Inferring fusion nuclear burnwidths with low gain photomultiplier impulse response functions

Area of Science:

• Nuclear Fusion
• Plasma Physics
• Diagnostic Techniques

Background:

• Inertial confinement fusion (ICF) implosions achieve high densities and temperatures for brief durations (approx. 100 ps).
• The Gamma Reaction History (GRH) diagnostic measures fusion burn evolution but is limited by photomultiplier tube (PMT) temporal resolution.

Purpose of the Study:

• To investigate the impact of reduced gain settings on PMT impulse response functions (IRFs) and their effect on inferred fusion burnwidths.
• To improve the accuracy of fusion burnwidth measurements in high-yield ICF experiments.

Main Methods:

• Utilized multichannel plate-based PMTs for photon signal amplification in GRH diagnostics.
• Developed and applied an analysis routine to deconvolve the PMT IRF from the measured signal.
• Calibrated PMTs at significantly reduced gain settings (three orders of magnitude lower than nominal).

Main Results:

• PMT IRFs were observed to widen by approximately 15% at reduced gain settings.
• The gain-dependent IRF correction can alter inferred nuclear burnwidths by up to 15%.

Conclusions:

• PMT performance is sensitive to gain settings, necessitating gain-dependent calibration for accurate ICF diagnostics.
• Accounting for the gain-dependent PMT IRF is crucial for precise determination of fusion burn evolution, especially at the National Ignition Facility.