Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session GI3: Direct and Indirect Drive ICF |
Hide Abstracts |
Chair: Chikang Li, Massachusetts Institute of Technology Room: Plaza F |
Tuesday, November 12, 2013 9:30AM - 10:00AM |
GI3.00001: Demonstrating Ignition Hydrodynamic Equivalence in Cryogenic DT Implosions on OMEGA Invited Speaker: V.N. Goncharov Demonstrating ignition hydrodynamic equivalence is one of the primary goals of direct-drive cryogenic implosions on OMEGA. It requires the shell reaching implosion velocities \textgreater\ 3.5 $\times $ 10$^{7}$ cm/s while maintaining the fuel adiabat below 3 and keeping the shell from breaking up as a result of the Rayleigh--Taylor instability. The cryogenic targets used for implosions on OMEGA are 860-$\mu $m-outer-diam CD shells filled with DT fuel. The shell thickness varies between 5 and 12 $\mu $m, and DT ice thickness between 40 and 65 $\mu $m. Experimental results demonstrate, however, that neutron-averaged areal density in excess of 80{\%} and yields above 25{\%} of 1-D predicted values are obtained if the fuel adiabat \textgreater\ 3.5 and shell in-flight aspect ratio (IFAR) is below 22. As the IFAR exceeds this value, the shell breaks up and the areal density and yield are reduced. Identifying the main source of shell nonuniformities that lead to performance degradation in low-adiabat designs is one of the main efforts of OMEGA cryogenic campaign. This talk will summarize progress in cryogenic target implosions over the last year and review the effect of target debris, early-time laser shinethrough, and fuel-pusher roughness on target performance. In addition, the effect of cross-beam energy transfer (a major source of hydroefficiency degradation in a direct-drive implosions) and its mitigation strategies (including high-$Z$ ablator layers, beam zooming, and laser wavelength shifts) will be discussed. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Tuesday, November 12, 2013 10:00AM - 10:30AM |
GI3.00002: Theory of Hydro-Equivalent Ignition for Inertial Fusion and Its Applications to OMEGA and the NIF Invited Speaker: R. Nora The theory of ignition for inertial confinement fusion (ICF) capsules\footnote{ R. Betti\textit{ et al.}, Phys. Plasmas \textbf{17}, 058102 (2010).} is applied to current cryogenic implosion experiments on the National Ignition Facility (NIF) and Omega Laser Facility. When applied to the NIF indirect-drive experiments at 1.4 to 1.6 MJ of laser energies, the Lawson product of the pressure and confinement time $P\tau $ is about 10 to 18 atm s---about half of that required for ignition at $\sim $5-keV temperature. For the latest OMEGA direct-drive--implosion experiments, $P\tau $ is about 3 atm s. The Lawson parameter $P\tau $ is computed in three different ways: (1) Using the theory of Betti \textit{et al.};\footnote{Betti, Phys. Plasmas \textbf{17} 058102} (2) the measured neutron yield and x-ray images of the imploded capsules; and (3) direct 2-D simulations that reproduce all the measured stagnation quantities (such as ion temperature, areal density, x-ray images, burn history, and neutron yield). In this paper, the theory of hydrodynamic similarity is developed in both 1-D and 2-D, and tested using multimode hydrodynamic simulations with code \textit{DRACO}\footnote{P. B. Radha\textit{ et al.}, Phys. Plasmas \textbf{12}, 032702 (2005).} of hydro-equivalent implosions (implosions with the same implosion velocity, adiabat, and laser intensity). The theory is used to scale the performance of OMEGA implosions to the NIF energies and determine the requirements for hydro-equivalent ignition. Hydro-equivalent ignition on OMEGA is represented by a cryogenic implosion that would scale to ignition on the NIF at 1.8 MJ of symmetric laser energy. It is found that a reasonable combination of neutron yield and areal density for OMEGA hydro-equivalent ignition is $\sim $4 $\times $ 10$^{13}$ and $\sim $0.3 g/cm$^2$. This performance has not yet been achieved on OMEGA. This work is supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Tuesday, November 12, 2013 10:30AM - 11:00AM |
