First measurement of the ¹⁰B(α,n)¹³N reaction in an ICF implosion at NIF: Initial steps toward the development of a radiochemistry mix diagnostic

During the deceleration phase of an ICF implosion, instabilities growth can lead to mixing between the ablator material and the thermonuclear fuel. Mixing is undesirable, as it reduces the performance of the capsule. One method to diagnose mixing is to study the x-ray emission from the burning fuel. However, double shell and pushered single shell designs for the National Ignition Facility (NIF) render this technique ineffective because they involve a high-Z shell surrounding the fuel that is opaque to x-rays. A possible alternative mix diagnostic involves measuring the interaction of alpha particles, produced in the D+T→α+n reaction, with the ablator material. The Radiochemical Analysis of Gaseous Samples (RAGS) facility at NIF allows for quantitative measurements of α-induced reactions.

We present the first measurement of the ¹⁰B(α,n)¹³N reaction in an ICF implosion, using a polar-direct-drive exploding pusher shot at NIF as a first step in the development of a radiochemistry mix diagnostics. Radiation-hydrodynamics calculations were performed in 1D to optimize the capsule design, and a charged-particle transport post-processor was developed to study α-induced reactions on the ablator material. Results indicate a large ¹³N production, measurable by RAGS. The target N201115-001 was successfully fielded on the NIF, and nitrogen from the ¹⁰B(α,n)¹³N reaction was indeed measured. The discussion of the experimental results is complicated by the shape asymmetry of the implosion, that requires further investigation beyond the initial 1D modeling. However, results are encouraging and suggest that radiochemistry can provide a practical diagnostic for NIF capsule dynamics.