Improved electron trajectory and power distribution in APPLE-knot undulator

Area of Science:

• Physics
• Accelerator Science
• Photon Science

Background:

• APPLE-II undulator faces challenges with high on-axis heat load at low photon energies.
• Existing APPLE-Knot designs suffer from non-zero second field integrals, causing electron beam deflection and impacting beam quality.
• This deflection can degrade electron beam brightness and power distribution in long undulator devices.

Purpose of the Study:

• To introduce a novel end-Knot section for the APPLE-Knot undulator.
• To symmetrize the undulator design for balanced output power distribution and electron trajectory compensation.
• To evaluate the performance of the symmetrized APPLE-Knot undulator, comparing it with the APPLE-II.

Main Methods:

• Development of a new end-Knot section to correct electron beam trajectory.
• Symmetrization of the APPLE-Knot undulator to achieve balanced power distribution.
• Comparative analysis of partial power, flux, and polarization between APPLE-Knot and APPLE-II.

Main Results:

• The symmetrized APPLE-Knot demonstrates a significant reduction in partial power in linear mode, with comparable flux to APPLE-II.
• A 41% reduction in hotspot size was achieved through symmetric power density distribution, with minimal flux loss (<5%).
• In circular mode at low photon energies, flux is constrained by the phase error inherent in the symmetric design.

Conclusions:

• The modified APPLE-Knot design effectively mitigates electron beam deflection and reduces on-axis heat load.
• Symmetrization enhances power density distribution, improving beam characteristics for applications.
• Further optimization is needed to address flux limitations in circular mode at low photon energies.