Inertial Confinement Fusion Energy Research Articles

A StarDriver-Class Laser Achieving 1 % Beam Uniformity in 1 ns

StarDriver was recently proposed as a highly flexible laser driver for inertial confinement fusion and high energy density physics. It envisions a laser drive consisting of many beamlets at an aperture where optical technology is well-developed, and each beamlet has energy ~100 J in a several times diffraction limited beam. Each beamlet has ~1.5THz of 2D SSD smoothing, but the ensemble of lasers has frequency bandwidth 2–10 %, thereby providing significant control of both hydrodynamic and laser-plasma instabilities. In this paper we illustrate the attractive features of the StarDriver concept with detailed calculations of beam smoothing for control of hydrodynamic instabilities in a direct drive ICF target, using a full 3D simulation of the laser drive. We describe here a StarDriver-class laser with 5120 physical beamlets disposed about the target chamber in 80 evenly spaced ports, each port containing 64 beamlets, each beamlet having about ~1.5THz of 2D SSD bandwidth and suitable phase plates, an aperture of ~65 mm, an energy of 80 J, and frequency-converted to ~351 nm. The drive at the target is ~400 kJ, has a well-behaved low L-mode spectrum, and smoothes very rapidly, reaching an asymptotic smoothness of <1 % in less than 1 ns. 2 MJ of drive at the same smoothing performance may be obtained by increasing the number of beamlets. An attractive feature of StarDriver is that the tolerances on the individual beamlet parameters are quite relaxed.

StarDriver: Recent Results on Beam Smoothing and 2ωpe Mitigation

StarDriver was recently proposed as a highly flexible laser driver for inertial confinement fusion and high energy density physics. It envisions a laser drive consisting of very many beams at an aperture and energy where the optical technology is well-developed, used in concert to create a large scale laser driver system. In this paper we describe a StarDriver–class laser with 5120 physical beamlets disposed about the target chamber in 80 evenly spaced ports, each port containing 64 beamlets, each beamlet having about ~1.5 THz of 2D SSD bandwidth and suitable phase plates, an aperture of ~65 mm, an energy of 80 J, and frequency-converted to ~351 nm. StarDriver has many beamlets at an aperture where optical technology is well-developed, and each beamlet has energy ~100 J in a several times diffraction limited beam. The ensemble of beamlets has frequency bandwidth 2%-10%, thereby providing significant control of both hydrodynamic and laser-plasma instabilities The drive at the target is ~400 kJ, has a well-behaved low L-mode spectrum, and smooth’s very rapidly, reaching an asymptotic smoothness of <1% in less than 1 ns. We also review recent results showing that the 2ωpe instability can be significantly reduced by 20 THz bandwidth.

Preliminary experimental results of tungsten wire-array Z-pinches on primary test stand

The Primary Test Stand (PTS) developed at the China Academy of Engineering Physics is a 20 TW pulsed power driver, which can deliver a ∼10 MA, 70 ns rise-time (10%–90%) current to a short-circuit load and has important applications in Z-pinch driven inertial confinement fusion and high energy density physics. Preliminary results of tungsten wire-array Z-pinch experiments on PTS are presented. The load geometries investigated include 15-mm-tall cylindrical single and nested arrays with diameter ranging from 13 mm to 30 mm, consisting of 132–300 tungsten wires with 5–10 μm in diameter. Multiple diagnostics were fielded to characterize the x-ray radiation from wire-array Z pinches. The x-ray peak power (∼50 TW) and total radiated energy (∼500 kJ) were obtained from a single 20-mm-diam array with 80-ns stagnation time. The highest x-ray peak power up to 80 TW with 2.4 ns FWHM was achieved by using a nested array with 20-mm outer diameter, and the total x-ray energy from the nested array is comparable to that of single array. Implosion velocity estimated from the time-resolved image measurement exceeds 30 cm/μs. The detailed experimental results and other findings are presented and discussed.

