Neutron emission time measurements for ICF targets

The neutron emission time for laser‐driven inertial confinement fusion targets is determined from data recorded with fast neutron and optical detector systems. Two types of neutron detectors are used. Radiation‐induced conductivity devices have a 130‐ps FWHM response and are sensitive to targets with yields greater than 5×1010 DT neutrons. They measure the average neutron emission time with a precision of ±50 ps and are fast enough to measure the neutron production rate within a target core as a function of time. Plastic scintillators coupled to microchannel‐plate photomultiplier tubes have a 1.2‐ns FWHM response and measure the average neutron emission time with a precision of ±75 ps for targets with yields greater than 106 neutrons. Streak cameras record the incident laser power. Optical fiducial signals that are injected into each detector are used to cross time between the detector systems. Measurements made on 1‐mm‐diam spherical targets irradiated with 23 kJ of 0.35‐μm light delivered in a temporally square 1.1‐ns pulse and yielding 1013 neutrons show a burn duration greater than 300 ps and an average neutron emission time of about 850 ps.