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Beam-dust interactions in an e$^+$e$^-$ collider

Kazuhito Ohmi, Hitoshi Fukuma, Shinji Terui

TL;DR

Beam-dust interactions in an e+e- collider investigates Sudden Beam Loss at SuperKEKB caused by dust and residual gas interactions with a high-current positron beam. The authors build a physics-based PIC framework to simulate dust heating, sublimation, and plasma formation around the beam, including gas ionization and the resulting electron/ion clouds, and they examine both drift and bending-field configurations. Their results show that electron clouds can focus while ions defocus, and that a graphite dust particle can charge up to around a few billion electrons and reach sublimation temperatures, producing a dense local plasma that induces large transverse kicks and significant momentum spread, potentially driving beam loss near the aperture. A multi-turn approach demonstrates how the local dust plasma can reach a quasi-steady state within roughly a hundred bunch passages and drive cumulative emittance growth, offering a plausible mechanism for the observed SBL and guiding future experiments and simulations.

Abstract

In recent electron-positron colliders designed and operated with very low emittance and high current, the energy density of the beam has increased significantly compared to earlier designs. Under these conditions, interactions between the beam and residual materials within the beam pipe exert considerable mutual influence. The residual materials are heated by the beam, leading to evaporation, charging, and possible fission, eventually resulting in a plasma state. Conversely, the beam undergoes emittance growth due to electromagnetic interactions with the resulting plasma. We investigate the effects of such dust-induced plasma on the beam through numerical simulations of these processes.

Beam-dust interactions in an e$^+$e$^-$ collider

TL;DR

Beam-dust interactions in an e+e- collider investigates Sudden Beam Loss at SuperKEKB caused by dust and residual gas interactions with a high-current positron beam. The authors build a physics-based PIC framework to simulate dust heating, sublimation, and plasma formation around the beam, including gas ionization and the resulting electron/ion clouds, and they examine both drift and bending-field configurations. Their results show that electron clouds can focus while ions defocus, and that a graphite dust particle can charge up to around a few billion electrons and reach sublimation temperatures, producing a dense local plasma that induces large transverse kicks and significant momentum spread, potentially driving beam loss near the aperture. A multi-turn approach demonstrates how the local dust plasma can reach a quasi-steady state within roughly a hundred bunch passages and drive cumulative emittance growth, offering a plausible mechanism for the observed SBL and guiding future experiments and simulations.

Abstract

In recent electron-positron colliders designed and operated with very low emittance and high current, the energy density of the beam has increased significantly compared to earlier designs. Under these conditions, interactions between the beam and residual materials within the beam pipe exert considerable mutual influence. The residual materials are heated by the beam, leading to evaporation, charging, and possible fission, eventually resulting in a plasma state. Conversely, the beam undergoes emittance growth due to electromagnetic interactions with the resulting plasma. We investigate the effects of such dust-induced plasma on the beam through numerical simulations of these processes.

Paper Structure

This paper contains 7 sections, 14 equations, 10 figures.

Table of Contents

  1. Introduction
  2. Interaction between residual gas and the beam
  3. Interaction between dust and the beam
  4. Simulation for interaction of beam and dust particles
  5. Multi-turn simulation
  6. Conclusion
  7. acknowledgement

Figures (10)

  • Figure 1: Distribution of electrons, ions, and beam particles after 10 bunch passages. Plots (a) and (b) display the electron and ion distributions, respectively. Plot (c) displays the vertical phase space distribution of the beam particles in the 10th bunch. The horizontal and vertical axes represent $x/\sigma_x$ and $y/\sigma_y$, respectively. The color scale in (a) and (b) represents density in units of m$^{-2}$.
  • Figure 2: Electron, ion and beam distributions during the interaction with the 10th bunch after 0, 3, 6 and 9 turns. The color scale represents density in units of $10^{16}$ m$^{-2}$.
  • Figure 3: Vapor pressure for Copper, Silicone and Carbon graphiteVPSICO.
  • Figure 4: Evolution of (a) dust temperature and (b) dust size.
  • Figure 5: Evolution per bunch passage of (a) dust charge, (b) ions charge, and (c) electron charge, and (d) the number of evaporated neutral atoms.
  • ...and 5 more figures