Speaker
Description
The use of polarized $^3$He ions in storage rings opens a new window to investigate nuclear forces, because the spin-dependent part of the differential cross section of the observed reactions must stem in first order from the neutron spin. Thus, nuclear polarized $^3$He$^{2+}$ beams can be regarded as an ideal substitute for polarized neutron beams. Polarized $^3$He ions were used in the 1960’s, but either the nuclear polarization and/or the usable intensity of the corresponding ion sources was rather small. Since then, several groups around the world have been working on the realization of an efficient polarized $^3$He ion source for injection into storage rings. Current concepts are based on the rapid ionization of optically-pumped polarized $^3$He gas with polarization values up to 0.8. Nevertheless, most of the different ionization processes tested so far result in large polarization losses.
A new approach at the Institute for Nuclear Physics in the Research Center Jülich promises to overcome the recent limitations with an intense (>10 μA) polarized $^3$He$^{1+}$ beam with a polarization up to P ~ 0.9 that can be used for stripping injection to feed storage rings. The method itself is similar to “optical pumping”, but instead of laser beams single radio-wave pulses are used to induce transitions within the hyperfine substates in the Zeeman region of a $^3$He$^{1+}$ beam at 4 keV. The corresponding photons are coherent and monochromatic, and the induced transitions at an energy level of $10^{-8}$ eV interfere with each other. Based on this phenomenon, the three substates of the F = 1 state can be pumped into a single substate with $m_F$ = +1 or -1. The corresponding polarization will be measured after acceleration to about 100 MeV due to the known analyzing powers of elastic scattering on protons with an existing polarimeter behind the cyclotron JULIC. In principle, this technique can be expanded to other ions, even heavy ions, and may open the door for a new generation of polarized ion sources or polarized fuel, thus increasing the energy output of future fusion reactors.
