The National Ignition Facility neutron time-of-flight system and its initial performance (invited)

Abstract

The National Ignition Facility (NIF) successfully completed its first inertial confinement fusion (ICF) campaign in 2009. A neutron time-of-flight (nTOF) system was part of the nuclear diagnostics used in this campaign. The nTOF technique has been used for decades on ICF facilities to infer the ion temperature of hot deuterium (D(2)) and deuterium-tritium (DT) plasmas based on the temporal Doppler broadening of the primary neutron peak. Once calibrated for absolute neutron sensitivity, the nTOF detectors can be used to measure the yield with high accuracy. The NIF nTOF system is designed to measure neutron yield and ion temperature over 11 orders of magnitude (from 10(8) to 10(19)), neutron bang time in DT implosions between 10(12) and 10(16), and to infer areal density for DT yields above 10(12). During the 2009 campaign, the three most sensitive neutron time-of-flight detectors were installed and used to measure the primary neutron yield and ion temperature from 25 high-convergence implosions using D(2) fuel. The OMEGA yield calibration of these detectors was successfully transferred to the NIF.

Measuring the absolute deuterium–tritium neutron yield using the magnetic recoil spectrometer at OMEGA and the NIF

“…5 At OMEGA, the MRS is complemented by neutron timeof-flight (nTOF) detectors. 6,7,17 The systematic uncertainty of the nTOF yield data is 5% at OMEGA, 18,9,19 while the systematic uncertainty associated with the OMEGA MRS and the NIF MRS yield is 9% and 4.3%, respectively. Figure 2 shows the determined MRS primary yields produced in gasfilled and cryogenic DT implosions, compared to nTOF primary yields, ranging from Y DT ∼2 × 10 12 to 2 × 10 14 .…”

“…Therefore, the yield will indicate if ignition [3][4][5] has occurred in experiments currently being conducted at the NIF. Many yield diagnostic techniques [6][7][8][9] exist, but the harsh ICF environment makes determining the absolute yield, with high accuracy, very challenging. Hence, multiple measurements conducted with different techniques are essential for establishing the fidelity of the resulting yield data.…”

Engineering architecture of the neutron Time-of-Flight (nToF) diagnostic suite at the National Ignition Facility

“…The diagnostic scintillators are all roughly 4.5 meters from Target Chamber Center (TCC) and are housed within lead or other shielding material 9 . used on Deuterium (D2) shots or any other neutron or X-ray generating shot of sufficient energy 11 . The scintillator is located nominally 4.5 m from TCC, with a line-of-sight through the diagnostic well wall at port 64-309.…”

Testing a new NIF neutron time-of-flight detector with a bibenzyl scintillator on OMEGA

“…It provides neutron yield and ion temperature of deuterium (D-D) and deuterium-tritium (DT) ambient and cryogenic implosions. The areal density is measured by nTOF techniques on the NIF using two nTOF20-Spec detectors 1 with an oxygenated xylene scintillator in two lines of sight for D-T yields above 10 12 . The areal density of the compressed core is an important observable in ICF experiments and is used to assess the performance of cryogenic DT experiments.…”