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 YO5: Fast Ignition |
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Chair: David Strozzi, Lawrence Livermore National Laboratory Room: Governor's Square 10 |
Friday, November 15, 2013 9:30AM - 9:42AM |
YO5.00001: A experimental study on the energy coupling efficiency from the heating laser to core plasma in the fast ignition experiment Yasunobu Arikawa, Takahiro Nagai, Yuki Abe, Sadaoki Kojima, Shohei Sakata, Zhe Zhang, Takahito Ikenouchi, Shinsuke Fujioka, Mitsuo Nakai, Hiroyuki Shiraga, Hiroaki Nishimura, Hiroshi Azechi The energy coupling efficiency from the heating laser to the core plasma was experimentally studied in the fast ignition integrated experiment. A set of physical parameters of the core plasma, such as the ion temperature, the areal density of the core plasma, and the size of the core plasma were firstly diagnosed in the GEKKO XII and LFEX. The energy spectrum of the hot electron was measured by using a series of x-ray spectrometers with the energy range from 10 keV to 30 MeV. The ion temperature of 0.84 keV from fast-heated core and 0.67 keV from un-heated core were measured. From these parameters the coupling efficiency from heating laser to the core was estimated to be 1.6 {\%}. Furthermore the coupling efficiency to the hot electron, the electron spectrum, and areal density of the core plasma were measured simultaneously, and these values were confirmed to be consistent with each other. The detailed result will be presented in the talk. [Preview Abstract] |
Friday, November 15, 2013 9:42AM - 9:54AM |
YO5.00002: Observation of Cu-K$\alpha $ emission in imploded core plasma by direct irradiation of ultra intense laser light Hideaki Habara, Tomoyuki Iwawaki, Toshinori Yabuuchi, Kazuo Tanaka, Yasunobu Arikawa, Shinsuke Fujioka, Hiroyuki Shiraga, Anle Lei, Mingsheng Wei, Richard Stephens, Farhat Beg, Hitoshi Sawada Direct irradiation of ultra intense laser light on the implosion plasma is one of attractive options of fast ignition. In our previous research, a stable single channel formation in a 1-directional expanded plasma up to several times critical density has been demonstrated [1]. However in the spherical implosion plasma, there are the possibilities for refraction or hosing of laser light during sub-mm propagation. Even if the laser propagates forthrightly, it is not clear that enough number of fast electrons can be generated toward the core. For this purpose, Cu-doped shell target is used to observe inside the imploded plasma via Cu-K$\alpha $ emission due to its high transmittance in coronal plasma surrounding the core. A ultra intense laser (UIL) light is irradiated on the imploded plasma at the maximum compression by changing the focused position in respect to the center of the core, corresponding to the critical density (Nc), Nc/4 and Nc/10 positions. Enhancement of Cu-K$\alpha $ emission is successfully observed at the core when UIL is focused on Nc. The results are compared with PIC simulations. \\[4pt] [1] A.L. Lei, et al., Phys. Plasmas 16, 056307 (2009). [Preview Abstract] |
Friday, November 15, 2013 9:54AM - 10:06AM |
YO5.00003: Simulations of Fuel Assembly and Fast-Electron Transport in Integrated Fast-Ignition Experiments on OMEGA A.A. Solodov, W. Theobald, K.S. Anderson, A. Shvydky, R. Epstein, R. Betti, J.F. Myatt, C. Stoeckl, L.C. Jarrott, C. McGuffey, B. Qiao, F.N. Beg, M.S. Wei, R.B. Stephens Integrated fast-ignition experiments on OMEGA benefit from improved performance of the OMEGA EP laser, including higher contrast, higher energy, and a smaller focus. Recent 8-keV, Cu-K$_{\alpha }$ flash radiography of cone-in-shell implosions and cone-tip breakout measurements showed good agreement with the 2-D radiation--hydrodynamic simulations using the code \textit{DRACO}. \textit{DRACO} simulations show that the fuel assembly can be further improved by optimizing the compression laser pulse, evacuating air from the shell, and by adjusting the material of the cone tip. This is found to delay the cone-tip breakout by $\sim $220 ps and