Laser Diagnostic for High Current H− Beams

Book excerpt: In the last 5 years, significant technology advances have been made in the performance, size, and cost of solid-state diode-pumped lasers. These developments enable the use of compact Q-switched Nd:YAG lasers as a beam diagnostic for high current H− beams. Because the threshold for photodetachment is only 0.75 eV, and the maximum detachment cross section is 4 x 10−17 cm2 at 1.5 eV, a 50 mJ/pulse Q-switched Nd:YAG laser can neutralize a significant fraction of the beam in a single 10-ns wide pulse. The neutral beam maintains nearly identical parameters as the parent H− beam, including size, divergence, energy, energy spread, and phase spread. A dipole magnet can separate the neutral beam from the H− beam to allow diagnostics on the neutral beam without intercepting the high-current H− beam. Such a laser system can also be used to extract a low current proton beam, or to induce fluorescence in partially stripped heavy ion beams. Possible beamline diagnostic systems will be reviewed, and the neutral beam yields will be calculated.