Neutron temporal diagnostic for high-yield deuterium–tritium cryogenic implosions on OMEGA

Abstract

A next-generation neutron temporal diagnostic (NTD) capable of recording high-quality data for the highest anticipated yield cryogenic deuterium-tritium (DT) implosion experiments was recently installed at the Omega Laser Facility. A high-quality measurement of the neutron production width is required to determine the hot-spot pressure achieved in inertial confinement fusion experiments-a key metric in assessing the quality of these implosions. The design of this NTD is based on a fast-rise-time plastic scintillator, which converts the neutron kinetic energy to 350- to 450-nm-wavelength light. The light from the scintillator inside the nose-cone assembly is relayed ∼16 m to a streak camera in a well-shielded location. An ∼200× reduction in neutron background was observed during the first high-yield DT cryogenic implosions compared to the current NTD installation on OMEGA. An impulse response of ∼40 ± 10 ps was measured in a dedicated experiment using hard x-rays from a planar target irradiated with a 10-ps short pulse from the OMEGA EP laser. The measured instrument response includes contributions from the scintillator rise time, optical relay, and streak camera.

Demonstration of Fuel Hot-Spot Pressure in Excess of 50 Gbar for Direct-Drive, Layered Deuterium-Tritium Implosions on OMEGA

“…This Letter demonstrates that a record hot-spot pressure P hs ¼ 56 AE 7 Gbar was inferred for direct-drive ICF cryogenic, layered deuterium-tritium implosions on OMEGA using a suite of diagnostics including an x-ray imager having a 6-μm spatial resolution and 30-ps temporal resolution [12] and a neutron rate detector with a 40-ps impulse response function [13]. This is nearly half of the ignition-threshold P hs ¼ 120-150 Gbar for direct-drive ICF scaled to NIF energies.…”

“…LILAC includes a nonlocal electron thermal conduction model [21], a CBET model [16], and a new CH first-principles equation of state [22]. The 1D simulations match the experimental observables throughout the implosion, including the scattered laser light energy and spectrum [23], shell trajectories [24], and neutron bang time [13].…”

“…[28], and the minimum hT i i n value is taken to minimize the effects of residual kinetic energy in the hot spot [29]. The time of peak neutron production and Δt burn were recorded with a measurement uncertainty of AE25 ps and AE10%, respectively [13].…”

Impact of imposed mode 2 laser drive asymmetry on inertial confinement fusion implosions

“…Bang times and burn histories for these experiments were measured using the OMEGA neutron temporal diagnostic (NTD). 59 Two separate and independent NTDs were used for the bang time measurement, one in OMEGA port H5 and one in port P11. The absolute uncertainty in each measurement is 650 ps.…”

“…To allow for direct comparison between measured and simulated burn histories, the simulated burn history must be broadened to account for the broadening effects impacting the measured data. These effects include 59 the impulse response of the NTD (40 6 10 ps FWHM), thermal broadening of the DT neutron spectrum, and the finite neutron transit time through the scintillator (20 ps FWHM). Measured burn histories are contrasted to Chimera-simulated burn histories in Fig.…”