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Purpose <p>The Beijing Electron Positron Collider II (BEPCII) has achieved a series of achievements in high-energy physics study. Along with the deepening of the research, more important physics is expected in higher-energy region (e.g., 2.35&#xa0;GeV). As the upper limit of BEPCII design energy is 2.1&#xa0;GeV, an urgent upgrade is required. To achieve a higher luminosity at higher energy, the number of RF cavities is increased from one to two in each ring, such that the delivered beam power could be doubled and the bunch length can be reduced. With a doubled beam current and reduced beta function at IP, a tripled luminosity at 2.35&#xa0;GeV is expected after the upgrade.</p> Method <p>The magnets in RF region are replaced with new ones which have smaller sizes, and the RF region is rearranged to accommodate two RF cavities in each ring. The accelerator design code SAD is used to rematch the linear lattice and do the dynamic aperture (DA) tracking. The candidate positions of new skew quadrupoles (SKQs) are ranked by the coupling correction capability. The code Accelerator Physics Emulation Studio (APES) is used to remodel the lattice. The impedance is simulated by CST and beam instability is evaluated accordingly.</p> Results <p>The layout is modified and the linear lattice is rematched. The dynamic aperture tracking result show that the lattice could meet the injection and collision requirements of BEPCII upgrade with reasonable margin. The locations of the new SKQs have been strategically selected, and the new SKQs demonstrate a remarkable improvement in coupling correction. APES modeling indicates that the lattice requires further investigation. The impedance and the beam instability evaluated results show enough margin for high-current operation.</p>

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Beam physics design for BEPCII upgrade

  • 期刊论文

  • 发表日期：

    2026年2月4日

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  • Huiping Geng,
  • Yanru Wei,
  • Weibin Liu,
  • Yudong Liu,
  • Yuan Zhang,
  • Jun Xing,
  • Chenghui Yu

摘要

Purpose

The Beijing Electron Positron Collider II (BEPCII) has achieved a series of achievements in high-energy physics study. Along with the deepening of the research, more important physics is expected in higher-energy region (e.g., 2.35 GeV). As the upper limit of BEPCII design energy is 2.1 GeV, an urgent upgrade is required. To achieve a higher luminosity at higher energy, the number of RF cavities is increased from one to two in each ring, such that the delivered beam power could be doubled and the bunch length can be reduced. With a doubled beam current and reduced beta function at IP, a tripled luminosity at 2.35 GeV is expected after the upgrade.

Method

The magnets in RF region are replaced with new ones which have smaller sizes, and the RF region is rearranged to accommodate two RF cavities in each ring. The accelerator design code SAD is used to rematch the linear lattice and do the dynamic aperture (DA) tracking. The candidate positions of new skew quadrupoles (SKQs) are ranked by the coupling correction capability. The code Accelerator Physics Emulation Studio (APES) is used to remodel the lattice. The impedance is simulated by CST and beam instability is evaluated accordingly.

Results

The layout is modified and the linear lattice is rematched. The dynamic aperture tracking result show that the lattice could meet the injection and collision requirements of BEPCII upgrade with reasonable margin. The locations of the new SKQs have been strategically selected, and the new SKQs demonstrate a remarkable improvement in coupling correction. APES modeling indicates that the lattice requires further investigation. The impedance and the beam instability evaluated results show enough margin for high-current operation.