Flat field anomalies in an x-ray charge coupled device camera measured using a Manson x-ray source

Area of Science:

• Nuclear Fusion Diagnostics
• X-ray Imaging Technology
• Semiconductor Device Characterization

Background:

• The Static X-ray Imager (SXI) is crucial for measuring x-ray positions from laser-target interactions at the National Ignition Facility (NIF).
• Accurate laser aiming, determined by SXI data, is essential for NIF's operational success.
• SXI utilizes large-format, x-ray-sensitive charge-coupled device (CCD) chips.

Purpose of the Study:

• To characterize and calibrate the SXI diagnostic.
• To assess the performance and identify potential errors of the CCD imagers.
• To evaluate the suitability of a Manson x-ray source for CCD characterization.

Main Methods:

• Utilized a multianode Manson x-ray source (up to 10 kV, 10 W) for imager calibration.
• Employed filtered x-ray beams with a spectral resolution (E/ΔE) of approximately 10.
• Measured x-ray beam intensity with a photodiode (accuracy <1% up to Si K edge, <5% higher).
• Assessed spectral efficiency across ten energy bands (930–8470 eV).

Main Results:

• Observed significant energy-dependent pixel sensitivity variations across the CCD, most pronounced at 8470 eV.
• Noted a decrease in maximum contrast below 4 keV, with geometric patterns remaining consistent.
• Identified debris, damage, and surface defects on the CCD chips.
• Demonstrated the Manson source's capability to reveal imaging errors distinct from visible CCDs.

Conclusions:

• The Manson x-ray source is a valuable tool for characterizing SXI CCD imagers.
• Energy-dependent sensitivity variations and physical defects impact SXI performance.
• Understanding these errors is vital for optimizing NIF laser alignment and experimental outcomes.