Full circuit calculation for electromagnetic pulse transmission in a high current facility

We describe herein for the first time a full circuit model for electromagnetic pulse transmission in the Primary Test Stand (PTS)---the first TW class pulsed power driver in China. The PTS is designed to generate 8--10 MA current into a $z$-pinch load in nearly 90 ns rise time for inertial confinement fusion and other high energy density physics research. The PTS facility has four conical magnetic insulation transmission lines, in which electron current loss exists during the establishment of magnetic insulation. At the same time, equivalent resistance of switches and equivalent inductance of pinch changes with time. However, none of these models are included in a commercially developed circuit code so far. Therefore, in order to characterize the electromagnetic transmission process in the PTS, a full circuit model, in which switch resistance, magnetic insulation transmission line current loss and a time-dependent load can be taken into account, was developed. Circuit topology and an equivalent circuit model of the facility were introduced. Pulse transmission calculation of shot 0057 was demonstrated with the corresponding code FAST (full-circuit analysis and simulation tool) by setting controllable parameters the same as in the experiment. Preliminary full circuit simulation results for electromagnetic pulse transmission to the load are presented. Although divergences exist between calculated and experimentally obtained waveforms before the vacuum section, consistency with load current is satisfactory, especially at the rising edge.

StarDriver: A Flexible Laser Driver for Inertial Confinement Fusion and High Energy Density Physics

We propose a novel method to minimize laser–plasma instabilities and improve laser–plasma coupling by the use of multi-beam laser architecture with a large system frequency bandwidth and many beamlets per unit solid angle. The StarDriver™, laser driver is constructed from 104 to 105 individual lasers, each delivering nominally 100 J in pulses of ~3–30 ns at a nominal wavelength of ~355 nm with better than 3–5 diffraction-limited performance. The beamlets are individually relatively narrowband to facilitate maximum laser performance, but the ensemble of beamlets span a wide frequency range. Currently available laser media enable Δω/ω ~ 2 % at 355 nm with the possibility of system bandwidths approaching 10 % in the future. The many beamlets of StarDriver™ provide optimal asymptotic smoothing for hydrodynamic instabilities (0–1 %), innovative focusing strategies including zooming, and the large bandwidth enables extremely rapid hydrodynamic smoothing times ~30 fs. The distribution of frequencies among the beamlets allows flexibility for fine control of the seeding of the Rayleigh–Taylor instability. The ultra-broad bandwidth combined with the large total k-spectrum of the laser drive in the plasma corona may enable complete suppression of the most problematic laser–plasma instabilities such as stimulated Brillouin backscatter, stimulated Raman scatter, cross-beam energy transfer, and the two plasmon decay instability. StarDriver™ offers potentially superior flexibility in laser drivers for inertial confinement fusion, enabling almost arbitrary sequencing of wavelength, polarization, focus, and fine control of the spatio-temporal properties of the drive in the corona. The highly modular strategy of StarDriver™ should enable an attractive development pathway as well as maximizing overall system efficiency.

Radiation sources with planar wire arrays and planar foils for inertial confinement fusion and high energy density physics research

This article reports on the joint success of two independent lines of research, each of them being a multi-year international effort. One of these is the development of innovative sources, such as planar wire arrays (PWAs). PWAs turned out to be a prolific radiator, which act mainly as a resistor, even though the physical mechanism of efficient magnetic energy conversion into radiation still remains unclear. We review the results of our extensive studies of PWAs. We also report the new results of the experimental comparison PWAs with planar foil liners (another promising alternative to wire array loads at multi-mega-ampere generators). Pioneered at UNR, the PWA Z-pinch loads have later been tested at the Sandia National Laboratories (SNL) on the Saturn generator, on GIT-12 machine in Russia, and on the QiangGuang-1 generator in China, always successfully. Another of these is the drastic improvement in energy efficiency of pulsed-power systems, which started in early 1980s with Zucker's experiments at Naval Research Laboratory (NRL). Successful continuation of this approach was the Load Current Multiplier (LCM) proposed by Chuvatin in collaboration with Rudakov and Weber from NRL. The 100 ns LCM was integrated into the Zebra generator, which almost doubled the plasma load current, from 0.9 to 1.7 MA. The two above-mentioned innovative approaches were used in combination to produce a new compact hohlraum radiation source for ICF, as jointly proposed by SNL and UNR [Jones et al., Phys. Rev. Lett. 104, 125001 (2010)]. The first successful proof-of-the-principle experimental implementation of new hohlraum concept at university-scale generator Zebra/LCM is demonstrated. A numerical simulation capability with VisRaD code (from PRISM Co.) established at UNR allowed for the study of hohlraum coupling physics and provides the possibility of optimization of a new hohlraum. Future studies are discussed.

