Measurement of apparent ion temperature using the magnetic recoil spectrometer at the OMEGA laser facility

Abstract

The Magnetic Recoil neutron Spectrometer (MRS) at the OMEGA laser facility has been routinely used to measure deuterium-tritium (DT) yield and areal density in cryogenically layered implosions since 2008. Recently, operation of the OMEGA MRS in higher-resolution mode with a new smaller, thinner (4 cm 2 , 57 µm thick) CD 2 conversion foil has also enabled inference of the apparent DT ion temperature (T ion) from MRS data. MRS-inferred T ion compares well with T ion as measured using neutron time-of-flight spectrometers, which is important as it demonstrates good understanding of the very different systematics associated with the two independent measurements. The MRS resolution in this configuration, ∆E MRS = 0.91 MeV FWHM, is still higher than that required for a high-precision T ion measurement. We show how fielding a smaller foil closer to the target chamber center and redesigning the MRS detector array could bring the resolution to ∆E MRS = 0.45 MeV, reducing the systematic T ion uncertainty by more than a factor of 4.

High yield polar direct drive fusion neutron sources at the National Ignition Facility

“…The neutron bang time is defined as the time of peak neutron production rate, measured from the beginning of the laser pulse request and the burn width τ is the FWHM of an approximate Gaussian fit to the burn history. Measured ion temperatures (T ˇion ) [60] are taken from the width of the neutron spectrum [61] measured by four neutron timeof-flight detectors with four unique target view angles [62,63]. When calculating a predicted yield from measured quantities by equation ( 2), the ion temperature T ion is estimated to be the minimum of the measured ion temperatures.…”

Implementation of the foil-on-hohlraum technique for the magnetic recoil spectrometer for time-resolved neutron measurements at the National Ignition Facility

“…The success of this concept has also prompted exploring modification of the OMEGA MRS 21 to allow for a closer, smaller foil to provide an independent T ion measurement on implosions of cryogenically layered targets. 22 sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.…”