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Donley, L.

Paper Title Page
FRPMN107 Observations of Rising Tune During the Injection Instability of the IPNS RCS Proton Bunch 4345
  • J. C. Dooling, F. R. Brumwell, L. Donley, K. C. Harkay, R. Kustom, M. K. Lien, G. E. McMichael, M. E. Middendorf, A. Nassiri, S. Wang
    ANL, Argonne, Illinois
  Funding: This work is supported by the U. S. DOE under contract no. W-31-109-ENG-38.

In the IPNS RCS, a single proton bunch (h=1) is accelerated from 50 MeV to 450 MeV in 14.2 ms. The bunch experiences an instability shortly after injection (<1 ms). During the first 1 ms, the beam is bunched but little acceleration takes place; thus, this period of operation is similar to that of a storage ring. Natural vertical oscillations (assumed to be tune lines) show the vertical tune to be rising toward the bare tune value, suggesting neutralization of space charge and a reduction of its detuning effects. Neutralization time near injection ranges from 0.25 ms - 0.5 ms, depending on the background gas pressure. Oscillations move from the LSB to the USB before disappearing. Measurements made with a recently installed pinger system show the horizontal chromaticity to be positive early but approaching zero later in the cycle. The vertical chromaticity is negative throughout the cycle. During pinger studies, two lines are observed, suggesting the formation of islands. Neutralization of the beam space charge implies the generation of plasma in the beam volume early in the cycle which may then dissipate as the time-varying electric fields of the beam become stronger.