Fuel areal density,

, is a fundamental quantity for ICF implosions. For current and future targets, areal densities are large enough that a variety of neutron based diagnostic techniques can be used to determine fuel (pR). These include measurements based on the secondary production of DT neutrons from initially pure deuterium fuel and, for higher (pR) values, techniques utilizing high energy tertiary neutrons or lower energy scattered neutrons. This paper describes these techniques and gives an overview of the current experimental status.

The first demonstration of a fuel density-radius product measurement using secondary nuclear fusion reactions is presented. This technique involves using neutrons and protons generated by DT {T(d,n)α} and D3He {3He(d,p)α} fusion reactions, respectively, in a pure deuterium fuel.

Ablative implosions of glass microballoon targets driven by twelve 0.53-jum laser beams have been studied by use of secondary DT and D 3 He fusion reactions in an initially pure deuterium fuel. The tritons and 3 He nuclei are products of primary DD fusion reactions. Comparisons with results of a hydrodynamic simulation indicate that collisional energy loss for these primary fusion products is strongly enhanced by fuel-pusher mixing taking place during the implosion.PACS numbers: 52.50. Jm, 52.70.Nc A current topic of interest in studies of high-density compression for inertial-confinement fusion is the stability of shell targets during implosions. Nonuniformity of laser irradiation and/or hydrodynamic instabilities may seriously limit the compressed fuel density by fuel-pusher mixing or, in a moderate case, nonuniform compression. Some direct evidence of fuel shape deformation has been observed by a-particle imaging. l However, to date no experimental study of fuel-pusher mixing has been carried out. In this Letter we present results of chargedparticle energy-loss measurements in the compressed fuel by use of secondary nuclear fusion reactions. 2 " 8 This method permits a study of fuel-pusher mixing in dense, compressed fuel. 7 Simultaneous yield measurements were carried out for primary DD neutrons, secondary DT neutrons, and secondary D 3 He protons generated in an initially pure deuterium fuel. The tritons and 3 He nuclei are first generated by primary DD reactions. Throughout this work, it is assumed that the yields of DD neutrons and DD protons are the same. After the tritons and 3 He nuclei suffer significant energy loss in the fuel, the DT cross section increases from the value at the triton birth energy (1.01 MeV) to a peak value at 0.17 MeV. In contrast, the D 3 He cross section decreases (except for a small initial increase) with decreasing 3 He energy from the value at the 3 He birth energy (0.82 MeV). Therefore, the yield ratio of the secondary D 3 He protons to the secondary DT neutrons YiplYin becomes a direct function of the energies of tritons and 3 He nuclei after their escape from the fuel. This ratio is only weakly dependent on fuel temperature and density. The calculated behavior of Yi p /Y2 n as a function of the escaping triton energy 8 Ej is shown in Fig. 1. For this calculation it was assumed that primary fusion products are uniformly produced in the spherical fuel with uniform temperature and density profiles. Since the escaping tritons have a broad energy distribution in this model, a characteristic triton energy is calculated for tritons traversing one fuel radius. For the energy-loss calculation, we used a standard expression for the charged-particle stopping power in a fully ionized plasma. 9 With the triton energy known from this ratio, the fuel areal density and the electron temperature can be determined from the yield ratio of the secondary DT neutrons to the primary DD neutrons Y2 n /Y\ n . This is shown in Fig. 2. For a given escaping triton energy, the yield ratio Y2 n /Y\ n ...

Thermonuclear burn time and burn duration in ablatively driven high-aspect-ratio targets have been measured. While the observed burn times were in agreement with results of a one-dimensional hydrodynamic simulation, the observed burn durations were excessively long.

Radiochemical measurements have been developed for the diagnostics of laser-driven implosion plasmas. The excellent calibration for neutron-yield measurement has been done using β-γ coincidence technique. The multiactivable tracer method has been examined for measuring the pusher areal density by means of a high-purity germanium detector. The first experimental success of the secondary nuclear fusion reaction method is also demonstrated for the direct measurement of the fuel ρR.