Figuring Method of High Convergence Ratio for Pulsed Ion Beams Based on Frequency-Domain Parameter Control

Area of Science:

• Optical Engineering
• Surface Metrology
• Fusion Energy Technology

Background:

• Continuous phase plates (CPPs) are crucial for inertial confinement fusion (ICF) applications, enabling beam smoothing and shaping.
• Large surface gradients (>2 μm/cm) on CPPs pose significant processing challenges for conventional continuous ion beam figuring (IBF) due to motion axis limitations and extra material removal.
• Existing IBF methods struggle with efficiency and precision when machining complex, large-gradient optical surfaces.

Purpose of the Study:

• To evaluate and compare the processing convergence of pulsed ion beam (PIB) figuring versus continuous ion beam figuring (IBF) for large gradient surfaces.
• To demonstrate the effectiveness of PIB in overcoming the limitations of IBF for fabricating high-precision optical components.
• To provide experimental and simulation-based evidence for the advantages of PIB in advanced optical manufacturing.

Main Methods:

• Utilized simulation and experimental approaches to assess the performance of both IBF and PIB techniques.
• Employed frequency-domain parameters to discretize the ion beam, creating a pulsed ion beam (PIB) with controlled pulse width and frequency.
• Focused on analyzing surface residuals and convergence ratios achieved by each machining method on large gradient surfaces.

Main Results:

• Pulsed ion beam (PIB) figuring demonstrated significantly better performance than continuous ion beam figuring (IBF) under identical beam diameter conditions.
• PIB achieved a substantially higher convergence ratio (γ = 8.47) compared to IBF (γ = 2.02).
• PIB resulted in markedly lower surface residuals (RMS = 27.48 nm) than IBF (RMS = 184.36 nm), indicating superior surface finish.

Conclusions:

• Pulsed ion beam (PIB) figuring offers a superior solution for machining large gradient surfaces, overcoming key limitations of continuous ion beam figuring (IBF).
• The discrete nature of PIB allows for higher machining efficiency and precision, with reduced surface errors.
• This research validates PIB as a promising technique for achieving higher convergence ratios in ion beam machining of complex optical surfaces.