Bulletin of the American Physical Society
2006 48th Annual Meeting of the Division of Plasma Physics
Monday–Friday, October 30–November 3 2006; Philadelphia, Pennsylvania
Session UO2: ICF III: Target Design |
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Chair: Valeri Goncharov, University of Rochester Room: Philadelphia Marriott Downtown Grand Salon H |
Thursday, November 2, 2006 9:30AM - 9:42AM |
UO2.00001: Optimizing the NIF ignition point design hohlraum and laser beam focal spot designs Debra Callahan, Denise Hinkel, Larry Suter, Paul Wegner, Steve Pollaine, Nathan Meezan, Nino Landen, John Lindl, Sham Dixit, Laurent Divol, Ed Williams, John Edwards, Bruce Langdon, Paul Bradley The first ignition tuning experiments on the National Ignition Facility will be performed in 2009 to be followed by ignition implosion experiments in 2010. Optimizing the coupling of laser energy into the hohlraum and choice of the characteristics of the laser focal spots, involve trade-offs in several areas. These include proximity to expected thresholds for laser plasma interactions (driven by laser intensity), the impacts of the focal spot size on x-ray symmetry, the degree to which the spots can be repointed within the laser entrance hole to adjust symmetry, the impact of the phase plate on the laser performance and the fabricability of the hohlraum and phase plates. This paper summarizes the work of a large design team that has concentrated on producing an integrated design for a hohlraum and focal spots consistent with laser performance that meets the requirements for ignition. [Preview Abstract] |
Thursday, November 2, 2006 9:42AM - 9:54AM |
UO2.00002: Lower Temperature Ignition Hohlraums for the National Ignition Facility Stephen Pollaine, Steve Haan, Larry Suter, Denise Hinkel, Darwin Ho, John Lindl The National Ignition Facility will start conducting indirect drive ignition tuning experiments in 2009 followed by ignition implosion experiments in 2010. The current ignition point design is a Be-ablator capsule inside a 300 eV hohlraum. Since laser intensity and power requirements decrease with radiation temperature, while hohlraum coupling efficiency increases, the optimum temperature for ignition may be less than 300eV. This optimum could be determined by a number of trade-offs, including estimated capsule margin, estimated levels of laser plasma interactions, implosion symmetry and required laser performance. We describe a detailed design study for a 270 eV ignition hohlraum, and examine the tradeoffs at this lower temperature. [Preview Abstract] |
Thursday, November 2, 2006 9:54AM - 10:06AM |
UO2.00003: Soft x-ray conversion efficiency and x-ray albedo of optimized high-Z cocktail mixtures for indirect drive ICF E. Dewald, M. Rosen, L. Suter, J. Schein, O. Jones, J. Albritton, S. Ross, D. Froula, P. Neumayer, O. Landen, S. Glenzer, C. Constantin, F. Girard, J.-P. Jadaud The use of high-Z mixtures called ``cocktails'' for hohlraum walls in the ignition design on NIF improves energetics and radiation uniformity by minimizing wall radiation losses. Recent experiments at the Omega laser facility were performed to measure ``1D'' x-ray conversion efficiency in spherical geometry and M-band fluxes of high-Z materials at laser intensities (10$^{14}$-10$^{15}$ W/cm$^{2})$ similar to future hohlraum ignition experiments on NIF. These results as well as the plasma parameters measured by 4w Thomson Scattering were compared for Au, U and Au-U cocktails. Furthermore, a separate set of experiments using double hohlraum targets was used to measure absolute x-ray wall albedo of Au and cocktails at higher radiation temperatures (180 eV) than in previous experiments. The results are compared to LASNEX simulations and their implication on the NIF ignition design is discussed. [Preview Abstract] |
Thursday, November 2, 2006 10:06AM - 10:18AM |
UO2.00004: Design of NIF ignition hohlraum with high-density carbon capsule Ogden S. Jones, Darwin D. Ho, Debra A. Callahan, Denise E. Hinkel, Nathan B. Meezan, Jose L. Milovich, Stephen M. Pollaine, Laurance J. Suter The current baseline NIF ignition target uses a cryogenic DT capsule with a doped beryllium ablator. An alternative design we are investigating uses a high-density carbon ablator instead. A high-density carbon ablator might have some fabrication advantages and it will absorb more x-ray energy than a beryllium capsule of the same size. Changing the ablator material also will change the plasma conditions inside the hohlraum and thus the laser plasma interaction. We report on calculations using HYDRA that were done to find the combination of hohlraum geometry, laser power, laser pointing, and inner cone to outer cone laser power fractions that resulted in a symmetric implosion giving substantial fusion yield. This work included an assessment of the sensitivity of the symmetry to various design parameters and estimates of the linear gain for laser plasma instabilities. [Preview Abstract] |
