Author: Chung, M.
Paper Title Page
Space-Charge Particle Resonances and Mode Parametric Resonances  
  • D. Jeon, J.-H. Jang
    IBS, Daejeon, Republic of Korea
  • Y.L. Cheon, M. Chung
    UNIST, Ulsan, Republic of Korea
  As the beam intensity increases in modern high-power accelerators, self-field effects of the beam become significant. There are two distinct families of space-charge halo mechanisms in high-intensity accelerators, and yet they need to be differentiated: resonances (particle resonances or incoherent resonances) and instabilities (parametric resonances or coherent resonances). What we call resonances are resonances of beam particles excited through the space-charge nonlinear multipoles. What we call instabilities are instabilities of the beam modes. Instabilities are also called parametric resonances because they are parametric resonances of the Vlasov-Poisson equations. They would better be called mode parametric resonances to distinguish them from particle parametric resonances. Resonances and instabilities may look alike in the phase space, and yet they have distinct differences. Instabilities (or mode parametric resonances) do not have the resonant frequency component. Various orders of resonances and instabilities are presented along with the beam distributions with which the particular mechanism is observed.  
slides icon Slides THAC2 [5.680 MB]  
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Mitigation of 4th Order Resonance and Envelope Instability by Beam Angular Momentum  
  • D. Jeon
    IBS, Daejeon, Republic of Korea
  • Y.L. Cheon, M. Chung, S.H. Moon
    UNIST, Ulsan, Republic of Korea
  For modern high-intensity linear accelerators, the well-known envelope instability and recently reported fourth-order particle resonance impose a fundamental operational limit: zero-current phase advance (sig0)<90deg. In particular, it has been discovered that the fourth-order particle resonance is always excited and manifested predominantly over the envelope instability along the drift-tube linac when sig0>90deg and sig<90deg. In this study, we present a novel method to mitigate the space-charge driven fourth-order resonance by introducing a new concept of ‘spinning beam’. Motivated by classical mechanics on the stability of spinning flying objects, ‘spinning beam’ has non-zero average canonical angular momentum under axisymmetric system. From the analytical and numerical simulation studies, we found that spinning beams have an intrinsic characteristic that can suppress the impact of the fourth-order resonance on emittance growth and the following envelope instability. Unlike other approaches to suppress the coherent instabilities, we have demonstrated beam spinning as a possible control knob for mitigating the fourth-order resonance to surpass the linac operational limit.  
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Summary WG-C  
  • M. Chung
    UNIST, Ulsan, Republic of Korea
  • C.-Y. Tan
    Fermilab, Batavia, Illinois, USA
  • D. Wollmann
    CERN, Meyrin, Switzerland
  Summary of the Working Group C (Accelerator Systems)  
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