increase the core areal density from $\sim $80 mg/cm$^{2}$ in the current experiments to $\sim $500 mg/cm$^{2}$ at the time of the OMEGA EP beam arrival before the cone-tip breakout. Simulations using the code \textit{LSP} of fast-electron transport in the recent integrated OMEGA experiments with Cu-doped shells will be presented. Cu-doping is added to probe the transport of fast electrons via their induced Cu K-shell fluorescent emission. This material is based upon work supported by the Department of Energy National Nuclear Security Administration DE-NA0001944 and the Office of Science under DE-FC02-04ER54789. [Preview Abstract] |
Friday, November 15, 2013 10:06AM - 10:18AM |
YO5.00004: Fast Electron Transport and Spatial Energy Deposition into Imploded High Density Plasmas using Cu-Doped CD Shell Targets L.C. Jarrott, M.S. Wei, A.A. Solodov, B. Qiao, C. McGuffey, W. Theobald, R.B. Stephens, C. Stoeckl, C. Mileham, F.J. Marshall, J. Delettrez, R. Betti, P.K. Patel, H.S. McLean, C.D. Chen, M.H. Key, H. Sawada, T. Yabuuchi, T. Iwawaki, H. Habara, J.J. Santos, D. Batani, F.N. Beg Fast electron spatial energy deposition is investigated in integrated cone-guided FI experiments by measuring fast electron induced Cu K-shell fluorescence emission using Cu doped CD shells attached to the Au cone. This work used the OMEGA laser (3$\omega $, 18 kJ) for fuel assembly, and a high intensity OMEGA EP beam (1$\omega $, 10 ps, 0.5 - 1.5 kJ, Ip \textgreater 1e19 W/cm2) focused onto the inner cone tip to produce fast electrons similar to previous FI heating experiments. Results showed an enhancement of 60{\%} in the total K$\alpha $ yield from the joint shots compared to driver only shots. Comparison of high and low contrast OMEGA-EP shots show enhancement in energy coupling with higher contrast. Experiments are modeled using LSP for fast electron generation and transport with DRACO predicted fuel assembly. [Preview Abstract] |
Friday, November 15, 2013 10:18AM - 10:30AM |
YO5.00005: Fast electron generation and transport from ten-picosecond laser-plasma interactions in the cone-guided fast ignition B. Qiao, L.C. Jarrott, C. Mcguffey, M.S. Wei, S. Chawla, A.A. Solodov, R.B. Stephens, P.K. Patel, H.S. McLean, F.N. Beg In fast ignition (FI) inertial confinement fusion, an essential element is the efficient conversion of the ignition laser energy into directional fast electrons and transport of the latter through the cone tip. Here, we report 2D PIC simulations of laser plasma interaction (LPI) and fast electron generation and transport using LSP code for recent cone-in-shell integrated FI experiments at the Omega laser facility. In the simulations, the exact OMEGA-EP laser parameter (10ps scale) is used and the initial preplasma condition inside the cone is calculated directly from the 2D rad-hydro modeling of the measured EP prepulse (21mJ), which exhibit a jet-structured density profile with critical surface extending 150$\mu $m away from the tip on axis. The result shows that a larger number of fast electrons escape sideway to the cone wall instead of going forward to the tip due to LPI in large-scale preplasma and laser bifurcation when interacting with the curved critical surface. It is also found that intense magnetic field traps the fast electrons inside low-density plasma affecting the coupling. Therefore, only 1{\%} of laser energy coupled into the fast electrons entering the tip. However with high contrast EP laser (prepulse \textless~1mJ), coupling increased to be 12{\%}. [Preview Abstract] |
Friday, November 15, 2013 10:30AM - 10:42AM |
