Identification of in-target proton energy distribution and proton-boron fusion reaction using radioactive byproduct detection*

The p-¹¹B fusion reaction (¹¹B(p, 2α)⁴He) is attracting renewed attention for IFE due to its aneutronic nature and use of room temperature solid fuel that is made of non-radioactive isotope. In the laser-driven approach, protons are accelerated by high-intensity laser irradiation of hydrogen-boron fuel to initiate the p-¹¹B reaction; the p-¹¹B avalanche reaction is theoretically discussed, and its experimental verification is ongoing. Direct observation of p-¹¹B reactions inside the fuel is challenging due to the significant deceleration of alpha particles (reaction products) in the fuel. Our approach utilizes a relativistic intensity LFEX laser to drive the primary p-¹¹B reaction in a hydrogen-boron fuel, along with the auxiliary reactions ¹⁰B(p, α)⁷Be and ¹¹B(p, n)¹¹C. The byproducts of ⁷Be and ¹¹C were captured by the collecter after the fuel explosion, and their quantities are measured to infer proton energy distribution in the fuel and the number of p-11B reactions by using the difference in cross-sections of the auxiliary reactions. The non-thermal p-¹¹B fusion reaction is discussed by comparing these values with numerical simulations.