEOP applications, but can also be applied to other processes that need to avoid unwanted magnetic fields.

Diffusive transfer of polarized 3He gas through depolarizing magnetic gradients

Transfer of polarized 3He gas across spatially varying magnetic fields will facilitate a new source of polarized 3He ions for particle accelerators. In this context, depolarization of atoms as they pass through regions of significant transverse field gradients is a major concern. To understand these depolarization effects, we have built a system consisting of a Helmholtz coil pair and a solenoid, both with central magnetic fields of order 30 gauss. The atoms are polarized via metastability exchange optical pumping in the Helmholtz coil and are in diffusive contact via a glass tube with a second test cell in the solenoid. We have carried out measurements of the spin relaxation during transfer of polarization in 3He at 1torr by diffusion. We explore the use of measurements of the loss of polarization taken in one cell to infer the polarization in the other cell.

Production of laser-polarized 3He gas via metastability exchange optical pumping for magnetic resonance imaging

Abstract The state-of-the-art in the production of hyperpolarized 3He gas for magnetic resonance imaging (MRI) of the human lungs is reviewed. The paper is focused on the metastability exchange optical pumping (MEOP) method, which is preferable in medical applications, because the polarized 3He gas is free of any contaminants. Two strategies, namely, “centralized” and “on-site” production, are compared from the point of view of efficiency, level of achievable polarization, and the cost. A novel design of the polarizer that is based on MEOP operating in nonstandard conditions is also presented. It is the most promising solution for the implementation of the technique in medical clinics, as it uses the magnetic field of the MRI scanner and operates at elevated 3He gas pressure.

Measurement of the Neutron Electric to Magnetic Form Factor Ratio atQ2=1.58 GeV2Using the ReactionHe→3(e→,e′n)pp

A measurement of beam helicity asymmetries in the reaction 3He[over →](e[over →],e'n)pp is performed at the Mainz Microtron in quasielastic kinematics to determine the electric to magnetic form factor ratio of the neutron GEn/GMn at a four-momentum transfer Q2=1.58 GeV2. Longitudinally polarized electrons are scattered on a highly polarized 3He gas target. The scattered electrons are detected with a high-resolution magnetic spectrometer, and the ejected neutrons are detected with a dedicated neutron detector composed of scintillator bars. To reduce systematic errors, data are taken for four different target polarization orientations allowing the determination of GEn/GMn from a double ratio. We find μnGEn/GMn=0.250±0.058(stat)±0.017(syst).

Measurement of the neutron electric form factor in the reaction at MAMI

A measurement of the ratio GnE/GnM at a four momentum transfer Q2 = 1.5 (GeV/c)2 has been carried out at the Mainz Microtron in 2008 in order to extract the electric Sachs form factor of the neutron (GnE) with the magnetic form factor (GnM) as input. MAMI-C provided a 1.5 GeV polarized electron beam, a polarized 3He gas target served as an effective polarized neutron target to allow the study of the process The scattered electrons were detected with a magnetic spectrometer of the A1-collaboration. To detect the recoil neutrons in coincidence with the electrons, a nucleon detector was installed. It consisted of a plastic scintillator array inside a heavy lead shield. Exploiting beam helicity asymmetries for different target polarization orientations, GnE/GnM can be extracted.

Measurement of the neutron beam polarization of BL05/NOP beamline at J-PARC

We measured the neutron beam polarization of the BL05/NOP (Neutron Optics and Physics) beamline at J-PARC with an accuracy of less than 10−3 using polarized 3He gas as a neutron spin analyzer. Precise polarimetry of the neutron beam is necessary to understand the beamline optics as well as for the asymmetry measurements of the neutron beta decay, which are planned in this beamline.

In-situ Polarized 3He-Based Neutron Polarization Analyzer for SNS Magnetism Reflectometer

We report here the construction and neutron transmission test results of an in-situ polarized 3He-based neutron polarization analyzer system for the Magnetism Reflectometer at the Spallation Neutron Source, Oak Ridge National Laboratory. The analyzer uses the Spin-Exchange Optical Pumping method to polarize the 3He nuclei of a cell of 3He gas. Polarized neutrons scattered from the sample are intercepted by the polarized 3He gas which strongly absorbs neutrons in one spin-state while allowing most neutrons in the other spin-state to pass through. To maintain a stable analyzing efficiency during an experiment, the 3He gas is continuously polarized in-situ on the instrument. Neutron transmission measurements showed that 73% 3He polarization was reached in this setup.

A high-pressure polarized 3He gas target for nuclear-physics experiments using a polarized photon beam

Following the first experiment on three-body photodisintegration of polarized $^3$He utilizing circularly polarized photons from High Intensity Gamma Source (HI$\gamma$S) at Duke Free Electron Laser Laboratory (DFELL), a new high-pressure polarized $^3$He target cell made of pyrex glass coated with a thin layer of sol-gel doped with aluminum nitrate nonahydrate has been built in order to reduce the photon beam induced background. The target is based on the technique of spin-exchange optical pumping of hybrid rubidium and potassium and the highest polarization achieved is $\sim$62% determined from both NMR-AFP and EPR polarimetry. The $X$ parameter is estimated to be $\sim0.06$ and the performance of the target is in good agreement with theoretical predictions. We also present beam test results from this new target cell and the comparison with the GE180 $^3$He target cell used previously at HI$\gamma$S. This is the first time that sol-gel coating technique has been used in a polarized $^3$He target for nuclear physics experiments.

Limits on short-range spin-dependent forces from spin relaxation of polarized 3He

A new limit is presented on the axion-like monopole–dipole P,T-non-invariant coupling in a range (10−4−1) cm. The gradient of spin-dependent nucleon–nucleon potential between 3He nucleus and nucleons and electrons of the walls of a cell containing polarized 3He gas should affect its spin relaxation rate. The limit is obtained from the existing data on the relaxation rate of spin-polarized 3He.

A high-pressure polarized 3He gas target for the High Intensity Gamma Source (HI [formula omitted]S) facility at Duke Free Electron Laser Laboratory

A new polarized 3He target has been developed for nuclear physics experiments utilizing the High Intensity Gamma Source (HI γ S) at the Duke Free Electron Laser Laboratory (DFELL). This target is designed for a broad program of physics employing high intensity polarized photons and a polarized 3He target as an effective polarized neutron target. We report the performance of this target based on the technique of spin-exchange optical pumping (SEOP). Due to the significantly larger photon beam size at the HI γ S facility than that of a typical electron beam at electron accelerator laboratories, the HI γ S 3He target contains a larger number of 3He nuclei than any polarized 3He targets reported previously. A target polarization on the order of 33–46% has been achieved from both a regular 3He–Rubidium (Rb) target and a hybrid target which contains a mixture of Rb and potassium. The target polarization has been determined within 3 % using both the Electron Paramagnetic Resonance (EPR) technique and the NMR–AFP (Adiabatic Fast Passage) technique.

Method to measure neutron beam polarization with 2×1 Neutron Spin Filter

A method to measure a beam polarization with the use of polarized 3He gas is discussed. It is shown that with a special design of Neutron Spin Filter cell it is possible to have fast and accurate measurement of the beam polarization. The accuracy of this method is analyzed.