YO5.00006: Electron beam collimation by self-generated magnetic fields in 10ps relativistic laser matter interaction M.S. Wei, R. Stephens, R. Mishra, A. Sorokovikova, J. Peebles, C. McGuffey, L. Jarrott, F. Beg, Y. Sentoku, H. McLean, P. Patel, W. Theobald Generation and transport of an intense, collimated fast electron beam in relativistic laser plasma interaction (LPI) is crucial for applications such as fast ignition. To date, most studies were limited to sub-ps pulses with energies of $\approx $0.1kJ. We have extended such investigation to 10ps pulse duration using the high-intensity high-contrast OMEGA EP laser with energies up to 1.5kJ to study beam collimation by self-generated magnetic fields. Targets are multi-layered solid foils consist of an Al substrate, a buried Cu layer and a thick CH back layer. Similar targets containing a thin (\textless 10$\mu $m) Au layer buried $\approx $10$\mu $m beneath the front Al layer are also used to examine the effect of transport material on beam collimation. Fast electron beam profile is diagnosed by 2D imaging the induced Cu K$\alpha $ emission. K$\alpha $ images from the Al transport targets show that 10ps LPI with the high-contrast pulses generate a more confined electron beam than that with low-contrast pulses, but with a large shot-to-shot variation. The Au transport targets consistently produce a stable, better-collimated electron beam with a spot size $\approx $50$\mu $m after propagating $\approx $150$\mu $m. Collisional PIC modeling results agree with the experiments. [Preview Abstract] |
Friday, November 15, 2013 10:42AM - 10:54AM |
YO5.00007: Optical Probe Measurements of a Plasma Channel for Fast Ignition S. Ivancic, D. Haberberger, W. Theobald, K.S. Anderson, D.H. Froula, D.D. Meyerhofer, K. Tanaka, H. Habara, T. Iwawaki The evacuation of a cavity in a plasma by a high-intensity laser beam is of practical importance to the channeling fast-ignition concept. The channel in the plasma corona of an imploded inertial confinement fusion capsule provides a clear path through the plasma so that the energy from second high-intensity laser can be deposited close to the dense core of the assembled fuel to achieve ignition. This study reports on experiments performed with the OMEGA EP Laser System using one of the short-pulse IR beams (1.25 kJ, 10 ps) to form a straight channel in a large blowoff plasma with an electron temperature of $\sim $1.5 keV that was generated by two nanosecond, kilojoule UV laser beams. The channel was measured to reach up to half the IR critical density with a channel width of $\sim $200 $\mu $m. Images were taken at different times showing the radial evolution of a strong blast wave from the channel walls. Individual filaments were observed at the critical surface indicating that the laser became unstable and broke up into multiple filaments. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944. [Preview Abstract] |
Friday, November 15, 2013 10:54AM - 11:06AM |
YO5.00008: Kinetic particle-in-cell modeling of PW laser interaction for HEDLP Andreas Kemp, Laurent Divol, Bruce Cohen We discuss new results on kinetic modeling of Petawatt laser-plasma interaction at relativistic intensities. We study the transition between bulk plasma heating through instabilities near the critical density where the laser is absorbed, and resistive heating in dense plasma. The goal of our effort is to adequately model the absorption layer in full-scale simulations of ongoing HEDLP experiments. [Preview Abstract] |
Friday, November 15, 2013 11:06AM - 11:18AM |
YO5.00009: Collimating Relativistic Electron Beams for Fast Ignition with Elliptical Magnetic Mirrors Holger Schmitz, Alex P.L. Robinson The Fast Ignition concept relies on the energy of the high energy electrons being delivered inside a small region in the fuel core. Large angular spreads of the forward moving electrons result in a reduction in the coupling efficiency into the core. In order to counteract this effect, measures have to be taken to concentrate the electrons towards the hot spot. A new elliptical mirror target geometry is presented that focuses electrons using self generated magnetic fields at resistivity gradients. Initial 2.5 dimensional collisional PIC simulations provide a proof of concept. It is shown that electrons are collimated rather than just channelled inside the high-Z material. Large scale hybrid simulations, with realistic length and time scales, assess the performance of the magnetic mirror concept under more realistic conditions. An increase of the coupling efficiency by a factor of 3 to 4 is found. The results show that the elliptical mirror concept is able to improve the prospects of Fast Ignition considerably. [Preview Abstract] |
