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Photoelectron trapping in quadrupole and sextupole magnetic fields
L F Wang1, H Fukuma, S Kurokawa
1High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan. wanglf@post.kek.jp
Summary
Photoelectrons can become trapped in magnetic fields, potentially causing coupled bunch instability in particle accelerators. This trapping is dependent on beam characteristics like bunch length and is a mirror field trap caused by beam disturbance.
Area of Science:
- Particle accelerator physics
- Plasma physics
- Beam dynamics
Background:
- Photoelectron clouds are a significant concern in particle accelerators, potentially leading to beam instabilities.
- Understanding the behavior of photoelectrons within magnetic fields is crucial for accelerator performance.
Purpose of the Study:
- To investigate a photoelectron-trapping phenomenon observed in simulations.
- To identify the conditions and mechanisms responsible for photoelectron trapping.
- To assess the impact of this trapping on accelerator stability, specifically coupled bunch instability.
Main Methods:
- Simulations of photoelectron cloud dynamics within quadrupole and sextupole magnetic fields.
- Analysis of photoelectron behavior, including trapping duration and longitudinal drift.
- Investigation of beam-dependent factors influencing trapping, particularly positron bunch length.
Main Results:
- A photoelectron-trapping phenomenon was identified in simulations.
- Photoelectrons can be trapped for extended periods in magnetic fields, even with significant bunch separation.
- Trapping is strongly dependent on beam parameters, notably bunch length; longer bunches can prevent trapping.
- The trapping mechanism is identified as a mirror field trap induced by beam disturbance.
Conclusions:
- Long-term photoelectron trapping in magnetic fields can lead to coupled bunch instabilities.
- Beam characteristics, especially bunch length, critically influence photoelectron trapping.
- The findings highlight the importance of managing photoelectron dynamics for stable accelerator operation.
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