Laser diagnostics for H− beam momentum and momentum spread

Abstract

Non‐invasive laser diagnostics are capable of measuring p absolutely and δp/p of high‐energy H− ion beams. A Q‐switched Nd:YAG laser, operating at 0.266 μm, can excite narrow auto‐ionizing resonances in the H− ion. The measured width of the resonances is sensitive to δp/p of the ion beam. Doppler tuning of the laser photon energy, by angle tuning, allows the absolute beam energy to be measured. The principle of these diagnostics was tested at LAMPF during a series of atomic physics experiments. It was found that the absolute energy of the H− beam could be measured to an accuracy of 10−4 and the momentum spread to an accuracy of 10−5. The diagnostic was sensitive to dephasing of a single rf module on the LAMPF linac. The applicability of this type of diagnostic for H− beams of different phase space and energy than LAMPF will be presented.