A compact tunable quadrupole lens for brighter and sharper ultra-fast electron diffraction imaging

Area of Science:

• Accelerator Physics
• Materials Science
• Electron Microscopy

Background:

• High-quality electron beams are crucial for advanced imaging techniques like ultrafast electron diffraction (UED).
• Previous methods for controlling electron beam properties had limitations in terms of tunability and cost.
• Optimizing beam size and divergence is essential for achieving high-resolution diffraction images.

Purpose of the Study:

• To design and experimentally validate a broadly tunable, low-cost transverse focusing lens system for MeV-energy electron beams.
• To demonstrate independent control over electron beam size and divergence.
• To enhance the quality of Bragg-diffraction images (BDI) for UED experiments.

Main Methods:

• Implementation of an electromagnetic (EM) quadrupole lens system.
• Utilizing the Robust Conjugate Directional Search (RCDS) algorithm for online optimization.
• Employing Bragg-diffraction imaging (BDI) for real-time beam divergence measurement and emittance determination.

Main Results:

• Achieved independent control of beam size and divergence for charges from 1 to 13 pC.
• Maintained a constant transverse beam size of 75 µm across the tested charge range.
• Demonstrated a nearly two-orders-of-magnitude increase in charge density compared to conventional solenoids.
• Enabled real-time measurement of beam divergence, crucial for online optimization.
• Observed significant improvements in BDI, including 3x higher peak intensity and 2x sharper peaks at 13 pC.

Conclusions:

• The developed EM quadrupole lens system offers a cost-effective and versatile solution for MeV electron beams.
• Real-time divergence measurement and optimization capabilities pave the way for advanced applications like single-shot ultrafast electron microscopy (UEM).
• The enhanced BDI quality opens new avenues for ultrafast imaging of material dynamics and molecular processes.