Thursday, November 2, 2006 10:18AM - 10:30AM |
UO2.00005: The effect of drive symmetry swings on imploded cores of ignition targets John Edwards, Debbie Callahan, Oggie Jones, Shon Prisbrey, Jose Milovich, Don Meeker, Dan Kalantar, Bob Turner, Nobuhiko Izumi, Bob Kirkwood Achieving conditions for ignition by compressing a capsule containing DT requires a high degree of drive symmetry, $<$ 1{\%} integrated in time. In the case of indirect drive this translates to obtaining sufficiently uniform X-ray deposition over the surface of the capsule, leading to a set of requirements on the laser performance that include accuracy of beam pointing within the hohlraum, as well as relative timing and power between the beams. In this paper we revisit the question of how drive symmetry swings can affect the implosion for current NIF 1MJ target designs, and how these swings can come about. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. UCRL-ABS-222989. [Preview Abstract] |
Thursday, November 2, 2006 10:30AM - 10:42AM |
UO2.00006: A Computational Study of Re-emission Balls Proposed for the NIF Ignition Symmetry Campaign D.J. Meeker, P. Amendt, E. Dewald, M.J. Edwards, J. Milovich, L. Suter Re-emission balls are high-Z spheres used as surrogates for ICF ignition capsules to detect and correct early-time asymmetries of radiation flux at the target. Emission from these balls mimics the incoming flux due to their high albedo, providing a useful symmetry diagnostic. Experiments on Nova by LANL [1] and LLNL used bismuth (Bi) as the surrogate, selected for its high albedo and insensitivity to the fluorescence of the gold hohlraum wall. We are studying the applicability of these capsules to the NIF symmetry campaign as a potential tuning mechanism to achieve the accuracies required for symmetric implosions. We will describe 2-D simulations that predict the emission of the Bi ball as a function of time, frequency, and spatial distribution, as well as quantifying surrogacy of re- emission balls. Using several tuning examples, we will show the resolution expected from this diagnostic. Suggestions for extending this technique to longer times will be discussed as well as describing 3-D effects from diagnostic viewing ports and an opposing hole to eliminate competing wall emission. [1] Delamater, Phys. Rev. E 53, 5240 (1996), Magelssen, Phys. Rev. E 57, 4663 (1998) [Preview Abstract] |
Thursday, November 2, 2006 10:42AM - 10:54AM |
UO2.00007: Time-dependent radiation drive asymmetry compensation in inertial fusion capsules Stephen A. Slutz, Roger A. Vesey, Mark C. Herrmann A new approach is presented which allows the design of inertial fusion capsules that can correct small time-dependent asymmetries in the radiation drive. The approach uses a mixture of materials within the capsule ablator, which can be adjusted as a function of polar angle to provide constant density, but varied opacity. An example of such a mixture is beryllium with small amounts ($<$1{\%} atomic fraction) of copper and gold. Thus, given a specific time-dependent radiation asymmetry, fractional doping levels of copper and gold can be determined within the ablator to make the ablation pressure symmetric. In general the doping fractions are a function of both the polar angle and the depth within the ablator. [Preview Abstract] |
Thursday, November 2, 2006 10:54AM - 11:06AM |
UO2.00008: Robust beam illumination in heavy ion inertial fusion Shigeo Kawata, K. Miyazawa, T. Someya, T. Kikuchi, A.I. Ogoyski In this paper an optimized new HIB illumination scheme is presented in order to realize a robust illumination scheme against a displacement of a direct-driven fuel pellet in an ICF reactor. In heavy ion inertial fusion (HIF) heavy ion beam (HIB) precise illumination is essentially important to obtain a sufficient fusion energy output. In direct-driven pellet implosion, HIBs illuminate a spherical target and the HIB deposition non-uniformity should be suppressed less than a few {\%}. In our study, we developed a 3D HIB illumination code [1] and a hydrodynamic implosion code for HIF studies. We have obtained an optimal HIB illumination scheme to minimize the HIB illumination non-uniformity on a direct-driven fuel pellet and to make the illumination scheme robust against a little pellet displacement dz in a fusion reactor chamber. The optimized HIB illumination scheme allows 200-300 [micron m] of dz in HIF [2]. [1] T. Someya, et.al, Phy.Rev.STAB, 7, 044701 (2004). [2] S. Miyazawa, et al., Phys. of Plasma, 12, 122702 (2005) [Preview Abstract] |
