Time-resolved characterization and energy balance analysis of implosion core in shock-ignition experiments at OMEGA

Abstract

Time-resolved temperature and density conditions in the core of shock-ignition implosions have been determined for the first time. The diagnostic method relies on the observation, with a streaked crystal spectrometer, of the signature of an Ar tracer added to the deuterium gas fill. The data analysis confirms the importance of the shell attenuation effect previously noted on time-integrated spectroscopic measurements of thick-wall targets [R. Florido et al., Phys. Rev. E 83, 066408 (2011)]. This effect must be taken into account in order to obtain reliable results. The extracted temperature and density time-histories are representative of the state of the core during the implosion deceleration and burning phases. As a consequence of the ignitor shock launched by the sharp intensity spike at the end of the laser pulse, observed average core electron temperature and mass density reach T $ 1100 eV and q $ 2 g/cm 3 ; then temperature drops to T $ 920 eV while density rises to q $ 3.4 g/cm 3 about the time of peak compression. Compared to 1D hydrodynamic simulations, the experiment shows similar maximum temperatures and smaller densities. Simulations do not reproduce all observations. Differences are noted in the heating dynamics driven by the ignitor shock and the optical depth time-history of the compressed shell. Time-histories of core conditions extracted from spectroscopy show that the implosion can be interpreted as a two-stage polytropic process. Furthermore, an energy balance analysis of implosion core suggests an increase in total energy greater than what 1D hydrodynamic simulations predict. This new methodology can be implemented in other ICF experiments to look into implosion dynamics and help to understand the underlying physics. V C 2014 AIP Publishing LLC. [http://dx.

A cylindrical implosion platform for the study of highly magnetized plasmas at LMJ

“…In particular, we propose using argon or krypton, or a combination of the two. Both elements have been previously used as spectroscopic tracers for ICF-related experiments [23][24][25][26] . While the dopant concentration will decrease the obtainable temperature owing to radiative losses, the choice of dopant will determine the plasma conditions that can be probed using spectroscopic diagnostics.…”

“…This can be observed by means of a spectroscopic tracer. For instance, Ar-doping of ICF implosions is commonly used to extract the density and temperature conditions of imploding cores 24,25,[36][37][38] . This technique exploits two basic properties of the Ar K-shell spectrum emitted from hot and dense plasmas: (1) the strong dependence on density of the Stark-broadened line shapes, and (2) the dependence (through the atomic population kinetics) of the relative intensity distribution of K-shell lines and associated satellite transitions on electron density and temper-ature.…”

Exploring extreme magnetization phenomena in directly-driven imploding cylindrical targets

“…IV and V. Since changes in the hydrodynamics translate into significant variations in the radial profiles of core temperature and density throughout the implosion collapse compared to the unmagnetized case, a way to bring information about the associated physics is by diagnosing the conditions of the imploding core. In this regard, given the success in past experimental campaigns of spherical implosions at OMEGA [42][43][44][45][46] and also in laser-heated cylindrical plasma experiments performed at Z related to the MagLIF preheat stage [47,48], here we propose to rely on time-resolved Ar K-shell spectroscopy. This diagnostic exploits two basic properties of the Ar K-shell spectrum emitted from hot, dense plasmas: (1) the Stark-broadened line shapes strongly depend on density and are relatively insensitive to variations in electron temperature, (2) the relative intensity distribution of K-shell lines and their associated satellites are sensitive to variations in electron temperature and density through the dependence to these parameters on the atomic level population kinetics.…”

Assessment of transient effects on the x-ray spectroscopy of implosion cores at OMEGA

“…Significant advances made in inertial confinement fusion (ICF) research have been enabled by x-ray spectroscopy, thus contributing to a better interpretation of the underlying physics and target performance, and to improvements in the predictive capability of simulation codes [1,2]. Among these achievements are: the measurement of target preheat due to fast electrons by means of Kα emission spectroscopy [3][4][5]; the extraction of spatially averaged electron temperature and density in implosion cores of direct-and indirect-drive implosions by analyzing Starkbroadened K-and L-shell line emissions [6][7][8][9][10][11][12][13][14]; the use of K-shell absorption spectroscopy to infer the conditions of the relatively cold imploding shell that confines the core [15][16][17][18][19]; the simultaneous determination of time-and space-averaged conditions for both core and shell in thick-wall targets by accounting for the attenuation of core x-ray emission in the compressed shell [20]; the time-resolved characterization and energy balance analysis of implosion core in shock-ignition experiments [21]; the quantitative evaluation of mixing of ablator material into the hot-spot of ignition-scale targets from the K-shell emission of mid-Z dopant elements [22][23][24]; the extraction of spatial profiles of temperature and density from the analysis of x-ray spectra and narrow-band images [25][26][27]; the asymmetry measurement of plasma temperature and density spatial profiles from pinhole space-resolved spectra [28]; and the observation of three-dimensional and laser imprinting effects in polar-drive implosions with gated spectrally resolved x-ray imaging [29]. Furthermore, the conditions achieved in laser-driven ICF capsules are similar to those in stellar interior environments, so this progress in ICF research is also likely to benefit applications in astrophysics [30].…”