Ion Temperature Measured with Radiation Hardened CVD Diamond Detector and 14-MeV ICF Fusion Neutrons using Short Time-of-Flight Paths

Abstract

Summary form only given. Traditionally, inertial confinement fusion (ICF) ion temperature has been measured using neutron time-of-flight techniques. Long flight paths and collimation are used to allow the neutron temporal distribution to broaden relative to the detector response and to eliminate signals from unwanted X-rays and scattered neutrons. Radiation detectors based on chemical vapor deposition (CVD) diamond are fast and radiation hard. Their low atomic number makes them relatively insensitive to X-rays and gamma-rays when compared with other solid-state detectors. Additional radiation hardening further increases the detector speed and reduces its sensitivity by introducing trapping sites that reduce carrier lifetime. A 10-mm diameter, 1-mm thick CVD diamond detector was hardened with a fluence of 1016 neut/cm2, and then used to measure ion temperatures with very short flight paths and no radiation shielding or collimation. Successful temperature measurements at short distances require careful characterization of and correction for the detector system prompt response. Sensitivity and time response for the detector system consisting of the CVD diamond detector, a long coaxial cable, and a 3-GHz transient recorder were measured with the detector 10 cm from targets emitting ~1011 14-MeV fusion neutrons. Detector system temporal response was less than 500 ps (FWHM). Temperatures were recorded for deuterium-tritium (DT) filled capsules that were irradiated at the OMEGA laser facility and produced ~1013 neutrons. The measurements were made using the identical system configuration used to measure the system response, but with the detector placed between 1.5 and 3.5 meters from the target. Ion temperatures unfolded from CVD diamond detector signals agree to better than 5% with temperatures measured with OMEGA's standard 12-meter scintillator-PMT based neutron time-of-flight system (nTOF).