Engineering topics

Glebov, V. Yu.

Publications and source records attributed to Glebov, V. Yu..

63 records · Page 4

DOE OSTI2018

Development of an inertial confinement fusion platform to study charged particle-producing nuclear reactions relevant to nuclear astrophysics

This paper describes the development of a platform to study astrophysically relevant nuclear reactions using inertial-confinement fusion implosions on the OMEGA and NIF laser facilities, with a particular focus on optimizing the implosions to study charged-particle-producing reactions. Primary requirements on the platform are high yield, for high statistics in the fusion product measurements, combined with low areal density, to allow the charged fusion products to escape. This is optimally achieved with direct-drive exploding pusher implosions using thin-glass-shell capsules. Mitigation strategies to eliminate a possible target sheath potential which would accelerate the emitted ions are discussed. The potential impact of kinetic effects on the implosions is also considered. The platform is initially employed to study the complementary T(t,2n)??, T(3He,np)?? and 3He(3He,2p)?? reactions. Proof-of-principle results from the first experiments demonstrating the ability to accurately measure the energy and yields of charged particles are presented. Lessons learned from these experiments will be used in studies of other reactions. The goals are to explore thermonuclear reaction rates and fundamental nuclear physics in stellar-like plasma environments, and to push this new frontier of nuclear astrophysics into unique regimes not reachable through existing platforms, with thermal ion velocity distributions, plasma screening and low reactant energies.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2018

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

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, $ΔE_{MRS}$ = 0.91 MeV FWHM, is still higher than that required for a high-precision T ion measurement. We show herein how fielding a smaller foil closer to the target chamber center and redesigning the MRS detector array could bring the resolution to $ΔE_{MRS}$ = 0.45 MeV, reducing the systematic T ion uncertainty by more than a factor of 4.

47 OTHER INSTRUMENTATION↗

DOE OSTI2018

Calibration of a neutron time-of-flight detector with a rapid instrument response function for measurements of bulk fluid motion on OMEGA

A newly developed neutron time-of-flight (nTOF) diagnostic with a fast instrument response function has been fielded on the OMEGA laser in a highly collimated line of sight. In this study, by using a small plastic scintillator volume, the detector provides a narrow instrument response of 1.7 ns full width at half maximum while maintaining a large signal-to-noise ratio for neutron yields between 10 10 and 10 14 . The OMEGA hardware timing system is used along with an optical fiducial to provide an absolute nTOF measurement to an accuracy of ~56 ps. The fast instrument response enables the accurate measurement of the primary deuterium-tritium neutron peak shape, while the optical fiducial allows for an absolute neutron energy measurement. The new detector measures the neutron mean energy with an uncertainty of ~7 keV, corresponding to a hot-spot velocity projection uncertainty of ~12 km/s. Finally, evidence of bulk fluid motion in cryogenic targets is presented with measurements of the neutron energy spectrum.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2018

A novel method to recover DD fusion proton CR-39 data corrupted by fast ablator ions at OMEGA and the National Ignition Facility

CR-39 detectors are used routinely in inertial confinement fusion (ICF) experiments as a part of nuclear diagnostics. CR-39 is filtered to stop fast ablator ions which have been accelerated from an ICF implosion due to electric fields caused by laser-plasma interactions. In some experiments, the filtering is insufficient to block these ions and the fusion-product signal tracks are lost in the large background of accelerated ion tracks. A technique for recovering signal in these scenarios has been developed, tested, and implemented successfully. The technique involves removing material from the surface of the CR-39 to a depth beyond the endpoint of the ablator ion tracks. The technique preserves signal magnitude (yield) as well as structure in radiograph images. The technique is effective when signal particle range is at least 10 um deeper than the necessary bulk material removal.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2018

Experimental evidence of a variant neutron spectrum from the T(T,2n)alpha reaction at center-of-mass energies in the range of 16-50 keV

Full calculations of six-nucleon reactions with a three-body final state have been elusive and a long-standing issue. We present neutron spectra from the T(t,2n)alpha (TT) reaction measured in inertial confinement fusion experiments at the OMEGA laser facility at ion temperatures from 4 to 18 keV, corresponding to center-of-mass energies (Ec.m.) from 16 to 50 keV. A clear difference in the shape of the TT-neutron spectrum is observed between the two Ec.m., with the 5He ground state resonant peak at 8.6 MeV being significantly stronger at the higher than at the lower energy. The data provides the first conclusive evidence of a variant TT-neutron spectrum in this Ec.m. range. In contrast to earlier available data, this indicates a reaction mechanism that must involve resonances and/or higher angular momenta than L=0. This finding provides an important experimental constraint on theoretical efforts that explore this and complementary six-nucleon systems, such as the solar 3He(3He,2p)alpha reaction.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2018

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

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[sup]2, 57-um thick) CD2 conversion foil has also enabled inference of the apparent DT ion temperature (Tion) from MRS data. MRS-inferred Tion compares well with T[sub]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, deltaEMRS=0.91 MeV FWHM, is still higher than required for a high-precision Tion measurement. We show how fielding a smaller foil closer to target chamber center and redesigning the MRS detector array could bring the resolution to deltaEMRS=0.45 MeV, reducing the systematic Tion uncertainty by more than a factor of 4.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2018

Experimental Evidence of a Variant Neutron Spectrum from the T ( t , 2 n ) α Reaction at Center-of-Mass Energies in the Range of 16–50 keV

Full calculations of six-nucleon reactions with a three-body final state have been elusive and a long-standing issue. We present neutron spectra from the T(t,2n)α (TT) reaction measured in inertial confinement fusion experiments at the OMEGA laser facility at ion temperatures from 4 to 18 keV, corresponding to center-of-mass energies (E c.m. ) from 16 to 50 keV. A clear difference in the shape of the TT-neutron spectrum is observed between the two E c.m. , with the 5 He ground state resonant peak at 8.6 MeV being significantly stronger at the higher than at the lower energy. The data provide the first conclusive evidence of a variant TT-neutron spectrum in this E c.m. range. In contrast to earlier available data, this indicates a reaction mechanism that must involve resonances and/or higher angular momenta than L = 0. Furthermore, this finding provides an important experimental constraint on theoretical efforts that explore this and complementary six-nucleon systems, such as the solar 3 He( 3 He,2p)α reaction.

42 ENGINEERING↗

DOE OSTI2018

Diffusion-dominated mixing in moderate convergence implosions

High-$Z$ material mixed into the fuel degrades inertial fusion implosions and can prevent ignition. Mix is often assumed to be dominated by hydrodynamic instabilities, but in this paper we report Omega data, using shells with ${\sim}150\mathrm{nm}$ deuterated layers to gain unprecedented resolution, which give strong evidence that the dominant mix mechanism is diffusion for these moderate temperature (${\lesssim}6$ keV) and convergence (${\sim}12$) implosions. Finally, small-scale instability-driven or turbulent mix is negligible.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2018

The control of hot-electron preheat in shock-ignition implosions

In the shock-ignition scheme for inertial confinement fusion, hot electrons resulting from laser–plasma instabilities can play a major role during the late stage of the implosion. This article presents the results of an experiment performed on OMEGA in the so-called “40 + 20 configuration.” Using a recent calibration of the time-resolved hard x-ray diagnostic, the hot electrons’ temperature and total energy were measured. One-dimensional radiation–hydrodynamic simulations have been performed that include hot electrons and are in agreement with the measured neutron-rate–averaged areal density. For an early spike launch, both experiment and simulations show the detrimental effect of hot electrons on areal density and neutron yield. Lastly, for a later spike launch, this effect is minimized because of a higher compression of the target.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