Abstract
Negative hydrogen ions are often used for injecting protons from linacs to storage rings via charge-exchange injection. In this process, the 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. We also demonstrate that the proportion of stripped H$^0$ colliding with a nearby beam pipe or machine-element walls presents only roughly 10\% of those lost in stripping; the remaining stripped particles traverse to the end of a linac or local straight section, which may relax the limits for allowable stripping-based beam loss in H$^-$ accelerators.
Highlights
The H− ion is useful for applications requiring the accumulation of high-intensity proton populations in a storage ring
Since the loss rate is limited for high β, this type of stripping is often predominant in the low-energy beam transport (LEBT) section adjacent to the ion source, where it is standard practice to inject a neutral diatomic gas to compensate for space charge
The tendency of H− ions to collide within a bunch can be the prevalent stripping mechanism in modern high intensity H− accelerators [41]
Summary
The H− ion is useful for applications requiring the accumulation of high-intensity proton populations in a storage ring These include neutron spallation, pion production for neutrino-physics studies, or injection into high-energy colliders [1,2,3]. In this context, chargeexchange injection strips H− ions of both electrons using either thin intercepting foils or laser stimulation [4]. A related phenomenon is double stripping, which typically occurs near the H− source This produces protons that can cause excessive activation or structural damage, if they are inadvertently accelerated and propagated as far as, for example, a junction where H− are diverted away from their linear trajectory toward an accumulator ring or other apparatus [6]. The interplay of Lorentz stripping and IBST (and their overall dependence on beam parametrization) is quantified
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