Friday, November 15, 2013 11:18AM - 11:30AM |
YO5.00010: Hybrid-PIC Simulations of Shock Formation in Laser-Irradiated Plasmas Adam Tableman, M. Tzoufras, F. Fiuza, W.B. Mori Shock generation by hot electron beams (with intensities ranging from 10$^{14}$ W/cm$^{2}$ to 10$^{16}$ W/cm$^{2})$ impinging on high density targets (10$^{24}$ /cm$^{3})$ is investigated using a 1D hybrid-PIC version of OSIRIS. The hybrid-PIC code uses a fluid model to follow electron transport at high densities. In these simulations an electron cathode is used as a proxy for hot electrons generated in under-dense regions by laser-plasma interactions. This approach enables control over the composition and energy distribution of the hot electrons entering the high density region, which, in turn, allows the direct study of hot electron energy deposition and the corresponding shock structure. Understanding how to harness the hot electrons to enhance shock formation will aid in designing Shock Ignition ICF targets with improved yield. [Preview Abstract] |
Friday, November 15, 2013 11:30AM - 11:42AM |
YO5.00011: Direct-heating of the imploded plasma by ultra-intense laser in the fast ignition scheme Atsushi Sunahara, Tomoyuki Johzaki, Hitoshi Sakagami, Hideo Nagatomo, Kunioki Mima, Yasunobu Arikawa, Shinsuke Fujioka, Hiroyuki Shiraga, Hiroshi Azechi For improving the energy coupling from the heating laser to the imploded core in FIREX project, we are trying to use laser-accelerated ions for heating plasma in addition to the heating by fast electrons. To estimate the core temperature heated by both fast electrons and fast ions, we have developed 1D integrated model. In our model, the electron transport and its energy deposition to the plasma are calculated by the ray-tracing method. The slope temperature of fast electrons is assumed to be function of the laser intensity. The conversion efficiency from the laser to forward fast electrons is assumed to be 40\%. For fast ions, the conversion efficiency and particle energy are calculated by the hole-boring model by S. C. Wilks PRL 69 (1992) 1383. We calculated the stopping power of each ion particle and its energy deposition on the core plasma. Our calculation show that ion heating can contribute to the heating of plasma core, and its contribution to the increase of the core temperature is not so small compared to that of fast electrons, since the ions has relatively short stopping range. We will show the dependence of core temperature on the heating laser energy, pulse duration, the divergence angle of particles, and the core density, respectively. [Preview Abstract] |
Friday, November 15, 2013 11:42AM - 11:54AM |
YO5.00012: Hydrodynamic Simulation of Frontal Collision of Two Identical Plane Thermonuclear Burning Waves Konstantin V. Khishchenko, Alexander A. Charakhch'yan A one-dimensional problem on synchronous bilateral action of two identical drivers on opposite surfaces of a plane layer of DT fuel with the normal or five times greater initial density is simulated numerically. The solution of the problem includes two thermonuclear burn waves propagating to collide with each other at the symmetry plane. A laser pulse with total absorption of energy at the critical density and a proton bunch that provides for a nearly isochoric heating are considered as drivers. A wide-range equation of state for the fuel, electron and ion heat conduction, self-radiation of plasma and plasma heating by $\alpha$-particles are taken into account. In spite of different ways of ignition, various models of $\alpha$-particle heat, whether the burning wave remains slow or transforms into the detonation wave, and regardless of way of such a transformation, the final value of the burn-up factor depends essentially on the only parameter $H\rho_0$, where $H$ is the half-thickness of the layer and $\rho_0$ is the initial fuel density. This factor is about 0.35 at $H\rho_0 \approx 1$~g/cm$^2$ and about 0.7 at $H\rho_0 \approx 5$~g/cm$^2$. [Preview Abstract] |
