Polarized 3He Ion Source Research Articles

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.

Development of a Polarized Helium-3 Source for RHIC and eRHIC

The addition of a polarized 3He ion source for use at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory would enable a host of new measurements, particularly in the context of a planned eRHIC. We are developing such a source using metastability exchange optical pumping to polarize helium-3, which will be then transferred into RHIC’s Electron Beam Ion Source for ionization. We aim to deliver nuclear polarization of near 70%, and roughly 10[Formula: see text] doubly-ionized 3He[Formula: see text] ions will be created in each 20 [Formula: see text]sec pulse. We discuss the design of the source, and the status of its development.

Development of a polarized 3He ion source for RHIC

A Polarized 3He Ion Source in under development for use at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The gas will be polarized using metastability exchange optical pumping, then transferred into the Electron Beam Ion Source for ionization. Nuclear polarization of order 70% is expected under optimal conditions, and roughly 1011 doubly-ionized 3He++ ions will be created in each 20 μs pulse.

Electron capture cross-sections between 3He + ion and rubidium vapor in the energy range 1.0–19 keV

Electron capture cross-sections have been measured for 3He + ions in Rb vapor. The deduced data were used for evaluating the performance of the proposed polarized 3He ion source (SEPIS) based on the spin-exchange collisions. Measurements of the 3He + beam components after passing through the target were made as a function of the Rb target thickness at energies ranging from 1.0 to 19 keV. The Rb vapor thickness was varied by changing the Rb cell temperature and the thicknesses were calibrated by observing the Faraday rotation angles of a probe laser ( λ = 782.0 nm ) penetrating the Rb vapor under the presence of a magnetic field ( ∼ 0.26 T ) . Assuming that the double electron capture and stripping of 3He 0 atoms are neglected, the electron capture cross-sections σ c were deduced. It was found that the observed energy dependence of σ c significantly deviated from that of the He + 4 + Cs system which was measured in the past. Lastly, the observed energy dependence of σ c was compared with the theoretical calculation assuming the semi-classical close-coupling method based on the molecular-orbital expansion. It was found that the calculated results, as a whole, reproduced the experimental results except for the data collected at 1 keV. This qualitative reproduction partly supports the appropriateness of the above theory which predicts the large spin-exchange cross-sections at low energies.

Polarized 3He 2+ ion source based on spin-exchange collisions between 3He + ion and polarized Rb atoms

A proposal is presented on the polarized 3He ion source based on the spin-exchange collisions of the low-energy 3He + ion with polarized alkali-metal atoms (Rb) which are optically pumped under the strong magnetic field. To transfer the electron polarization of 3He + ion to the 3He nucleus, we offer to use the Sona transition based on a non-adiabatic transition method. For efficiently ionizing 3He + ion to form 3He 2+ ion, 3He + ion is stripped with a gas/foil stripper after accelerating 3He +. As a compact ionizer for polarized 3He + ions, an EBIS (Electron Beam Ion Source) ionizer operated with a high magnetic field is also proposed.

Non-uniform 3He polarization formed by multiple collisions of a fast 3He + ion with polarized Rb vapor in a strong magnetic field

We investigated the spatial distribution of a polarization in 3He beam expected from a novel polarized 3He ion source based on electron pumping, i.e., multiple electron capture and stripping collisions of an incident fast 3He + ion with a polarized Rb vapor in a strong axial magnetic field. For this purpose, a Monte Carlo simulation was carried out for 19 keV 3He + ions with varying Rb vapor thickness, magnetic field, and beam emittance. The calculated results showed a distribution of the 3He polarization that we call a “polarization hole”, which has a low polarization area around the beam axis. The parameters characterizing the polarization hole, i.e., the polarization and radius of the hole, were found to depend on the Rb vapor thickness, the magnetic field, the beam size, and the angular divergence of the initial beam. These parameters were successfully reproduced with analytical functions deduced from a probability density function prescription. This provides a powerful tool to treat complex phenomena of multiple collisions in strong magnetic fields without performing time-consuming Monte Carlo calculations.

Ion optics for multiple charge exchange collisions determined by means of Monte Carlo simulation

A novel type of polarized He3 ion source based on “electron pumping” was recently proposed. This ion source requires multiple electron capture and stripping collisions of He+3 ions with polarized alkali atoms under a strong magnetic field (2–3 T). Since these processes may induce a serious increase in the emittance and reduction of polarized beam intensity, we investigated them in detail by using the Monte Carlo simulation. It was found that there is (1) increase in the emittance results not from angular broadening but from a beam size enlargement, (2) the phenomena under magnetic field B are simplified by a collisionless phenomenon under a weaker magnetic field (effective magnetic field) Beff defined by Beff≃(λ+0/(λ+0+λ0+))B, where λ+0 and λ0+ are mean free paths for He+3 ions and He03 atoms traveling in the alkali vapor.

Development of RCNP polarized 3He ion source based on electron pumping

We constructed a new polarized 3He ion source in order to establish a method of principle of “electron pumping” and experimentally prove its validity. Electron pumping utilizes multiple electron capture and stripping collisions of 3He + with rubidium atoms whose vapor thickness is much thicker than that used in an ordinary optical pumping polarized ion source. Special care was paid in the design of a rubidium vapor cell, a pumping laser and a beam transport system. We present details of the device and report the present status of the development.

A scheme for a polarized 3He ion source with a resonant charge-exchange plasma ionizer

A scheme for a polarized 3He 2+ ion source based on resonant charge-exchange between polarized 3He atoms and unpolarized 4He 2+ ions is proposed. Polarized atoms in this scheme are produced by optical pumping with metastability exchange. The polarized atoms are stored then in a storage cell. Unpolarized 4He 2+ ions are formed in a separate unpolarized plasma source and are injected into the charge-exchange region in which the polarized 3He 2+ ions are produced by the resonant charge-exchange of the polarized 3He atoms with the unpolarized 4He 2+ ions. It is expected that the polarized 3He 2+ ion beam produced in this scheme will have high intensity and polarization.

Polarized 3He Ion Source Based on the 23S1 Metastable State

This 3He polarized ion source is based on the 23S1 metastable atomic state. We produce an intense metastable beam, 6 × l015p.sec-1.sr-1, of energies between 0.07 and 0.1 eV, using a cold cathode discharge. The separation and focussing of Zeeman components (F=1/2 mF=1/2) and (F=3/2 mF=3/2) is effected with a sextupole of varliable gap. An adiabatic RF transition enhances the nuclear polarization (theoretical) to 100%. Most design parameters of the source are now frozen for operation inside the H.V. terminal of a CN van de Graaff, but the source is of universal use in (+) ion accelerators.