Thursday, November 2, 2006 11:06AM - 11:18AM |
UO2.00009: Controlling the yield of high yield ignition capsules L. Suter, S. Haan, G. Strobel, M. Eyler The National Ignition Facility ultimately has the potential to drive capsules that absorb in excess of 500kJ of energy. Such capsules are very robust and may produce yields of many hundreds of mega-joules. For a number of reasons, lower yield but equally robust versions of these capsules might also be useful for experiments. Consequently, we have investigated controlling the yield of high yield capsules by replacing a significant fraction of the DT fuel with other materials, such as ablator. These first studies indicate that replacing the DT with an equal rho-r of other-material reduces the yield but also reduces the margin for ignition. This paper quantifies that observation and tests the hypotheses for the change in margin such as differences in the equations of state or the outer DT's playing a subtle role in ignition. [Preview Abstract] |
Thursday, November 2, 2006 11:18AM - 11:30AM |
UO2.00010: Progress in Laser-Driven Dynamic Hohlraum Implosions S.G. Glendinning, J.F. Hansen, R.P.J. Town, J. Frenje, R. Petrasso We have been studying the use of laser driven dynamic hohlraums\footnote{Herrmann, M.C. et al., BAPS, DPP Nov. 2003.} (LDDH) to drive implosions of an inner D$_{2}$ filled glass capsule. In the LDDH, a radiatively collapsed shock driven in a Xenon-filled capsule confines radiation in a spherically convergent geometry, leading to a small, hot hohlraum. In contrast, a radiatively collapsed shock is not produced when a lower-Z gas fill such as neopentane (C$_{5}$H$_{12}$) replaces the Xenon, and the implosion is driven by the collision of the outer shell and the inner shell. While the neutron yields of the two contrasting systems are predicted to be very similar, the x-ray signatures are predicted to be quite different, as are the fuel and shell areal densities. We have fielded both systems in experiments on the Omega laser at the University of Rochester. In these experiments the inner capsules are 0.23 mm diameter and the outer capsules, 0.97 mm diameter, are irradiated with $\sim$ 21 TW of 3$\omega$ for $\sim$ 1 ns. We will report on results from the two kinds of experiments and compare the results with simulations. [Preview Abstract] |
Thursday, November 2, 2006 11:30AM - 11:42AM |
UO2.00011: Shock Ignition of Thermonuclear Fuel with High Areal Density R. Betti, K.S. Anderson, C. Zhou, J. Perkins, M. Tabak, P. Bedrossian, K.N. LaFortune In the shock-ignition concept,\footnote{ C. Zhou and R. Betti, Bull. Am. Phys. Soc. \textbf{140}, 50 (2005).} massive cryogenic shells are first imploded with a low-implosion velocity on a low adiabat using an adiabat-shaping laser-pulse. While the low-implosion velocity yields a small, dense, but cold, hot spot, the low adiabat of the fuel leads to large values of the areal density. The assembled fuel is then ignited from the central hot spot heated by the collision of a spherically convergent \textit{ignitor} shock and the return shock. The ignitor shock can be driven by the same driver used in the assembly and the resulting thermonuclear gain can be significantly larger than in standard hot-spot ignition for equal driver energy. We present the results of one- and two-dimensional simulations used to assess the sensitivity of the thermonuclear gain to hot-electron preheating, laser imprinting, and inner-surface roughness. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement Nos. DE-FC02-04ER54789 and DE-FC52-92SF19460. [Preview Abstract] |
Thursday, November 2, 2006 11:42AM - 11:54AM |