Friday, November 15, 2013 11:54AM - 12:06PM |
YO5.00013: Correlated Electron Stopping in Fast Ignition Plasmas Ian Ellis, Frank Graziani, David Strozzi, Michael Surh, Paul Grabowski, Viktor Decyk, Frank Tsung, Warren Mori The effect of correlated electron stopping on Fast Ignition is an open question. In this process, the wake produced by an electron modifies the dynamics and stopping power of the electrons that travel behind it. Others have studied this process in detail in the context of non-relativistic ion beam stopping. Aside from theoretical studies, the process has been largely ignored for relativistic electron stopping. By comparing non-relativistic stopping results with the scalable molecular dynamics code ddcMD, we demonstrate that Particle-in-Cell (PIC) codes are useful tools for studying the process. We present some correlated electron stopping results from the UCLA PIC code QuickPIC. [Preview Abstract] |
Friday, November 15, 2013 12:06PM - 12:18PM |
YO5.00014: Indirect-drive pre-compression of CH coated cone-in-shell target with guiding wire for fast ignition Weimin Zhou, Yuqiu Gu, Lianqiang Shan, Baohan Zhang Compared with central ignition of laser fusion, fast ignition separates compression and ignition thus it can relax the requirements on the implosion symmetry and the driven energy. The Research Center of Laser Fusion has begun the related experimental researches on fast ignition based on SHENGUANG II laser facility. The small scale cone-in-shell target with guiding wire for fast ignition was pre-compressed by the SHENGUANG II eight 260J/2ns/3$\omega $ laser beams indirectly since beam smoothing was not available currently. To minimize the mixing of the compressed fuel and high-Z vapor produced by the M-line emission from the gold holhraum, a 3$\mu $m CH foil was coated on the full outer surface of the cone and guiding wire. The maximum density of the compressed cone-in-shell target 1.3 ns after the lasers' irradiation on the inside wall of hohlraum is about 5.0 g/cm3, and the implosion velocity is close to 1.9*10$^{7}$ cm/s, which are well consistent with the simulation results with two-dimensional radiation hydrodynamic code. Experimental results and simulation results also demonstrated the coated CH foil could minimize the mixing effectively. By the appropriate design, target can remain robust before the maximum compression, that is, the time while the hot electrons produced by ignition laser pulse deposit energy in the compressed fuel. [Preview Abstract] |
Friday, November 15, 2013 12:18PM - 12:30PM |
YO5.00015: Enhanced Proton Beam Focusing due to Proximal Target Structures on the 1.25 kJ OMEGA EP Laser Chris McGuffey, J. Kim, B. Qiao, F.N. Beg, M.S. Wei, P. Fitzsimmons, M. Evans, R.B. Stephens, J. Fuchs, S.N. Chen, P.M. Nilson, D. Canning, D. Mastrosimone, M.E. Foord, H.S. McLean Understanding how to generate and control laser-driven proton beams has shown significant progress in the last 15 years. However, to exploit promising applications, practical aspects must be addressed, such as the effect of structures holding the target and dynamics when the beam enters any sample. Using the $1.25kJ$, $10ps$ OMEGA EP BL laser and spherically curved C targets we studied the spot size of a high-density proton beam directed at a Cu foil using three target mounting configurations: 1 on a stalk, 2 with an open-sided wedge structure on the back, and 3 with a conical structure. The brightness of Cu $K\alpha$ fluorescence from the center of the foil was weakest from the stalk-mounted target, 5x brighter with the wedge, and 8x brighter with the cone, indicating enhanced focusing due to the structures. Plasma features and fields from the interaction were temporally and spatially resolved using proton radiography from a separate broad-spectrum proton beam ($0-40MeV$) driven by OMEGA EP SL. We also discuss a follow-on experiment that will study transport of the proton beam through various materials. [Preview Abstract] |
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