Abstract
The Oak Ridge Spallation Neutron Source comprises a 1 GeV, 1.5 MW linear accelerator followed by an accumulator ring and a liquid mercury target. To manage the beam loss caused by the ${H}^{0}$ excited states created during the ${H}^{\ensuremath{-}}$ charge-exchange injection into the accumulator ring, the stripper foil is located inside one of the chicane dipoles. This has some interesting consequences that were not fully appreciated until the beam power reached about 840 kW. One consequence was sudden failure of the stripper foil system due to convoy electrons stripped from the incoming ${H}^{\ensuremath{-}}$ beam, which circled around to strike the foil bracket and cause bracket failure. Another consequence is that convoy electrons can reflect back up from the electron catcher and strike the foil and bracket. An additional contributor to foil system failure is vacuum breakdown due to the charge developed on the foil by secondary electron emission. In this paper we detail these and other interesting failure mechanisms and describe the improvements we have made to mitigate them.
Highlights
The Spallation Neutron Source accelerator [1] comprises a 1 GeV, 60 Hz, HÀ ion beam linac with a 1.5 MW design beam power, followed by an accumulator ring with charge-exchange injection to compress the 1 ms long pulses from the linac to $700 ns
Corrugated nanocrystalline diamond stripper foils [2] have been in use since the beginning of formal operations in 2006
The first failure mechanism is simple: the lower portion of the L-shaped bracket was too close to the foil, so that some of the convoy electrons struck the bracket on their first revolution around the magnetic field lines
Summary
Brookhaven National Laboratory, Upton, New York 11973, USA (Received 30 November 2010; published 23 March 2011). To manage the beam loss caused by the H0 excited states created during the HÀ charge-exchange injection into the accumulator ring, the stripper foil is located inside one of the chicane dipoles. This has some interesting consequences that were not fully appreciated until the beam power reached about 840 kW. One consequence was sudden failure of the stripper foil system due to convoy electrons stripped from the incoming HÀ beam, which circled around to strike the foil bracket and cause bracket failure. In this paper we detail these and other interesting failure mechanisms and describe the improvements we have made to mitigate them
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