New beam neutralization concept: Laser photodetachment in a magnetic field

The major advantage of laser photodetachment as a method for neutralizing a negative ion beam is that the emittance increase can be made as small as desired. Since the momentum of the photon is negligible, it is only the recoil from the leaving electron that causes any beam spread in photodetachment. The closer the laser is turned to the threshold frequency, the smaller the relative energy of the electron and atom, and the smaller the recoil. The problem with photodetachment is the high laser power requirement. The cross section approaches zero as the laser frequency approaches the detachment threshold. As a consequence, for a high-brightness application it is estimated that the laser power required would exceed the anticipated beam power. It is shown that the imposition of a solenoidal magnetic field in the neutralization region may make photodetachment practical, by enhancing the cross section.