Stripping Mechanisms and Remediation for H$^-$ Beams

Abstract

Negative hydrogen ions, or H − , are often used for accumulating protons in storage rings via chargeexchange injection. In this process, its two electrons are stripped by a foil or laser to produce protons which can be merged with an existing beam without significantly affecting its dynamics, allowing high intensities of protons to be accumulated. However, this capability comes with the drawback that the outer electron of an H − ion has a low binding energy and can easily be stripped away prior to injection. This paper addresses the following stripping mechanisms: interactions with residual gas in the beam pipe, blackbody radiation from accelerator components, and electromagnetic fields from accelerator optics (Lorentz-force stripping) and particles within the bunch itself (intrabeam stripping); with a discussion on how to avoid excessive activation from stripped H 0 particles and protons. In addition, particle tracking simulations are used to demonstrate that the proportion of stripped H 0 particles which traverse to the end of a linac or local straight section, presents a significant fraction of the lost power from the beam (compared with the more problematic H 0 colliding with the beam pipe or machine-element walls); this may relax the limits for allowable stripping-based beam loss in H − accelerators.