GI3.00003: Measurement of Two-Plasmon--Decay Dependence on Plasma Density Scale Length Invited Speaker: D. Haberberger An accurate understanding of the plasma scale-length ($L_{\mathrm{q}}$) conditions near quarter-critical density is important in quantifying the hot electrons generated by the two-plasmon--decay (TPD) instability in long-scale-length plasmas. A novel target platform was developed to vary the density scale length and an innovative diagnostic was implemented to measure the density profiles above 10$^{21}$ cm$^{-3}$ where TPD is expected to have the largest growth. A series of experiments was performed using the four UV (351-nm) beams on OMEGA~EP that varied the $L_{\mathrm{q}}$ by changing the radius of curvature of the target while maintaining a constant $I_{\mathrm{q}}$/$T_{\mathrm{q}}$. The fraction of laser energy converted to hot electrons ($f_{\mathrm{hot}})$ was observed to increase rapidly from 0.005{\%} to 1{\%} by increasing the plasma scale length from 130 $\mu $m to 300 $\mu $m, corresponding to target diameters of 0.4 mm to 8 mm. A new diagnostic was developed based on refractometry using angular spectral filters to overcome the large phase accumulation in standard interferometric techniques. The angular filter refractometer measures the refraction angles of a 10-ps, 263-nm probe laser after propagating through the plasma. An angular spectral filter is used in the Fourier plane of the probe beam, where the refractive angles of the rays are mapped to space. The edges of the filter are present in the image plane and represent contours of constant refraction angle. These contours are used to infer the phase of the probe beam, which are used to calculate the plasma density profile. In long-scale-length plasmas, the diagnostic currently measures plasma densities from $\sim $10$^{19}$ cm$^{-3}$ to $\sim $2 $\times $ 10$^{21}$ cm$^{-3}$. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. \\[4pt] In collaboration with D. H. Edgell, S. X. Hu, S. Ivancic, R. Boni, C. Dorrer, and D. H. Froula (Laboratory for Laser Energetics, U. of Rochester). [Preview Abstract] |
Tuesday, November 12, 2013 11:00AM - 11:30AM |
GI3.00004: Methods of Optimal Control of Laser-Plasma Instabilities Using Spike Trains of Uneven Duration and Delay (STUD Pulses) Invited Speaker: Bedros Afeyan We have recently introduced and extensively studied a new adaptive method of LPI control [1-5]. It promises to extend the effectiveness of laser as inertial fusion drivers by allowing active control of stimulated Raman and Brillouin scattering and crossed beam energy transfer. It breaks multi-nanosecond pulses into a series of picosecond (ps) time scale spikes with comparable gaps in between. The height and width of each spike as well as their separations are optimization parameters. In addition, the spatial speckle patterns are changed after a number of successive spikes as needed (from every spike to never). The combination of these parameters allows the taming of parametric instabilities to conform to any desired reduced reflectivity profile, within the bounds of the performance limitations of the lasers. Instead of pulse shaping on hydrodynamical time scales, far faster (from 1ps to 10 ps) modulations of the laser profile will be ~needed to implement the STUD pulse program for full LPI control. We will show theoretical and computational evidence for the effectiveness of the STUD pulse program to control LPI. The physics of why STUD pulses work and how optimization can be implemented efficiently using statistical nonlinear optical models and techniques will be explained. We will also discuss a novel diagnostic system employing STUD pulses that will allow the boosted measurement of velocity distribution function slopes on a ps time scale in the small crossing volume of a pump and a probe beam. Various regimes from weak to strong coupling and weak to strong damping will be treated. Novel pulse modulation schemes and diagnostic tools based on time-lenses used in both microscope and telescope modes will be suggested for the execution of the STUD pule program.\\[4pt] [1] B. Afeyan, http://meetings.aps.org/link/BAPS.2009.DPP.TO5.7, www.lle.rochester.edu/media/publications/ \\[0pt] [2] B. Afeyan and S. Huller, Europ. Phys. J. Web of Conferences (in press, 2013); also arXiv:1210.4462v1 (2012) \\[0pt] [3] S. Huller and B., Europ. Phys. J. Web of Conferences (in press, 2013); also also arXiv:1210.4480v1 (2012) \\[0pt] [4] B. Afeyan and S. Huller, Submitted to Phys. Rev. Lett., 2013 and arXiv1304.3960. \\[0pt] [5] B. Albright, L. Yin and B. Afeyan. Submitted to Phys. Rev. Lett. 2013 and arXiv1304.4814. [Preview Abstract] |
