An optical technique for measuring divergence, beam profile, and aiming direction, of relativistic negative hydrogen ions
Description: A novel, nonobstructive diagnostic technique for high energy H/sup minus/D/sup minus/ ion beams is described. This scheme employs spectroscopic techniques designed to measure beam profile, perpendicular velocity spread (i.e., divergence), and orientation of multiMeV H/sup minus/ beams. The basic principle of this method is to photoneutralize a small portion of the H/sup minus/ beam in a way such that the photodetachment process results in the formation of excited hydrogen atoms in the n = 2 levels. Observation of fluorescence from spontaneous decay of H(sp) andor induced deacy of H(2s) can be readily used to determine beam profile. Doppler broadening measurements can be used to determine velocity spread from which beam emittance is calculated. With off-the-shelf instruments resolutions of 1 mm for beam profile and 2 x 10/sup minus/2) ..pi.. cm-mrad are possible. For photodetachment, the best commercially available laser is found to be ArF eximer laser. The analysis is performed for the 200 MEV BNL Linac. The laser, which has a pulse duration which has a pulse duration which is of 10/sup minus/5) of the linac can produce sufficient signal at a negligible beam loss. In addition, measurements of minute Doppler shifts of this Lyman-Alpha radiation by a spectrograph could in principle resolve beam direction to within 1.57 ..mu..rad. The process under consideration has a resonance known as the shape resonance. As the following literature review indicates, the total cross section is known and there is a reasonable agreement between theory and experiment. There are no experimental measurements of partical cross sections. nevertheless, there are theoretical estimates which agree within 15%. 10 refs., 1 fig.
Date: February 1, 1988
Creator: Hershcovitch, A.
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