Polarized ³ He ^- ion source with hyperfine state selection

High beam polarization is essential to the scientific productivity of a collider. Polarized ³ He ions are an essential part of the nuclear physics programs at existing and future ion-ion and electron-ion colliders such as BNL's RHIC and eRHIC and JLab's ELIC. Ion sources with performance exceeding that achieved today are a key requirement for the development of these next generation high-luminosity high-polarization colliders. The development of high-intensity high-brightness arc-discharge ion sources at the Budker Institute of Nuclear Physics (BINP) has opened up an opportunity for realization of a new type of a polarized ³ He ^- ion source. This report discusses a polarized ³ He ^- ion source based on the large difference of extra-electron auto-detachment lifetimes of the different ³ He ^- ion hyperfine states. The highestmomentum state of 5/2 has the largest lifetime of τ ∼ 350 μs while the lowermomentum states have lifetimes of τ ∼ 10 μs. By producing ³ He ^- ion beam composed of only the |5/2, ±5/2> hyperfine states and then quenching one of the states by an RF resonant field, ³ He ^- beam polarization of 90% can be achieved. Such amethod of polarized ³ He ^- production has been considered before; however, due to low intensities of the He ⁺ ion sources existing at that time, it was not possible to produce any interesting intensity of polarized ³ He ^- ions. The high-brightness arc-discharge ion source developed at BINP can produce a high-brightness ³ He ⁺ beam with an intensity of up to 2 A allowing for selection of up to ∼1-4mA of ³ He ^- ions with ∼90% polarization. The high gas efficiency of an arc-discharge source is important due to the high cost of ³ He gas. Some features of such a PIS as well as prototype designs are considered. An integrated ³ He ^- ion source design providing high beam polarization could be prepared using existing BNL equipment with incorporation of new designs of the 1) arc discharge plasma generator, 2) extraction system, 3) charge exchange jet, and 4)magnetic separation system.