The multi-point X-ray source and phase contrast imaging used on implosion experiment

Traditional implosion backlight imaging experiment has disadvantages of nonuniform X-ray source, low contrast ablator interface and high requirement for diagnostic device tuning precision. A novel design of multi-point X-ray source combined with phase contrast imaging developed and optimized based on experimental research performed on Shenguang-II facility is presented. The novel design can obtain high-quality experimental result with uniform X-ray source, clear interface between ablator and inner DD gas and large image view. At the same time, the new design using diagnostic silt instead of diagnostic hole improves tuning precision. The experimental result proposes that novel design of laser driven plasma point x-ray source combined with phase contrast imaging has advantage of area X-ray source combined with absorb imaging and can be widely used in inertial confinement fusion and high energy density physics.

Plasma source development for the NDCX-I and NDCX-II neutralized drift compression experiments

AbstractCompressed ion beams are being studied as a driver for inertial confinement fusion energy and for the creation of matter in the high-energy-density regime. In order to facilitate compression of a positive ion charge bunch longitudinally and transversely beyond the limit determined by the space-charge field of the bunch, a source of charge-neutralizing electrons must be provided. Plasma sources have been developed for the NDCX-I and NDCX-II experimental facilities, both for the 2-m-long, field-free drift regions, and for the small-diameter interior of the multi-Tesla final focus solenoid. Barium titanate based cylinders with a high dielectric coefficient are used to line the wall of the 2-m-long drift region and by applying a 9 kV pulse between the inner and outer surfaces of the cylinders, plasma with a density in the 1010 cm−3 range is formed. Results are presented from experiments using this plasma source on NDCX-I. A compact plasma source 5.1 cm long and 3.8 cm in diameter, also made using the barium titanate based material, has been developed for use in the bore of the final focus solenoid. Plasma generated near the wall of the plasma source will follow the fringing magnetic field lines of the solenoid and help to fill the bore of the magnet with plasma. Improved designs for the barium titanate plasma sources are being considered that use different inner-surface electrode materials and structures, and also use a modified electrical driver employing a spark gap crowbar switch. In addition, plasma source designs using so-called flashboard technology have been developed. In the flashboard plasma source, high density plasma is formed when the applied high voltage pulse causes a series of breakdowns between isolated copper patches aligned in rows along the surface of the 0.2 mm thick flashboard.

Inertial confinement fusion energy R&D and nuclear proliferation: The need for direct and transparent review

Proliferation concerns have generally been associated with the acquisition of the fissile material needed for nuclear weapons; however, the spread of the knowledge needed to build very light and powerful weapons that can be carried long distances by missiles is also a serious concern. Such knowledge could accelerate and destabilize regional arms races, and lead to the deployment of powerful weapons able to target the US and its allies. Classified weapons-related information has previously spread through the international effort to harness inertial confinement fusion. Success in achieving net fusion gain in the National Ignition Facility at the Lawrence Livermore National Laboratory could lead to greatly increased R&D in inertial confinement fusion worldwide, along with increased proliferation risks. The authors write that these issues have not yet been adequately addressed and require direct and transparent examination so that means to mitigate risks can be assessed and residual risks can be balanced against potential benefits.

X-Ray Absorption Spectroscopy for ICF Target Characterization

An instrumentation of X-ray absorption spectroscopy (XAS) was developed to measure the areal density of any element with an atomic number Z > 17. In contrast to X-ray fluorescence, which is affected by spatial dopant nonuniformity, an element can be accurately measured by XAS regardless of its own distribution or the presence of other elements in a sample. Furthermore, no reference standard is needed to achieve ±3% 1Ã accuracy. This method has been used to measure the average contents of specific elements in a variety of inertial confinement fusion and high energy density targets. It validates the average dopant concentration measured by contact radiography and differential radiography.

Hypervelocity macroscopic particle impact fusion with DT methane

Hypervelocity impact (HVI) is a very important workbench in high energy density (HED) physics studies. In this paper, we will discuss the physics of the impact of a macroscopic particle (macron) at the speed of up to ( ∼ 1000 km / s ) to an immobile target, and its differences from other HED drives. As HVIs can create ultra high energy density, we believe that with a proper design, they can be very efficient drives to inertial confinement fusion energy (IFE). We will propose a fusion scheme of this concept, investigate the physics involved in detail, and present the preliminary simulation results. These investigations show that the scheme is very promising.

The National Ignition Facility and the Golden Age of High Energy Density Science

The National Ignition Facility (NIF) is a 192-beam Nd:glass laser facility being constructed at the Lawrence Livermore National Laboratory to conduct research in inertial confinement fusion (ICF) and high energy density science. When completed, NIF will produce 1.8 MJ, 500 TW of ultraviolet light, making it the world's largest and highest energy laser system. The NIF is poised to become the world's preeminent facility for conducting ICF and fusion energy research and for studying matter at extreme densities and temperatures.