Tuesday, November 12, 2013 11:30AM - 12:00PM |
GI3.00005: Quantitative studies of kinetic effects in direct- and indirect-drive Inertial Confinement Fusion implosions Invited Speaker: Hans Rinderknecht A comprehensive set of experiments using shock-driven implosions has been conducted to quantitatively study kinetic effects by exploring deviations from hydrodynamic behavior in plasmas relevant to inertial confinement fusion (ICF). Two types of targets were imploded at OMEGA to create $\sim$10 keV, $\sim$10$^{22}$ cm$^{-3}$ plasmas with conditions comparable to the incipient hotspot in ignition designs: thin-glass targets filled with mixtures of D$_{2}$ and $^{3}$He gas; and thin deuterated-plastic shells filled with $^{3}$He. In the thin-glass experiments, the gas pressure was varied from 1 to 25 atm to scan the ion-mean-free path in the plasma at shock burn. The observed nuclear yields and temperatures deviated more strongly from hydrodynamic predictions as the ion-mean-free path increased to the order of the plasma size. This result provides the first direct experimental evidence how kinetic effects impact yields and ion temperature. The ratio of D to $^{3}$He was also varied while maintaining the fuel mass density. As the D fraction was reduced, the DD and D$^{3}$He fusion products displayed an anomalous yield reduction. Separation of the D and $^{3}$He ion species across the strong (Mach $\sim$10) shock-front will be discussed as the likely cause of this result. Finally, thin-CD shells filled with $^{3}$He produced significantly more D$^{3}$He-protons when imploded than is explained by hydrodynamic mix models. This result suggests a kinetic form of mix dominates at the strongly-shocked shell-gas interface.\\[4pt] This work was performed in collaboration with C. Li, M. Rosenberg, A. Zylstra, H. Sio, M. Gatu Johnson, F. S\'{e}guin, J. Frenje, and R. Petrasso (MIT), V. Glebov, C. Stoeckl, J. Delettrez, and C. Sangster (LLE), J. Pino, P. Amendt, C. Bellei, and S. Wilks (LLNL), G. Kagan, N. Hoffmann and K. Molvig (LANL), and A. Nikroo (GA) and was supported in part by the NLUF, FSC/UR, U.S. DOE, LLNL and LLE. [Preview Abstract] |
Tuesday, November 12, 2013 12:00PM - 12:30PM |
GI3.00006: Multi-species and kinetic effects in ICF plasmas Invited Speaker: Claudio Bellei Traditionally, numerical codes that are used in the ICF community treat the plasma as an average-species fluid, neglecting the presence of multiple ion species, self-consistent electric (and magnetic) fields and kinetic effects. As compute power increases, multi-species, collisional particle-in-cell simulations of dense fusion plasmas are now becoming feasible. These simulations reveal rich and complex physics that has so far been mostly unexplored in the context of ICF implosions. This talk will present highly detailed simulations that push the boundary of conventional ICF modeling. In particular, we will show how gradients in pressure, temperature and electrostatic potential can lead to appreciable ion species separation as the ion-ion mean free paths increase during convergence of the spherical shock in the inner gas of an ICF capsule [1,2]. The effects of species separation on fusion yield in ICF targets will be discussed. In addition, a kinetic description of the shock physics reveals characteristics of a weakly collisional system, including ion diffusion across the shock and reflection of the upstream ions at the shock front [3]. When these (strong) shocks propagate across an interface that separates different materials (such as an ablator-gas interface), they can push a fraction of the ions from the ablator into the gas, enhancing mix. How this mix influences neutron yield will be examined.\\[4pt] [1] P. A. Amendt, S. C. Wilks, C. Bellei, et al., Physics of Plasmas 18, 056308 (2011);\\[0pt] [2] C. Bellei, P. A. Amendt, S. C. Wilks, et al., Physics of Plasmas 20, 012701 (2013);\\[0pt] [3] C. Bellei, P. A. Amendt, S. C. Wilks, et al., Physics of Plasmas 20, 044702 (2013). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700