Bulletin of the American Physical Society
2005 47th Annual Meeting of the Division of Plasma Physics
Monday–Friday, October 24–28, 2005; Denver, Colorado
Session LZ1: Mini-conference on Fast Ignition Status and Prospects II |
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Chair: Richard Freeman, Ohio State University Room: Adam's Mark Hotel Plaza Ballroom D |
Wednesday, October 26, 2005 2:00PM - 2:40PM |
LZ1.00001: New science opportunities in multi-kJ, petawatt laser facilities relevant to fast ignition Peter Norreys The near completion of second generation multi-kJ lasers around the world opens a host of new and interesting opportunities to investigate high intensity laser-plasma interaction physics phenomena that are directly relevant to fast ignition. I will review the facilities now under construction in the United States, Japan and Europe together some of the most interesting proposed physics investigations that they are designed to address. The latter will be illustrated by results obtained from recent experiments that have been performed on the Vulcan petawatt laser facility. They include: the study of the different plasma instabilities that affect energy transport in high temperature, dense plasmas, particularly the two-stream and the Weibel instabilities; new diagnostic techniques to measure strong magnetic fields that are generated during the interaction; the production of high brightness X-ray harmonic and radiation backlighting sources; the generation of relativistic particles in ultra-intense laser-produced plasmas and their potential diagnostic applications. [Preview Abstract] |
Wednesday, October 26, 2005 2:40PM - 3:00PM |
LZ1.00002: Fast ignition research project; FIREX at ILE, Osaka Kunioki Mima The construction of the LFEX which is a heating laser of 10kJ/ 10ps/1.06 $\mu$ m will be completed before the end of 2007. The expected rise time of the short pulse LFEX is less than 1ps and the focus diameter is smaller than 30 $\mu$ m. As the front end of the laser, OPCPA is introduced to improve the contrast ratio to less than 10$^{-8}$ . For pulse compression, segmented dielectric gratings will be used. The R\&D for the coherent combining of the pulse compressed segmented beam has started. After the completion of LFEX, we will start the integrated experiment in 2008. Cone shell target implosion is studied by experiments and simulations for the FIREX-I target design. The detail of implosion hydrodynamics has been explored, and possibility of high density implosion was demonstrated. By the heating simulation, we found that the cone top is heated up to a few 100 keV by electrostatic and electromagnetic collective interactions between relativistic electrons and back ground electrons. This reduces the laser relativistic electron energy to enhance the stopping power and the delayed heating of the core plasma due to the energy confinement at the top of the cone continues for a long time. Those processes related to the core heated will be effective in the FIREX experiments. The scalability of these processes will be verified in the FIREX-I experiment and related theory and simulation research. The detail physics of the process, target fabrication and future FIREX-II project will be shown in this presentation. [Preview Abstract] |
Wednesday, October 26, 2005 3:00PM - 3:40PM |
LZ1.00003: Integrated Simulation for Core Heating of Fast Ignition Targets Tomoyuki Johzaki, Hideo Nagatomo, Hitoshi Sakagami, Tatsufumi Nakamura, Yasuyuki Nakao, Kunioki Mima In the recent fast heating experiments with cone-guided targets at Osaka University, imploded cores were heated up to $\sim $ 800eV with a high coupling efficiency. The mechanism of the effective heating, however, has not been clarified until now. To simulate the overall physics and identify the crucial physics in the fast heating, we developed a multidimensional integrated code system `Fast Ignition Integrated Interconnecting code' (FI$^{3}$ code), which includes all important physics form the implosion to the core heating. The integrated simulations show that in the low density plasma between cone tip and compressed core, strong microinstabilities are induced by fast electron beam, which moderates the spectrum of fast electron entering the core. As the results, the core is effectively heated by the relatively low energy component of fast electrons. We will show the imploded core profiles of cone-guided targets and core heating properties. This work is supported by MEXT, the Grant-in-Aid for Creative Scientific Research (15GS0214). [Preview Abstract] |
Wednesday, October 26, 2005 3:40PM - 4:00PM |