Power Flow Design Constraints for a Recyclable Transmission Line for Z-Pinch IFE

A recyclable transmission line (RTL) carries power from the pulsed-power driver to the fusion target in a z-pinch-driven inertial-confinement fusion energy (IFE) system. In order to minimize the driver voltage, the RTL inductance must be small, requiring a short, low-impedance, magnetically insulated transmission line (MITL). However, the large linear current density that flows in the electrodes at small radius near the load resistively heats the anode surface, leading to anode plasma formation and ion emission. If the impedance of the RTL is too small, large ion current losses can occur and large electron flow currents can be launched into the z-pinch load region. These problems are avoided by choosing the line impedance at the load end of the RTL to be well above the effective impedance of the imploding load. By gradually reducing the impedance along the line moving from the load to the driver, the RTL inductance can be controlled. But, if the impedance is varied too rapidly along the line, significant electron flow current losses can occur. The impact of these constraints on the RTL design of an IFE system is discussed and a compromise design with reasonable power coupling efficiency is established.

Power Flow in a Magnetically Insulated Recyclable Transmission Line for aZ-Pinch-Driven Inertial-Confinement-Fusion Energy System

Power flow in a recyclable transmission line (RTL) for a z-pinch-driven inertial-confinement fusion energy (IFE) system is studied. In a magnetically insulated transmission line, plasma forms by explosive emission on the cathode but emission from the anode does not occur. However, in an RTL, the large linear current density that flows in the electrodes at small radius near the load resistively heats the anode surface, leading to anode plasma formation and ion emission. If the impedance of the RTL is too small, large ion current losses can occur and large electron flow currents can be launched into the z-pinch load region. If only the boundary current drives the z-pinch load, then these large electron flow currents can introduce a polarity effect with more bound current in the anode than the cathode. While being mindful of the IFE system requirement to maintain a small RTL inductance, these problems are avoided by choosing the line impedance at the load end of the RTL to be well above the effective impedance of the imploding load. In this case, the ion current losses are tolerable and the electron flow current is negligibly small. For the present baseline design with a peak current of 60 MA driving a 100-ns implosion, these power flow constraints require a gap of order 2 mm or more at the load end of the RTL

The national ignition facility: Path to ignition in the laboratory

The National Ignition Facility (NIF) is a 192-beam laser facility presently under construction at LLNL. When completed. NIF will be a 1.8-MJ, 500-TW ultraviolet laser system. Its missions are to obtain fusion ignition and to perform high energy density experiments in support of the U.S. nuclear weapons stockpile. Four of the NIF beams have been commissioned to demonstrate laser performance and to commission the target area including target and beam alignment and laser timing. During this time, NIF demonstrated on a single-beam basis that it will meet its performance goals and demonstrated its precision and flexibility for pulse shaping, pointing, timing and beam conditioning. It also performed four important experiments for Inertial Confinement Fusion and High Energy Density Science. Presently, the project is installing production hardware to complete the project in 2009 with the goal to begin ignition experiments in 2010. An integrated plan has been developed including the NIF operations, user equipment such as diagnostics and cryogenic target capability, and experiments and calculations to meet this goal. This talk will provide NIF status, the plan to complete NIF, and the path to ignition.

The first experiments on the national ignition facility

A first set of shock propagation, laser-plasma interaction, hohlraum energetics and hydrodynamic experiments have been performed using the first 4 beams of the National Ignition Facility (NIF), in support of indirect drive Inertial Confinement Fusion (ICF) and High Energy Density Physics.

The national ignition facility: path to ignition in the laboratory

The National Ignition Facility (NIF) is a 192-beam laser facility presently under construction at LLNL. When completed, NIF will be a 1.8-MJ, 500-TW ultraviolet laser system. Its missions are to obtain fusion ignition and to perform high energy density experiments in support of the US nuclear weapons stockpile. Four of the NIF beams have been commissioned to demonstrate laser performance and to commission the target area including target and beam alignment and laser timing. During this time, NIF demonstrated on a single-beam basis that it will meet its performance goals and demonstrated its precision and flexibility for pulse shaping, pointing, timing and beam conditioning. It also performed four important experiments for Inertial Confinement Fusion and High Energy Density Science. Presently, the project is installing production hardware to complete the project in 2009 with the goal to begin ignition experiments in 2010. An integrated plan has been developed including the NIF operations, user equipment such as diagnostics and cryogenic target capability, and experiments and calculations to meet this goal. This talk will provide NIF status, the plan to complete NIF, and the path to ignition.

