Collisonal pumping for the production of intense spin-polarized neutral BEAMS: target considerations

Neutral-beam heating and/or fueling offers the possibility of establishing deuteron and triton spins oriented parallel to the magnetic field (or antiparallel to the field). It is believed that the polarizations can be maintained by guide fields until the particles are within the reactor. A beam suitable for this magnetic fusion-energy application would require five to six orders of magnitude increase in polarized beam intensity from the limits imposed by present technology, which is on the order of 10-100 μA. We have recently proposed that ampere-sized beams of nuclear-spin-polarized ions and atoms can be produced by multiple atomic collisions in an electron-spin-polarized medium. By analogy to optical pumping, we have called the process ''collisional pumping.'' Such pumping will occur when an ion beam passes through a thick electron-spinpolarized target in a low magnetic field. As an ion in the beam undergoes a succession of electron-capture and -loss collisions, polarization is transferred from the electron to the nucleus through the hyperfine interaction. After a sufficient number of charge-changing collisions, both the electron and nuclear polarization of the beam will be pumped to the electron polarization of the target. We have analyzed and theoretically demonstrated several examples of collisional pumping; the case that lends itself to earliest testing is that of a low-energy (0.1 - 10 keV/u) hydrogen or deuterium beam passing through a thick electron-spin-polarized alkalivapor target in a low magnetic field