Average neutron time-of-flight instrument response function inferred from single D-T neutron events within a plastic scintillator

Neutron time of flight (nToF) detectors for inertial fusion experiments

Neutrons generated in Inertial Confinement Fusion (ICF) experiments provide valuable information to interpret the conditions reached in the plasma. The neutron time-of-flight (nToF) technique is well suited for measuring the neutron energy spectrum due to the short time (100 ps) over which neutrons are typically emitted in ICF experiments. By locating detectors 10s of meters from the source, the neutron energy spectrum can be measured to high precision. We present a contextual review of the current state of the art in nToF detectors at ICF facilities in the United States, outlining the physics that can be measured, the detector technologies currently deployed and analysis techniques used.

Neutron time-of-flight detectors (nTOF) used at Sandia's Z-Machine

Neutron time-of-flight (nTOF) detectors have been used on Sandia National Laboratories' Z-Machine for inertial confinement fusion and magnetized liner fusion experiments to infer physics parameters including the apparent fuel-ion temperature, neutron yield, the magnetic-radius product (BR), and the liner rho-r. Single-paddle, dual-paddle, and co-axial scintillation nTOF detectors are used in axial lines-of-sight (LOS) and LOS that are 12° from the midplane. Detector fabrication, characterization, and calibration are discussed.

Gated liquid scintillator detector for neutron time of flight measurements in a gas-puff Z-pinch experiment

Detection of secondary D(t, n)⁴He neutrons produced when thin argon or krypton gas shells implode on a deuterium gas target is a very challenging task because the secondary neutron yield is a small fraction of the primary neutron yield and because the implosion is often accompanied by an intense hard X-ray burst. We built a large volume neutron time of flight (nTOF) detector using liquid scintillator (xylene solvent with small quantities of wavelength shifting PPO + bis-MSB fluors) in an attempt to increase the detection probability for secondary neutrons in our staged Z-pinch experiments at the 1 MA Zebra pulsed-power generator. Two fast, gated microchannel plate photomultiplier tubes detect the light created in 21 liters of liquid. The hard X-rays were successfully suppressed in the recorded nTOF traces, but we found no evidence of secondary neutrons. The signal quality from the primary D(d, n)³He neutrons was higher compared to the signal quality from a plastic scintillator nTOF, thus providing a more reliable estimate of the deuterium ion temperature at the pinch stagnation time. Cross-calibration with a silver activation detector enables standalone neutron yield measurement.