Chemical Compatibility of Silica Aerogel Processes with ICF Hohlraums

Inertial Confinement Fusion (ICF) energy hohlraums are composed of a high-Z material filled with foam. Because of the small pore size and transparency, silica aerogels are used in some ICF targets. The traditional synthesis of silica aerogels require sol-gel polymerization of silicon alkoxide followed by supercritical drying. Some constituents in sol-gel polymerization have been found to contribute to leaching of certain metals at the silica/metal interface. Since the hohlraums are composed of metals, possible chemical reactivity at the silica aerogel and metal hohlraum interface was investigated. The hohlraums studied are aluminum lined with either copper or copper/chromium. Upon initial inspection, the aerogel appeared transparent and uniform, however, closer inspection of the copper wall suggested possible leaching. Alternatively the quality of the aerogel in the copper-chromium hohlraum was very poor with the chromium layer of the hohlraum and some copper completely etched. Control experiments were used to determine the cause of the leaching. When copper is in the presence of sol-gel constituents, Cu2+ ion formed, thus leaching copper from the hohlraum walls. In the presence of chromium, Cr2O72- or CrO42- was identified in solution with the Cu2+, these anions are believed to form copper chromite under the aerogel synthesis procedures utilized.

Studies of Strongly Coupled Plasmas Using Intense Heavy Ion Beams at the Future FAIR Facility: the HEDgeHOB Collaboration

AbstractThis paper shows with the help of numerical simulations that the high intensity bunched beam of uranium that will be available at the future FAIR (Facility for Antiprotons and Ion Research) facility [W.F. Henning, Nucl. Inst. Meth. B, 214 (2004) 211] at Darmstadt, will be a very efficient tool to create High‐Energy‐Density (HED) states in matter (including strongly coupled plasmas) in the laboratory. We have simulated hydrodynamic and thermodynamic response of targets made of different materials including aluminum and lead. These simulations have been carried out using a two‐dimensional hydrodynamic computer code, BIG‐2. Our simulations show that one can create a plasma with a plasma coupling parameter, Γ, of the order of 5. Such plasmas are believed to exist in stars, brown dwarfs and giant planets. Experimental study of such systems is therefore of great importance to our understanding of the universe. It has also been theoretically predicted that the stopping power of strongly coupled plasmas will be less than that of ideal plasmas. This could have very important implications for inertial confinement fusion energy production schemes. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Pulsed-power-driven high energy density physics and inertial confinement fusion research

The Z accelerator [R. B. Spielman, W. A. Stygar, J. F. Seamen et al., Proceedings of the 11th International Pulsed Power Conference, Baltimore, MD, 1997, edited by G. Cooperstein and I. Vitkovitsky (IEEE, Piscataway, NJ, 1997), Vol. 1, p. 709] at Sandia National Laboratories delivers ∼20MA load currents to create high magnetic fields (&amp;gt;1000T) and high pressures (megabar to gigabar). In a z-pinch configuration, the magnetic pressure (the Lorentz force) supersonically implodes a plasma created from a cylindrical wire array, which at stagnation typically generates a plasma with energy densities of about 10MJ∕cm3 and temperatures &amp;gt;1keV at 0.1% of solid density. These plasmas produce x-ray energies approaching 2MJ at powers &amp;gt;200TW for inertial confinement fusion (ICF) and high energy density physics (HEDP) experiments. In an alternative configuration, the large magnetic pressure directly drives isentropic compression experiments to pressures &amp;gt;3Mbar and accelerates flyer plates to &amp;gt;30km∕s for equation of state (EOS) experiments at pressures up to 10Mbar in aluminum. Development of multidimensional radiation-magnetohydrodynamic codes, coupled with more accurate material models (e.g., quantum molecular dynamics calculations with density functional theory), has produced synergy between validating the simulations and guiding the experiments. Z is now routinely used to drive ICF capsule implosions (focusing on implosion symmetry and neutron production) and to perform HEDP experiments (including radiation-driven hydrodynamic jets, EOS, phase transitions, strength of materials, and detailed behavior of z-pinch wire-array initiation and implosion). This research is performed in collaboration with many other groups from around the world. A five year project to enhance the capability and precision of Z, to be completed in 2007, will result in x-ray energies of nearly 3MJ at x-ray powers &amp;gt;300TW.