LZ1.00004: Fuel Assembly for Fast Ignition Inertial Confinement Fusion R. Betti, C. Zhou Large densities and areal densities (\textit{$\rho $R}) of compressed thermonuclear fuel lead to high gains and low ignition energies in fast-ignition inertial confinement fusion. It is well known that high densities and high \textit{$\rho $R} can be achieved by driving the imploding shell on a low adiabat. However, low adiabat pulses are difficult to realize in practice because of the extreme contrast ratio between peak and foot laser power. A recent advancement in direct-drive pulse design has provided a pulse shape that mitigates the power contrast ratio and enhances the ablative stabilization of the RT instability while driving the capsule on a very low adiabat. The laser pulse, referred to as the relaxation (RX) pulse design, consists of a short prepulse followed by a power shutoff and the main laser pulse. Massive cryogenic shells can be imploded with a low implosion velocity on a low inner adiabat with an RX pulse. The low velocity and the shaped adiabat also prevent a significant growth of the RT instability. Target designs for a 25-, 100-, and 750-kJ driver are presented. One-dimensional simulations show fuel assemblies with \textit{$\rho $R} of 0.7--3 g/cm$^{2}$ and peak densities of 400--700 g/cc obtained with implosion velocities of 1.7--2.5 $\times $ 10$^{7}$ cm/s This work has been supported by the U.S. DOE under Cooperative Agreements ER54789 and DE-FC03-92SF19460. [Preview Abstract] |
Wednesday, October 26, 2005 4:00PM - 4:20PM |
LZ1.00005: Scaling of Energy Deposition in Fast Ignition Targets R.B. Campbell, S.A. Slutz, T.A. Mehlhorn, Dale Welch We examine the scaling to ignition of the energy deposition of laser generated electrons in compressed fast ignition cores. Relevant cores have densities of several hundred g/cm$^{3}$, with a few keV initial temperature. As the laser intensities increase approaching ignition systems, on the order of a few 10$^{21}$W/cm$^{2}$, the hot electron energies expected to approach 100MeV[1]. Most certainly anomalous processes must play a role in the energy transfer, but the exact nature of these processes, as well as a practical way to model them, remain open issues. Traditional PIC explicit methods are limited to low densities on current and anticipated computing platforms, so the study of relevant parameter ranges has received so far little attention. We use LSP[2] to examine a relativistic electron beam (presumed generated from a laser plasma interaction) of legislated energy and angular distribution is injected into a 3D block of compressed DT. Collective effects will determine the stopping, most likely driven by magnetic field filamentation. The scaling of the stopping as a function of block density and temperature, as well as hot electron current and laser intensity is presented. Sub-grid models may be profitably used and degenerate effects included in the solution of this problem. Sandia is operated by Sandia Corporation, for the USDOE. [1] A. Pukhov, \textit{et. al.,} \textit{Phys. Plas.} \textbf{6}, p2847 (1999) [2] D. R. Welch \textit{et al.}, \textit{Comput. Phys.Commun.} \textbf{164}, p183 (2004). [Preview Abstract] |
Wednesday, October 26, 2005 4:20PM - 4:40PM |
LZ1.00006: Full scale explicit PIC simulation of fast ignition experiments Yasuhiko Sentoku, Andreas Kemp Recent experiments at ILE using the GEKKO laser coupled to the PW laser system have demonstrated the cone guiding FI concept [{\it Kodama, Nature, 2002}]. Compressed cores at densities of 50-100 g/cm$^3$ within 30-50 $\mu$m diameter are expected to be located 20-30$¥mu$m from the cone tip. The PW laser is supposed to heat the core up to 1 keV based on the observed neutron yields. To understand this core heating process, we have performed one-dimensional particle in cell code ({\it PICLS1d}), which simulates the fast electron generation by ultra-short intense laser pulse, the fast electron transport through the coronal plasma, and the energy deposition in the core. In general, PIC simulations have the limitation to simulate extremely dense and low temperature plasmas due to the numerical heating. We are currently working to reduce computational cost of explicit PIC calculations, and have succeeded in extending the spatial cell size to the plasma skin length, which is much larger than the Debye length of the core plasma, and also suppressing the numerical heating. This enables us to simulate a core density plasma in a 100 µm spatial scale over picoseconds. We have carried out the {\it PICLS1d} simulations with parameters similar to the ILE experiment. The results are disscussed in this talk. This work was supported by DOE/NNSA-UNR grant DE-FC52-01NV14050. [Preview Abstract] |
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