UO2.00012: Shock-Ignited High Gain/Yield Targets for the National Ignition Facility L.J. Perkins, K.N. LaFortune, P. Bedrosiian, M. Tabak, A. Miles, S. Dixit, R. Betti, K. Anderson, C. Zhou Shock-ignition, a new concept for ICF ignition [C.Zhou, R.Betti Bull APS, v50, 2005], is being studied as a future option for efficiently achieving high gains in large laser facilities such as NIF. Accordingly, this offers the potential for testing: (1)High yield (up to 200MJ), reactor-relevant targets for inertial fusion energy (2)High fusion yield targets for DOE NNSA stockpile application (3)Targets with appreciable gain at low laser drive energies (gains of 10's at 150kJ) (4)Ignition of simple, non-cryo (room temperature) single shell gas targets at (unity gain). By contrast to conventional hotspot ignition, we separate the assembly and ignition phases by initially imploding a massive cryogenic shell on a low adiabat (alpha 0.7) at low velocity (less than 2e7cm/s) using a direct drive pulse of modest total energy. The assembled fuel is then separately ignited by a strong, spherically convergent shock driven by a high intensity spike at the end of the pulse and timed to reach the center as the main fuel is stagnating and starting to rebound. Like fast ignition, shock ignition can achieve high gains with low drive energy, but has the advantages of requiring only a single laser with less demanding timing and spatial focusing requirements. [Preview Abstract] |
Thursday, November 2, 2006 11:54AM - 12:06PM |
UO2.00013: Simulations of high-gain direct-drive inertial confinement fusion targets J.W. Bates, A.J. Schmitt, S.P. Obenschain, D. Colombant, S.T. Zalesak, D.E. Fyfe Using the FAST radiation hydrocode, we report in this presentation on continuing numerical studies of the hydrodynamic stability of inertial-confinement-fusion targets. Our discussion focuses on a particular class of ``high-gain'' direct-drive targets that are irradiated with approximately 2.5 MJ of KrF laser light, and have fusion energy yields exceeding 100 times that value according to one-dimensional simulations. We model several different temporally-varying laser pulses --- including so-called ``relaxation'' and ``decaying-shock'' profiles with preceding ``spikes'' --- and examine the two-dimensional stability and gain characteristics for each. Both single-mode and broad-band outer-surface perturbations are considered, and where possible, their evolution is compared to quasi-analytical expressions for ablative Rayleigh-Taylor growth. [Preview Abstract] |
Thursday, November 2, 2006 12:06PM - 12:18PM |
UO2.00014: 0.5MJ Targets for an IFE Fusion Test Facility K.N. LaFortune, L.J. Perkins, P. Bedrossian, R. Betti, A. Schmitt, S. Obenschain There has been much recent progress in the development of both the source and targets for laser-driven, inertial confinement fusion (ICF). The next step to apply this approach to inertial fusion energy (IFE) is to build a facility that has all the required components of a reactor and demonstrates the reliability and robustness. The Fusion Test Facility proposed by NRL is one such facility [S.Obenschain, Bull. APS v50, 2005]. The cost, complexity and scale of any fusion test facility are driven by the energy required for the fusion target. As the laser-target physics has become better understood, target geometries that require less drive energy have been found. Using conventional hotspot ignition, rad-hydro-burn simulations using HYDRA of low-drive-energy, direct-drive reactor targets requiring just 0.5 MJ of drive energy to achieve gain of 10's are being studied. 1-D scoping studies have been performed to outline the source requirements. Good agreement with comprehensive, time-dependent 1-D simulations in LASNEX has been obtained for integral quantities such as gain, yield and ignition margins. The robustness of the small targets has been explored with 2-D stability studies. Shock ignition of similar targets could be employed to achieve yet higher gains with similar drive energies. [Preview Abstract] |
Thursday, November 2, 2006 12:18PM - 12:30PM |
UO2.00015: Development of a Continuous multi-thousand shot electron beam pumped KrF rep-rate laser for fusion energy Patrick M. Burns, Matt Myers, John D. Sethian, Matthew F. Wolford, John L. Giuliani, Robert H. Lehmberg, Stuart Searles, Moshe F. Friedman, Frank Hegeler, Reginald Jaynes The Electra laser system is currently being developed at the Naval Research Laboratory to serve as a test bed for laser driver technologies needed for an inertial fusion energy power plant. 730 J oscillator results as well as advancement of the laser physics and the pulse power technologies give us projections of $>$7{\%} wall plug efficiency for an IFE system. The Electra main amplifier in oscillator configuration has run continuously at 1 Hz, 2.5 Hz, and 5 Hz for multi-thousand shot runs. This paper will discuss recent results of the Electra program at the Naval Research Laboratory including measurements of the main amplifier's focal profile. Issues addressed will include development paths for cathode, window coating, and foil durability to attain the durability required for a fusion power plant. [Preview Abstract] |
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