• Open Access

Coherent resonance stop bands in alternating gradient beam transport

K. Ito, H. Okamoto, Y. Tokashiki, and K. Fukushima
Phys. Rev. Accel. Beams 20, 064201 – Published 22 June 2017
An article within the collection: IPAC 2014 Conference Edition

Abstract

An extensive experimental study is performed to confirm fundamental resonance bands of an intense hadron beam propagating through an alternating gradient linear transport channel. The present work focuses on the most common lattice geometry called “FODO” or “doublet” that consists of two quadrupoles of opposite polarities. The tabletop ion-trap system “S-POD” (Simulator of Particle Orbit Dynamics) developed at Hiroshima University is employed to clarify the parameter-dependence of coherent beam instability. S-POD can provide a non-neutral plasma physically equivalent to a charged-particle beam in a periodic focusing potential. In contrast with conventional experimental approaches relying on large-scale machines, it is straightforward in S-POD to control the doublet geometry characterized by the quadrupole filling factor and drift-space ratio. We verify that the resonance feature does not essentially change depending on these geometric factors. A few clear stop bands of low-order resonances always appear in the same pattern as previously found with the sinusoidal focusing model. All stop bands become widened and shift to the higher-tune side as the beam density is increased. In the space-charge-dominated regime, the most dangerous stop band is located at the bare betatron phase advance slightly above 90 degrees. Experimental data from S-POD suggest that this severe resonance is driven mainly by the linear self-field potential rather than by nonlinear external imperfections and, therefore, unavoidable at high beam density. The instability of the third-order coherent mode generates relatively weak but noticeable stop bands near the phase advances of 60 and 120 degrees. The latter sextupole stop band is considerably enhanced by lattice imperfections. In a strongly asymmetric focusing channel, extra attention may have to be paid to some coupling resonance lines induced by the Coulomb potential. Our interpretations of experimental data are supported by theoretical predictions and systematic multiparticle simulations.

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  • Received 23 February 2017

DOI:https://doi.org/10.1103/PhysRevAccelBeams.20.064201

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Accelerators & Beams

Collections

This article appears in the following collection:

IPAC 2014 Conference Edition

A collection of articles that expand upon original research presented at the 2014 International Particle Accelerator Conference (June 15-20, 2014, Dresden, Germany).

Authors & Affiliations

K. Ito, H. Okamoto*, Y. Tokashiki, and K. Fukushima

  • Graduate School of Advanced Sciences of Matter, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8530, Japan

  • *Corresponding author. okamoto@sci.hiroshima-u.ac.jp
  • Present address: Facility for Rare Isotope Beams, Michigan State University, East Lansing, MI 48824, USA.

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Vol. 20, Iss. 6 — June 2017

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